Freezing is a behavioral response that many animals exhibit when scared. This is a measurable response that researchers use to study the fear learning process in rodents. If an animal is conditioned to fear a high-pitched sound, for instance, it will freeze when the sound is played.

During fear extinction, as the animal learns to no longer fear the sound, less freezing will be observed.

The authors are interested in the function of the IL mPFC, and how it is affected by the injection of BDNF.

The targeted injection is achieved by using a stereotaxic setup, which is a highly precise, 3D guiding system that allows researchers to place a canula into specific regions of the brain. The canula is just a hollow tube that allows for the delivery of drugs or other fluids to that brain region.

Once the canula is in place, BDNF can be directly injected into the region of interest at any time.

Consolidation is a series of events following the initial acquisition of a memory trace that leads to its retention.

Epigenetic regulation is the process of altering gene expression levels without mutating the DNA itself.

For instance, if a cell needs to increase the expression of a specific gene, it can change the microstructure of the DNA in the area of that gene, making it more accessible for transcription into RNA.

NMDA receptors are found in nerve cells and are activated by the excitatory neurotransmitter glutamate. These receptors are involved in memory function in the brain.

After the animal has formed an association between the tone and the shock, it will freeze when it hears the tone. However, if the tone is presented enough times in the absence of the shock, the mouse will eventually stop showing a fear response to the tone through a process known as fear extinction.

A rodent model in which a neutral auditory cue (high-pitched beep) is paired with an aversive stimulus (footshock), resulting in the formation of an associative fear memory.

After repeated presentations of the paired stimuli, the animal will experience fear in response to the tone alone.

A term used to describe the ability of neuronal synapses to change their strength, becoming stronger or weaker in response to changes in their activity levels.

BDNF is a protein in the brain (and peripheral nervous system) that supports the survival, growth, and differentiation of neurons involved in memory.

The medial prefrontal cortex is a region of the brain that is associated with cognitive and executive processes such as working memory and decision-making.

The infralimbic subregion of the medial prefrontal cortex is necessary for the inhibition of conditioned fear after extinction.

Behavior in different species that arose from a common ancestral gene.

Simplest.

Acceptable or agreeable to the taste.

The amount of time between the free rat being placed in the arena and the door opening.

To free.

In agreement.

The opposite of selfish. Thinking or acting in the interest of someone else. Putting the well-being of another above your own.

A group used in a study that have something in common.

Meaningful, noteworthy, important.

Pierced with holes.

Conditioned behavior in which an individual gives up trying to escape a painful situation after repeatedly failing to escape. http://dictionary.reference.com/browse/learned+helplessness

Learned helplessness occurs when an animal is repeatedly subjected to an aversive stimulus that it cannot escape. Eventually, the animal will stop trying to avoid the stimulus and behave as if it is utterly helpless to change the situation.

Even when opportunities to escape are presented, this learned helplessness will prevent any action http://psychology.about.com/od/lindex/f/earned-helplessness.htm

Learned helplessness is also a model for depression in rodents.

Reduced or suppressed.

Voluntarily helping others.

Actions that help others caused by a feeling of empathy.

Condition of the mind that drives a behavior

The Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Flora is an international United Nations agreement between governments.

The goal is to ensure that international trade with specimens of wild animals and plants does not threaten their survival. CITES implements controls in the international trade with specimens of selected species.

Voronoi diagrams or polygons divide a plane into regions based on distance to certain points of interest. They have distance information that can help answer questions like “which object is closest to point P?” and “where is the nearest hospital from point Q?”

A Markov chain refers to a sequence of random events or variables, where each event is dependent on the previous event.

In biology, Markov chain algorithms are often used to model population processes or to describe gene frequencies in populations.

Here, the researchers used a statistical method to model complicated allele distributions and assign geographic locations to seized ivory.

A stretch of repetitive DNA in which sequences of base pairs are repeated, typically two to seven times.

Example: GATC GATC GATC GATC GATC

Allele frequency is the relative frequency of a particular allele (or gene variant) in a population. Allele frequencies are shown as fractions or percentages.

An allele is one of two or more alternative forms of a gene that are located at the same position (genetic locus) on a chromosome.

The genotype is the genetic makeup of an organism. It can also refer to the two inherited alleles of a particular gene.

A species that is crucial to how an ecosystem functions. If the keystone species were removed, the ecosystem would dramatically change or cease to exist.

Ivory is a hard, creamy white material that is derived from tusks and incisor teeth of animals, including elephants.

There are two subspecies of African elephants, the African forest elephant and the African savanna elephant.

Transnational organized crime involves associations or groups of individuals that profit from the sale of illegal goods across national borders, creating international illegal markets.

Activities of transnational organized crime include drug trafficking, human trafficking, money laundering, sale of counterfeit goods, and illegal wildlife trade.

