MUTATIONS AFFECTING NEUROGENESIS AND BRAIN MORPHOLOGY IN THE ZEBRAFISH, DANIO-RERIO

In a screen for embryonic mutants in the zebrafish a large number of m utants were isolated with abnormal brain morphology, We describe here 26 mutants in 13 complementation groups that show abnormal development of large regions of the brain, Early neurogenesis is affected in whit e tail (wit), During segmentation stages, homozygous wit embryos displ ay an irregularly formed neural keel, particularly in the hindbrain, U sing a variety of molecular markers, a severe increase in the number o f various early differentiating neurons can be demonstrated, In contra st, late differentiating neurons, radial glial cells and some nonneura l cell types, such as the neural crest-derived melanoblasts, are much reduced, Somitogenesis appears delayed, In addition, very reduced numb ers of melanophores are present posterior to the mid-trunk, The wit ph enotype is reminiscent of neurogenic mutants in Drosophila, such as No tch or Delta, In mutant parachute (pac) embryos the general organizati on of the hindbrain is disturbed and many rounded cells accumulate loo sely in the hindbrain and midbrain ventricles, Mutants in a group of 6 genes, snakehead(snk), natter (nat), otter (ott) fullbrain (ful) vipe r (vip) and white snake (wis) develop collapsed brain ventricles, befo re showing signs of general degeneration, atlantis (atl), big head (bi d), wicked brain (win), scabland (sbd) and eisspalte (ele) mutants hav e different malformation of the brain folds, Some of them have transie nt phenotypes, and mutant individuals may grow up to adults.