68 Matching Annotations
  1. Jul 2020
    1. anterior

      This is an anatomical term which refers to the front of the body, or near the head.

      In the case of planaria, it refers to the head.

    2. posterior

      This is anatomical term which refers to the back of the body, or near the hind end of the body.

      In the case of planaria, it refers to the the hind end.

    3. C. Y. Logan, J. R. Miller, M. J. Ferkowicz, D. R. McClay, Development 126, 345 (1999).

      This work is part of the foundation that the Wnt signaling pathway is well established chemical pathway in embyrogenesis. This is important, because embryos contain stem cells which require direction for migration and differentiation much the the regeneration in adult planarians.

    4. C. E. Rocheleau et al., Cell 90, 707 (1997

      This research was the first to identify the set of genes in C. elegans (a simple nematode invertebrate model) that were used in the experimental RNAi silencing by Alvarado and colleagues. Evidence was also provided that showed a potential role in early embryonic development.

    5. S. Q. Schneider, B. Bowerman, Dev. Cell 13, 73 (2007).

      The data confirm that β-catenin regulates cell fate in two very distant animal species, which suggest that β-catenin has an ancient metazoan origin.

    6. A. H. Wikramanayake et al., Nature 426, 446 (2003).

      The authors in this study show that β-catenin plays a role in cell adhesion and body plan development in sea urchins, a primitive invertebrate animal. This research provides additional evidence the β-catenin is an evolutionarily important molecule and its role has been maintained over time across the animal kingdom.

    7. 1. S. Schneider, H. Steinbeisser, R. M. Warga, P. Hausen, Mech. Dev. 57, 191 (1996).

      The authors used two vertebrate models, zebrafish and frogs, to identify that β-catenin via the Wnt signaling pathway plays a role in dorsal-ventral polarity. This research suggest that β-catenin is an important molecule because it has been found to play similar roles in both vertebrates and invertebrates.

    8. R. Stadeli, R. Hoffmans, K. Basler, Curr. Biol. 16, R378 (2006)

      The data provided insight into how the Wnt signaling pathway and β-catenin target gene activation. This foundational information provided understanding of how RNAi could be used to silence the genes associated with control of this pathway.

    9. H. Yokoyama, H. Ogino, C. L. Stoick-Cooper, R. M. Grainger, R. T. Moon, Dev. Biol. 306, 170 (2007).

      Some amphibian species have the ability to regenerate limbs. The data suggest that Wnt/β-catenin signaling plays an essential role in this process. These results again confirm that β-catenin is present across various animal species. A full understanding of regeneration in vertebrates may lead to potential treatments for human organ regeneration.

    10. T. H. Morgan, Am. Nat. 38, 502 (1904)

      Morgan was a pioneer in the field of genetics. His theory that polarity, or development of two axes in animals was a direct result of the presence of a yet unidentified molecule. This theory has stood the test of time and provides the foundation of this research.

    11. P. W. Reddien, A. Sánchez Alvarado, Annu. Rev. Cell Dev. Biol. 20, 725 (2004).

      Earlier research by Alvarado and colleagues identified the types of tissue that are able to regenerate from a blastema that forms after tissue damage. Without previously identifying this role, the current research would not be possible.

    12. RNAi-treated animals were then amputated to assess the role of the silenced genes during regeneration

      Once the silenced genes were introduced to the planaria via diet, amputations were conducted.

    13. the remaining trunk formed one anterior and one posterior blastema, which then differentiated to replace the missing structures

      After amputation, the trunk of the control worms that remained developed a blastema. A blastema is a mass of cells that tell other cells to differentiate (become different cell types) and sends them to the correct location in the body. In injured animals, blastemas help direct tissue regeneration. You can find out more about blastemas and regeneration through this link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5753424/

    14. RNAi of a single β-catenin (Smed-βcatenin-1), both dishevelled homologs (Smed-dvl-1;Smed-dvl-2), or APC (Smed-APC-1)

      Each of these proteins were silenced individually using RNAi and then incorporated into a food source for planarians. The experimental group was divided into three and each was fed one type of the RNAi food for 8 days. Amputations were then completed on all experimental animals on Day 9.

