Acanthosis nigricans.
Acanthosis nigricans is thickened, velvety, hyperpigmented skin associated with a variety of endocrine disorders, malignancies and medications.
Acanthosis Nigricans↗
Biomedical subjects
David S Williams
Publications and source records attributed to David S Williams.
Arrhythmogenic right ventricular dysplasia.
Arrhythmogenic right ventricular dysplasia is a type of nonischemic cardiomyopathy that is characterized by fibrofatty replacement of the right ventricle and is an important cause of ventricular arrhythmias in younger people.
Adult↗
Role of myosin VIIa and Rab27a in the motility and localization of RPE melanosomes.
Myosin VIIa functions in the outer retina, and loss of this function causes human blindness in Usher syndrome type 1B (USH1B). In mice with mutant Myo7a, melanosomes in the retinal pigmented epithelium (RPE) are distributed abnormally. In this investigation we detected many proteins in RPE cells that could potentially participate in melanosome transport, but of those tested, only myosin VIIa and Rab27a were found to be required for normal distribution. Two other expressed proteins, melanophilin and myosin Va, both of which are required for normal melanosome distribution in melanocytes, were not required in RPE, despite the association of myosin Va with the RPE melanosome fraction. Both myosin VIIa and myosin Va were immunodetected broadly in sections of the RPE, overlapping with a region of apical filamentous actin. Some 70-80% of the myosin VIIa in RPE cells was detected on melanosome membranes by both subcellular fractionation of RPE cells and quantitative immunoelectron microscopy, consistent with a role for myosin VIIa in melanosome motility. Time-lapse microscopy of melanosomes in primary cultures of mouse RPE cells demonstrated that the melanosomes move in a saltatory manner, interrupting slow movements with short bursts of rapid movement (>1 RR01183m/second). In RPE cells from Myo7a-null mice, both the slow and rapid movements still occurred, except that more melanosomes underwent rapid movements, and each movement extended approximately five times longer (and further). Hence, our studies demonstrate the presence of many potential effectors of melanosome motility and localization in the RPE, with a specific requirement for Rab27a and myosin VIIa, which function by transporting and constraining melanosomes within a region of filamentous actin. The presence of two distinct melanosome velocities in both control and Myo7a-null RPE cells suggests the involvement of at least two motors other than myosin VIIa in melanosome motility, most probably, a microtubule motor and myosin Va.
Animals↗
Myosin Va is required for normal photoreceptor synaptic activity.
Myosin Va is an actin-based motor molecule, one of a large family of unconventional myosins. In humans, mutations in MYO5A cause Griscelli syndrome type 1 and Elejalde syndrome, diseases characterized by pigmentation defects and the prepubescent onset of severe neurological deficits that ultimately lead to a shortened lifespan. Mutations in the Myo5a gene in mouse cause the dilute series of mouse mutants, demonstrating that myosin Va is involved in pigmentation and neural function. Although the reason for the pigmentation abnormalities is well understood, the role of myosin Va in neural function is not. Myosin Va has been found in synaptic terminals in the retina and brain. We report here new physiological evidence for a role of myosin Va in synaptic function. Photoreceptor synapses in neurologically affected myosin Va mutant mice have both anatomical and physiological abnormalities. Thus, myosin Va is required for normal photoreceptor signalling, suggesting that it might function in central nervous system synapses in general, with aberrant synaptic activity potentially underlying the neurological defects observed in dilute lethal mice and patients with Griscelli syndrome type 1 and Elejalde syndrome.
Animals↗
Toxicity of familial ALS-linked SOD1 mutants from selective recruitment to spinal mitochondria.
One cause of amyotrophic lateral sclerosis (ALS) is mutation in ubiquitously expressed copper/zinc superoxide dismutase (SOD1), but the mechanism of toxicity to motor neurons is unknown. Multiple disease-causing mutants, but not wild-type SOD1, are now demonstrated to be recruited to mitochondria, but only in affected tissues. This is independent of the copper chaperone for SOD1 and dismutase activity. Highly preferential association with spinal cord mitochondria is seen in human ALS for a mutant SOD1 that accumulates only to trace cytoplasmic levels. Despite variable proportions that are successfully imported, nearly constant amounts of SOD1 mutants and covalently damaged adducts of them accumulate as apparent import intermediates and/or are tightly aggregated or crosslinked onto integral membrane components on the cytoplasmic face of those mitochondria. These findings implicate damage from action of spinal cord-specific factors that recruit mutant SOD1 to spinal mitochondria as the basis for their selective toxicity in ALS.
