Spen and Hox proteins as part of a conserved regulatory code that is required to repress the development of skeletal structures. K.A. Mace , W. McGinnis. Cell & Dev Biol, Univ California, San Diego, La Jolla, CA.

   The skeletons of insects and mammals are so different in form and composition that there has rarely been speculation about common origins. We are pursuing the hypothesis that there is a conserved regulatory code for skeletal development that is shared by both invertebrates and vertebrates. This putative code involves Spen and Hox proteins, which regulate which cells will generate hard sclerites in the Drosophila body plan. Spen and Hox both have mammalian homologs that also have been implicated in the control of bone formation. Our results thus far indicate that Spen, an RRM motif protein, is a DNA-binding, homeotic protein that acts in parallel with the Antennapedia and Teashirt proteins to repress the transcription of Dopa decarboxylase (Ddc) and pale (tyrosine hydroxylase) and the formation of head skeleton in the trunk. Gel shift assays indicate that the DNA-binding domain of Spen binds to a portion of the upstream regulatory region of Ddc. Dopa decarboxylase and Tyrosine hydroxylase proteins are both components of an enzymatic pathway required for the development of highly sclerotized insect cuticle. This pathway generates aromatic quinones that are secreted to cross-link an extracellular mix of collagen and chitin into a thick, hard exoskeleton. It is believed that primitive metazoan skeletons were generated in a similar manner, and vertebrates have apparently varied this scheme by the deposition of calcium phosphate crystals to form a bony endoskeleton. We will report results from a variety of experiments in Drosophila and other animals to test whether there is a common set of proteins that control where skeletal features develop.