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B. Janke, B. Lorenz, M.N. Preising; Alternative Splicing in AIPL1 – Implications On Function And The Mutational Spectrum . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2481.
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Background: AIPL1 is the fourth gene involved in Leber’s Congenital Amaurosis (LCA4), the most frequent cause for congenital blindness in children. Mutations in AIPL1 underly a severe form of LCA, characteristically including earliest onset and rapid loss of vision. Methods: Full length transcripts of AIPL1 were amplified by RT–PCR from neuroretinal RNA obtained from an eye enucleated from a female donor aged 75 years without any indication of retinal disorders. Enucleation was performed at surgery for an extended bone tumor of the face. AIPL1 clones were sequenced to confirm the completeness of the insert. A mutational screen by direct sequencing was performed on genomic DNA of the donor for exon 3 of AIPL1. Results: Two different transcripts of AIPL1 were amplified at various amounts by RT–PCR, isolated, and subcloned into pDRIVE vectors (Quiagen). The major clone corresponded to the full–length transcript. The minor clone was present at about 10% and is a variant of AIPL1, lacking the entire exon 3. Mutation screening in exon 3 showed a frequent sequence variation (IVS2–10a>c) in intron 2 so far considered to be a polymorphism. IVS2–10a>c was present in the homozygous state in the donor. Conclusions: This splice variant has been published in GenBank without any indication to its origin. IVS2–10a>c is predicted to leave the splice score unaffected as calculated by SPLICEVIEW. Interestingly a transcript could be generated that lacks exon 3 which completely harbors the first of three tetratricopeptide domains, a functionally important motif of AIPL1. Since only a few sequence variations including a very frequent polymorphism could be identified in exon 3 the question arises whether exon 3 is necessary for proper function or whether the first tetratricopeptide domain can be omitted with functional deficit. If the minor transcript in this study is a naturally occurring AIPL1 isoform produced from different messengers, which function does it perform in photoreceptor cells? The answers may have an impact upon the assessment of the previously reported LCA4 causing mutations, especially those occuring in exon 3 of AIPL1.
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