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Early schisis cavities in the retinal bipolar cell layer accompanied by progressive loss of cone and rod photoreceptor cells are the hallmark of the retinoschisin-deficient (Rs1h–/Y) murine retina. With this study we aimed at elucidating the molecular events underlying the photoreceptor cell death in this established murine model of X-linked juvenile retinoschisis. We show that photoreceptor degeneration in the Rs1h–/Y mouse is due to apoptotic events peaking around postnatal day 18. Cell death is accompanied by increased expression of initiator and inflammatory caspases but not by downstream effector caspases. The strong induction of caspase-1 (Casp1) prompted us to explore its involvement in the apoptotic process. We therefore generated double knock-out mice deficient for both retinoschisin and Casp1. No direct influence of the Casp1 genotype on apoptosis could be identified although striking differences in the overall number of resident microglia were observed independent of the Rs1h genotype.

Retina and retinal pigment epithelium (RPE) cells are of neuroectodermal origin with highly specialized functions in light perception. Identification and characterization of genes differentially expressed in these cells will greatly aid our understanding of their functional roles in retinal biology. As a source enriched for gene transcripts from the retina/RPE, we generated a human retina and a bovine RPE cDNA library applying the PCR-based technique of suppression subtractive hybridization (SSH). Sequencing of 1,080 retina and 2,350 RPE SSH clones resulted in the identification of 321 and 343 non-redundant human transcripts, respectively. Of these, only 27 genes were in common between the two cDNA libraries. One transcript expressed exclusively in retina and RPE is the novel gene C4orf11 which is comprised of four exons on chromosome 4q21.2. We report the full-length cloning of two isoforms of C4orf11, 919 bp and 857 bp in length, both of which contain four identical open reading frames (ORFs). While ORFs 1 to 3 show no homologies to known proteins or protein domains, ORF4 reveals 50% sequence identity to RPE-spondin, a hypothetical protein on 8q13.3 with unknown function. We demonstrate that both the retina and the RPE SSH cDNA libraries are excellent resources for identifying known and novel genes exclusively or abundantly expressed in the retina/RPE complex. In combination with other approaches such as microarray analysis or serial analysis of gene expression (SAGE), the availability of highly sensitive and specific SSH cDNA libraries will facilitate the comprehensive description of the retina/RPE transcriptome.

X-linked juvenile retinoschisis (RS) has previously been localized to a 7–8 cM interval between markers at (DXS43, DXS207) and (DXS274, DXS41). Our analysis of more than 300 meioses in two multigeneration RS families identified eight recombinant RS chromosomes and narrowed the RS locus to an interval between DXS987 and DXS443. Our data suggest the following order of loci: Xpter – DXS207 -DXS987 – ([DXS418 – DXS999], RS) – DXS443 – DXS365 – DXS274 – Xcen.

Mutations in the human vitelliform macular dystrophy type 2 (VMD2) gene are known to cause autosomal dominant Best macular dystrophy (BMD), a degenerative disorder of the central retina. VMD2, together with VMD2L1, VMD2L2 and VMD2L3, belong to a closely related gene family characterized by several transmembrane (TM) spanning helical domains and an invariant arginine, phenylalanine and proline (RFP) tripeptide motif, thus termed VMD2 RFP-TM. The four genes are thought to encode a novel family of anion channels. We now report the cloning and characterization of the murine orthologs by combining biocomputational analyses and molecular genetic approaches. While the murine Vmd2, Vmd2l1 and Vmd2l3 genes are functional, murine Vmd2l2p was found to be a non-transcribed pseudogene. Expression profiling of the murine Vmd2 RFP-TM family members revealed tissue-restricted expression with predominant transcription of Vmd2 in testis, of Vmd2l1 in colon and of Vmd2l3 in heart. Differential splicing was observed for Vmd2l3 in a number of tissues (e.g. in brain, retina/RPE, kidney) although the functional importance of the splice variants remains to be determined.

The gene encoding claudin-1 (CLDN1) has been mapped to human chromosome 3 (HSA3; 3q28→q29) using a radiation hybrid panel. Employing fluorescence in situ hybridization (FISH) we here show that a human P1-derived artificial chromosome (PAC) containing CLDN1 detects the orthologous sites in chromosomes of the great apes, chimpanzee, gorilla, and orangutan. Furthermore, the chromosomal position of CLDN1 was determined in mouse chromosomes by FISH. The position of fluorescent signals is confined to a single chromosomal site in both great apes and mouse and in each case maps to the chromosomal region that has conserved synteny with HSA3 (PTR2q28, GGO2q28, PPY2q38 and MMU16B1). Using a gene-specific probe our results are consistent with reports of the striking similarity of great ape and human genomes as illustrated previously by chromosome painting.

In situ hybridization using a repeated element specific for the human pseudoautosomal region, DXYZ2, revealed the presence of this repeat in the early replicating portion of the sex chromosomes of the great apes. This segment, as well as the DXYZ2 repeats, are located in band Xp22.3 and in a telomeric or subtelomeric region of the Y chromosome. These segments may therefore represent pseudoautosomal regions, as in man.

In a representative sample of primate species, including simians (Catarrhini and Platyrrhini) and prosimians (Lemuriformes and Lorisiformes), high-resolution, early replication banding revealed a homoeologous early replicating segment at the ends of both sex chromosomes. The DXYZ2 element, a repeated sequence specific for the human pseudoautosomal region, is con served in the genomes of all primate species studied and is specifically localized in the distal early replicating segments of the X and Y chromosomes. Thus, cytogenetic and molecular evidence is presented of a highly conserved sex-chromosomal segment in primates. The pseudoautosomal behavior of this segment is discussed.