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Comment by comboy | Hacker News Reader

> They found that the cells surrounding the suppressed tissue communicated with the placenta, which then signaled the rest of the organism’s tissues—including the other hind leg—to slow their growth until the hindered limb caught up.

Can somebody dumb it down for me? It's fascinating but I still don't understand how do they communicate. Is it done through nervous system? Presumably not because it's not reaching all tissues and it's probably not yet fully developed at that point. So how does it happen? If it's just releasing some chemicals it seems hard to imagine that it could be accurate. Plus how would the slower limb know that these chemicals come from it and it does not need to slow down growth. How does something know that it is slower than it should be? So many questions.

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At this point of development, the communication is done via release of chemical factors which bind to other cells and cause changes. The general problem of pattern formation in embryonic development has been extensively studied; see here: https://en.wikipedia.org/wiki/Pattern_formation and https://en.wikipedia.org/wiki/Reaction%E2%80%93diffusion_sys...

I'm oversimplifying, bjut it's basically the gradient of a chemical that acts as a control variable.

The associated paper to the article is:

https://journals.plos.org/plosbiology/article/file?id=10.137...

p.15 has a summary of what they propose, e.g., density of p21+ chondrocytes, as an inhibitor:

"Because we found that the extent of compensatory proliferation does not linearly correlate with cell density—but it does with the proportion of p21+ chondrocytes — we posit that density plays a permissive rather than an instructive role and that stress signals emanating from p21+ chondrocytes are needed as well."

that's text I can't interpret, unfortunately. It's highly speculative and ambiguous.

Recently there's been some conjecture that bioelectricity guides embryonic development as well: https://www.quantamagazine.org/brainless-embryos-suggest-bio...

From a layman's perspective, there are some really exciting developments happening in the field of morphogenesis!

Yes it's "just releasing some chemicals", vast and complex regulatory networks of chemicals.

They then did RNAseq experiments (measures which genes are transcribed [are active]) in the two legs separately and looked for statistically significant differences (which genes are active in the injected leg but not the other one?) and found:

"enrichment of several pathways related to stress and immune responses in the left cartilage.In particular, we found several stress-related transcripts that shared a similar left–right pattern of expression within each embryo"

Theory of growth control, Shang

Also neural crest cells.

A good book is the spark in the machine . It’s more of speculative literature tying past scientific studies in medical history with predictions ancient Chinese physicians made with how energy flows through the body vis conductive fascial pathways. Heavily covers embryonic development and formation of our body

Your questions seems to me very important, thanks for phrasing them in a much better way than I did.

(I just posted at the same time as you)

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