THE ACHAETE-SCUTE COMPLEX PRONEURAL GENES CONTRIBUTE TO NEURAL PRECURSOR SPECIFICATION IN THE DROSOPHILA CNS

Background: The Drosophila central nervous system (CNS) develops from a segmentally reiterated array of 30 neural precursors. Each precursor acquires a unique identity and goes through a stereotyped cell lineag e to produce an invariant family of neurons and/or glia. The proneural genes achaete, scute and lethal of scute are required for neural prec ursor formation in the Drosophila CNS, and are expressed in overlappin g subsets of 'proneural cell clusters' from which a single neural prec ursor later develops. Vertebrate achaete-scute homologues are expresse d early during neurogenesis, and promote neurogenesis, neuronal develo pment and/or differentiation. The Drosophila proneural achaete-scute g enes govern neural precursor formation, but their role in specifying n eural precursor identity has not been tested. Results: Here, we test t he role of the Drosophila achaete-scute genes in specifying neural pre cursor identity, focusing on the well characterized CNS MP2 precursor. MP2 delaminates from a cluster of achaete-scute-expressing ectodermal cells. In an achaete-scute double mutant, MP2 formation was reduced ( to 11-14%) as expected because of the function of proneural genes in p romoting neural precursor formation. Surprisingly, we also observed th at the developing MP2 precursors were incorrectly specified and acquir ed traits characteristic of adjacent neural precursors. In rescue expe riments, achaete or scute, but not lethal of scute, completely restore d the normal MP2 identity. Conclusions: These results demonstrate that the achaete-scute complex genes specify aspects of neural precursor i dentity in the Drosophila CNS. Given the phylogenetically conserved fu nction of these genes, our results raise the possibility that achaete- scute homologues may help specify neural precursor identity in other o rganisms.