The achaete-scute complex proneural genes contribute to neural precursor specification in the Drosophila CNS

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 lineage to produce an invariant family of neurons and/or glia. The proneural genes achaete, scute and lethal of scute are required for neural precursor formation in the Drosophila CNS, and are expressed in overlapping subsets of 'proneural cell clusters' from which a single neural precursor later develops. Vertebrate achaete-scute homologues are expressed early during neurogenesis, and promote neurogenesis, neuronal development and/or differentiation. The Drosophila proneural achaete-scute genes govern neural precursor formation, but their role in specifying neural precursor identity has not been tested.

Here, we test the role of the Drosophila achaete-scute genes in specifying neural precursor 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 promoting neural precursor formation. Surprisingly, we also observed that the developing MP2 precursors were incorrectly specified and acquired traits characteristic of adjacent neural precursors. In rescue experiments, achaete or scute, but not lethal of scute, completely restored the normal MP2 identity.

These results demonstrate that the achaete-scute complex genes specify aspects of neural precursor identity in the Drosophila CNS. Given the phylogenetically conserved function of these genes, our results raise the possibility that achaete-scute homologues may help specify neural precursor identity in other organisms.