BAGPIPE-DEPENDENT EXPRESSION OF VIMAR, A NOVEL ARMADILLO-REPEATS GENE, IN DROSOPHILA VISCERAL MESODERM

Two homeobox-containing genes, tinman and bagpipe, play important role s during the specification of the midgut visceral musculature from the mesoderm during Drosophila embryogenesis. Expression of tinman in the dorsal mesoderm activates the expression of the bagpipe gene in segme ntal subsets of those cells, which then become determined to form the midgut visceral mesoderm. Understanding how the bagpipe gene affects t his specification requires the isolation and characterization of its d ownstream target genes. Using an enhancer trap line that expresses its marker in the midgut visceral mesoderm, we have cloned and characteri zed a novel gene (vimar) that is expressed embryonically in the mid an d hindgut visceral mesoderm, as well as in the CNS and PNS. The expres sion of this gene in the midgut visceral mesoderm initiates shortly af ter bagpipe expression and depends on bagpipe function. Maternal and z ygotic transcripts are produced from this gene by alternative polyaden ylation, and encode the same 634-amino acid protein. The vimar protein contains 15 tandem copies of the Armadillo repeat, a protein interact ion domain, and is similar to mammalian Smg guanine dissociation stimu lator protein, which stimulates the activity of a number of different p21 small G-proteins. These results, together with the observed lethal ity of vimar mutations, indicate that vimar is one of the bagpipe targ et genes that are required for normal development and differentiation of the midgut visceral mesoderm. (C) 1998 Elsevier Science Ireland Ltd .