Bioinformatic approaches for identification and characterizationof olfactomedin related genes with a potential role in pathogenesis ofocular disorders

摘要

Purpose: To identify olfactomedin domain containing proteins, whichare expressed in the eye and have similarity to myocilin, to test aspotential candidates for eye diseases. Most of the mutations in myocilincausing primary open angle glaucoma are located in the olfactomedindomain. In vitro experiments demonstrated interaction between optimedinand myocilin through the conserved olfactomedin domains of the proteinsin rats, and it was speculated that optimedin might have a role in thepathogenesis of ocular disorders. Hence, we aimed to identify myocilinrelated human proteins having conserved olfactomedin domains withpotential to interact between them and examine the expression patternsin the eye by bioinformatics approaches. This endeavor would have thepotential to identify new candidate genes for eye diseases in generaland glaucoma in particular to be tested by wet-lab experiments.Methods: Proteins with homology to myocilin were selected by BLASTpat the NCBI server. cDNA sequences and corresponding genomic contigswere retrieved. Pairwise BLAST was done to investigate the genestructure. The human EST database and NEIBank were searched against theselected cDNAs to look for tissue specific expression of thetranscripts.Results: The study led to the identification of three groups ofproteins encoded by three different genes; Noelin 1 (9q34.3),Noelin 2 (19p13.2), and Noelin 3 (1p22) encompassing 45,575 bp,82,679 bp, and 1,93,421 bp of the genomic sequence, respectively.Genomic structures, alternate usage of exons, and molecular evolution ofthe Noelins were determined. Similar structures of the genes,splicing patterns and high levels of homology shed light on therelatedness and molecular evolution of this group of olfactomedinrelated proteins. Strikingly, however, Noelin 1 and Noelin 3were found to be expressed as multiple splice variants while only asingle spliced transcript could be identified for Noelin 2. A humanEST database search suggested the expression of all three Noelingenes in the brain but only two (Noelin 1 and Noelin 2) in theeye despite experimental evidence for expression of Noelin 3 inocular tissue. Myocilin was determined to have similar levels (60-61%)of homology with all three Noelin gene products (Noelin 1_v1, Noelin2_v1, and Noelin 3_v1) at the conserved olfactomedin domains.Conclusions: Mammalian Noelin 1 evolved from its precursor,followed by evolution of Noelin 3 and Noelin 2 by geneduplication events. Myocilin might have evolved from Noelin 2 bygene duplication followed by exon fusion. Noelin 1 and Noelin 2could be tested as candidate genes for eye diseases based on theirexpressions in the eye and shared olfactomedin domains with Myocilinin the C-termini of the respective proteins.