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Retinal degeneration slow (rds) in mouse results from simple insertion of a t haplotype-specific element into protein-coding exon II.

Retinal degeneration slow (rds) is a semidominant mutation of mice that causes dysplasia and degeneration of rod and cone photoreceptors. Mutations in RDS, the human ortholog of the rds gene, are responsible for several inherited retinal dystrophies including a subset of retinitis pigmentosa. The normal rds locus encodes rds/peripherin, an integral membrane glycoprotein present in outer segment discs. Genomic libraries from wildtype and rds/rds mice were screened with an rds cDNA, and phage lambda clones that span the normal and mutant loci were mapped. We show that in mice, rds is caused by the insertion into exon II of a 9.2-kb repetitive genomic element that is very similar to the t haplotype-specific element in the H-2 complex. The entire element is included in the RNA products of the mutant locus. We present evidence that rds in mice represents a null allele.

Alleles↗

Diversity of expression of the sensory neuron-specific TTX-resistant voltage-gated sodium ion channels SNS and SNS2.

The differential distribution of two tetrodotoxin resistant (TTXr) voltage-gated sodium channels SNS (PN3) and SNS2 (NaN) in rat primary sensory neurons has been investigated. Both channels are sensory neuron specific with SNS2 restricted entirely to those small dorsal root ganglion (DRG) cells with unmyelinated axons (C-fibers). SNS, in contrast, is expressed both in small C-fiber DRG cells and in 10% of cells with myelinated axons (A-fibers). All SNS expressing A-fiber cells are Trk-A positive and many express the vanilloid-like receptor VRL1. About half of C-fiber DRG neurons express either SNS or SNS2, and in most, the channels are colocalized. SNS and SNS2 are found both in NGF-responsive and GDNF-responsive C-fibers and many of these cells also express the capsaicin receptor VR1. A very small proportion of small DRG cells express either only SNS or only SNS2. At least four different classes of A- and C-fiber DRG neurons exist, therefore, with respect to expression of these sodium channels.

Animals↗

A novel Cys-214-Ser mutation in the peripherin/RDS gene in a Japanese family with autosomal dominant retinitis pigmentosa.

We have screened for possible disease-causing mutations in the peripherin/retinal degeneration slow (RDS) gene in 13 Japanese families with autosomal dominant retinitis pigmentosa (ADRP). Using polymerase chain reaction-single strand conformation polymorphism analysis, a novel mutation at codon 214 was found in which the highly conserved cysteine was replaced with a serine in one family. The mutation at codon 214 was found in all three affected siblings of this family, but none of the 40 normal control individuals had this mutation. These results strongly suggest that the mutation is pathogenic for RP in this family. The clinical phenotype for this family is a late-onset form of ADRP.

Age of Onset↗

Structural and developmental analysis of the mouse peripherin/rds gene.

Mutations in the peripherin/rds gene have been reported to be associated with different forms of human autosomal dominant retinitis pigmentosa (ADRP) and macular degeneration (MD). To better understand the disruptive role of these mutations, knowledge of the structure-function relationship of the peripherin/rds gene is needed. To facilitate that, genomic clones encoding the mouse gene were isolated using bovine cDNA sequences as probes. Sequence analysis of clone lambda 6-1-1, that contained the entire coding sequence for the mouse peripherin/rds, yielded the exon-intron organization of the gene. The gene is composed of three exons (581, 247, and 213 bp) and two introns with the first and second introns 8.6 kb and 3.7 kb in size, respectively. Two major (1.6 and 2.7 kb) and three minor (4.0, 5.5, 6.5 kb) transcripts were detected on RNA blots. The major transcripts first appeared in the brain at embryonic day 13 and in the retina at postnatal day 1. Transcripts were missing in brain and eye of mice at embryonic day 15. Several transcription start sites were mapped within 26 nucleotides approximately 200 bp upstream from the translation initiation site. However, transcripts varied in the lengths of their 3' untranslated portion as a result of the utilization of different polyadenylation signals.

Amino Acid Sequence↗

Signal transduction in the retina and inherited retinopathies.

