THE DROSOPHILA HOMEOTIC TARGET GENE CENTROSOMIN (CNN) ENCODES A NOVELCENTROSOMAL PROTEIN WITH LEUCINE ZIPPERS AND MAPS TO A GENOMIC REGIONREQUIRED FOR MIDGUT MORPHOGENESIS

The products of the homeotic genes in Drosophila are transcription fac tors that are necessary to impose regional identity along the anterior -posterior axis of the developing embryo. However, the target genes un der homeotic regulation that control this developmental process are la rgely unknown. We have utilized an immunopurification method to clone target genes of the Antennapedia protein (ANTP). We present here the c haracterization of centrosomin (cnn), one of the target genes isolated using this approach. The spatial and temporal expression of the cnn g ene in the developing visceral mesoderm (VM) of the midgut and the cen tral nervous system (CNS) of wild-type and homeotic mutant embryos is consistent with the idea that cnn is a homeotic target. In the VM, Ant p and abdominal-A (abd-A) negatively regulate cnn, while Ultrabithorax (Ubx) shows positive regulation. In the CNS, cnn is regulated positiv ely by Antp and negatively by Ubx and abd-A. Characterization of a cDN A encoding CNN predicts a novel structural protein with three leucine zipper moths and several coiled-coil domains exhibiting limited homolo gy to the rod portion of myosin. Immunocytochemical results demonstrat e that the cnn encoded protein is localized to the centrosome and the accumulation pattern is coupled to the nuclear and centrosome duplicat ion cycles of cleavage. In addition, evidence suggests that the expres sion of the can gene in the VM correlates with the morphogenetic funct ion of Ubx in that tissue, i.e., the formation of the second midgut co nstriction. The centrosomal localization of CNN and the involvement of microtubules in midgut morphogenesis suggest that this protein may pa rticipate in mitotic spindle assembly and the mechanics of morphogenes is through an interaction with microtubules, either directly or indire ctly.