EVOLUTION OF NEUROBLAST IDENTITY - 7-UP AND PROSPERO EXPRESSION REVEAL HOMOLOGOUS AND DIVERGENT NEUROBLAST FATES IN DROSOPHILA AND SCHISTOCERCA

In the Drosophila CNS, early neuroblast formation and fate are control led by the pair-rule class of segmentation genes. The distantly relate d Schistocerca (grasshopper) embryo has a similar arrangement of neuro blasts, despite lack of known pair-rule gene function. Does divergent pair-rule gene function lead to different neuroblast identities, or ca n different patterning mechanisms produce homologous neuroblasts? We u se four molecular markers to compare Drosophila and Schistocerca neuro blast identity: seven-up, prospero, engrailed, and fushi-tarazu/Dax, I n both insects some early-forming neuroblasts share key features of ne uroblast identity (position, time of formation, and temporally accurat e gene expression); thus, different patterning mechanisms can generate similar neuroblast fates. In contrast, several later-forming neurobla sts show species-specific differences in position and/or gene expressi on; these neuroblast identities seem to have diverged, suggesting that evolution of the insect central nervous system can occur through chan ges in embryonic neuroblast identity.