The long-term goal of this research program is to elucidate those molecular mechanisms that are essential for ?A-crystallin (Cryaa) gene expression in the lens, and to unravel general lens regulatory mechanisms that follow similar principles of gene regulation. A loss of Cryaa expression or expression of mutant ?A-crystallin proteins is not compatible with lens transparency and results in lens opacification. Compromised lens transparency leads to cataract formation, a disease of the lens responsible for nearly half of the cases of blindness worldwide. We have now identified a """"""""core"""""""" gene regulatory network (GRN), comprised of Pax6, c-Maf and crystallin genes, which is responsible for lens-specific expression of all crystallin genes. Through the identification of two FGF-responsive regions in c-Maf and Cryaa genes, we can now link FGF signaling, a key lens differentiation signal transduction pathway, with crystallin gene expression. In addition, FGF2 stimulates expression of a small group of microRNAs that targets 3'-UTR of c-Maf. These data suggest that c-Maf expression is underbpositive and negative-feedback FGF- dependent control. A hallmark of tissue-specific GRNs is their spatial localization as """"""""transcriptional factories"""""""" within the 3D-structure of lens fiber cell nuclei. This proposal will (1) Determine the molecular functions of th FGF-responsive c-Maf promoter and Cryaa distal enhancer DCR1 followed by genome- wide identification of global FGF-regulated networks in the lens, (2) Establish posttranscriptional regulation of c-Maf through FGF2-dependent miRs, and (3) Examine dynamic changes of chromatin structure in differentiating lens fiber cell nuclei and to identify transcriptional factoies that include the Cryaa locus. These data will lay the foundation for understanding the molecular basis of lens fiber cell differentiation through FGF signaling, action of specific DNA-binding transcription factors, modulatory miRs and their target genes, and 3D-organization of lens fiber cell chromatin.
This application is relevant to human health as the lens cataract is a major cause of worldwide blindness. Age-related cataracts generally develop in men and women after their 40th birthday due to the progressive breakdown of the ocular lens structure. The prevalence of cataracts is expected to increase as life expectancy in both developed and underdeveloped countries continues to improve. Current treatment for senile cataracts generally consists of a surgery that replaces the opaque lens with an artificial intraocular lens. Although the surgery is performed routinely in the US at a rate of 1.8-2 million patients per year, it represents a major Medicare reimbursement category. It has been estimated by the National Eye Institute, NIH (Bethesda, MD) that a 10-year delay in the onset of cataracts could decrease the number of surgeries needed by almost one half, thus significantly decreasing vision care costs. The ?A crystalline is the most abundant structural component of the human lens;its abnormal function and/or expression causes lens opacification. Mutations in genes encoding lens regulatory proteins such as PAX6, cMAF and CBP studied here and CRYAA itself are known to cause human congenital cataracts.
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