Evolution of signalling pathways
Pioneering work by Spemann and Mangold in early 1920’s on Salamanders ,where they transplanted a specific piece of embryonic tissue into another embryo resulting in a two headed Salamander.This probably could be the first indication that cells talk to each other through secreted signals.Since then lot of work has gone into the field of signalling pathways which led to identification of various players of this process.Genetic and biochemical data suggest that multicellular organisms largely depend on few evolutionary conserved signalling pathways for proper patterning and specification events during development.Most interactions between cells during embryonic development involve Hegdehog, Wnt ,BMP,receptor tyrosine kinase ,Notch,JAK/STAT and Nuclear hormone pathways.
Cambrian explosion (543-505 million years ago) is considered to be watershed in animal evolution and members of all extant animals were believed to be already present during that era.The diversity in body plan among members of various phyla is huge,which depends upon configuration of secreted signals and specific selector genes.As these body plans were already existed by mid cambrian age and are conserved till now,which also signifies that signalling pathways evolved in pre cambrian times before the diversity in body plan occured.This also justifies why diverse organisms like sponges,arthropods,chordates share similar signalling pathways.
During the course of evolution these signalling pathways evolve new complex ways to pattern,which includes cross talking of different signalling pathways.Understanding how these pathways evolved might provide insights into how a few signalling pathways can generate so much cellular and morphological diversity during the development of individual organisms and the evolution of animal body plans.
Reference:
1) Gerhart J.
1998 Warkany lecture: signaling pathways in development.
Teratology. 1999 Oct;60(4):226-39. Review.
2) André Pires-daSilva & Ralf J. Sommer
The evolution of signalling pathways in animal development.
Nature Reviews Genetics 4, 39-49 (January 2003) | doi:10.1038/nrg977
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