Biomedical subjects

Samir S Deeb

Publications and source records attributed to Samir S Deeb.

22 records · Page 2Linked to original sources

PubMedDate not supplied

Expression of rinx/vsx1 during postnatal eye development in cone-bipolar, differentiating ganglion, and lens fiber cells.

PURPOSE: To investigate the expression pattern of the homeobox transcription factor Rinx (also referred to as Vsx1) during postnatal eye development of the mouse. METHODS: We cloned the mouse Rinx gene, inferred the sequence of the encoded protein, and prepared polyclonal antibodies against it. Immunohistochemical analysis (IHC) and in situ hybridization were employed to localize Rinx in postnatal and adult mouse eyes. Double-labeled IHC either with anti-protein kinase C (PKC, a marker of rod bipolar cells) or anti-vimentin (a marker of Muller glial cells) antibodies was performed in the adult retina. Rinx mRNA was also analyzed by reverse transcription-polymerase chain reaction in the lens. RESULTS: At P0 and P4 (postnatal days), Rinx-immunoreactive cells included retinal ganglion cells (RGC), cells of the innermost nuclear layer (INL) and of presumptive INL, differentiating lens fiber cells, and a few cells of the presumptive outer nuclear layer (ONL). At P8, both Rinx protein and mRNA were detected in the middle of the INL, and in RGC, but not in the lens. When the mice were 8 weeks of age, only a subset of nuclei in the outer half of the INL expressed both Rinx protein and mRNA. Double-labeling IHC indicated that Rinx- and either PKC- or vimentin-labeled cells were not colocalized. Therefore, Rinx is most likely expressed in adult cone bipolar cells and possibly in horizontal cells. CONCLUSIONS: Rinx may play important roles in the differentiation and maintenance of cone bipolar cells. Rinx is unique among members of this family of homeodomain proteins in that it may also be involved in differentiation of RGC and lens fiber cells.

Amino Acid Sequence↗

PubMedDate not supplied

Molecular genetics of color-vision deficiencies.

The normal X-chromosome-linked color-vision gene array is composed of a single long-wave-sensitive (L-) pigment gene followed by one or more middle-wave-sensitive (M-) pigment genes. The expression of these genes to form L- or M-cones is controlled by the proximal promoter and by the locus control region. The high degree of homology between the L- and M-pigment genes predisposed them to unequal recombination, leading to gene deletion or the formation of L/M hybrid genes that explain the majority of the common red-green color-vision deficiencies. Hybrid genes encode a variety of L-like or M-like pigments. Analysis of the gene order in arrays of normal and deutan subjects indicates that only the two most proximal genes of the array contribute to the color-vision phenotype. This is supported by the observation that only the first two genes of the array are expressed in the human retina. The severity of the color-vision defect is roughly related to the difference in absorption maxima (lambda(max)) between the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the L pigment accounts for the subtle difference in normal color vision and influences the severity of red-green color-vision deficiency. Blue-cone monochromacy is a rare disorder that involves absence of L- and M-cone function. It is caused either by deletion of a critical region that regulates expression of the L/M gene array, or by mutations that inactivate the L- and M-pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutants in the genes encoding the cone-specific alpha- and beta-subunits of the cGMP-gated cation channel as well as in the alpha-subunit of transducin have been implicated in this disorder.

Animals↗

PubMedDate not supplied

Cone visual pigments of the Australian marsupials, the stripe-faced and fat-tailed dunnarts: sequence and inferred spectral properties.

Studies of color vision in marsupial mammals have been very limited. Two photoreceptor genes have been characterized from the tammar wallaby, but a third cone pigment was suggested by microspectrophotometric measurements on cone photoreceptors in two other species, including the fat-tailed dunnart, Sminthopsis crassicaudata. To determine the sequence and infer absorption maxima of the cone photoreceptor pigments of S. crassicaudata and the related stripe-faced dunnart (Sminthopsis macroura), we have used evolutionarily conserved sequences of the cone pigments of other species, including the tammar wallaby, to design primers to amplify the S. macroura and S. crassicaudata pigment sequences by the polymerase chain reaction (PCR) using genomic DNA or retinal cDNA as a template. These primers will be useful for amplifying cone opsin coding sequences from a variety of vertebrates. Amplified products were directly sequenced to determine gene structure and coding sequences. The inferred amino acid sequences of the cone visual pigments indicated that both species have middle-wave-sensitive (MWS) pigments with a predicted absorption maximum (lambda(max)) at 530 nm, and ultraviolet-sensitive (UVS) pigments with a predicted lambda(max) at 360 nm. The MWS pigments of the two species differ by two, and UVS by three amino acid positions. No evidence was obtained for a third cone pigment in either species.

Amino Acid Sequence↗

PubMedDate not supplied

Mutually exclusive expression of the L and M pigment genes in the human retinoblastoma cell line WERI: Resetting by cell division.

The key steps in the evolution of full trichromatic color vision in primates include duplication of the ancestral pigment gene to form the L and M pigment gene array on the X chromosome, mutually exclusive expression of the L and M pigment genes in cone photoreceptors, and formation of a retinal mosaic with randomly distributed L and M cones. Previous work using transgenic mice has indicated that a locus control region adjacent to this array of genes plays an important role in their mutually exclusive expression in respective cone cells (Smallwood et al., 2002). However, the mechanism by which this is accomplished is unknown. We searched for a cellular model system to investigate the mechanism of this mutually exclusive expression. We previously showed that the undifferentiated human retinoblastoma cell line WERI expresses L and M cone opsin but not rod opsin genes. We now show that WERI cells express the L and M pigment genes in a mutually exclusive manner, in that either L or M pigment mRNA is expressed in a single cell. Importantly, clonal analysis showed that single WERI cells that express either L or M generate, upon cell division produce, a mixed population of L- or M-expressing cells. These results indicate, first, that cell division resets L or M pigment gene expression, most likely due to disassembly and reassembly of LCR-promoter DNA-protein complexes during cell division. Second, a retinal mosaic with near-random distribution of L and M cones may have been generated automatically after duplication of the ancestral gene to form the L and M pigment genes. Third, determination of L and M cone identity may not require external molecular cues during differentiation, and is consistent with the idea that L and M cones are not intrinsically different.

Blotting, Northern↗