Lecithin-retinol acyltransferase (LRAT), an enzyme present mainly in the retinal pigmented epithelial cells and liver, converts all-trans-retinol into all-trans-retinyl esters. In the retinal pigmented epithelium, LRAT plays a key role in the retinoid cycle, a two-cell recycling system that replenishes the 11-cis-retinal chromophore of rhodopsin and cone pigments. We disrupted mouse Lrat gene expression by targeted recombination and generated a homozygous Lrat knock-out (Lrat؊/؊) mouse. Despite the expression of LRAT in multiple tissues, the Lrat؊/؊ mouse develops normally. The histological analysis and electron microscopy of the retina for 6 -8-week-old Lrat؊/؊ mice revealed that the rod outer segments are ϳ35% shorter than those of Lrat؉/؉ mice, whereas other neuronal layers appear normal. Lrat؊/؊ mice have trace levels of all-trans-retinyl esters in the liver, lung, eye, and blood, whereas the circulating all-trans-retinol is reduced only slightly. Scotopic and photopic electroretinograms as well as pupillary constriction analyses revealed that rod and cone visual functions are severely attenuated at an early age. We conclude that Lrat؊/؊ mice may serve as an animal model with early onset severe retinal dystrophy and severe retinyl ester deprivation.Lecithin-retinol acyltransferase (LRAT) 1 converts all-transretinol (vitamin A) to all-trans-retinyl esters in several tissues, including the liver, lung, pancreas, intestine, testis, and the retinal pigmented epithelium (RPE) (1-5). LRAT activity in the RPE has been studied for more than 60 years (6), but the enzyme was only recently identified on the molecular level as a 25-kDa integral membrane protein (7). All-trans-retinyl esters are intermediate compounds in a metabolic pathway ("visual cycle" or "retinoid cycle") that recycles 11-cis-retinal, the chromophore of rhodopsin and cone pigments (for review, see Refs. 8 -10). In this cycle, all-trans-retinal dissociates from rhodopsin and cone pigments after photobleaching. In the photoreceptors, all-trans-retinal is reduced to all-trans-retinol and subsequently exported to the adjacent RPE. In the RPE, alltrans-retinol is esterified by LRAT and stored. All-trans-retinyl esters have been suggested to be the substrate for a putative isomerohydrolase in the RPE (11) and for a retinyl ester hydrolase that produces all-trans-retinol, a substrate for the putative isomerase (for review, see Ref. 12). Ultimately, 11-cisretinol is produced, oxidized to 11-cis-retinal, and exported to the photoreceptors. In the rod and cone photoreceptor outer segments, 11-cis-retinal recombines with opsins to form rhodopsin and cone pigments (for review, see Ref. 8).Human LRAT cDNA was cloned from a retinal-RPE cDNA library (7) and rodent Lrat cDNA from liver and other tissues (13-15). Lrat mRNA was shown to be a 5.0-kb species expressed in the RPE, and the multiple transcripts based on differential polyadenylation were detected in several other tissues known for the highest LRAT activity (13). The human LRAT polypeptide consisted of 230 ...

