Regulation of cytokine signaling components in developing rat retina correlates with transient inhibition of rod differentiation by CNTF.
Ciliary neurotrophic factor (CNTF) is known to inhibit the differentiation of rod photoreceptors from postmitotic precursor cells. During early postnatal development, photoreceptor precursors lose their responsiveness to CNTF. The underlying events causing this change in responsiveness are unknown. Moreover, whether rods express CNTF receptor alpha, a prerequisite for a direct response to the factor, is controversial. Since morphological studies have previously produced conflicting results, we have analyzed the expression of cytokine receptor components and potential ligands in the rat photoreceptor layer by real-time reverse transcription with the polymerase chain reaction after laser microdissection and by immunoblotting. Cytokine effects on rods were studied in explant cultures from newborn rat retina. CNTF receptor alpha (CNTFR alpha) and leukemia inhibitory factor receptor ss (LIFRss) were expressed in immature photoreceptors. Expression of the CNTF-specific alpha-subunit (but not of LIFRss) was downregulated specifically in the photoreceptor layer in parallel with the appearance of opsin-positive rods. The decrease of CNTFR alpha levels in explant cultures was closely correlated with the loss of precursor cell responsiveness to CNTF. Increasing the CNTF concentration in the culture medium led to prolonged CNTFR alpha expression and, concomitantly, to persistent inhibition of rod differentiation. Application of CNTF and LIF in vitro induced phosphorylation of STAT3. Inducibility of STAT3 activation by CNTF decreased with photoreceptor maturation, whereas the LIF effect persisted. Our results thus indicate that CNTF acts directly on photoreceptor precursors inhibiting their differentiation via activation of the JAK/STAT3 signal transduction pathway, and that this effect is temporally limited because of the downregulation of CNTFR alpha.
Hertle
Daniel
D
Institute of Anatomy and Cell Biology, University of Freiburg, P.O. Box 111, 79001, Freiburg, Germany.
Schleichert
Michael
M
Steup
Andreas
A
Kirsch
Matthias
M
Hofmann
Hans-Dieter
HD
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D020934:Ciliary Neurotrophic Factor / Q000494:pharmacology / Q000502:physiology*; D053739:Ciliary Neurotrophic Factor Receptor alpha Subunit / Q000096:biosynthesis* / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D053605:Leukemia Inhibitory Factor / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D053606:Receptors, OSM-LIF / Q000187:drug effects / Q000378:metabolism; D012160:Retina / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
D020934:Ciliary Neurotrophic Factor; D053739:Ciliary Neurotrophic Factor Receptor alpha Subunit; D053605:Leukemia Inhibitory Factor; D053606:Receptors, OSM-LIF; D050796:STAT3 Transcription Factor