THE LEAVING OR Q-FRACTION OF THE MURINE CEREBRAL PROLIFERATIVE EPITHELIUM - A GENERAL-MODEL OF NEOCORTICAL NEURONOGENESIS

Neurons of neocortical layers Il-VI in the dorsomedial cortex of the m ouse arise in the pseudostratified ventricular epithelium (PVE) throug h 11 cell cycles over the six embryonic days 11-17 (E11-E17). The pres ent experiments measure the proportion of daughter cells that leave th e cycle (quiescent or Q fraction or Q) during a single cell cycle and the complementary proportion that continues to proliferate (proliferat ive or P fraction or P; P=1-Q). Q and P for the PVE become 0.5 in the course of the eighth cycle, occurring on E14, and Q rises to similar t o 0.8 (and P falls to similar to 0.2) in the course of the 10th cycle occurring on E16. This indicates that early in neuronogenesis, neurons are produced relatively slowly and the PVE expands rapidly but that t he reverse happens in the final phase of neuronogenesis. The present a nalysis completes a cycle of analyses that have determined the four fu ndamental parameters of cell proliferation: growth fraction, lengths o f cell cycle, and phases Q and P. These parameters are the basis of a coherent neuronogenetic model that characterizes patterns of growth of the PVE and mathematically relates the size of the initial proliferat ive population to the neuronal population of the adult neocortex.