A place of significant activity or danger.

Illegal hunting, killing, or capturing of wild animals.

What are conspecific alarms? Conspecific means that the individuals belong to the same species.

Thus these alarms are signals that one individual calls out to warn other individuals in the same species. Think of meerkats.

Here the editor summarizes the key findings ("la la la") and outlines the general impact of the work ("la").

Melissa can edit as SitC

Shelby can also edit as SitC

It is common for a paper to contain an "Acknowledgments" section to thank the people and organizations without whom the study could not have occurred, but who were not sufficiently involved in the study to be included as authors on the paper.

Commonly included in this section are funding agencies that provided the money for the study, core facilities that (in exchange for a fee) provided services or instruments to perform assays included in the study, and collaborators who provided reagents or materials for the study.

A technique that first separates individual chemicals present in a sample (via liquid chromatography) and then identifies what those chemicals are by measuring the masses of the particles in those separated chemicals (via mass spectrometry).

Liquid chromatography separates out the different chemicals in the sample by forcing a liquid containing the sample at a very high pressure through a column. This column contains a solid material that the particles in the sample will cling to.

Different chemicals in the sample will interact slightly differently with that solid material, and so they will flow through the column at different rates. This causes them to separate out so the investigators can look at each of these chemicals individually in the next step and try to figure out what they are.

Mass spectrometry allows investigators to identify what the now-separated chemicals are by measuring the mass-charge ratio of the particles that make up the chemicals.

In order to do this, the chemicals are bombarded with electrons, causing some of their molecules to break apart into charged fragments. Those charged fragments are then run through an electromagnetic field, and naturally separate according to their mass-charge ratio.

The pattern of separation that results is called a "mass spectrum." By looking at the masses of the individual particles that make up a chemical, we can guess what that chemical is.

For example, if the mass spectrum told us that we had 2 particles the mass of a hydrogen atom and 1 particle the mass of an oxygen atom, we would deduce that we had a water molecule on our hands.

An organism that moves pollen from the male reproductive organs of a flower to the female reproductive organs of flower, resulting in fertilization.

Without pollinators, many types of flowers would not be able to reproduce. Types of pollinators include honey bees, butterflies, and hummingbirds.

See more about pollinators in this video from National Geographic: People, Plants, and Pollinators

Myosin is the motor protein for the cytoskeletal protein actin. These two proteins make up much of the cytoskeleton in muscle cells and thus myosin is good marker for skeletal muscle.

The authors can not possibly show a picture of every single animal they performed this experiment on so they show two "representative" animals.

That is, two animals that best show what they saw in the rest of the animals.

Prevented.

The grouping of all anterior gradient proteins (see below).

The axis extending from the shoulder (proximal) to the tips of the fingers (distal).

In other words, "proximal or distal identity." Proximal meaning near the point of attachment versus distal meaning away from the point of attachment.

A cell surface protein studied for its roles in salamander limb regeneration. To date, the Prod 1 gene is only present in salamander species.

CRE Integrases/recombinases (causes recombination) are a family of enzymes which catalyze recombination, i.e., exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome.

They delete segments of DNA flanked by LoxP sites (floxed) in experimental animals, and can generate animals with mutations limited to certain cell types (tissue-specific knockouts) or animals with chemically inducible mutations (time-specific inducible knockouts).

Herd immunity is a key principle in infectious disease vaccination. Epidemiologists, scientists who study patterns in disease, have discovered that if you vaccinate the majority of people in a population even those who are not vaccinated don't catch the infectious disease. This effect is because the likelihood of coming into contact with anyone else who could also get sick is so small (because everyone else is vaccinated).

Further thoughts: Does herd immunity apply to NON-infectious disease vaccines, like a hypothetical vaccine that could prevent heart disease?

Hint: does your risk for heart disease depend on if your close contacts have heart disease?

Still confused or want to learn more? VIsit http://www.vaccines.gov/basics/protection (vaccines.gov) for a more detailed explanation and pictures.

High-Income countries are those countries whose residents make good living wages. Examples include the US, England, Japan, and many others. This is in contrast to low-income countries where there is more poverty and thus more disease and higher mortality rates (more death) for many diseases.

It is important to know that this study is considering high-income countries because the outcomes of many of the nonmeasles infectious diseases are worse, and more children die in low-income countries. This makes the ability to study how measles effects these outcomes more difficult.

This topic will be discussed more later in the paper in a Previous Work annotation.

Infectious diseases are illnesses that can be passed from one person to another, like the flu. These are the diseases whose outcomes are examined in this paper.

Non-infectious diseases are like heart disease or diabetes which you cannot catch from someone else. Non-infectious diseases are NOT important for this paper and have not been shown to be effected by measles.

