Cytokine Signal Transduction in Retinal Development

描述（由申请人提供）：本研究的长期目标是阐明细胞外信号影响祖细胞命运规范和神经元分化的机制。提出的研究重点是睫状体神经营养因子（CNTF）样细胞因子在小鼠视网膜中的作用机制。在发育过程中，CNTF影响感光细胞、双极细胞和Muller胶质细胞的分化；而在成熟视网膜中，CNTF在各种哺乳动物模型中增强视网膜神经节细胞存活并防止光感受器变性。

DESCRIPTION (provided by applicant): The long-term goal of this research is to elucidate mechanisms by which cell-extrinsic signals influence progenitor cell fate specification and neuronal differentiation. The proposed study focuses on mechanisms by which ciliary neurotrophic factor (CNTF)-like cytokines act in the mouse retina. During development, CNTF affects the differentiation of photoreceptor cells, bipolar cells, and Muller glia; while in the mature retina, CNTF enhances retinal ganglion cell survival and prevents photoreceptor degeneration in various mammalian models. We have demonstrated that CNTF differentially activates intracellular signaling pathways in proliferating progenitors and postmitotic neurons in the neonatal retina; CNTF-dependent inhibition of rod photoreceptor differentiation requires STAT function, whereas CNTF-enhanced production of Muller glia involves both STAT and ERK activities. We hypothesize that STAT and ERK signaling play distinct roles in retinal progenitor cells and in postmitotic cells. To test this hypothesis, we will perturb cytokine signaling pathways using cell type-specific promoters and mutant signaling proteins in the postnatal retina. We have also observed that persistent CNTF signals trigger only transient retinal signal transduction, which correlates with an up-regulation of the cytokine signaling inhibitor SOCS3. We hypothesize that the negative regulation of cytokine signals by SOCS3 is critical for proper retinal development. To elucidate the function of SOCS3, we will misexpress SOCS3 and inhibit SOCS3 expression by RNA interference-mediated gene inhibition. It has been shown that viral mediated CNTF expression in the rds mutant retina rescues photoreceptor cell death, but causes abnormal cell morphology and retinal function. We will characterize signaling events in CNTF treated rds retina and test if the survival of photoreceptors is mediated by cytokine activated Muller glia. We have also begun to screen for cytokine target genes in the postnatal retina by microarray analyses. Potential candidate target genes will be validated by RT-PCR, in situ hybridization, Western blot, and promoter sequence analyses. Interactions between STAT transcription factors and target gene promoters will be examined by promoter binding assays. These proposed studies will advance our understanding of cytokine signaling mechanisms in the normal developing retina and in a mutant model of photoreceptor degeneration.