Investigation of Chx10 in development of the neural retina and microphthalmia
ChxlO is a homeobox transcription factor essential for the development of the vertebrate eye. A mutation in the human gene CHX10 causes microphthalmia and a similar phenotype is observed in the ocular retardation, ChxlO null mouse. Lack of ChxlO causes a reduction in proliferation of neural retinal progenitor cells (RPCs) in the developing retina, resulting in a reduction in the size of the eye. The aim of this study was threefold: to identify downstream targets of the ChxlO gene and discover more about the role of ChxlO at a molecular level, to further characterise the ChxlO'1' phenotype and the behaviour of the mutant RPCs, and to investigate the possibility that the ChxlO''" retina harbours stem cell-like cells. Firstly, Affymetrix GeneChip technology was used to compare the gene expression profile of wild type retina with that of the ChxlO null retina during early development. Significant differential expression was observed for 34 characterised genes genes involved in neuronal differentiation were down-regulated whereas genes involved in retinal pigmented epithelium (RPE) specification were up- regulated. These findings highlight a novel role for ChxlO in maintaining the neural retina/RPE boundary. Secondly, experiments aimed at characterising ChxlO''' RPCs showed that they exhibit altered cycling properties compared to wild type RPCs and that their differentiation to neural retinal cells is delayed. The data resulting from these studies support a model in which the transition from Gl phase of the cell cycle to S phase or to differentiation is disrupted in the ChxlO''' retina. Finally, a population of proliferating cells was discovered in the adult ChxlO''' retina, which showed neurogenic properties and formed neurospheres in culture, a point of interest in the context of retinal stem cell research. The study conducted here has offered valuable clues as to how ChxlO affects retinal progenitor cell proliferation and differentiation at both a molecular and a cellular level. It is hoped this work will contribute to the current knowledge of eye development in general, and ChxlO's involvement in this process in particular.