Cerebellar granule cells elaborate neurites before mitosis.

Neuronal birth and neurite outgrowth have been regarded as discrete, sequential stages of development. However, we recently found that sympathetic neuroblasts often elaborate axons before mitosis, in culture [E. Wolf, I.B. Black, E. DiCicco-Bloom, Mitotic neuroblasts determine neuritic patterning of progeny, J. Comp. Neurol. 367 (1996) 623-635] and in vivo [E. Wolf, I.B. Black, E. DiCicco-Bloom, Central and peripheral neuroblasts elaborate neurites prior to division in vivo and in vitro, Soc. Neurosci. Abstr. 21 (1995) 785; E. Wolf, I.B. Black, E. DiCicco-Bloom, Mitotic neuroblasts engage in axonal outgrowth and pathfinding in vivo, Soc. Neurosci. Abstr. 22 (1996) 525]. Here, we report that cerebellar granule cells often divide with heritable neurites in vitro. Therefore, mitotic CNS precursors, in addition to peripheral neuroblasts, simultaneously undergo proliferation and process formation. Potentially, neurites on dividing precursors may allow target fields to influence directly the course of neurogenesis.