Cell degeneration in the developing optic lobes of the sine oculis and small-optic-lobes mutants of Drosophila melanogaster

摘要

Inthesmall-optic-lobes(sol)andsineoculis(so)mutantsofDrosophilamelanogasterextensivecelldeathoccursintheopticlobesduringthefirsthalfofpupaldevelopment.Gynandromorphfliesshowthatthesolmutationactsprimarilyoncellsofthemedullacortex.Degenerationofmedullarganglioncellsoccursatanearlystageofcellulardifferentiation,whentheiraxonshavenotyetparticipatedintheformationofthesecondopticchiasma.Thesogene,ontheotherhand,actsontheeyeanlagen.Theanalysisofchimericfliesdemonstratesthatdegenerationintheopticlobesofsofliesisaconsequenceofeyereduction.Atthelevelofthesecondopticchiasmaextensiveaxonaldegenerationcanbeobservedinthemutant.Neuronsseemtodieaftertheirfailuretoestablishasufficientnumberoffunctionalcontacts.Insol;sodoublemutants,themutationaleffectsarecumulativecausingcompletedegenerationofcolumnarcelltypesinpupaewithoutanyeyeanlage.Thetinyrudimentsoftheopticlobesineyelessdoublemutantsstillcontaintangentialneuronsofthemedullaandofthelobulacomplex.Thecentralbrainisreducedinsizeduetothemissingvisualfibers,however,itsoverallappearanceissurprisinglynormal.