Effect of the weaver (wv) mutation on cerebellar neuron differentiation. I. Qualitative observations of neuron behavior in culture.

A mutant gene dose-dependent inhibition of cerebellar granule cell neuron survival and neurite growth in dissociated cultures of cerebellum from 7-day-old heterozygous (+/wv) and homozygous (wv/wv) weaver mutant mice (M. Willinger, D. M. Margolis, and R. L. Sidman. (1981), J. Supramol. Struc. 17, 79-86) has previously been observed. In the present phase-contrast study time-lapse microcinematography was performed between 10 and 80 hr in culture to determine which properties of neurite growth and neuron migration are affected by weaver gene expression. Neurite growth in +/+ cultures is rapid and discontinuous. Neurites are thin and cylindrical. Membrane movement occurs only at the growth cone. Growth cone contact with cell aggregates or glial somas results in the cessation of cone advancement and the induction of translocation of the neuronal soma toward the astrocyte. In cultures of +/wv and wv/wv cerebellar cells, abnormal neurite growth is characterized by frequent neurite retractions and reinitiations. Neuronal somas and neurite shafts are motile during elongation. Homozygous neurites and cones are pleomorphic. Normal, +/wv, and wv/wv neurons undergo nuclear translocation. Like +/+ neurons, +/wv neurons migrate in response to growth cone-cell soma contact. In contrast, homozygous soma frequently reverse direction and migrate independently of cell contact. Granule cell death occurs with increasing frequency with increasing gene dosage. Neurons are unusually active prior to the rapid onset of cell death. In summary, the weaver mutation impairs granule cell differentiation by affecting neurite maintenance, membrane motility, and neuron morphology. The loss of viability appears to be independent of, or secondary to, these targets of gene action.