On 2016 Jul 27, Duke RNA Biology Journal Club commented:

This is a summary of a journal club discussion:

This is one of four articles using similar imaging techniques to study translation in living cells published at the same time. These publications add to the growing number of techniques used to image translation such as mature fluorescent proteins Yu J, 2006, TRICK Halstead JM, 2015, and RNA-binding protein/mRNA co-fluorescence Wu B, 2015. The technique presented in this article is similar to the last except that it uses Suntag to image the nascent chain and PP7 aptamers on the mRNA. The colocalization of the two represents active translation in polysomes.

The technique is novel because co-localization is detected as the protein is translated. This brings fluorescent V4-peptide antibodies into concentrated foci at a single point, and can thus be used to follow multiple rounds of translation. Because of this, only detection of the translated protein is needed and indeed, past the first figure, the mRNA fluorescence is not shown. Fast changes in translation can be detected as shown using the ATF4 ORF construct translational response to stress shown in Figure 4 with the possibility of extending the time of tracking to hours by anchoring the mRNA Yan X, 2016 or using fast 3D imaging techniques. One unusual observation the authors made was the vast heterogeneity of transcript translation within a single cell; at any given time only a subset of the transcripts undergo translation and translation rates may vary depending on as yet unknown factors. A related observation is the diffusion of polysomes within the cell: polysomes translating cytosolic transcripts have slower diffusion rates in the perinuclear region of the cell compared to the cytoplasm. This could be due to the restrictive architecture of a membranous area but the exact mechanism remains unknown. A second surprising observation indicates mRNAs that have begun translation and are associated with polysomes can be transported in dendrites, contrary to earlier reports Besse F, 2008. However, the authors cannot detect if translation is temporarily stalled during transport.

While this technique makes substantial findings in the area of single transcript translation behavior, there are limitations. All in all, these images are dots that respond to translation inhibitors, meaning the resolution is not good enough to detect codon resolution and should be coupled with other techniques to verify observations and determine their mechanism. Additionally, since detection of the nascent chain wouldn’t be detected until the majority of the V4 peptides were translated, initiation would be overlooked; however, TRICK is an existing technique for studying the first round of translation.Our main criticism with this technique is the extensive construct engineering that must be performed which raises concerns over disturbing the mRNA and protein functions from both the PP7 aptamers, the Suntag peptides and an ornithine decarboxylase tag to facilitate rapid degradation of the protein. These engineering steps add over 2 kb to the original gene. Additionally, an antibody against the Suntag and a fluorescent PP7 coat protein must be expressed in the cytosol. While the constructs studied did not cause harm to the cell, each construct of interest must be tested individually. Along this line, while there is the possibility to multiplex by changing the aptamer loop or peptide-antibody combination, it would be difficult to multiplex above two individual transcripts. Thus large-scale studies involving individual translation dynamics of mRNA subsets would remain time consuming and technically challenging.

A quick comparison with the three other papers show agreements among all of them Iwasaki S, 2016 however, there is a great opportunity to learn by reading the papers to compare experimental approaches of three groups. We look forward to see what novel findings this technique uncovers as it becomes adopted in different laboratories.

On 2016 Jul 27, Duke RNA Biology Journal Club commented:

This is a summary of a journal club discussion:

This is one of four articles using similar imaging techniques to study translation in living cells published at the same time. These publications add to the growing number of techniques used to image translation such as mature fluorescent proteins Yu J, 2006, TRICK Halstead JM, 2015, and RNA-binding protein/mRNA co-fluorescence Wu B, 2015. The technique presented in this article is similar to the last except that it uses Suntag to image the nascent chain and PP7 aptamers on the mRNA. The colocalization of the two represents active translation in polysomes.

The technique is novel because co-localization is detected as the protein is translated. This brings fluorescent V4-peptide antibodies into concentrated foci at a single point, and can thus be used to follow multiple rounds of translation. Because of this, only detection of the translated protein is needed and indeed, past the first figure, the mRNA fluorescence is not shown. Fast changes in translation can be detected as shown using the ATF4 ORF construct translational response to stress shown in Figure 4 with the possibility of extending the time of tracking to hours by anchoring the mRNA Yan X, 2016 or using fast 3D imaging techniques. One unusual observation the authors made was the vast heterogeneity of transcript translation within a single cell; at any given time only a subset of the transcripts undergo translation and translation rates may vary depending on as yet unknown factors. A related observation is the diffusion of polysomes within the cell: polysomes translating cytosolic transcripts have slower diffusion rates in the perinuclear region of the cell compared to the cytoplasm. This could be due to the restrictive architecture of a membranous area but the exact mechanism remains unknown. A second surprising observation indicates mRNAs that have begun translation and are associated with polysomes can be transported in dendrites, contrary to earlier reports Besse F, 2008. However, the authors cannot detect if translation is temporarily stalled during transport.

While this technique makes substantial findings in the area of single transcript translation behavior, there are limitations. All in all, these images are dots that respond to translation inhibitors, meaning the resolution is not good enough to detect codon resolution and should be coupled with other techniques to verify observations and determine their mechanism. Additionally, since detection of the nascent chain wouldn’t be detected until the majority of the V4 peptides were translated, initiation would be overlooked; however, TRICK is an existing technique for studying the first round of translation.Our main criticism with this technique is the extensive construct engineering that must be performed which raises concerns over disturbing the mRNA and protein functions from both the PP7 aptamers, the Suntag peptides and an ornithine decarboxylase tag to facilitate rapid degradation of the protein. These engineering steps add over 2 kb to the original gene. Additionally, an antibody against the Suntag and a fluorescent PP7 coat protein must be expressed in the cytosol. While the constructs studied did not cause harm to the cell, each construct of interest must be tested individually. Along this line, while there is the possibility to multiplex by changing the aptamer loop or peptide-antibody combination, it would be difficult to multiplex above two individual transcripts. Thus large-scale studies involving individual translation dynamics of mRNA subsets would remain time consuming and technically challenging.

A quick comparison with the three other papers show agreements among all of them Iwasaki S, 2016 however, there is a great opportunity to learn by reading the papers to compare experimental approaches of three groups. We look forward to see what novel findings this technique uncovers as it becomes adopted in different laboratories.