Importantly, these nonmeasles infectious diseases include opportunistic infections mentioned previously.

Immunosuppression is when the body's defense mechanism against disease, called the immune system no longer works as well as it should

Gamma Transformation

The number of immunomodulated individuals (after measles infection) was diveded by the total population of interest. This means that the data is presented as a percent of the whole rather than absolute numbers.

It is important to look at data such as this as a percent of the whole and not just total numbers so that the numbers can be compared across time and across populations. For example, if a total of 50 people out of 100 people get sick and die from some illness, that is a very high number or rate of death (50%). However, if 50 people die out of 1 million who got sick, then even though it is the same number of people who died, it is a much much lower rate of death per person (0.005%). When the number of people who are ill is divided by the total population at risk for the illness, the answer to the division problem is essentially rate or the prevalence of the illness in the population.

Once the 'baseline prevalence' of measles immune-amnesia was calculated, the authors used a tool from statistics, called a gamma function, to make theoretical calculations of how many people from this 'baseline prevalence' would truly still have immune amnesia, at a certain point in time since the measles infection.

The purpose of using the gamma function was to create a distribution of immune-amnesia with time following measles. For example, if the immune amnesia would last for 3 years, it wouldn't make sense, biologically, to assume that 100% of children have immune-amnesia at the end of three years since getting measles and then 0% have immune-amnesia 1 day later, at the beginning of the fourth year since getting measles. The gamma function allowed a smooth gradient where 100% of children had immune amnesia directly following measles infection and this gradually dropped over time to 0% of children with immune amnesia by, for example, four years following measles. In the study, how long it took to reach 0% was what was defined by the gamma function.

Incidence is how much of something first happens within a given amount of time. There is another term called prevalence that is similar, but has an important difference. In diseases, for example, incidence is 'how much new disease there is over a certain time-period,' while prevalence is how much disease there is at a given point in time. This distinction is especially important for diseases that may last a long time. For example, if 100 people each year get HIV, the incidence is 100 new cases of HIV per year. However, because HIV does not go away, the prevalence, or number of people with HIV in a population at a certain time, will be much higher because it will include not just the 100 people who just got HIV, but also all of the people who still have HIV due to infections in previous years.

For example, you can see a graph of measles incidence in the US here. You will notice that it is plotted by when on the X-axis, and how many on the Y-axis.

The incidence of measles significantly drops after vaccination because this provides host resistance to the disease

Host resistance describes how well an individual (the host for the disease) can resist getting a disease (resistance).

For example, if you get the chickenpox vaccine, it is extremely unlikely you will ever get the chickenpox disease. This means that you have a lot of host resistance against chickenpox (because you got the vaccine). It would also be true if you got the chickenpox disease once, you would be resistant to getting it again. Both are examples of host resistance.

In this context, they are describing that the opposite is true. If you get the measles disease there is a prolonged effect decreasing your host resistance to other diseases for 2-3 years.

Keep reading to learn about how this could be the case, and why it is so important around the world.

Opportunistic infections describe pathogens (things that make you sick like bacteria, viruses and fungi) that take advantage of when people's immune systems are weak. Under normal conditions these opportunistic pathogens DO NOT make you sick, but if you have some problem that reduces your immune system's ability to protect you, like a recent sickness or malnutrition, then opportunistic pathogens can make you sick.

Opportunistic pathogens/infections are important in medicine because they can make treating sick people very complicated. For example, AIDS patients don't actually die because the HIV virus made them sick. Victims of AIDS most often die because their immune system is so damaged they cannot fight off opportunistic pathogens. Learn more about why these opportunistic infections are so devastating at AIDS.gov.

Social-emotional learning is a particular approach to teaching people how to manage and process their emotions.

This study is randomly assigning half of the treatment group to social-emotional learning to see if this kind of curriculum has any effect on rates of violent activity.

The link below provides more detail on what social-emotional learning entails and can help you consider why this would be an important part of this kind of study:

http://greatergood.berkeley.edu/article/item/how_social_emotional_learning_transforms_classrooms

External validity refers to the ability to say that we could expect these same results in other contexts.

When experiments are conducted in social settings, external validity is not something we can expect to acquire because different social, economic and cultural contexts would have different effects on the outcomes.

Proximal refers to something that is near to, or in close proximity to, a point of reference. Proximal is a term commonly used in research because research is always striving to explain cause and effect relationships.

Proximal causes are those causes that are thought to be part of the relationship, but are perhaps not the ultimate source of the relationship.

In this case, hostile attribution bias, or the problem of assuming other people's intent is hostile, even when it isn't, is thought to be the proximal cause.

A randomized controlled trial is one of many ways to conduct a scientific experiment.

Many people are selected for the experiment, but only some people are randomly selected to receive the intervention that is being tested for.