Aging↗
Cadherin 23 is a component of the tip link in hair-cell stereocilia.
Mechanoelectrical transduction, the conversion of mechanical force into electrochemical signals, underlies a range of sensory phenomena, including touch, hearing and balance. Hair cells of the vertebrate inner ear are specialized mechanosensors that transduce mechanical forces arising from sound waves and head movement to provide our senses of hearing and balance; however, the mechanotransduction channel of hair cells and the molecules that regulate channel activity have remained elusive. One molecule that might participate in mechanoelectrical transduction is cadherin 23 (CDH23), as mutations in its gene cause deafness and age-related hearing loss. Furthermore, CDH23 is large enough to be the tip link, the extracellular filament proposed to gate the mechanotransduction channel. Here we show that antibodies against CDH23 label the tip link, and that CDH23 has biochemical properties similar to those of the tip link. Moreover, CDH23 forms a complex with myosin-1c, the only known component of the mechanotransduction apparatus, suggesting that CDH23 and myosin-1c cooperate to regulate the activity of mechanically gated ion channels in hair cells.
Alternative Splicing↗
Pemphigus.
Pemphigus vulgaris and the related pemphigus vegetans, pemphigus foliaceus and pemphigus erythematous, are associated with the highest mortality among primary skin diseases. Typical findings are illustrated.
Disease Progression↗
Differential spatial and temporal phosphorylation of the visual receptor, rhodopsin, at two primary phosphorylation sites in mice exposed to light.
Phosphorylation of rhodopsin critically controls the visual transduction cascade by uncoupling it from the G-protein transducin. The kinase primarily responsible for this phosphorylation is rhodopsin kinase, a substrate-regulated kinase that phosphorylates light-activated rhodopsin. Protein kinase C has been implicated in controlling the phosphorylation of both light-activated and dark-adapted rhodopsin. Two of the major rhodopsin phosphorylation sites in vivo, Ser(334) and Ser(338), are effective protein kinase C phosphorylation sites in vitro, while the latter is preferentially phosphorylated by rhodopsin kinase in vitro. Using phosphospecific antibodies against each of these two sites, we show that both sites are under differential spatial and temporal regulation. Exposure of mice to light results in rapid phosphorylation of Ser(338) that is evenly distributed along the rod outer segment. Phosphorylation of Ser(334) is considerably slower, begins at the base of the rod outer segment, and spreads to the top of the photoreceptor over time. In addition, we show that phosphorylation of both sites is abolished in rhodopsin kinase(-/-) mice, revealing an absolute requirement for rhodopsin kinase to phosphorylate rhodopsin. This requirement may reflect the need for priming phosphorylations at rhodopsin kinase sites allowing for subsequent phosphorylation by protein kinase C at Ser(334). In this regard, treatment of mouse retinas with phorbol esters results in a 4-fold increase in phosphorylation on Ser(334), with no significant effect on the phosphorylation of Ser(338). Our results are consistent with light triggering rapid priming phosphorylations of rhodopsin by rhodopsin kinase, followed by a slower phosphorylation on Ser(334), which is regulated by protein kinase C.
Amino Acid Sequence↗
A naturally selected dimorphism within the HLA-B44 supertype alters class I structure, peptide repertoire, and T cell recognition.
