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Q Chen, K Nishiyama, JW Lee, ME Rayborn, KG Shadrach, JG Hollyfield; Cloning and Characterization of Mouse SPACRCAN . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1437.
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Purpose: The interphotoreceptor matrix (IPM) has been implicated in providing supportive micro-environments for photoreceptors. A number of specific molecules are novel to the IPM, but their roles have not been clearly established. Detailed analysis of specific IPM molecules should yield important information as to their function. As a first step towards this goal, we have cloned and initiated characterization of SPCARCAN in mouse retina. Method: PCR amplification of a mouse retina cDNA library and 5'RACE were used to clone the cDNA. The cDNA sequence was used as a template for a Blast search for its corresponding genomic sequence. Northern blot analysis was used to study its tissue specific expression pattern. RT-PCR and immunocytochemistry were used to study its developmental expression pattern in retina. Results: Like its homolog in human and rat, mouse SPACRCAN has a signal peptide at the N-terminal, a large central mucin domain with numerous N-link and O-link glycosylation sites, two GAG attachment sites, four HA-binding motifs, two EGF-like domains, and a hydrophobic stretch of a 24 amino acid near the C-terminal. Comparison of the genomic structure between mouse and human SPACRCAN showed significant structure conservation. Analysis of the promoter regulatory region revealed several important regulatory elements, including Ret-1/PCE-1, six copies of PIRE, Ret-4, three copies of AP-1, CRE, and five copies of GATA3. Northern blot analysis showed that SPACRCAN mRNA is specifically expressed in retina and pineal gland. Like the rat, SPACRCAN mRNA in mouse was detectable as early as embryonic day 15. However, the earliest stage that SPACRCAN immunoreactivity could be detected was at postnatal day 8, when photoreceptor outer segments are in the initial process of elongation. Conclusion: The presence of numerous unique regulatory elements in the promoter region may be involved in determining SPACRCAN's developmental and tissue specific expression pattern. Early expression of SPACRCAN and its characteristic molecular features suggest that SPACRCAN may be important in early development of photoreceptor outer segments.
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