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D.V. Bosenko, E.V. Semina; Characterization of New Isoforms of Human PITX2 Gene and Expression of PITX Genes in Human Tissues . Invest. Ophthalmol. Vis. Sci. 2005;46(13):43.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The PITX2 gene plays important role during embryonic development of multiple systems in different species. Normal PITX2 expression is critical for proper formation of human eye, as individuals with altered PITX2 function develop glaucoma. We aimed to identify all possible PITX2 isoforms expressed in human eye. Methods: RNA was extracted from immortalized human embryonic iris cells (cell line Hs680) and used in 5’– and 3’–RACE experiments, primers located in different exons of PITX2 were employed. The resulting products were cloned, sequenced and matched with genomic PITX2 sequence. PCR products corresponding to different PITX2 isoforms were detected by electrophoresis of PCR products obtained with isoform–specific primers and cDNA that was obtained from multiple ocular tissues and cell lines. Results: The PITX2 gene was originally shown to contain six exons that encode three alternative transcripts (PITX2 A, B and C). We identified several new exons of PITX2 (isoforms E, F and G) with two of them located further upstream of the most 5’ known PITX2 exon. With these new transcripts, a total number of PITX2 isoforms amounts to seven and of different PITX2 proteins to three. Each PITX2 isoform is made by alternative splicing and differential use of four promoters. Some isoforms contain dissimilar N–terminal domains, which are thought to be involved in the interaction of PITX2 with other factors while all isoforms share in common the HD and C–terminal region. Expression analysis of all PITX2 isoforms and two other PITX genes in a panel consisting of different ocular tissues identified that PITX2 A, B, C and F are strongly expressed in adult ocular tissues such as cornea, iris, choroid and sclera and in corresponding cell lines. The newly identified PITX2F isoform was shown to be the most eye–specific, while other isoforms are strongly expressed in other non–ocular systems as well. The PITX3 gene was expressed in adult lens and PITX1 gene products were found in cornea, choroid and sclera Conclusions: PITX2 gene is strongly expressed in adult ocular tissues that may indicate to its function in eye maintenance in addition to role in development. Novel exons and isoforms of PITX2 gene have been identified. One of these isoforms, PITX2F, that is expressed from a new alternative promoter, was shown to be most active in eye tissues that makes it a likely candidate for involvement in isolated ocular phenotypes in human patients.
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