HLA-B*4402 and B*4403 are naturally occurring MHC class I alleles that are both found at a high frequency in all human populations, and yet they only differ by one residue on the alpha2 helix (B*4402 Asp156-->B*4403 Leu156). CTLs discriminate between HLA-B*4402 and B*4403, and these allotypes stimulate strong mutual allogeneic responses reflecting their known barrier to hemopoeitic stem cell transplantation. Although HLA-B*4402 and B*4403 share >95% of their peptide repertoire, B*4403 presents more unique peptides than B*4402, consistent with the stronger T cell alloreactivity observed toward B*4403 compared with B*4402. Crystal structures of B*4402 and B*4403 show how the polymorphism at position 156 is completely buried and yet alters both the peptide and the heavy chain conformation, relaxing ligand selection by B*4403 compared with B*4402. Thus, the polymorphism between HLA-B*4402 and B*4403 modifies both peptide repertoire and T cell recognition, and is reflected in the paradoxically powerful alloreactivity that occurs across this "minimal" mismatch. The findings suggest that these closely related class I genes are maintained in diverse human populations through their differential impact on the selection of peptide ligands and the T cell repertoire.
Alleles↗
Abnormal phagocytosis by retinal pigmented epithelium that lacks myosin VIIa, the Usher syndrome 1B protein.
Mutations in the myosin VIIa gene (MYO7A) cause Usher syndrome type 1B (USH1B), a major type of the deaf-blind disorder, Usher syndrome. We have studied mutant phenotypes in the retinas of Myo7a mutant mice (shaker1), with the aim of elucidating the role(s) of myosin VIIa in the retina and what might underlie photoreceptor degeneration in USH1B patients. A photoreceptor defect has been described. Here, we report that the phagocytosis of photoreceptor outer segment disks by the retinal pigment epithelium (RPE) is abnormal in Myo7a null mice. Both in vivo and in primary cultures of RPE cells, the transport of ingested disks out of the apical region is inhibited in the absence of Myo7a. The results with the cultured RPE cells were the same, irrespective of whether the disks came from wild-type or mutant mice, thus demonstrating that the RPE is the source of this defect. The inhibited transport seems to delay phagosome-lysosomal fusion, as the degradation of ingested disks was slower in mutant RPE. Moreover, fewer packets of disk membranes were ingested in vivo, possibly because retarded removal of phagosomes from the apical processes inhibited the ingestion of additional disk membranes. We conclude that Myo7a is required for the normal processing of ingested disk membranes in the RPE, primarily in the basal transport of phagosomes into the cell body where they then fuse with lysosomes. Because the phagocytosis of photoreceptor disks by the RPE has been shown to be critical for photoreceptor cell viability, this defect likely contributes to the progressive blindness in USH1B.
Animals↗
Abnormal neurofilament transport caused by targeted disruption of neuronal kinesin heavy chain KIF5A.
To test the hypothesis that fast anterograde molecular motor proteins power the slow axonal transport of neurofilaments (NFs), we used homologous recombination to generate mice lacking the neuronal-specific conventional kinesin heavy chain, KIF5A. Because null KIF5A mutants die immediately after birth, a synapsin-promoted Cre-recombinase transgene was used to direct inactivation of KIF5A in neurons postnatally. Three fourths of such mutant mice exhibited seizures and death at around 3 wk of age; the remaining animals survived to 3 mo or longer. In young mutant animals, fast axonal transport appeared to be intact, but NF-H, as well as NF-M and NF-L, accumulated in the cell bodies of peripheral sensory neurons accompanied by a reduction in sensory axon caliber. Older animals also developed age-dependent sensory neuron degeneration, an accumulation of NF subunits in cell bodies and a reduction in axons, loss of large caliber axons, and hind limb paralysis. These data support the hypothesis that a conventional kinesin plays a role in the microtubule-dependent slow axonal transport of at least one cargo, the NF proteins.
Animals↗
Mouse models for Usher syndrome 1B.
Photoreceptor cell degeneration was not detected in any of the shaker1 alleles, except for a small but significant loss of photoreceptor cells found in Myo7a(4626SB/4626SB) mice that were also homozygous mutant for Cdh23v. Perhaps greater and/or faster photoreceptor cell loss that is dependent on mutant Myo7a can be effected by having additional mutant USH1 genes in the genetic background. In any case, it is argued that shaker1 mice are a useful model for testing USH1B gene therapy, due to the presence of mutant phenotypes other than photoreceptor cell death.
