INDUCTION AND MAINTENANCE OF DIFFERENTIATION OF RAT LENS EPITHELIUM BY FGF-2, INSULIN AND IGF-1

The differentiation of rat lens epithelial cells to fibre cells can be mimicked using lens epithelial explants, which differentiate in vitro when exposed to fibroblast growth factor (FGF). A previous study demo nstrated that FGF is required only for initiation of differentiation: once induced by FGF, differentiation can be maintained by insulin (as assessed by following the accumulation of fibre-cell specific crystall ins). The aim of this investigation was to determine whether insulin-l ike growth factor 1 (IGF-1) can also maintain differentiation and to i nclude a cellular analysis of explants undergoing insulin-or IGF-maint ained differentiation in vitro. Measurement of the accumulation of alp ha-, beta- and gamma-crystallins showed that IGF-1, like insulin, can replace FGF-2 in directing the pulses of alpha-, beta- and gamma-cryst allin gene expression once differentiation is initiated by FGF-2. Cell s in both the peripheral and the central region of the explants respon ded. Immunolocalization of alpha, beta- and gamma-crystallins in these explants showed that a 15 min pulse of FGF-2 triggered the differenti ation of only a few cells, whereas a 12 hr pulse primed virtually all the cells for differentiation. This indicates that in explants, indivi dual cells differ in the rate at which they can respond to FGF-2. (C) 1998 Academic Press.