In this paper, an attempt is made to highlight some of the recent developments in genetics to understand the group of inherited eye disorders referred to as retinitis pigmentosa (RP). Of the seven genes identified, six are expressed specifically in the photoreceptor cells and four encode the enzymes involved in the phototransduction pathway. A short discussion is presented of the tremendous phenotypic heterogeneity. An understanding of RP requires knowledge of other genetic and environmental factors as well as tests to measure the status of the patient's photoreceptor cells in various disease stages.

3',5'-Cyclic-GMP Phosphodiesterases↗

Early death of neural crest cells is responsible for total enteric aganglionosis in Sox10(Dom)/Sox10(Dom) mouse embryos.

Intestinal aganglionosis results from homologous genetic defects in humans and mice, including mutations of Sox10, which encodes a transcription factor expressed in neural crest cells. To gain insight into the embryological basis for this condition, the phenotype and pathogenesis of intestinal aganglionosis in Sox10(Dom)/Sox10(Dom) embryos were studied. The distribution of enteric neural precursors and other neural crest derivatives in Sox10(Dom)/Sox10(Dom) embryos was analyzed with immunochemical and transgenic markers. The ability of wild-type neural crest cells to colonize Sox10(Dom)/Sox10(Dom) intestinal explants was evaluated by appositional grafts under the renal capsule. Apoptosis was studied by TUNEL labeling. Sox10(Dom)/Sox10(Dom) embryos died pre- or perinatally with total enteric aganglionosis and hypoplasia or agenesis of nonenteric ganglia. Mutant crest cells failed to colonize any portion of the Sox10(Dom)/Sox10(Dom) gut, but wild-type neural crest cells were able to colonize explanted segments of Sox10(Dom)/Sox10(Dom) embryonic intestine. In Sox10(Dom)/Sox10(Dom) embryos, apoptosis was increased in sites of early neural crest cell development, before these cells enter the gut. Sox10(Dom)/Sox10(Dom) embryos are one of many genetic animal models for human Hirschsprung disease. The underlying problem is probably not the enteric microenvironment, since Sox10(Dom)/Sox10(Dom) intestine supports colonization and neuronal differentiation by wild-type neural crest cells. Instead, excessive cell death occurs in mutant neural crest cells early in their migratory pathway. Comparison with other models suggests that genetic heterogeneity of aganglionosis correlates with different pathogenetic mechanisms.

Animals↗

Glial growth factor restricts mammalian neural crest stem cells to a glial fate.

Growth factors and cytokines are thought to influence the development of uncommitted progenitor cell populations, but the issue of how these factors act on individual cells remains controversial. Such factors may act simply as selective mitogens or survival factors for cells that undergo lineage restrictions stochastically. Alternatively, they may instruct or bias multipotent cells to choose one lineage at the expense of others. Here we show that glial growth factor (GGF), previously defined as a Schwann cell mitogen, strongly suppresses neuronal differentiation of rat neural crest stem cells while promoting or allowing glial differentiation. Quantitative clonal analysis suggests that the action of GGF is likely to be instructive rather than selective. Taken together with the expression pattern of GGF, these data suggest a lateral signaling model for the diversification of cell types within developing peripheral ganglia.

Animals↗

Acidic and basic fibroblast growth factors delay the maturation of neural crest-derived neurons.

Neural crest (NC) cultures were prepared from lumbosacral segments of 12 day rat embryos and maintained in a defined medium. Post-mitotic, flat, neurofilament+ neurons with broad neuritic processes ('nascent neurons') appeared within 24 h. Timing of the next stage in neuronal differentiation, the formation of bipolar, phase-bright cells that bound tetanus toxin with long, slender neurites ('bipolar neurons'), was markedly influenced by acidic or basic fibroblast growth factor (FGF). The transition from nascent to bipolar neuron occurred several days prematurely in medium without added FGF, but took place with a time-course like that in vivo when 10 ng/ml of acidic or basic FGF was added.

Animals↗

Characterization of developmental stage and neuronal potential of the rat PNS-derived stem cell line, RT4-AC.

