Thus Drosophila CBP is required for the activation of Cubitus interruptus target genes such as patched , and CBP is required for the activator function of Ci but not for the repressor function. These observations have been used to explain how two pathways can interfere with each other. PKA phosphorylates dCREB2 and this signaling function appears to repress Hh target genes such as dpp . The ventral and cephalic furrows appear normal, but the mesodermally derived internal tissues and a block of ectodermal cells are often missing. On the basis of this phenotype, the Drosophila CBP mutant was named nejire , which means 'twist' in Japanese.
Mesoderm formation is crucial event that takes place during early embryogenesis.
Drosophila CBP mutants, devoid of both maternal and zygotic nejire expression, fail to express twi and therefore generate twisted embryos. This is explained by results showing that dCBP is necessary for Dorsal-mediated activation of the twi promoter. In vitro Dorsal has been shown to bind the N-proximal portion of Drosophila CBP in a phosphorylation independent manner. CBP not only exerts an effect on DNA transcription by acting as a histone transacetylase, but it can also acetylate transcription factors. In addition CBP can exert an inhibitory effect on transcription.