These kinds of studies are often referred to as the gold standard. When pharmaceuticals are still in the development stage, randomized controlled trials are used to test the drug's effectiveness.

Violence can be considered a public health crisis not only because it can lead to mortality, but because those involved often end up needing health care services.

The Centers for Disease Control has identified youth violence as a public health crisis. They report that in 2008 more than 656,000 young adults between the ages of 10 and 24 were treated in emergency rooms for injuries related to violence.

In terms of mortality, homicide kills more young black males than the 9 leading causes of death combined.

A lab technique that uses short DNA sequences to amplify a specific region of the genome. These short DNA sequences are called primers. They anneal to genomic DNA and serve as a starting point for DNA polymerase to replicate the DNA at that location.

PCR applies multiple cycles of heating and cooling temperatures, creating the ideal conditions for many rounds of replication. This technique is often used to determine the genotype of an animal at a specific gene.

This YouTube video goes over the technique in more detail.

https://www.youtube.com/watch?v=iQsu3Kz9NYo

CRISPR stands for "Clustered Regularly Interspaced Short Palindromic Repeats" and Cas9 refers to the protein that is associated with CRISPR. CRISPRs are DNA sequences that are transcribed into RNA.

Cas9 protein is guided to a specific DNA sequence by the CRISPR RNA. Because Cas9 is a nuclease, meaning that is cuts DNA, it cleaves the DNA at the sequence specified by the CRISPR RNA.

A statistical term. Summation of all the elements divided by their number.

Normally, the last step during drinking water purification is a disinfection step.

Chlorine is the most commonly used chemical.

Although effective in killing harmful pathogens, chlorine can react with natural organic matter and form harmful byproducts (e.g., trihalomethanes [THM], bromate, chlorite, etc.).

For additional information

Comes from the natural processes in the environment such as decomposition of organic matter.

Examples include proteins, amino acids, polysaccharides, and humic and fulvic acids, etc. (Reference)

That is, evolutionarily conserved or kept the same throughout the evolution of salamanders and humans.

A protein that contains a high number of cysteine amino acids.

The 3D tertiary structure of these proteins has not been solved.

Doing this would allow for one to compare how related their structures are at the tertiary level. This is as opposed to looking just at the amino acid sequence (primary structure), which may mislead one into thinking that they are very different.

However, it could very well be the case that the primary structures are very different, but the tertiary structures very similar.

Of note, the 3D structure of Prod1 has now been solved. See, Garza-Garcia et al. (2009) PLOS ONE e7123, and the interaction between mammalian AG2 and C4.4 appears important in models of pancreatic cancer (Arumugam et al., Molecular Cancer Therapeutics 14, 941-51 [2015]).

More than expected or normally found.

A sixth digit on a human hand would be supernumerary.

Standard deviation. A statistical measure that helps demonstrate how far values are from the mean.

In this case, the mean is 8.3 and most values are expected to be within the range of five to 11.6 (+/- 3.3 from the mean).

How many times over the baseline

For instance, if Jenny has five flowers and Howard has 50, Howard has 10-fold more flowers than Jenny.

For that example, Jenny sets the baseline and Howard has some number-fold greater flowers than her.

A molecule that can be incorporated into DNA like thymidine (T). This is a nonnaturally occurring molecule, so it is useful for determining how often new nucleotides are being incorporated into DNA.

For an in-depth discussion of bromodeoxyuridine (BrdU) pulse labeling, see the annotation for figure 6.

A picture of BrdU versus dT (thymidine) can be seen here

This can be broken into three parts.

Mean: Average

Stimulation index: The ratio of cells in s-phase to the total number of cells counted.

S-phase: The portion of the cell cycle where DNA strands are duplicated or copied.

In other words, the average ratio of number of cells where DNA is being duplicated compared to the total number of cells.

The cells were "maintained," or kept in medium containing 1% serum for the rest of their life span.

In vertebrate cell culture, most cells are grown in a medium containing "serum." Often this is fetal bovine serum.

The blood from a cow fetus is withdrawn and only the serum is kept. The serum contains proteins, nutrients, and other molecules, but does not contain any other cells.

The components of fetal bovine serum can vary greatly, but in general, its addition to cell culture medium is necessary for keeping cells healthy.

Like Cos7 cells, newt blastema cells are able to be kept outside of the living organism in an artificial medium that provides nutrients, or in other words, kept in "culture."

On both sides, i.e., both the left and right limb were amputated.

Often large structures are too large to perform immunostaining or other visualization techniques on.

To get around this the tissue can be "sectioned": cut into very thin layers. Often this tissue will be sliced into micrometer-thick slices (1/1000 millimeter).

The space outside the cell.

You likely have heard of "differentiation," when a stem cell starts turning into a more specialized cell such as a skin cell or muscle cell.

