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C Toomes, AJ Churchill, CF Inglehearn; Two New Exons in the Human OPA1 Gene Identified Through Comparative Studies With the Mouse . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2418.
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Purpose: The OPA1 gene was recently identified as the mutated gene causing dominant optic atrophy on chromosome 3q28. In order to initiate comparative studies and as a prerequisite for future genetic manipulation we obtained the sequence of the murine orthologue. Methods: The sequence of mouse Opa1 was determined by a combination of database homology searches, sequencing IMAGE clones and RT-PCR. The presence of the novel exons within human OPA1 was determined by BLAST analysis and RT-PCR. The expression pattern of the different splice variants in a wide range of human tissues was determined by RT-PCR. Results: A murine mRNA of 3,608 bp encoding a protein of 1015 amino acids was identified. Comparison of the deduced mouse sequence with the published human sequence indicated that two extra exons were present in the mouse. The first new exon is 54 bp long and was designated exon 4a as it follows the original exon 4. The second new exon, 5a, contains 111 bp and follows the original exon 5. Searching the genomic sequence surrounding the human OPA1 gene with the new mouse exon sequences confirmed their presence in human. RT-PCR analysis showed that exon 5a is expressed at low levels in all tissues tested with the exception of liver and kidney where it forms part of the major transcript. Exon 4a alone, and exons 4a and 5a together, are expressed at very low levels in all tissues examined. Conclusions: The original published sequence of the human OPA1 encoded a 960 amino acid protein. We have shown that two new exons form the basis for splice variants within the OPA1 gene, the longest transcript identified so far encoding a protein of 1015 amino acids. The original transcript appears to be the major mRNA in all tissues examined with the exception of liver and kidney where the major mRNA species contains exon 5a. The function of different isoforms of OPA1 present in such a tissue specific manner is unknown at present. Mutation screening reports have only identified mutations in a maximum of 57% of patients, screening of these new exons may increase this detection rate.
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