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A. Uysal, F. Ozcan, Y. Ozmen, G. Kuser, K. Bugra–Bilge; The Identification of Salt–Inducible Kinase 2 (SIK2) Orthologue in Rat Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3151.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To obtain a full length clone of SIK2 for further studies to elucidate its function in retina. Methods: Multiple PCR analyses were performed using retinal cDNA as template and primers derived from conserved sequences between mouse SIK2 and predicted rat similar to salt–inducible kinase–2 (SSIK2, LOC315649) genes. 5’RACE was applied to define the start site of SIK2 mRNA. Homology analysis was performed between rat and mouse SIK2 genes. Transcript sizes were determined by Northern analysis using DIG–labeled probe. Cell–specific expression in retina was analyzed by RT–PCR. Results: Two clones, 7 kb (rSIK2–1) and 7.5 kb (rSIK2–2) in length, were generated from retinal RNA. rSIK2–2 has an extra exon in 3’UTR region indicating that the clones represent alternatively spliced gene products. The putative open reading frame encodes a 932 aa long protein. Sequencing revealed a 252 aa–serine–threonine kinase domain with 99% homology with the reported mouse SIK2 gene product. 3’ end sequences of rat and mouse SIK2 show greatest variation. Moreover, rat SIK2s have significantly longer 3’UTR than their mouse counterpart. Northern blot analysis has also revealed two bands with approximate sizes of 7 kb and 7.5 kb, confirming the presence of splice forms of rat SIK2 in this tissue. RT–PCR results indicate that the gene is expressed in inner and outer retinal cells. Conclusions: SIK2, a member of the AMPK family of Ser/Thr kinases, is highly conserved between rat and mouse. SIK2 is widely expressed in retinal cells in addition to the tissues reported previously. The long 3’UTR might suggest that its translation is tightly regulated. Since SIK2 is implicated in modulation of CREB–dependent gene activity, it is tempting to suggest SIK2 takes part in cell differentiation and survival pathways in retinal cells.
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