Evolutionary Change in Gut Specification in Caenorhabditis Centers on the GATA Factor ELT-3 in an Example of Developmental System Drift

Cells in a developing animal embryo become specified by the activation of cell-type-specific gene regulatory networks. The network that specifies gut nematode Caenorhabditis elegans has been subject study for more than two decades. In this network, maternal factors SKN-1/Nrf and POP-1/TCF activate zygotic GATA factor cascade consisting regulators MED-1,2 → END-1,3 ELT-2,7, leading to specification early embryos. Paradoxically, MED, END, ELT-7 are present only species closely related C. elegans, raising question how can be without them. Recent work found ELT-3, an endodermal role acts simpler ELT-3 ELT-2 specify distant species. may thus represent ancestral pathway. review, we describe elucidation propose model which complex might have formed. Because evolution occurred change phenotype, it is example phenomenon Developmental System Drift.