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

PURPOSE. To identify and characterize genes expressed in the iris. METHODS. A human adult iris cDNA library was constructed and subjected to a differential selection screen to identify genes preferentially expressed i n iris or trabecular tissue versus those expressed in lymphoblasts. Selecte d cDNAs were partially sequenced. Novel cDNAs were chosen for further analy sis. The cDNAs were localized within Chromosomes using a radiation hybrid ( RH) mapping panel. The tissue expression profile of each cDNA was found thr ough computer-based searches. One novel cDNA was subjected to 5' rapid ampl ification of cDNA ends and Northern blot analysis. RESULTS. Of 24 differentially selected clones, 14 cDNAs had homology to kno wn genes, whereas the other 10 were previously uncharacterized cDNA clones. IR185 was one novel iris cDNA identified. Northern blot analysis with IR18 5 indicated that it is expressed in human fetal liver as a 2.7-kb transcrip t and in adult iris as a 1.6-kb transcript. Computer-based searches of publ ic databases and reverse transcription-polymerase chain reaction experiment s have determined that IR185 is also expressed in retina. RH mapping experi ments have localized IR185 to the chromosomal interval 1q31-q32, near the l oci for age-related degeneration (1q25-q31) and retinitis pigmentosa 12 (1q 31-q32), and IR185 is in the region for posterior column ataxia with retini tis pigmentosa (1q31-q32). It has a 996-bp open reading frame encoding a pu tative protein with homology to the small leucine-rich proteoglycan (SLRP) family. The IR185 gene has been tentatively named oculoglycan. CONCLUSIONS. 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 pathog enesis of ocular disease. IR185 is a tentative candidate for one eye disord er genetically localized to chromosome 1q31-q32.