Expression of the transcriptional cofactors/histone acetyltransferases CBP andp300 during mouse development and their functional interactions with Gli transcription factors

Normal embryonic development requires precise regulation and coordination of different signaling pathways. One of these signaling cascades, the hedgehog (Hh) pathway, has been of major interest for developmental biologists. Sonic hedgehog (Shh), a vertebrate Hh protein, is involved in patterning several tissues during embryogenesis. Gli transcription factors (Gli1, Gli2, Gli3) mediate Shh signaling in vertebrates. In vertebrates there are two co-factors CBP and p300 that interact with several transcription factors and modify their activity. They are thought to act in the cell nuclei as integrators of different signaling pathways.; Evidence for co-operation between vertebrate Gli proteins and CBP/p300 comes from phenotypes of human developmental disorders and studies in Drosophila. Mutations in Gli3 cause Greig cephalic polysyndactyly syndrome (GCPS) in humans, which is characterized by limb abnormalities and craniofacial defects. A similar phenotype is observed in Rubinstein-Taybi syndrome (RTS) patients, who have a mutation in CBP gene suggesting functional interactions between Glis and CBP. Furthermore, Drosophila CBP, dCBP, was shown to interact with the Drosophila Gli homologue Cubitus interruptus (Ci) and was required for activation of Hh target genes.; The research presented in this thesis contributes to a better understanding of the roles of transcriptional cofactor CBP/p300 in vertebrate development and in activation/modification of Gli protein function. I describe in detail how CBP and p300 proteins are expressed during mouse neurogenesis and organogenesis providing the first evidence for developmentally regulated expression of CBP and p300 in the thesis. Interestingly, there is a good correlation between CBP/p300 expression and phenotypes in mutant mice lacking CBP or p300 function and in patients with Rubinstein-Taybi syndrome. These studies indicate that CBP and p300 are coexpressed with Gli genes in the limb mesenchyme, dorsal neural tube and craniofacial mesenchyme. However, absence of CBP/p300 expression in some Shh responsive tissues like in the floor plate suggests that CBP/p300 is not always required for Shh signaling. I further demonstrate that p300 functions as a transcriptional co-activator for all Glis. I also examined whether CBP directly interacts with Gli1, Gli2 and GIB in vitro. I could not detect any interaction between Gli proteins and CBP-CREB binding domain.