Isolation of a novel iris-specific and leucine-rich repeat protein (oculoglycan) using differential selection

To identify and characterize genes expressed in the iris.

A human adult iris cDNA library was constructed and subjected to a differential selection screen to identify genes preferentially expressed in iris or trabecular tissue versus those expressed in lymphoblasts. Selected cDNAs were partially sequenced. Novel cDNAs were chosen for further analysis. The cDNAs were localized within chromosomes using a radiation hybrid (RH) mapping panel. The tissue expression profile of each cDNA was found through computer-based searches. One novel cDNA was subjected to 5' rapid amplification of cDNA ends and Northern blot analysis.

Of 24 differentially selected clones, 14 cDNAs had homology to known genes, whereas the other 10 were previously uncharacterized cDNA clones. IR185 was one novel iris cDNA identified. Northern blot analysis with IR185 indicated that it is expressed in human fetal liver as a 2.7-kb transcript and in adult iris as a 1.6-kb transcript. Computer-based searches of public databases and reverse transcription-polymerase chain reaction experiments have determined that IR185 is also expressed in retina. RH mapping experiments have localized IR185 to the chromosomal interval 1q31-q32, near the loci for age-related degeneration (1q25-q31) and retinitis pigmentosa 12 (1q31-q32), and IR185 is in the region for posterior column ataxia with retinitis pigmentosa (1q31-q32). It has a 996-bp open reading frame encoding a putative protein with homology to the small leucine-rich proteoglycan (SLRP) family. The IR185 gene has been tentatively named oculoglycan.

Differential selection is a technique that has been useful in identifying genes specific to a variety of tissues. This is the first time this technique has been applied to the iris. Characterizing genes highly or uniquely expressed in the iris can assist in clarifying our understanding of iris function and lead to a better understanding of the molecular pathogenesis of ocular disease. IR185 is a tentative candidate for one eye disorder genetically localized to chromosome 1q31-q32.