Dedifferentiation is the exact opposite of that. Now, cells that were originally part of the limb start becoming more like progenitor cells.

These dedifferentiated cells can give rise to the cell type of origin.

The layer of skin below the epidermis (the top layer of skin). This holds many different types of living cells including nerves, vasculature, as well as fibroblasts, which make an important contribution to the blastema after limb transection.

For an example using human skin see here

A general term for any part of the body that secretes a substance (i.e., proteins). Remember nAG is likely a secreted protein, so a gland would be a reasonable place to find it.

"Pentosan sulfate" cells, an immortal cell line derived from mouse brain cells.

Remember, nAG is a secreted protein. The myc-tagged nAG they have transfected should be secreted just like the wild-type protein.

Often referred to as "coimmunoprecipitation." Protein complexes are able to be separated by binding an antibody to one of the proteins in that complex.

That antibody is usually bound to something heavy (agarose polysaccharides extracted from seaweed) or magnetic to allow for separation.

Epitope-tagged proteins have small stretches of amino acids added to the normal, wild-type protein. Often these additional amino acids create an epitope, an antibody-binding region.

This allows for the use of standard antibodies. Now, an antibody doesn't have to be created for each protein, only to the epitope tag, which usually can be added easily to many different proteins.

Note that in this paper the authors use both antibodies to the sequence of nAG itself, as well as antibodies to an epitope tag added to nAG. Why are they using both approaches?

An immortal cell line derived from mouse kidney that acts like fibroblasts (the cells that produce collagen in your skin, among other functions).

A common type of tertiary structure found in proteins. It gets it's name from protein thioredoxin, which has this type of fold in it.

A mucus secreting gland found at the head of frog embryos. It helps stick the frog to rocks and other substrates.

Many AG family proteins are found in glands and secretory epithelia.

Motor neurons are necessary for controlling skeletal muscle tissue and sensory neurons for sensing the environment (i.e., temperature, pain, etc.).

Nerve impulses from motor neurons travels toward the periphery of the organism to control muscle function.

Nerve impulses from sensory neurons travel toward the central nervous system.

Specialized epidermal tissue surrounding the area where the limb has been removed. This tissue is found adjacent to the mesenchymal progenitor cells.

The region and environment where stem cells responsible for forming the new limb are found.

These cells are supported by local signals from other cells and tissues, which ensures that stem cells in this location remain stem cells.

There is higher expression (i.e., more protein) in the proximal limb and the farther distal you travel the less-and-less Prod1 expression you find.

Lymphocyte antigen 6 (LY-6). A superfamily of proteins found in a variety of organisms that often share the characteristic of being GPI-anchored.

The function of these proteins is extremely diverse. They have a 3D structure that allows them to interact with a large variety of other proteins. In turn, this provides them with a large array of potential functions.

In other words, a determinant of what makes the structure distal or proximal.

Unlike embryonic stem cells (ESCs), mesenchymal stem cells are a type of multipotent stem cell. That is, they cannot become every single type of cell found in the body, but they can become a smaller subset of cell types.

These cells are able to become mesenchymal tissue such as cartilage, muscle, and connective tissue.

The initial separation of two cells that occurs at the end of mitosis.

A structure in animal cells that is involved in mitosis. During cell division, two centrosomes are located at opposite ends of the cell, and they extend fibers called microtubules that pull the chromosomes apart at anaphase. If there are more than two centrosomes, the chromosomes may not be evenly divided among daughter cells, which could lead to cell death or the development of tumors.

Also, centrosomes are duplicated simultaneously with DNA during S phase. So, if there are more than two centrosomes, there is likely also an excess of DNA generated by extra rounds of replication.

The critical point in cell division when the sister chromatids are physically pulled apart to opposite sides of the cell.

The authors incorporated foreign DNA into cells with the drug resistance gene. The resistance allows cells that contain the foreign DNA to survive treatment with the drug, while other cells will die.

Connective tissue cells that produce the extracellular matrix and collagen, which hold tissues together and help repair tissue damage.

A protein that can increase or decrease the expression of a particular gene in response to a signal. In this case, activated p53 increases the expression of p21.

Programmed cell death. In mature organisms, this mechanism eliminates unhealthy or damaged cells. During development, it removes unnecessary cells.

The genetic makeup of a cell at the DNA level as opposed to "phenotypes," which are the observed traits of a cell or an organism.

This gene codes for a protein that provides resistance to a harmful drug, typically an antibiotic. Scientists can transfer this gene to new cells to make the cells resistant to a drug, allowing these cells to be selectively propagated.

A targeting vector is a piece of foreign DNA that can be taken up by a cell. The goal is often to incorporate the sequence in the host cell genome.

A process of exchanging sections of DNA between two similar DNA sequences that cells can use to repair broken DNA.

