Cell-cycle regulation and cell-type specification in the developing Drosophila compound eye.

During nervous system development stem cell daughters must exit the proliferative cycle to adopt specific neural and glial fates and they must do so in the correct positions. Cell proliferation in the central nervous system occurs in neuroepithelia such as the neural retina and the ventricular zones. As cells are assigned specific fates they migrate out of the plane of the epithelium to form higher layers. Recent evidence from the Drosophila compound eye suggests that a novel mode of Ras pathway regulation may be crucial in both cell-cycle exit and neural patterning: "MAP Kinase cytoplasmic hold".