CaBP1-8 are neuronal Ca 2+ -binding proteins with similarity to calmodulin (CaM). Here we show that CaBP4 is specifically expressed in photoreceptors, where it is localized to synaptic terminals. The outer plexiform layer, which contains the photoreceptor synapses with secondary neurons, was thinner in the Cabp4 −/− mice than in control mice. Cabp4 −/− retinas also had ectopic synapses originating from rod bipolar and horizontal cells that extended into the outer nuclear layer. Responses of Cabp4 −/− rod bipolars were reduced in sensitivity about 100-fold. Electroretinograms (ERGs) indicated a reduction in cone and rod synaptic function. The phenotype of Cabp4 −/− mice shares similarities with that of incomplete congenital stationary night blindness (CSNB2) patients. CaBP4 directly associated with the C-terminal domain of the Ca v 1.4 α 1 -subunit and shifted the activation of Ca v 1.4 to hyperpolarized voltages in transfected cells. These observations indicate that CaBP4 is important for normal synaptic function, probably through regulation of Ca 2+ influx and neurotransmitter release in photoreceptor synaptic terminals.L-type Ca 2+ channels are involved in neuronal differentiation and outgrowth and in synaptic plasticity 1,2 . At many ribbon synapses, Ca 2+ influx through L-type Ca 2+ channels triggers neurotransmitter release 3-5 . The α 1 -subunit of the L-type Ca v 1.4 channel (Ca v 1.4α1) is specific to photoreceptors and is present at highest density in the synaptic terminals 5,6 . Compared with other L-type Ca 2+ channels, Ca v 1.4 channels are activated at relatively more negative voltages and show slow inactivation 7-9 , important properties for the ability of photoreceptors to sustain continual glutamate release in the dark 4,10 . Null mutations in Ca v 1.4α1 are responsible for an X-linked disorder, CSNB2 (refs. 11 ,12 ). ERGs of these patients indicate that a deficit may occur in transmission of signals from rod photoreceptors to bipolar cells. In mice, deletion of the β 2 -subunit, another component of the photoreceptor L-type channel, alters the expression of Ca v 1.4 and produces a phenotype similar to that seen in CSNB2 patients 13 .CaBPs, a subfamily of calmodulin (CaM)-like neuronal Ca 2+ -binding proteins 14 , modulate voltage-dependent Ca 2+ channels (VDCCs) and inositol triphosphate receptors 15-17 . Here we show that CaBP4, which has only been partially characterized in silico 14 , is found specifically

Purpose To describe the histological development of the human central retina from fetal week (Fwk) 22 to 13 years. Design Retrospective observational case series Methods Retinal layers and neuronal substructures were delineated on foveal sections of fixed tissue stained in azure II-methylene blue and on frozen sections immunolabeled for cone, rod or glial proteins. Postmortem tissue was from 11 eyes at Fwk 20–27; 8 eyes at Fwk 28–37; 6 eyes at postnatal 1 day to 6 weeks; 3 eyes at 9–15 months; and 5 eyes at 28 months-13 years. Results At Fwk20–22 the fovea could be identified by the presence of a single layer of cones in the outer nuclear layer. Immunolabeling detected synaptic proteins, cone and rod opsins and Muller glial processes separating the photoreceptors. The foveal pit appeared at Fwk25, involving progressive peripheral displacement of ganglion cell, inner plexiform and inner nuclear layers. The pit became wider and shallower after birth, and appeared mature by 15months. Between Fwk25 and Fwk38, all photoreceptors developed more distinct inner and outer segments, but these were longer on peripheral than foveal cones. After birth the foveal outer nuclear layer became much thicker as cone packing occurred. Cone packing and neuronal migration during pit formation combined to form long central photoreceptor axons, which changed the outer plexiform layer from a thin sheet of synaptic pedicles into the thickest layer in the central retina by 15 months. Foveal inner and outer segment length matched peripheral cones by 15 months and was 4× longer by 13 years. Conclusions These data are necessary to understand the marked changes in human retina from late gestation to early adulthood. They provide qualitative and quantitative morphological information required to interpret the changes in hyper- and hypo-reflexive bands in pediatric spectral domain optical coherence tomography (SDOCT) images at the same ages.

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant disorder caused by a CAG repeat expansion. To determine the mechanism of neurotoxicity, we produced transgenic mice and observed a cone-rod dystrophy. Nuclear inclusions were present, suggesting that the disease pathway involves the nucleus. When yeast two-hybrid assays indicated that cone-rod homeobox protein (CRX) interacts with ataxin-7, we performed further studies to assess this interaction. We found that ataxin-7 and CRX colocalize and coimmunoprecipitate. We observed that polyglutamine-expanded ataxin-7 can dramatically suppress CRX transactivation. In SCA7 transgenic mice, electrophoretic mobility shift assays indicated reduced CRX binding activity, while RT-PCR analysis detected reductions in CRX-regulated genes. Our results suggest that CRX transcription interference accounts for the retinal degeneration in SCA7 and thus may provide an explanation for how cell-type specificity is achieved in this polyglutamine repeat disease.