In molecular biology, scientists can take advantage of this process to replace specific genes (targets) with modified DNA sequences.

A measure of the amount of cells in a population that are currently undergoing mitosis.

Microtubules are tubular protein structures that are a component of the cell's skeleton (the cytoskeleton). They are also important for cell division, during which they pull sister chromatids apart in anaphase.

A drug that causes cells to arrest in M phase, right before cell division. It is often used in experiments to collect cells in M phase, either to study mitotic pathways or to make sure that all cells in a culture are synchronized in the same phase.

The nonmitotic portion of the cell cycle (G1, S, and G2 phases) during which a cell grows and replicates its DNA.

Growth and replication are followed by division, the mitotic (or M) phase of the cycle.

Researchers can take a sample of cells from a patient and grow them in a dish. These cells are called a "line," and can be repeatedly grown and studied for years.

Many different lines are commercially available for researchers. Because each line comes from a different person and a different tissue type, they will all have different characteristics. Particularly with cancer cell lines, there will often be mutations in important genes, so it is critical to select a line that is appropriate for what you are studying.

These are proteins that initiate DNA replication.

Replication must occur once and only once during each cell cycle. Therefore, the licensing factors are tightly controlled (spatially and temporally) so that replicated DNA does not replicate a second time before cell division.

A stop in the cell cycle before the cell progresses to the M phase where mitosis takes place. This occurs as a result of the activation of a checkpoint at the end of G2.

A stop in the cell cycle before the cell progresses to the S phase where DNA is replicated. This occurs as a result of the activation of a checkpoint at the end of G1.

Checkpoints are specific points in the cell cycle at which the cell must confirm certain characteristics, such as its size or DNA content, before passing to the next phase. This is to ensure that cells do not replicate DNA or divide when major problems exist, such as DNA damage.

As this paper explains, p53 plays a very important role in checkpoints.

Last phase of the cell cycle during which mitosis (cell division) occurs. The cell divides into two daughter cells that each have the same number of chromosomes.

First gap phase of the cell cycle, between mitosis (M phase) and DNA replication (S phase). Cells typically grow in size during G1.

A checkpoint toward the end of this phase ensures that the cell has no DNA damage to move on to the next phase (the S phase).

"G" is short for "gap."

Phase of the cell cycle during which DNA replication (synthesis) occurs. "S" is short for "synthesis."

Cytokinesis occurs during the M phase of the cell cycle and refers to the division of the cytoplasm during cell division.

Cyclin-dependent kinases (CDKs) are important cell cycle regulators. Kinases are enzymes that add a phosphate to other proteins to activate or inhibit their function—a process known as phosphorylation.

CDKs are always present in the cell but become active only when they are bound to other proteins called cyclins. Cyclins were originally identified as proteins whose concentration cycles up and down, depending on the phase of growth. Not all proteins in this class fluctuate in this manner. Regardless, the association of CDK-cyclin complexes regulates the progression through each phase like clockwork.

Some additional regulatory proteins activate CDK-cyclin complexes, stimulating the cell cycle. Others inactivate CDK-cyclins or prevent their activation, which inhibits cell cycle progression. Among the inhibitory proteins are p53 and p21.

p53 is an important protein that is inactivated in many cancers. p53 can sense DNA damage, and accordingly causes the cell cycle to arrest.

The arrest of the cell cycle allows for the DNA to be repaired. Alternatively, p53 can initiate cell death, or apoptosis, in response to DNA damage.

Pial is an adjective derived from"pia mater," the delicate, fibrous, and highly vascular membrane forming the innermost of the three coverings of the brain and spinal cord.

Na+/Ca2+ exchanger 1

Colony-stimulating factor-1 receptor.

DNA recombination involves the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome.

In genetics, a locus (plural loci) from the Latin word for "place" is the specific location of a gene, DNA sequence, or position on a chromosome.

In genetics, a promoter is a region of DNA that initiates transcription of a particular gene.

Promoters are located near the transcription start sites of genes, on the same strand and upstream on the DNA (toward the 5' region of the sense strand).

Endogenous means relating to or produced by metabolic synthesis in the body.

Tamoxifen is an estrogen receptor antagonist.

The op/op (osteopetrotic) mutant mouse possesses an inactivating mutation in the colony-stimulating factor-1 (CSF-1) gene, which results in the absence of certain macrophages, including defective osteoclasts (macrophages of the bone), resulting in osteopetrosis.

Osteopetrosis ("marble bone disease") is an extremely rare inherited disorder whereby the bones become thick, but their increased size does not improve their strength. Instead, their disordered architecture results in weak and brittle bones.

A gate is a numerical or graphical boundary that can be used to define the characteristics of cells.

During embryogenesis, the three germ layers (endoderm, mesoderm, and ectoderm) are formed, from which all body tissues will later develop.