    15. Anatomically, two organ systems with characteristic asymmetries along the A/P axis were examined: (i) the central nervous system (CNS), composed of two anterior cephalic ganglia (brain) and two ventral cords projecting posteriorly (Fig. 1G), and (ii) the digestive system, consisting of a single anterior and two posterior gut branches (Fig. 1K)

      To identify anatomical characteristics that follow an anterior/posterior axis position (head vs tail), the researchers looked at two organs - the primitive brain and the primitive spinal cord of the planaria . This is important to determine, because it allows researchers to identify which molecules direct cells to become a certain cell type as well the molecule that directs the cells to their respective locations in the body.

    16. Our results indicate that β-catenin activity is a key target of polarity specification in planarians, providing mechanistic insight into the old, unanswered question of how blastema fate is controlled. We propose that the evolutionarily ancient β-catenin protein, in a manner reminiscent of its role during metazoan embryogenesis (6, 8), acts as a molecular switch in adult planarians and that it may play a similar role in the adult tissues of other animals.

      This research using planaria as a model organism, suggests that β-catenin is an important molecule that has been retained over evolutionary time. It acts as as switch to determine cell fate during embyrogenesis and in adult tissue. It is suggested that this hypothesis may be the same for other species and provides important insights in organ regeneration.

    17. With respect to putative downstream effectors, planarians can regenerate double heads after pharmacological gap junction inhibition, and β-catenin is implicated in gap junction formation and function (19–21).

      Nogi and colleagues identified the role of gap junctions, which allow ions or other small molecules to move between cells, at the planarian amputation sites.

      Shaw and colleagues determined the role of microtubules in the formation of gap junctions. The ability of cells to stick together (cell adhesion) is crucial to this formation.

      Guger and colleagues identified that β-catenin may play a role in communication between cells via gap junctions.

    18. Both blastemas of Smed-βcatenin-1(RNAi) worms adopted an anterior fate, resulting in animals with two heads of opposite orientation (penetrance = 100%, n = 39).

      All of the planaria with the β-catenin silenced developed two heads, with the second head in the location where the tail should be.

    19. We cloned and determined the expression patterns of all identifiable homologs of core pathway components (Fig. 1A) and silenced them, individually or in combinations, on the basis of likelihood of redundancy as gleaned from the expression data (figs. S1 to S6 and table S1).

      In this initial part of the experiment, the researchers identified the components of the Wnt signaling pathway found in S. mediterranea and made copies of the genes. Then, using RNAi, each component was silenced individually, and then was silenced in selected groupings to determine the role of each chemical and whether there was overlap in their functions. RNAi was fed to the planaria to introduce the silenced protein.

    20. More than 100 years ago, T. H. Morgan reported that fragments with closely spaced anterior and posterior amputation planes occasionally regenerate two-headed animals (22, 23)

      This early (1800s) research on planarians provides an essential background for the regenerative capabilities of planaria. The observations from this research is essential for understanding planaria today.

    21. Indeed, β-catenin regulation can be Wnt-independent in vertebrate cells, and Dishevelled remains the most upstream known β-catenin regulator during early sea urchin development (14, 17, 18)

      This research shows that β-catenin plays a role in all animal species studied including vertebrates and invertebrates, but how it is regulated in vertebrate animals may be different than in invertebrates. This is important to understanding stem cell regulation because it appears to regulated differently in planaria (invertebrate) than in humans (vertebrate).

    22. protrusions

      Here, protrusions refer to bulges of cells.

    23. periphery

      Refers to the outer edge.

