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Tamar Ben-Yosef, Mariela J. Nevet, Sharon Vekslin; Characterization Of Ceramide Kinase-Like (CERKL) In The Mammalian Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1640.
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CERKL mutations are associated with severe retinal degeneration. CERKL encodes for a novel ceramide kinase (CERK)-like protein. Both CERK and CERKL harbor a kinase domain related to the diacylglycerol kinases, a Pleckstrin Homology domain, and a CERK-specific region, bearing a putative calcium/calmodulin binding motif. Several studies have been conducted to prove a biochemical similarity between CERK and CERKL enzymatic activities. However, so far there has been no evidence that CERKL phosphorylates ceramide or any other lipid substrate in vitro or in vivo. CERKL’s function in the retina is unknown. The purpose of this work is to characterize CERKL’s retinal expression pattern and function.
RT-PCR analysis of mouse retina RNA was used to study Cerkl’s expression at various developmental time points, and to identify its various splice-isoforms. A specific anti-CERKL antibody was used to study the localization of the endogenous CERKL protein in the mouse retina. A calcium-overlay assay was used to determine whether CERKL actually binds calcium. To identify CERKL-binding proteins we used the Ras-Recruitment system.
Cerkl is expressed in the mouse eye as early as embryonic day 14. In the mouse retina CERKL is located in the ganglion cell layer, in amacrine cells of the inner nuclear layer, and in photoreceptors. CERKL is highly expressed in cone photoreceptors, while its expression level in rod photoreceptors is very low. Based on a calcium-overlay assay, CERKL does not appear to bind calcium. Several putative CERKL-binding proteins were identified, including some that are known to take part in the phototransduction cascade.
Cerkl’s expression in both mature and embryonic mouse retina, in addition to the severe retinal phenotype associated with human CERKL mutations, indicate that this gene plays a crucial role in retinal activity, and that it may be important for retinal development as well. The high expression level of CERKL in cones correlates with the CERKL-associated phenotype in humans, which involves severe cone degeneration. The identified CERKL-binding partners indicate that CERKL may be linked to the phototransduction cascade.
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