Spatiotemporal expression pattern of ceramide kinase-like in the mouse retina

PURPOSE: The CERKL gene encodes for ceramide kinase-like, a novel protein of unknown function. CERKL mutations are associated with a severe retinal phenotype. The purpose of this work was to investigate alternative splicing, and the temporal and spatial expression pattern of CERKL in the mouse retina. METHODS: Reverse Transcription-Polymerase Chain Reaction (RT–PCR) analysis of mouse retina RNA was used to study the expression of Cerkl at various developmental time points, and to identify its various splice-isoforms. A specific anti-CERKL antibody was developed and used for immunostaining to study the localization of the endogenous CERKL protein in retina-derived cell lines and in the mouse retina. RESULTS: Cerkl is expressed in the mouse eye as early as embryonic day 14. A total of seven different Cerkl splice-isoforms were identified in the mouse retina. The subcellular localization of CERKL in retina-derived cell lines is variable: CERKL is diffusely distributed in the cytoplasm, and in many cells, it is highly concentrated in the perinuclear region. In most, but not all cells, CERKL is also highly concentrated in the nucleus. 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; however, its expression level in rod photoreceptors is very low. In cultured cells, CERKL is detected in the nucleus, but in retinal cells in situ, it is mostly located in the cytoplasm. CONCLUSIONS: The expression of Cerkl in both mature and embryonic mouse retina and 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. Whether nucleocytoplasmic transport of CERKL actually occurs in vivo under certain conditions and its functional significance remain to be discovered.