Glaucoma is a chronic blinding neurodegenerative disease characterized by the progressive loss of retinal ganglion cells and degeneration of the optic nerve. Although significant progress has been made in the field of the genetics of this disease, the majority of these studies have so far examined rarer forms of the disease that exhibit Mendelian inheritance patterns. The majority of glaucomas, however, are complex genetic diseases that have multiple interacting loci that affect an individual's susceptibility. One possible area of susceptibility is the genetically controlled cell death program that is executed by dying ganglion cells. We have used experimental genetics in mice to help identify potential susceptibility alleles that could affect this process. A screen of 15 inbred mouse lines for the amount of ganglion cell loss after optic nerve crush revealed 2 lines with varying resistance to this procedure. The resistant phenotype was found to be inherited as a dominant trait, and genome wide mapping has identified the responsible gene to be located within a 25 cM interval of chromosome 5 (Chr5.loc34-59). This locus has been named Retinal ganglion cell susceptible 1 (Rgcs1). We propose to extend these observations by continuing to fine map the Rgcs1 locus to narrow the region of interest. Fine mapping will begin using SNP analysis to refine the interval to a predicted 10 cM region, followed by the generation of Interval Specific Congenic Lines (ISCLs) to dissect the region into 1 cM overlapping intervals. In addition, we will use in silico mapping to help define candidate genes of interest in the interval as it becomes smaller. To date, we have used this approach to identify 7 potential candidates from among the 578 genes known to exist in this region. Candidate genes will be characterized by quantitative and qualitative analyses between the two parental inbred strains. During the course of generating ISCLs, we will also create a substrain of DBA/2J mice to examine the role that the Rgcs1 locus plays in susceptibility to glaucoma. Wild type DBA/2J mice carry the resistant allele. Interestingly, these mice also develop chronic inherited glaucoma, which may seem like a paradox, but could also be consistent with a true susceptibility allele. Our test of the role of Rgcs1 in glaucoma, will be to cross the susceptible Rgcs1 locus from BALB/cByJ animals onto the DBA/2J background to generate the substrain DBA/2J.BALBRgcs1. We expect these mice to develop elevated intraocular pressure, and by virtue of carrying a susceptible Rgcs1 allele, a more severe form of glaucoma. Lastly, as we acquire more information on the mouse Rgcs1 locus, we will begin to interrogate the syntenic region of the human genome by examining for SNP differences in key candidate genes using a data set of human glaucoma patients housed at the Center for Human Genetics at Duke University.
This proposal describes studies designed to identify and characterize a gene located in a region of mouse chromosome 5 that affects retinal ganglion cell survival after optic nerve crush. We will also test the ability of this chromosomal region to affect ganglion cell survival in a mouse model of glaucoma, and then extend these observations to determine if the corresponding locus/gene affects glaucoma in humans. The significance of this work is that it will help elucidate some of the susceptibility alleles associated with the complex trait of glaucoma. Finding and characterizing these alleles will lead to better diagnosis and treatment regimes for individuals with glaucoma.
