Thread by @CanAztekin

After a year since #biorxiv, I am glad that this story found its home at @Dev_journal. Huge thanks to my colleagues @GurdonInstitute @MarioniLab, and people who reached out after #biorxiv submission! Here is the lengthy Tweetorial and some notes.
journals.biologists.com/dev/article/do…

We want to know why mammals fail at regen their arms or legs. However, we do not even know if we have cell types to perform such a feat.

To answer this, we use pre-metamorphic frogs/tadpoles. Gladly, my leg doesn’t look like a frog leg, but tadpoles are the most similar lab animal developing their limbs like mammals and can regen limbs + older they get, they fail at regen. So, what`s going different?

For a long time, it has been hypothesised that regen requires a “special” skin tissue (instead of a scar as in mammals), and the absence of this tissue was suggested to cause regen-incompetency.

However, what kind of cells are present in this tissue? Maybe us mammals don’t have them? Previously, it was suggested that these animals may be re-forming limb development associated cells. But, we did not have comprehensive cellular analysis testing this hypothesis.

By single-cell transcriptomics, we found that indeed tadpoles re-use their developmental cell type programme (AER cells) to form a “special” skin tissue and hey, we also had AER cells when were in our mother’s belly!

Along the way, contrary to what we hoped, we found tadpoles do not use the same cell types to regen their limbs and tails- although there could be similar genes and tissue morphologies. Hence, we needed a simpler system like tail regen but to study limb regen

Working with tadpoles is quite challenging – they need min 3L large aquariums and love moving around - experimenting is hard! To overcome these, we decided to try growing their limbs in a dish, so we wont need aquariums or worry about movement.

After changing an existing protocol, we established a robustly working method where we can finally study limb regen in a dish – to some extent. By using these cultures, we were able to gain a lot of new insights on regen and “special” skin tissue.

Then we switched back to our focus: as mammals also have AER during embryonic development, then why cant mammals reform them upon amputations? For this, we asked what is different in regen-incompetent tadpoles?

Previously, it was suggested that cells basically become incompetent to contribute to regen. However, this hypothesis was not able to explain some other phenotypes in the literature and some of our experiments #checkthepaper

By using our limbs in a dish approach, we did many experiments that we would not be able to do using whole animals. Results strongly direct that secreted factors assoc with bone forming cells can block AER cells, even if the other cells are competent for regen.

So, our results propose manipulation to bones may be needed to kick-start limb regen ability, in addition to other barriers to regen (e.g. scarring). There are still a lot of explore, please check the paper & peer review history

Why aquatic animals are good/terrestrials are bad at limb regen? Could a more robustly working skeletal system be selected over limb regen ability for terrestrials? Undoubtedly, there is more to the story than gene exp or immune system diff btw animals

Of course, the implications of our model for Wolverine remains unclear: having an adamantium skeleton may have improved his regen abilities? #LOL And we still have a lot to explain with Deadpool #nerd @Marvel

PS: before @Dev_journal, this paper showed me the extent of dysfunctionality in the peer review system. BUT, not everything is bad! Thanks to #biorxiv, made many new colleagues; new projects nurtured; collabs formed. Clearly this is the way to go forward for science! #FutureIsNOW