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Despite the evolutionary distance between fruit flies and mosquitoes,similarities in their embryonic patterning do exist. However, differences in the morphology of their extra-embryonic membranes (EMs) have evolved: whereas Drosophila has one EM (the amnioserosa), the malaria mosquito, Anopheles gambiae, has distinct amnion and serosa tissues. Yury Goltsev and colleagues (see p. 2415) now show that changes in the expression of the dorsal gene network underlie morphological changes in the EMs of these Diptera. Specifically, the occurrence of two EMs in A. gambiae correlates with a broader domain of Decapentaplegic (Dpp) signalling. Studies of dorsal-ventral patterning gene expression profiles in A. gambiaereveal that this expanded Dpp domain arises from the restricted expression of the Dpp inhibitor, Sog. High-affinity Dorsal-binding sites in the Drosophila sog enhancer drives broad sog expression. By contrast, the mosquito sog enhancer contains low-affinity Dorsal-binding sites, which can restrict sog expression in the Drosophila mesoderm. Subtle changes in the Dorsal patterning network have thus altered the morphology of a single EM to form two.

© 2007.
2007