In situ patterns of nuclear replication in brain ganglia ofl(2) gl 4 mutant larvae ofDrosophila melanogaster

The1(2) gl ⁴ mutation (a deletion mutation of a recessive oncogene) ofDwsophila melanogaster causes neuroblastoma in the optic centres of brain of late third instar larvae. We have studied thein situ patterns of DNA synthesis in these brains by immunocytochemical detection of cells incorporating 5-bromodeoxyuridine. It was seen that1 (2)gl ⁴ brains from younger 3rd instar larvae had fewer replicating cells than in wild type larvae of comparable age but in brain ganglia of olderl (2) gl ⁴ larvae the number of replicating cells was much higher. The spatial distribution of replicating cells in optic lobes of brain ganglia of1 (2) gl ⁴ larvae was disturbed from early 3rd instar stage, much before the tumourous growth was morphologically detectable. The stereotyped pattern of asymmetrical cell divisions of the neuroblasts and their progeny cells was also not seen in1 (2) gl ⁴ brain ganglia. Therefore, it appears that thel (2)gl ⁴ product has an important role early in development to determine the temporal and spatial patterns of neuroblast cell division in developing brains.