Alleles↗
Screen for usher syndrome 1B mutations in the ovine myosin VIIa gene.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Isolation and culture of primary mouse retinal pigmented epithelial cells.
Explore the source record for details and available documents.
Animals↗
Cdh23 mutations in the mouse are associated with retinal dysfunction but not retinal degeneration.
Mutations in the cadherin 23 gene (CDH23) cause Usher syndrome type 1D in humans, a disease that results in retinitis pigmentosa and deafness. Cdh23 is also mutated in the waltzer mouse. In order to determine if the retina of the waltzer mouse undergoes retinal degeneration and to gain insight into the function of cadherin 23 in the retina, we have characterized the anatomy and physiology of retinas of waltzer mouse mutants. Three mutant alleles of Cdh23 were examined by histology and electroretinography (ERG). ERGs of the three Cdh23 mutant groups revealed two of them to have abnormal retinal function. One allele had a- and b-waves that were only approximately 80% of Cdh23 heterozygotes. Another allele had a significantly faster implicit time for both the a- and b-waves of the ERG. No anatomical abnormality was detected in any of the Cdh23 mutants by light microscopy. Because the mutant Cdh23 phenotype was found to be similar to the previously reported retinal phenotype of Myo7a mutant mice, the orthologue of another Usher syndrome (type 1B) gene, we generated mice that carried mutations in both genes to test for genetic interaction in the retina. No functional interaction between cadherin 23 and myosin VIIa was detected by either microscopy or ERG.
Alleles↗
Cocaine revisited.
Insurance companies often test applicants for the presence of cocaine. Because a positive test may automatically preclude further consideration, such cases often never reach the medical director. The negative impact of cocaine use on insurability is reviewed.
Cardiovascular Diseases↗
Identification of a dominant self-ligand bound to three HLA B44 alleles and the preliminary crystallographic analysis of recombinant forms of each complex.
A naturally processed and presented ligand that is shared by human leukocyte antigen (HLA) B*4402, B*4403 and B*4405 molecules has been identified in peptides isolated from immunoaffinity purified HLA B44 complexes. This peptide derived from HLA DPalpha residues 46-54, an endogenous product of HLA DP expressed in the cell line Hmy2.C1R, is a prominent peptide in the mass spectra of species isolated as bound peptides from each allele when the three HLA B44 subtypes were introduced as transfected gene products. Recombinant truncated forms of HLA B*4405(1-276), HLA B*4403(1-276), HLA B*4402(1-276) and beta(2)-microglobulin have been prepared as inclusion bodies in Escherichia coli and refolded in the presence of the DPalpha(46-54) peptide and purified by a combination of size exclusion and anion exchange chromatography. This material was determined to be correctly folded based on detection of a conformational epitope recognized by the W6/32 monoclonal antibody. Large, plate-like crystals of the three complexes were produced using polyethylene glycol as the precipitant. All the crystals belong to the space group P2(1)2(1)2(1) with unit cell dimensions of approximately a=51, b=82, c=110 A. The crystals of three B44/DPalpha complexes diffracted to a resolution of 1.9 A or better. For the first time, using this natural, high abundance ligand of the HLA B44 molecules we have successfully expressed and refolded the three HLA B44 molecules and produced crystals amenable to structural studies.
Alleles↗
Actin-based motor properties of native myosin VIIa.
Myosin VIIa has critical roles in the inner ear and the retina. To help understand how this protein functions, native myosin VIIa was tested for mechanoenzymatic properties. Myosin VIIa was immunoprecipitated from retinal tissue and found to be associated with calmodulin in a Ca(2+)-sensitive manner. Myosin VIIa Mg-ATPase activity was detected; in the absence of Ca(2+) (i.e. with bound calmodulin), it was stimulated by f-actin with a K(cat) of 4.3 s(-1) and with 7 microM actin required for half-maximal activity. In a sliding filament motility assay, myosin VIIa moved actin filaments with a velocity of 190 nm s(-1). These results demonstrate that myosin VIIa is a calmodulin-binding protein and a bona fide actin-based motor.
Actins↗