Retinal cell types are generated during a series of discrete temporal intervals during the course of neurogenesis. The molecular mechanism by which retinal progenitors successively acquire and lose competence to generate specific cell types is largely unknown. Studies of ES cell differentiation, however, have provided insights into how this might occur. Prior to lineage commitment, the regulatory sequences of many cell-specific genes are marked by histone modifications characteristic of both transcriptionally active and repressed chromatin. These domains of bivalent chromatin are proposed to both facilitate recruitment of transcription factors that direct cell fate specificatio and to prime these genes for rapid activation following lineage commitment. We hypothesize that similar mechanisms may control the developmental competence of retinal progenitors. To address this question, we propose to use ChIP-Seq to map the genomic distribution of histone modifications associated with transcriptional regulation in both early and late-stage retinal progenitors. In parallel, we will determine whether changes in histone modifications directly correlate with changes in the genomic distribution of CHX10 and LHX2, two progenitor-specific transcription factors that regulate proliferation of early-stage progenitors and lineage commitment of late-born cell types. We anticipate that this work will provide a comprehensive map of active enhancers and promoters in retinal progenitor cells, and serve as the basis for future functional studies of the role of epigenetic processes in the regulation of retinal cell fat specification. These studies may also help inform research aimed at producing ccell-based therapies for blinding disorders, and help ensure the efficient generation of specific cell types that have been lost in disease.
Studies using embryonic stem cells have suggested that changes in histone modifications during development play a central role in regulating cell fate specification. We plan to comprehensively map the pattern of histone modification in retinal progenitors at different developmental stages to determine if a similar process occurs during retinal development. These studies will enhance our understanding of disorders of retinal development such as microophthalmia, and provide a new avenue for developing cell-based therapies for treatment of degenerative retinal diseases such as macular degeneration and glaucoma.