The work is reported in the March 7th issue of Current Biology by David Matus and colleagues at the University of Hawaii and Stony Brook University.
To understand the evolution of body-plan patterning, the researchers isolated a particular set of genes from a tiny translucent cnidarian, the starlet sea anemone, Nematostella vectensis. The genes were the anemone's version of genes known to be responsible for organizing the dorso/ventral axis in bilateral animals.
Matus and colleagues found that two types of proteins--so-called TGFß ligands and an antagonist protein that functions in opposition to the ligands--encoded by these genes are expressed differently in anemones than they are in bilateral animals like flies and frogs. In those animals, the proteins are expressed on opposite sides of the dorsal/ventral axis very early in embryogenesis, during gastrulation. However, the researchers found that the anemone ligands and their antagonist protein are at first expressed together--then, as gastrulation proceeds, the proteins become segregated into different germ layers, with the TGFß ligands and downstream components deployed exclusively in the endoderm, or inner germ layer.
It therefore appears that the ancient, ancestral function for this signaling system may have been to determine the different germ layers of the developing embryo in animals that lacked a bilateral body plan. Over evolutionary time, the genes acquired a new and important role in establishing the dorso/ventral axis, eventually leading to the diversity of bilateral animals present today.
The researchers include David Q. Matus and Mark Q. Martindale of the University of Hawaii in Honolulu, Hawaii; Gerald H. Thomsen of Stony Brook University in Stony Brook, New York.
This work was supported by grants from the NSF and NASA to M.Q.M. and NIH Grant HD032429 to G.H.T.
Matus et al.: "Dorso/Ventral Genes Are Asymmetrically Expressed and Involved in Germ-Layer Demarcation during Cnidarian Gastrulation." Publishing in Current Biology 16, 499–505, March 7, 2006. DOI 10.1016/j.cub.2006.01.052 www.current-biology.com
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