RT4 is a family of cell lines derived from a rat peripheral neurotumor and consists of a multipotential stem cell line that spontaneously gives rise to three derivative cell types: one glial-like and two neuronal-like. Previous studies have established that the RT4 glial derivative expresses many properties of Schwann cells; however, the neuronal designation of the other RT4 derivatives is less well substantiated. To further characterize the developmental stage and lineages represented by the RT4 stem cell and its derivatives we examined the expression of 16 marker genes whose expression is either specific to neurons or in some cases, neural tissue. Taken together our results indicate that (i) the RT4 neuronal-like derivatives express only immature neuronal properties, (ii) the RT4 cell lines most closely resemble neural crest derivatives from embryonic day 10 to 12 in the rat, (iii) treatment with cAMP and steroids, although capable of promoting process extension by the RT4 neuronal-like derivatives, did not affect the expression of any of the 16 marker genes examined, and (iv) when compared to other neural stem cell systems, RT4-AC generates the most immature neuronal derivatives.

Animals↗

The human retinal degeneration slow (RDS) gene: chromosome assignment and structure of the mRNA.

Retinal degeneration slow (rds) is a mouse neurological mutation that is characterized phenotypically by abnormal development of rod and cone photoreceptors followed by their slow degeneration. This phenotype resembles the pathologic abnormalities seen in retinitis pigmentosa. The mouse rds gene has recently been cloned. Here we present the sequence of a full-length cDNA clone of the human RDS mRNA. We show that in human retina there are two RDS transcripts of 3.0 and 5.5 kb. By analysis of DNA from a panel of human X hamster somatic cell hybrids, and by direct in situ hybridization, we show that the RDS gene is located on the proximal short arm of human chromosome 6. Finally, we present information on the frequency of several observed restriction fragment length polymorphisms using the RDS cDNA. This information is of potential value for testing linkage of the RDS gene to the disease phenotype in families with retinitis pigmentosa.

Amino Acid Sequence↗

The retinal degeneration slow (rds) gene product is a photoreceptor disc membrane-associated glycoprotein.

Mice homozygous for the retinal degeneration slow (rds) mutation exhibit abnormal development of photoreceptor cells, followed by their slow degeneration. We have recently cloned the rds gene and determined the structure of the wild-type rds mRNA. Here we show that the gene is expressed exclusively in photoreceptor cells. We demonstrate that it encodes a 39 kd membrane-associated glycoprotein that is restricted to photoreceptor outer segments. By electron microscopy, we show that the rds protein is distributed uniformly within outer segment discs. The developmental appearance of the rds protein coincides with outer segment disc formation. We propose that the rds protein functions as an adhesion molecule for stabilization of the outer segment discs.

Amino Acid Sequence↗

Complete rescue of photoreceptor dysplasia and degeneration in transgenic retinal degeneration slow (rds) mice.

retinal degeneration slow (rds) is a semidominant mutation of mice with the phenotype of abnormal development of rod and cone photoreceptors, followed by their slow degeneration. The rds gene has been putatively cloned and its novel protein product initially characterized biochemically. In the present study we undertook to correct in vivo the retinal phenotype of mice with the rds mutation. We assembled a transgene containing a regulatory segment of the opsin gene positioned upstream of the wild-type rds coding region. Mice from three transgenic lines, homozygous for the rds mutation, were analyzed for expression of the transgene and for their retinal phenotypes. In two high expressing lines, we observed complete reversion to wild-type retinal morphology. In a third, low expressing line, we observed a retinal phenotype intermediate between wild type and rds/rds, suggesting partial rescue of the mutation. These results constitute formal proof that we have cloned the rds gene.

Animals↗

Genetic determinants of visual functions.

Recent studies on the molecular genetics and biochemistry of cone and rod photoreceptors have contributed significantly to our understanding of the basis for variation in normal and anomalous color vision in human populations, and for some of the hereditary eye diseases characterized by retinal degeneration.

Amino Acid Sequence↗

Transient suppression of the vesicular acetylcholine transporter in urinary bladder pathways following spinal cord injury.