Neuroepithelium is the part of the embryonic ectoderm that gives rise to the nervous system .

Cephalic means relating to the head or the head end of the body. From the Latin "cephalicus," and from the Greek "kephalikos," meaning head.

The head mesenchyme is a type of undifferentiated connective tissue, which primarily originates from a mixture of cranial neural crest and head mesoderm cells.

These cells eventually give rise to the skeletal elements (skull and facial bones), connective tissue, and musculature of the vertebrate head.

Yolk sac is a membranous sac of most vertebrates that encloses the yolk. It is attached in most animals (as in humans) through the yolk stalk with the intestinal cavity of the embryo, and is supplied with blood vessels that transport nutritive yolk products to the developing embryo.

Located outside an embryo.

Being able to survival high radiation levels.

Read more about parabiotic mice here:

http://www.jove.com/video/50556/parabiosis-in-mice-a-detailed-protocol

Bone marrow is the soft, organic, spongelike material in the cavities of bones. It is a network of blood vessels and special connective tissue fibers that hold together a composite of fat and blood-producing cells.

Its chief function is to manufacture blood cells including erythrocytes, leukocytes, and platelets.

Leukocytes encompass all white blood cells, including monocytes, lymphocytes, granulocytes, and macrophages

Congenic bone marrow chimeras are mice that are genetically identical with the exception of one gene.

Hematopoeisis refers to the process of production and differentiation of all blood cell types .

A hematopoietic wave is an influx of cells that can originate from different sites of hematopoiesis such as the yolk sac, the fetal liver, and the bone marrow, or from the same site at different times under certain conditions (e.g., inflammation).

Time immediately before or after birth.

As opposed to polynuclear phagocytes (ex.: neutrophils), monocytes, macrophages. and dendritic cells have one nucleus and are called mononuclear phagocytes.

Ontogeny refers to the complete developmental history of an individual organism, or, here in this study, of a cell population.

Myeloid cells are differentiated descendants of common myeloid progenitors of hematopoietic stem cells in the bone marrow. They include granulocytes, monocytes, macrophages, and dendritic cells.

Initially, the adjective“myeloid” defined cells related or derived from the bone marrow. However, it also defines cells that are not “lymphoid,” i.e., cells related to lymphocytes that include T and B cells, as well as NK cells and innate lymphoid cells.

Performed in a living organism, from the Latin for "within the living."

Lineage tracing is the identification of all progeny, i.e., descendants, of a defined cell population or a single cell.

Homeostasis is the state of balance or equilibrium from the Greek "homœos," meaning "similar," and "stasis," meaning "standing still."

Hematopoietic cells are all blood cells that derive from hematopoietic stem cells present in the adult bone marrow.

Pathogenesis refers to the cause or origin of the pathology of a disease.

Macrophages are a type of white blood cell.

As scavengers of the immune system, macrophages engulf and destroy self-antigens, foreign pathogens (such as bacteria and viruses), cancer cells, and other cellular debris via a process called phagocytosis.

Microglia are a type of glial cell that are the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system.

The cerebral vasculature is the collection of blood vessels that supplies blood to the brain.

There are two types of cerebral vasculature: anterior and posterior, which supply blood to the front and back portions of the brain, respectively.

The arteries carry oxygenated blood with glucose and other nutrients; whereas the veins carry deoxygenated blood back to the heart.

The microvascular network is the vasculature consisting of small blood vessels (diameter less than 100 microns). A large amount of oxygen is supplied throughout the brain by these networks.

SMAD proteins are signaling molecules located in the cytoplasm of a cell.

Phosphorylation of SMAD proteins indicates the activation of these proteins.

Activated SMADs lead to a cascade of signaling events for gene transcription in the nucleus to regulate diverse biological functions.

The BMP/TGF-beta signaling pathway has an important role in cell growth, differentiation, and development of biological systems.

Pericytes are contracting cells that wrap around endothelial cells in the blood vessels. These cells are capable of constricting blood vessels.

Green fluorescent protein is a fluorescent protein marker used to tag a protein of interest, allowing visualization of movement of the protein of interest.

Endothelial progenitors are a rare population of cells in the blood that give rise to endothelial cells. Endothelial cells form the lining of blood vessels.

Magnetic resonance imaging (MRI) is a radiological imaging technique to observe the anatomy and physiology of the body. MRI uses magnetic fields and radiowaves (there is no ionizing radiation) to form images of the body.

Currently, MRI is considered to be the better method (compared with CT scans) for brain imaging.

Typically, an angiogram is an imaging test that uses x-rays to visualize blood vessels in the body. In this case the word "angiogram" is used to denote the 3D reconstruction of the z-stacks. They did not do x-rays.

