A complex regulatory network in a diploblast

The Wnt genes produce signalling proteins that play important roles in early development, regulating cell proliferation, differentiation and migration. It's hugely important, used in everything from early axis specification in the embryo to fine-tuning axon pathfinding in the nervous system. The way they work is that the Wnt proteins are secreted by cells, and they then bind to receptors on other cells (one receptor is named Frizzled, and others are LRP-5 and 6), which then, by a chain of cytoplasmic signalling events, removes β-catenin from a degradation pathway and promotes its import into the nucleus, where it can modify patterns of gene expression. This cascade can also interact with the cytoskeleton and trigger changes in cell migration and cell adhesion. The diagram below illustrates the molecular aspects of its function.

This is greatly simplified, of course. There are different pathways and different roles in different cells under different conditions. Mammals have 19 Wnt genes, so far, and as I mentioned above, have diverse functions. The obvious questions are where all this complexity originated, and what role the original Wnt gene played. One way to answer this question is to examine simpler organisms that separated from our messily complicated lineage long, long ago, and by comparison, try to infer what Wnt genes were present in our last common ancestor. Kusserow et al. (2005) have done this in a sea anemone, Nematostella vectensis, and got a somewhat surprising answer: our last common ancestor with a diploblast also had an elaborate array of Wnt genes.

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