Ciliary neurotrophic factor as a transient negative regulator of rod development in rat retina.
OBJECTIVE
Ciliary neurotrophic factor (CNTF) has been shown to inhibit the developmental expression of rod differentiation markers in rat retinal cultures. The present study was undertaken to investigate whether CNTF transiently inhibits rod differentiation or induces irreversible changes in the developmental fate of rod precursors.


METHODS
The effects of CNTF on rod differentiation were monitored in organotypic slice cultures from early postnatal rat retinas by quantification of opsin-immunoreactive cells. The in vitro formation of the photoreceptor layer was analyzed by light and electron microscopy. The developmental expression of the CNTF receptor in photoreceptors was determined by immunoblot analysis.


RESULTS
CNTF did not interfere with the generation of rod precursors, their morphologic differentiation, or the formation of the outer nuclear layer. Inhibition of rod differentiation was reversible. In the continuous presence of CNTF the number of opsin-positive cells increased at a normal rate but with a delay of 3 to 4 days. Developing rods became resistant to CNTF, both in vivo and in vitro, and this correlated temporally with the downregulation of CNTF receptor expression. Receptor downregulation was inhibited by CNTF in a dose-dependent manner. At higher CNTF concentrations with sustained receptor expression, the CNTF-induced decrease in opsin expression was accompanied by an increase in the expression of a bipolar cell marker in rod precursors located in the photoreceptor layer.


CONCLUSIONS
These data indicate that, although rod precursors exhibit some phenotypic plasticity in the presence of CNTF, the factor does not induce a switch in the developmental fate of rod precursors but plays a role as a transient and reversible negative regulator of rod differentiation.
Institute of Anatomy I, University of Freiburg, Freiburg, Germany.
Steffen
S
Schulz-Key
Hans-Dieter
HD
Hofmann
Christian
C
Beisenherz-Huss
Carola
C
Barbisch
Matthias
M
Kirsch
D000818:Animals; D000831:Animals, Newborn; D000911:Antibodies, Monoclonal; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D020934:Ciliary Neurotrophic Factor / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D007124:Immunoenzyme Techniques; D008855:Microscopy, Electron, Scanning; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D020801:Receptor, Ciliary Neurotrophic Factor / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism
D000911:Antibodies, Monoclonal; D020934:Ciliary Neurotrophic Factor; D020801:Receptor, Ciliary Neurotrophic Factor; D017299:Rod Opsins