    24. Under these conditions, anterior blastemas were properly fated, indicating that the misspecification phenotype of Smed-APC-1(RNAi) depends on Smed-βcatenin-1 (Fig. 2C). Additionally, posterior blastemas adopted an anterior fate, indicating that the Smed-βcatenin-1(RNAi) phenotype does not depend on APC activity. The combined data show that signaling through β-catenin occurs at posterior amputations and is necessary and sufficient to specify tail fate. In contrast, signaling through β-catenin is blocked or never occurs at anterior amputations, and this is necessary and sufficient to specify head fate. The premature expression of the anterior marker in Smed-βcatenin-1(RNAi) worms may indicate that in wild-type planarians, β-catenin inhibition does not immediately follow amputation (Fig. 2A). We suggest that β-catenin activity acts as a molecular switch to specify head versus tail fate in planarians.

      These data suggest that the presence or absence of β-catenin is necessary during early development of the blastema so that the cells differentiate into either a head or a tail. The presence of β-catenin in the anterior end after amputation directs cells to become the head, while its absence in the posterior blastema is necessary for the cells to differentiate into the tail.

    25. This is consistent with the multiple roles of Dishevelled in different pathways

      When compared to past research, the resulting effects of the silencing of Smed-dvl-1(RNAi) and Smed-dvl-2(RNAi) are similar to previous results.

      See the Nature of Science in the Next Generation Science Standards.

    26. After head and tail amputations of control worms

      In a controlled experiment, there are two groups: 1) one is controlled, which means that all conditions are held constant or the same and 2) experimental group, in which a defined variable is changed. In this case, the experimental group was treated with RNAi, while the control group was not. This allows scientists to compare the two groups to determine if what they changed in the experimental group was due to that variable.

    27. planaria, we analyzed the canonical Wnt signaling system in Schmidtea mediterranea

      The goal for this series of experiments was to better understand the Wnt signaling system because it is found many animal species ranging from invertebrates to vertebrates. The Wnt signaling system is a pathway found in most animal species. It is one of the most important cell signaling systems because of its control over how and when cells divide, change into specific cell types, and move to the area of the body that they belong during embryonic development. This includes directly how stem cells allow for renewal of damaged tissues.

      You can find more information on this pathway here: https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/wnt-signaling-pathway

    28. signaling pathways

      A series of linked chemical pathways in which one chemical in the series activates another chemical in the pathway, which ultimately leads to a specific cell function.

    29. Schmidtea mediterranea

      This is an image depicting this common planarian.

  2. Jun 2020
    1. silencing

      Turning a gene off so that it does not go through transcription and translation (gene expression) which prevents the production of its protein product (β-catenin) being made by the cell.

    2. During embryonic development of both vertebrates and invertebrates, β-catenin regulates a variety of cellular processes, including organizer formation, cell fate specification, proliferation, and differentiation (1–9)

      Schneider and colleagues identified that β-catenin regulates dorsal-ventral polarity in vertebrates (animals with backbones).<br> Later research identified that β-catenin is modulated by the Wnt signaling pathway. It plays a role in forming groups of embryonic cells that direct the initial formation of the neural plate (basis for the nervous system) and the complete body axis (head vs feet ends of an organism) of the animal.

    3. In adult animals, the Wnt/β-catenin pathway participates in regeneration and tissue homeostasis; misregulation of this pathway can lead to degenerative diseases and cancer in humans (9–12)

      Several studies identified the role of β-catenin in regeneration of tissues and its potential relationship to degenerative diseases and cancer, which are both related to regulation of cell division. Identification of active β-catenin in adult tissue is important for potential treatment of these disease.

      Watch this video to find out more about the relationship between cell division and cancer: https://www.hhmi.org/biointeractive/eukaryotic-cell-cycle-and-cancer

    4. In response to upstream cues, such as Wnt ligands binding to Frizzled receptors, β-catenin accumulates in nuclei (Fig. 1A) and invokes transcriptional responses that direct the specification and patterning of tissues (13, 14)

      Stadeli and colleagues research indicates that β-catenin plays a major role in regulating the body pattern and head/tail orientation of cells during development.

    5. constitutive degradation

      The regulated breakdown of a cell or cellular product, which is used to control gene expression and ultimately cellular function. In this case, the breakdown of APC leads to an increase in β-catenin.

