The genetic dissection of the fruitless gene's functions during embryogenesis in Drosophila melanogaster.

摘要

The fruitless (fru) gene in Drosophila melanogaster is a multifunctional gene having sex-specific functions in the regulation of male sexual behavior and sex-nonspecific functions affecting adult viability and external morphology. While much attention has focused on fru's sex-specific roles, little is known about its sex-nonspecific functions. The embryonic central nervous system (CNS) is a prime model system in which to study the genetic control of axonal outgrowth and proper CNS formation. I have examined fru's sex-nonspecific role in embryonic neural development. fru transcripts and FRU proteins from sex-nonspecific promoters are expressed beginning at the earliest stages of neurogenesis and subsequently in both neurons and glia. In embryos that lack most or all fru function, Fasciclin II- and BP102-positive axons appeared to defasciculate from their normal pathway and fasciculate along aberrant neuronal pathways, suggesting that one of fru's sex-nonspecific roles is to regulate axonal differentiation. I next examined whether the loss of fru function in FRU-expressing neuronal precursors causes neuronal fate change. Analysis of fru mutant embryos revealed a lack of Even-skipped (Eve) staining in Eve-expressing neurons, ectopic Eve staining in non-Eve-expressing neurons and mispositioned dorsal Eve-expressing neurons, which suggests that fru functions to maintain neuronal identity rather than to specify neuronal fate. In fru mutants these defects in axonal projections and in Eve staining were rescued by the expression of specific fru transgenes.; To better understand fru's function in the formation of the embryonic CNS, I dissected out fru's function in neuron and glia through a genetic interaction study. fru genetically interacts in neurons with longitudinal lacking to make proper axonal projections, In addition, fru might be in the same genetic pathway as roundabout (robo), a repulsive guidance receptor, and commissureless, a downregulator of Robo, to ensure proper axonal pathfinding. Surprisingly, fru interacts with tramtrack and glial cells missing to repress neuronal differentiation in the lateral glia and with single-minded for the development of midline glia. Taken together, fru function is required for proper axonal pathfinding in neurons and for proper development of lateral and midline glia.