Over at Telic Thoughts, Techne has posted an excellent analysis that digs a little deeper into the hypothesis of front-loading evolution, adding to its plausibility and making potentially fruitful connections. He/she focuses on the Hedgehog pathway since it “plays a fundamental role in cell patterning, cell proliferation and participates in the development of tissues and organs during the stages of animal development.” Very good. Techne then does some digging and finds that most of the tools for the metazoan pathway toolkit are present in prokaryotes.
Looking at the hh-signaling pathway, there seem to be very little innovation, and a lot of co-option of pre-existing information into new functions.
But while this clearly strengthens the FLE hypothesis, Techne finds something even more interesting:
Also note that the origin of multicellular body plans roughly coincide with an increase in atmospheric oxygen pressure as well as the first bona fide hedgling. Remember, hedglings are the only examples of post-translational sterolation (addition of cholesterol) of proteins in contempory biology. Why is this interesting? Well, oxygen is needed for cholesterol synthesis, more importantly, oxygen is needed for placing the hydroxyl group in the 3-position of cholesterol which plays a crucial role in subsequent transformations (including sterolation). Thus, while large parts of the hh-signaling pathway was present, a little extra oxygen was needed to unlock multicellular signaling capabilities of hedglings.
Very cool! Techne adds:
Therefore, words like “pre-existing”, “latent” and “potential” seem apt in describing the hedghog signaling pathway and the unfolding of multicellular body plans in relation to the increase in atmospheric oxygen pressure. “Innovation” perhaps not so much, seeing that only real innovation was bought on about by life itself namely the increase in atmospheric oxygen. This increase in atmospheric oxygen in turn seemed to have unlocked the pathways to multicellular body plans (>3 cell types).
Another keen observation. And here Techne may be the first to have his/her finger on a fairly solid and specific example that illustrates the connection between terraforming and front-loading metazoan life. In other words, a consortium of single-celled organisms not only possessed, as a group, a toolkit for metazoan complexity, but were responsible for terraforming the ancient Earth – pumping oxygen into the atmosphere so that at sometime in the future, this oxygen could unlock the “multicellular signaling capabilities of hedglings.”
Be sure to read the whole article.