    6. caused striking alterations in the anteroposterior (A/P) identity of regenerating tissues

      Silencing of β-catenin, both dishevelled homologs (Smed-dvl-1;Smed-dvl-2), or APC (Smed-APC-1) disrupted the ability of the cells to determine whether they belonged in the front or back of the animal during regeneration.

    7. Smed-dvl-1(RNAi);Smed-dvl-2(RNAi) worms also regenerated heads from both blastemas but displayed additional phenotypes, including ectopic and supernumerary photoreceptors in the anterior region.

      Smed-dvl-1(RNAi);Smed-dvl-2(RNAi) planarian groups also developed two heads, as well as extra photoreceptor cells in locations where are they are not typically found on the anterior portion of the body.

    8. We therefore used the anterior and posterior markers to investigate the onset of blastema differentiation in control and RNAi-treated trunk fragments (Fig. 2, A and B).

      With the knowledge from the previous experiment that regulation of β-catenin occurs earlier in the Wnt signaling pathway, the researchers were able to use the anterior/posterior markers to identify the time period during which the stem cells of the blastema differentiated in both the control and experimental animals.

    9. In control animals at 12 hours after amputation, the anterior marker was virtually undetectable, whereas the posterior marker was clearly evident in the posterior blastema; 24 hours after amputation, the two markers recapitulated the A/P specificity seen later during regeneration and in adult animals (Fig. 1, O and S; Fig. 2, A and B). However, in Smed-βcatenin-1(RNAi) trunks, the anterior marker was expressed at both ends by 12 hours and maintained throughout the experiment, whereas the posterior marker remained markedly reduced (Fig. 2, A and B). The reverse was observed in Smed-APC-1(RNAi) trunks (Fig. 2, A and B). Consistent with the inferred time window for β-catenin signaling, Smed-βcatenin-1 and Smed-APC-1 were expressed at both ends in wild-type animals by 12 hours (fig. S7). These results indicate that β-catenin and APC act very early to determine blastema identity.

      Alvarado and colleagues surmised from the results of the previous experiment that β-catenin was regulated early in the blastema identify development. In comparing the migration and differentiation timing between both β-catenin and APC-1 with the control animals, they were able to confirm that indeed it occurred that blastema cell identity occurred very early.

    10. We next used animals silenced for both Smed-βcatenin-1 and Smed-APC-1 to test whether the Smed-APC-1(RNAi) phenotype results from increased β-catenin activity.

      In this set of experiments, Alvarado and colleagues were trying to identify if increased amounts of β-catenin regulates that expression of Smed-APC-1.

    11. We then explored whether the β-catenin switch plays a role in blastema identity regardless of the A/P location or angle of amputation. Indeed, the head fragments of Smed-βcatenin-1(RNAi) and Smed-dvl-1(RNAi);Smed-dvl-2(RNAi) worms regenerated a head from the posterior wound (penetrance = 79%, n = 24; penetrance = 82%, n = 33, respectively), and the tail fragments of Smed-APC-1(RNAi) worms regenerated a tail from the anterior wound (penetrance = 67%, n = 27; Fig. 3, A to E, and movie S4). After longitudinal amputation along the midline, control animals formed a blastema along the A/P axis and regenerated mediolaterally (Fig. 3, F, J, N, and R). In contrast, Smed-βcatenin-1(RNAi) and Smed-dvl-1(RNAi);Smed-dvl-2(RNAi) worms regenerated anterior tissue and developed multiple ectopic heads along the lateral edge (Fig. 3, G, H, K, L, O, P, S, and T).

      In this fourth set of experiments, the researchers wanted to identify the role of β-catenin at different amputation locations for the experiment animals while different genes were silenced and then comparing this to control animals with no genes silence but the same amputations. Amputations included removing the head or tail to see if the head or tail itself would regenerate. In addition, some animals were divided in half longitudinally (lenthwise) and some were divided in half mediolaterally (divided into anterior and posterior halves).

    12. Our data indicate that β-catenin activity is regulated during lateral regeneration and that the β-catenin switch can dominantly misspecify regenerating tissues regardless of A/P position or amputation angle.

