BASIC FIBROBLAST GROWTH-FACTOR PROLONGS THE PROLIFERATION OF RAT CORTICAL PROGENITOR CELLS IN-VITRO WITHOUT ALTERING THEIR CELL-CYCLE PARAMETERS

Basic fibroblast growth factor (bFGF) has been shown to influence the survival, proliferation and differentiation of a variety of cell types in the nervous system. In this investigation we have examined the act ion of bFGF on: (i) the rate of proliferation; (ii) cell cycle paramet ers; (iii) the maintenance of cell division; (iv) the recruitment of q uiescent cells; and (v) the degree of differentiation of cortical prog enitor cells in cultures prepared from E16 rat embryos. The proliferat ion rate (labelling index) of cortical progenitor cells doubled in the presence of bFGF over 48 h. However, the lengths of the cell cycle ph ases were unchanged. Clones marked with a recombinant retrovirus on th e first day in vitro (DIV) grew significantly larger in the presence o f bFGF. Furthermore, many of the clones examined in control cultures h ad ceased to divide after a maximum of four cell cycles, whereas almos t all clonally related cells were still dividing in the presence of bF GF 4 days later, i.e. for at least six cell cycles. Basic FGF also sti mulated the division of quiescent progenitor cells, which otherwise wo uld have differentiated or undergone cell death. The degree of neurona l and glial differentiation was studied after 5 DIV using MAP-2 and GF AP immunocytochemistry. In the presence of bFGF, the percentage of MAP -2-labelled cells was less than half that of control cultures, whereas the number of cells immunoreactive for nestin (a marker of progenitor cells) remained very high. Cells immunoreactive for GFAP were present in bFGF-treated cultures, yet were extremely rare in control conditio ns. These experiments show that bFGF, a potent mitogen for cortical pr ogenitor cells, has no effects on the parameters of their cell cycle b ut extends their proliferative capability, promotes their survival and delays their differentiation into neurons.