Neurogenesis in Drosophila

Abstract Neurogenesis is the process by which neurons are born during the development of an animal. The nervous system entails great cellular diversity and is the most complex of any organ system. A developing animal needs to harness sophisticated cellular and genetic mechanisms to ensure the orderly generation of large numbers of neurons in the right places and times, and in the right numbers. A long history of molecular genetic studies in the fruit fly, Drosophila melanogaster , has provided many insights into how this is achieved. Neurogenesis involves the initial patterning of the ectoderm, the formation of neural precursor cells from the ectoderm and the formation of neurons from these precursors through fixed lineages involving asymmetric cell division. Many of the concepts uncovered apply to neurogenesis in other animals. Indeed, many of the molecular mechanisms are highly conserved. Key Concepts: The fruit fly has relatively few neurons in its nervous system, making it tractable to detailed developmental analysis. The arrangement of these neurons is, as far as is known, very precisely determined by the mechanisms controlling neurogenesis during development. Neurons are the progeny of neural precursor cells that derive from the ectoderm. The precursor cells are specified by the action of proneural transcription factors, which are opposed by Notch signalling in the process of lateral inhibition. At their formation, the precursors are already specified to contribute specific neuronal progeny via fixed lineages of cell division. For the PNS, neural precursor identity is endowed by proneural factors, their cofactors. For the CNS, neuroblasts have unique identities according to their location, due to their inheriting different combinations of ectodermal patterning factors. Within the fixed division lineages, cellular diversity arises through asymmetric cell division, which is driven largely by asymmetrically localised and inherited cell fate determinants.