Cerebrovasculature refers to the blood vessels in the brain, especially the arteries that supply blood to the brain.

An increased sense of smell.

There are three types of neurons in the central nervous system: sensory neurons, interneurons, and motor neurons.

Interneurons enable communication between sensory and motor neurons.

Rostral and caudal are directionality terms used for the brain.

Rostral, or anterior, refers to the front end (near nose) and caudal, or posterior, refers to the back end.

Neural stem cells differentiate into neuroblasts. A neuroblast is a dividing cell, which gives rise to a neuron.

The hippocampus is a C-shaped structure in the brain that functions for learning, memory, and spatial navigation.

The dendate gyrus is a subsection of the hippocampus. Neurogenesis also occurs in the dentate gyrus of the hippocampus.

Ki67 is a cellular marker for proliferating cells.

Sox2 is a transcription factor that marks stem cells.

Olig2 is a transcription factor that is a marker for progenitor cells. Progenitor cells give rise to differentiated cells.

The brain can be sectioned into three different planes called coronal, sagittal, and horizontal/axial.

Coronal sections are vertical dissections, similar to slices from a loaf of bread.

The subventricular zone is located in the walls of the lateral ventricles. This zone is one of the two main sites of neurogenesis in the adult mammalian brain. The lateral ventricles contain cerebrospinal fluid and are part of the ventricular system in the body.

Parabiosis means “living beside.” Parabiosis can be between animals of different strains or different weight, age, or any other parameter.

In this study, parabiosis is the process of sewing an old mouse and a young mouse together so they share one vascular system.

Heterochronic parabiosis is when parabiosis is performed between animals of different ages. Isochronic is same age.

Chemokines are chemical signaling molecules secreted by cells that induce changes in signaling pathways of another neighboring cell(s).

'Re-wiring' of neuronal synaptic connections in oder to adapt to environmental changes.

Neurogenic potential is the ability to generate mature neurons for the process of neurogenesis.

Proliferation refers to the continuous division of a cell, and differentiation is the process where a stem cell acquires a specialized cell fate.

Neurovascular diseases occur from sudden blockage of the normal blood flow to the brain or deterioration of the vasculature.

Examples include ischemic strokes or brain aneurysms.

Neurodegenerative diseases result primarily in the loss of function and death of neurons leading to progressive loss of structure in a region of the brain.

Examples include amyotrophic lateral sclerosis, Parkinson’s, and Huntington disease.

Vascular remodeling is the process of altering the 3D structure and architecture of blood vessels.

Generation of neurons from neural stem cells and neural progenitor cells.

Neural stem cells are cells that are able to self-renew, and are capable of differentiating into any cell type in the central nervous system.

A specialized microenvironment favorable to the regulation of stem cells in the nervous system.

The central nervous system is a complex network of nerve tissues that control functions of the body. It consists of the brain and spinal cord.

Cellular materials (materials with a significant amount of porosity) present a number of properties (namely low weight, high sound absorption, crashworthiness, high permeability, thermal properties) that make them suitable for a large range of applications.

Metamaterials are a class of objects whose properties are related to the geometrical properties of the constituting structure and not to the mechanical properties of the constituting material.

These metamaterials present properties not obtained with regular materials.

Buckling is a phenomenon of instability: A slender structure submitted to a compressive load can bend and deform in the direction perpendicular to the compression axis.

The structure will then be submitted to a bending load rather than a compression load.

Ductile is the opposite of brittle. A ductile material can deform plastically without breaking when subjected to a load.

A brittle material submitted to a stress breaks without significant deformation.

A tetrakaidecahedron, also called tetradecahedron (from the Greek words tetra, four, and deca, 10) is a polyhedron with 14 faces.

A material is said to present hysteresis if its behavior depends on the current loads applied and on the history of the past loads.

For example, a material that presents hysteresis will not sustain the same stresses if the strains are increasing or decreasing: The stress-strain curve will present a loop.

This parameter characterizes the ability of a material to withstand loads tending to reduce its size in one dimension.

It is defined as the maximum force per unit area of a material to withstand loadings before it fails plastically (i.e., in a permanent and irreversible way) or fractures.

Young's modulus is a parameter used to characterize the stiffness of a material.

It is defined as the ratio between the stress (force per unit area) and the strain (displacement normalized by the initial length) and it is expressed in Pa.

Sintering is the process of forming a solid mass of material by heating or pressuring particles of this material without reaching the melting point.

Atomic Layer Deposition is a method to deposit a thin film on a substrate. It consists of exposing the surface of the substrate to gaseous species.

Electroless nickel plating is a chemical technique to deposit a layer of nickel alloy on a solid piece made of another metal or of plastic.

Scanning electron microscopy is a technique used to image the surface of a sample with a high resolution. (The resolution is in the nanometer scale.)