      The results form the fourth set of amputation experiments suggests that β-catenin is regulated at locations of amputation.

    13. Ectopic photoreceptors were visible in the tail of all (n = 20) Smed-βcatenin-1(RNAi) animals and none of the control animals (Fig. 4, G, H, M, and N). Intact RNAi-treated animals also exhibited ectopic lateral protrusions, formed a brain in the tail region, and expressed the anterior marker posteriorly (Fig. 4, I to L and O to R, and movie S6). The molecular basis for such a change of A/P polarity in an adult organism was previously unknown.

      The results of the observations of the unamputated animals with silenced genes allowed the researchers to identify that β-catenin plays a role in the anterior/posterior identity of cells in adult animals. This mechanism was not previously known.

    14. Together, our data demonstrate the fundamental importance of β-catenin in the maintenance of polarity and cell fate during tissue regeneration and homeostasis in planarians (fig. S8). Our findings reveal a dynamic control of β-catenin in adult animals that is not readily apparent during the progression of embryogenesis: The precise quantity and location of regenerating tissue is different for each individual and for each regeneration event, newly regenerated tissues must integrate with the old, and ongoing homeostatic cell turnover may require sustained instructive cues.

      This research identified previously unknown roles of β-catenin. Previous research identified the role it plays in embryogenesis with regard to cell fate and migration. However, identification of its multiple roles in adult tissue regeneration and homeostasis was not previously identified.

    15. regeneration

      Planarians are masters of regeneration, but why? Read this article to find out more: https://www.hhmi.org/news/single-adult-cell-flatworm-crafts-new-body

    16. The mechanisms that differentiate anterior from posterior and direct the replacement of the appropriate missing body parts are unknown

      Find out another method Dr. Alvarado is using to identify the origin of the regenerative abilities in planarians in this article and watch the short video to find out more: https://www.hhmi.org/news/searching-source-planarians-regenerative-powers

    17. planarians

      Why is important to study planarians? This interview with the lead author of this study explains why its important to conduct research on understudied animals: https://biobeat.nigms.nih.gov/2019/10/interview-with-a-scientist-unlocking-the-secrets-of-animal-regeneration-with-alejandro-sanchez-alvarado/

    18. transcriptional output

      The copying of DNA into mRNA, which is the first step in the process known as gene expression.

      Watch this video to learn more about the role of transcription and transcription factors: https://www.hhmi.org/biointeractive/signal-molecules-trigger-transcription-factors

    19. regenerate

      Regeneration in this case, refers to the replacement of lost or damaged tissue.

      This video will help you understand the process of tissue regeneration: https://www.hhmi.org/biointeractive/tissue-regeneration-animals

    20. We therefore observed unamputated (intact) worms 14 days after the final RNAi feeding.

      In the fourth series of experiments using the various amputation location, it was noted that in some of the experimental animals that several photoreceptors and brains developed in the wrong location on the same animal. To understand why this happened, unamputated worms had the same genes silenced as the experimental animals and were observed for two weeks.

    21. We noted that misspecified heads and tails in RNAi-treated worms moved independently from the rest of the animal, hence this tissue was functioning autonomously (movies S1 to S3). We conclude that silencing Smed-βcatenin-1, Smed-dvl-1(RNAi);Smed-dvl-2(RNAi), or Smed-APC-1 is sufficient to misspecify blastema identity.

      Both heads and tails that developed in the wrong locations functioned separate from the the movements of the rest of the animal. The RNAi silencing changed the cellular identity of the stem cells so that they migrated to the wrong location and incorrect cell differentiation.

    22. Smed-sFRP-1, a homolog of secreted Frizzled-related proteins (sFRP), was expressed in an arch of cells capping the anterior edge of the animal. In contrast, Smed-fz-4, a homolog of Frizzled receptors, was expressed at the posterior edge in a posterior-to-anterior gradient. We refer to Smed-sFRP-1 and Smed-fz-4 as the “anterior marker” and the “posterior marker,” respectively, in all subsequent analyses.

