Gene expression profile of the rat eye iridocorneal angle: NEIBank expressed sequence tag analysis.

PURPOSE: To characterize gene expression pattern in the combined tissues of the rat iridocorneal angle by expressed sequence tag (EST) analysis, as part of the NEIBank project. METHODS: RNA was extracted from dissected tissues of the rat iridocorneal angle (iris, ciliary body, trabecular meshwork, and Schlemm's canal) and used to construct unamplified, non-normalized cDNA libraries in the pSPORT1 vector. Approximately 5000 clones were sequenced from the 5'-end. Clones were clustered and identified using the GRIST software, a procedure based on BLAST comparisons. Complete sequences of several novel cDNAs showing eye-preferred expression patterns were obtained. The expression patterns of several genes have been investigated by Northern blot and in situ hybridization, as well as by RT-PCR. RESULTS: After analysis and removal of non-mRNA sequences, 2195 independent clusters, potentially representing individual eye angle-expressed clones were obtained. The expression profile of the combined rat eye angle tissues was more similar to that of the human iris than to human trabecular meshwork. Several cDNAs encoding transcription factors essential for normal eye development and function including Pax-6, Six3, c-Maf, Maf1, Sox-4, Foxc1, Rx, and Ldb2 were present among sequenced clones. A number of tested cDNAs showed eye-preferred expression patterns. Myocilin, which is abundant in human eye angle tissues, was not observed in the rat collection; however, transcripts for three other olfactomedin-domain proteins were seen. Latrotoxin receptor (CL1AA) and optimedin were shown to be expressed in the iris and ciliary body, as well as in the ganglion and inner nuclear cell layers of the retina, whereas the rat orthologue of the human HNOEL-iso gene was expressed in the iris and sclera and less actively in the trabecular meshwork, retina, and optic nerve. CONCLUSIONS: The iridocorneal libraries are a good source of novel uncharacterized genes and molecular markers for the tissues of the eye angle. Although myocilin is not abundantly expressed in rat eye angle, other olfactomedin-containing genes are expressed there and may play important roles in normal eye function and disease.

Optimedin: a novel olfactomedin-related protein that interacts with myocilin.

Mutations in the MYOC gene may lead to juvenile open-angle glaucoma with high intraocular pressure, and are detected in about 4% of people with adult onset glaucoma. Most of these mutations are found in the third exon of the gene encoding the olfactomedin-like domain located at the C terminus of the protein. Another olfactomedin-related protein, known as noelin or pancortin, is involved in the generation of neural crest cells. Here we describe the identification of a novel olfactomedin-related gene, named optimedin, located on chromosome 1p21 in humans. Optimedin and noelin are both expressed in brain and retina. However, unlike noelin, rat optimedin is also highly expressed in the epithelial cells of the iris and the ciliary body in close proximity to the sites of Myoc expression. In the human eye, optimedin is expressed in the retina and the trabecular meshwork. Both optimedin and myocilin are localized in Golgi and are secreted proteins. The presence of mutant myocilin interferes with secretion of optimedin in transfected cells. Optimedin and myocilin interact with each other in vitro as judged by the GST pulldown, co-immunoprecipitation and far-western binding assays. The C-terminal olfactomedin domains are essential for interaction between optimedin and myocilin, while the N-terminal domains of both proteins are involved in the formation of protein homodimers. We suggest that optimedin may be a candidate gene for disorders involving the anterior segment of the eye and the retina.