CILIARY NEUROTROPHIC FACTOR PROMOTES CHICK PHOTORECEPTOR DEVELOPMENT IN-VITRO

Previous in vitro studies have convincingly demonstrated the involveme nt of diffusible factors in the regulation of photoreceptor developmen t, We now provide evidence that ciliary neurotrophic factor (CNTF) rep resents one of these regulatory molecules. In low density monolayer cu ltures prepared from embryonic day 8 chick retina, photoreceptor devel opment was studied using the monoclonal antiopsin antibody rho-4D2 as a differentiation marker, The number of cells aquiring opsin immunorea ctivity, determined after 3 days in vitro, was increased up to 4-fold in the presence of CNTF to maximally 10.5% of all cells, Basic fibrobl ast growth factor or taurine both of which have been reported to stimu late opsin expression in rat retinal cultures and other neurotrophic f actors tested (nerve growth factor, brain derived neurotrophic factor) had no effect, The EC(50) of the CNTF effect (2.6 pM) was virtually i dentical to that measured for other CNTF receptor mediated cellular re sponses, Conditioned medium produced by cultured retinal cells (most l ikely glial cells) exhibited opsin stimulating activity identical to t hat of CNTF, Stimulation of opsin expression was specific for morpholo gically less mature photoreceptors and obviously restricted to rods, s ince changes in the number of identifiable cone photoreceptors express ing opsin immunoreactivity (10% of all cones) were not detectable. Mea surement of the kinetics of the CNTF reponse revealed that the factor acted on immature opsin-negative progenitors and that CNTF effects wer e unlikely to reflect enhanced cell survival, Proliferation of photore ceptors was also unaffected, as demonstrated by [H-3]thymidine autorad iography, With prolonged culture periods a gradual decrease in the num ber of opsin-positive cells was observed both in controls and in the c ontinuous presence of CNTF, This decrease could be partly prevented by the addition of 1 mM taurine, Our results suggest that CNTF acted as an inductive signal for uncommitted progenitor cells or during early s tages of rod photoreceptor differentiation, whereas other extrinsic st imulatory activities seemed to be required for further maturation.