      The use of the anterior and poster markers will allow the researchers to determine if posterior cells are indeed moving to the posterior end and if anterior cells are moving to the anterior end in the RNAi treated animals.

    23. we used two markers identified during our in situ analyses that are specifically expressed at the anterior and posterior ends of intact and regenerating animals (Fig. 1, A, O, and S)

      Genes that are expressed only at the anterior or posterior ends were tagged to identify their location in both control and experimental animals while they are regenerating. This allows the researchers to identify the extent to which the stem cells were affected when silencing the proteins. Researchers can compare the control animal's cell migration to the the cell migration in the experimental animals for each of the silenced genes and gene combinations.

    24. The “posterior” head of Smed-βcatenin-1(RNAi) and Smed-dvl-1(RNAi);Smed-dvl-2(RNAi) animals contained a characteristically anterior nervous system and gut, as did the “anterior” head

      The results of the anatomical analysis indicate that the head located in the posterior region in the experimental animals resembled cells usually found in the anterior region as part of the nervous system. This indicates that stem cells did not locate to the correct position for a head when these genes were silenced.

    25. In contrast, the “anterior” tail of Smed-APC-1(RNAi) animals was devoid of discernible brain tissue and exhibited posterior structures, as did the “posterior” tail (Fig. 1, J and N)

      By silencing this protein, stem cells were directed to both anterior and posterior regions of the body, but were directed to become anatomical tails, with not formation of brain tissue present in either end.

    26. A/P misspecification

      The cells that were supposed to be in the posterior end migrated to the anterior end of the animal, or vice versa.

    27. To address whether these changes were superficial or reflected a fate transformation of internal cell types and organ systems, we used anatomical and molecular markers of A/P identity.

      In order to determine whether the changes in anterior/posterior identity were temporary changes that influenced the cells to act like a different cell type or whether DNA expression itself was permanently change, Alvarado and colleagues examined the location of the anatomical structures that regenerated. In addition, they identified the active molecular markers, which are chemicals that will help identify the activity of cells in a specific area to determine what type of cell they are. In this research, the markers direct the cells where to go (anterior or posterior). Some are active only for certain time periods of the regeneration process.

    28. On the other hand, Smed-APC-1(RNAi) animals regenerated tails from both amputation planes

      Silencing fo the Smed-APC-1 resulted in each end of the animal developing a tail.

    29. upstream components

      The chemicals at the beginning of the signaling pathway.

    30. protein perdurance

      How long the protein lasts as part of the signaling pathway.

    31. penetrance

      The percentage or proportion of individuals with the genotype that present the phenotype. In other words, organisms may have the genes by may not show the trait. You can find more information about these terms in this article: https://www.ncbi.nlm.nih.gov/books/NBK22090/

    32. Hence, loss of APC leads to a rise in β-catenin levels that is sufficient to drive transcriptional responses (15)

      This early research provides evidence for the importance of chemical signaling pathways as the major form of cell-to-cell communication and play a role in the body throughout an animal's lifetime.

    33. Dishevelled has multiple functions but plays an essential role as a positive regulator of β-catenin by inhibiting the destruction complex (16)

      Wallingford and colleagues found evidence for the important role that the protein known as Dishevelled plays in cell fate (how cells know what type of cell to become); how cells know where to go (head or tail), and how cells interact with each other in the animal body. Dishevelled has been found to play this same role across many animal species, which indicates its importance.

    34. homeostasis

      The ability or tendency of an organism to maintain internal stability. This includes maintaining certain ranges of physiological processes such as temperature, pH, or ions such as calcium.

    35. anteroposterior

      Genes are used to create both a front and a back for an organism during early embryonic development.

    36. molecular switch

      A molecule, such as a protein, than controls gene expression by either turning it on or off.

    37. cell adhesion

      Specialized protein complexes that allow cells to stick to each other.

    38. freshwater planarians

      Freely swimming flatworms from the taxonomic class Turbellaria that inhabit freshwater.

    39. amputation

      For most organisms it involves removal of a limb. Planaria do not have limbs, so in this case refers to removing either the front or hind end of the body.