Characterization of Drosophila BRAP2/IMP

Abstract

BRCA1-interacting protein 2 (BRAP2)/Impedes mitogenic signal propagation (IMP) was known to bind to the nuclear localization signal motif of BRCA1 and p21, and also modulate sensitivity of the MAP kinase cascade by limiting functional assembly of the Raf-MEK-MAPK through its ubiquitin E3 ligase activity. However, its in vivo functions remain elusive. Therefore, I generated the ectopic expression lines and the deletion mutants of Drosophila BRAP2. Here, I demonstrated that dBRAP2 could regulate cellular proliferation, apoptosis, development of central nervous system, and cell fate determination. Overexpression of dBRAP2 C248S and C313S, both of which E3 ubiquitin ligase activity are impaired, in wing discs led to a crumpled-wing phenotype, while dBRAP2 wild type did not. It was shown that this phenotype resulted from apoptosis. Surprisingly, ectopic expression of dBRAP2 wild type and mutants in eye did not affect the number of photoreceptor cells, which is regulated by Ras/MAPK pathway, in contrast to previous reported data. In addition, dBRAP2 mutant flies died at third instar larval stage with a considerable cell death in the imaginal discs and a small brain phenotype, and showed a melanotic tumor phenotype with highly activated immune response. In embryonic stage, the developmental defects in the central nervous system were observed. In the mitotic clones of dBRAP2 null allele, the number of the photoreceptor cells did not increase, rather, the photoreceptors, cone cells, pigment cells and bristles in one ommatidium was disrupted in consistent with the overexpression data. The wing vein formation was normal, but the bristles of the wings were cut or vanished in the mitotic clones. Taken together, these results from gain-offunction and loss-of-function mutants revealed that dBRAP2 is involved in the regulation of the neurogenesis, immune response, neuron cell fate determination, and proliferation of epithelial cells, independent of Ras/MAPK pathway.