THE ROLE OF THE MSH HOMEOBOX GENE DURING DROSOPHILA NEUROGENESIS - IMPLICATION FOR THE DORSOVENTRAL SPECIFICATION OF THE NEUROECTODERM

Development of the Drosophila central nervous system begins with the d elamination of neural and glial precursors, called neuroblasts, from t he neuroectoderm. An early and important step in the generation of neu ral diversity is the specification of individual neuroblasts according to their position. In this study, we describe the genetic analysis of the msh gene which is likely to play a role in this process. The msh/ Msx genes are one of the most highly conserved families of homeobox ge nes, During vertebrate spinal cord development, Msx genes (Msx1-3) are regionally expressed in the dorsal portion of the developing neuroect oderm, Similarly in Drosophila, msh is expressed in two longitudinal b ands that correspond to the dorsal half of the neuroectoderm, and subs equently in many dorsal neuroblasts and their progeny. We showed that Drosophila msh loss-of-function mutations led to cell fate alterations of neuroblasts formed in the dorsal aspect of the neuroectoderm, incl uding a possible dorsal-to-ventral fate switch. Conversely, ectopic ex pression of msh in the entire neuroectoderm severely disrupted the pro per development of the midline and ventral neuroblasts. The results pr ovide the first in vivo evidence for the role of the msh/Msx genes in neural development, and support the notion that they may perform phylo genetically conserved functions in the dorsoventral patterning of the neuroectoderm.