The aim of this study was to examine the expression profile of the vesicular acetylcholine transporter (VAChT), which is a cholinergic pre-synaptic marker, in the lower neural tract following spinal cord injury (SCI) and its effect on coordination of micturition. In adult female Sprague-Dawley rats, SCI was induced by complete transection of the spinal cord at T9. At various time points, 3, 7, 14 and 28 days, after SCI, cystometry was performed on conscious rats. Bladder areflexia was observed during the first week. Twenty-eight days after SCI the rats showed reflex contractions and voiding. The expression of VAChT was examined with immunohistochemistry. The number of VAChT-positive nerve terminals, which were surrounding neuronal soma, was transiently decreased in pelvic ganglion and spinal cord (L1, L2, L6 and S1). In particular VAChT terminals surrounding motor neurons in the ventral horn and autonomic pre-ganglion cells were dramatically decreased from 3 to 14 days after SCI. Similarly, and the number of VAChT-positive fibers in the bladder wall was also decreased. The intensity of VAChT terminals recovered in all above regions in conjunction with recovery of bladder function. These observations indicate that the transient decrease of the VAChT-positive nerve might cause a failure of cholinergic neuronal transmission along the urinary bladder tract after SCI. As the cholinergic system was recovered at least in rat, the functional recovery of neurogenic bladder syndrome in SCI patients may become possible by further understanding the mechanism underlying the recovery of cholinergic system in rat.

Afferent Pathways↗

Minocycline delays photoreceptor death in the rds mouse through a microglia-independent mechanism.

PURPOSE: Minocycline, a semi-synthetic tetracycline antibiotic is reported to be neuroprotective in degenerative and ischaemic models of central nervous system disease, via mechanisms involving suppression of both cytotoxic microglial activity and caspase-dependent apoptosis. We have investigated the effect of minocycline treatment on a mouse model of retinitis pigmentosa, an inherited photoreceptor neurodegenerative disorder, and contrasted this with the effect of depleting retinal microglia using liposomal clodronate. METHODS: rds mice were treated intraperitoneally from the second postnatal day (P2) with either daily minocycline until P16, P18, P21, P24 and P27 or alternative day clodronate liposomes until P16. Immunohistochemical and immunofluorescent methods were applied for the detection of microglia (F4/80) and apoptosis (TUNEL and caspase 3 activation). RESULTS: Photoreceptor apoptosis was delayed by minocycline treatment but not, ultimately, prevented. Markedly reduced expression of activated caspase 3 was observed in photoreceptors at the early time point, corresponding with the reduced level of apoptosis. Delayed photoreceptor apoptosis due to minocycline treatment was associated with a 50% reduction in the numbers of microglia at early timepoints. Liposomal clodronate treatment also resulted in a marked reduction in the number of microglia (63% reduction in microglia), but in contrast to minocycline treatment, this had no effect on photoreceptor apoptosis. CONCLUSIONS: Minocycline appears to delay photoreceptor apoptosis through a microglia-independent action. Although microglial cytotoxicity has been implicated during other models of neurodegeneration, microglia are unlikely to play such a role in this model of photoreceptor dystrophy.

Animals↗

Analysis of the neurogenic potential of multipotent skin-derived precursors.

Multipotent precursors similar to stem cells of the embryonic neural crest (NC) have been identified in several postnatal tissues, and are potentially useful for research and therapeutic purposes. However, their neurogenic potential, including their ability to produce electrophysiologically active neurons, is largely unexplored. We investigated this issue with regard to skin-derived precursors (SKPs), multipotent NC-related precursors isolated from the dermis of skin. SKP cultures follow an appropriate pattern and time-course of neuronal differentiation, with proliferating nestin-expressing SKPs generating post-mitotic neuronal cells that co-express pan-neuronal and peripheral autonomic lineage markers. These SKP-derived neuron-like cells survive and maintain their peripheral phenotype for at least 5 weeks when transplanted into the CNS environment of normal or kainate-injured hippocampal slices. Undifferentiated SKPs retain key neural precursor properties after multi-passage expansion, including growth factor dependence, nestin expression, neurogenic potential, and responsiveness to embryonic neural crest fate determinants. Despite undergoing an apparently appropriate neurogenic process, however, SKP-derived neuron-like cells possess an immature electrophysiological profile. These findings indicate that SKPs retain latent neurogenic properties after residing in a non-neural tissue, but that additional measures will be necessary to promote their differentiation into electrophysiologically active neurons.

Animals↗