Biomedical subjects

Jeremy Nathans

Publications and source records attributed to Jeremy Nathans.

At least 19 recordsLinked to original sources

PubMed2006

Order from disorder: Self-organization in mammalian hair patterning.

Hairs, feathers, and scales normally exhibit precise orientations with respect to the body axes. In Frizzled6 (Fz6)(-/-) mice, the global orientation of hair follicles is disrupted, leading to waves, whorls, and tufts, each comprising many hundreds of hairs. By analyzing the orientation of developing hair follicles, we observed that the nearly parallel arrangement of wild-type (WT) hairs arises from fields of imperfectly aligned follicles, and that the Fz6(-/-) hair patterns arise from fields of grossly misoriented or randomly oriented follicles. Despite their large size, both mutant and WT hair follicles display a remarkable and unexpected plasticity, reorienting on a time scale of days in what seems to be a self-organized refinement process. The essential features of this process can be studied with a simple cellular automata model in which a local consensus "rule" acts iteratively to bias each hair's orientation in favor of the average orientation of its neighbors. These experiments define two systems for hair orientation: a global orienting system that acts early in development and is Fz6-dependent, and a local self-organizing system that acts later and is Fz6 independent.

Animals↗

PubMed2006

Mutational analysis of Norrin-Frizzled4 recognition.

Norrin and Frizzled4 (Fz4) function as a ligand-receptor pair to control vascular development in the retina and inner ear. In mice and humans, mutations in either of the corresponding genes lead to defects in vascular development. The present work is aimed at defining the sequence determinants of binding specificity between Norrin and the Fz4 amino-terminal ligand-binding domain (the "cysteine-rich domain" (CRD)). The principal conclusions are as follows: 1) Norrin binds to the Fz4 CRD and does not detectably bind to the 14 other mammalian Frizzled and secreted Frizzled-related protein CRDs; 2) Norrin and Xenopus Wnt8 recognize largely overlapping regions of the Fz4 CRD; 3) surface determinants on the Fz4 and Fz8 CRDs that allow Norrin to distinguish between these two CRDs reside within several small regions on one face of the CRD; 4) Norrin function depends critically on three pairs of cysteines that form the highly conserved trio of disulfide bonds shared among all cystine knot proteins, but the remaining two putative disulfide bonds are less important; 5) Norrin-CRD binding depends on a largely contiguous group of amino acids in the extended beta-sheet domain of Norrin that are predicted to face away from the interface between the two monomers in the Norrin homodimer; 6) Norrin-CRD binding is strongly modulated by interactions involving charged amino acid side chains; and 7) Norrin-CRD binding is enhanced approximately 10-fold by the addition of heparin. These observations are discussed in the context of Frizzled signaling and the structure and function of other cystine knot proteins.

Amino Acid Sequence↗

PubMed2006

Macular degeneration: recent advances and therapeutic opportunities.

The central retina mediates high acuity vision, and its progressive dysfunction due to macular degeneration is the leading cause of visual disability among adults in industrialized societies. Here, we summarize recent progress in understanding the pathophysiology of macular degeneration and the implications of this new knowledge for treatment and prevention. The past decade has witnessed remarkable advances in this field, including the development of new, non-invasive retinal imaging technologies, the development of animal models for macular disease, and the isolation of many of the genes responsible for both early- and late-onset macular diseases. These advances have set the stage for the development of effective mechanism-based therapies.

Aging↗

PubMed2006

Effects of L1 retrotransposon insertion on transcript processing, localization and accumulation: lessons from the retinal degeneration 7 mouse and implications for the genomic ecology of L1 elements.

The retinal degeneration 7 (rd7) mouse is a naturally occurring model of enhanced S-cone syndrome, Goldman-Favre syndrome and clumped pigmentary retinopathy in humans, allelic disorders caused by inactivation of a photoreceptor-specific nuclear hormone receptor, NR2E3. We show here that the rd7 mutation arose from the antisense insertion of a long interspersed nuclear element (LINE-1) (or L1) into exon 5 of the mouse Nr2e3 gene. L1 insertion blocks splicing of Nr2e3 intron 5 by separating an inefficient splice donor from essential splicing enhancers within exon 5, with the result that incompletely spliced transcripts accumulate to high levels at the mutant Nr2e3 locus in photoreceptor nuclei. The high efficiency of transcription through the 7 kb L1 was unexpected and led us to compare the effect on transcript abundance of sense or antisense L1 insertions in transfected cells. In a variety of sequence contexts antisense L1 insertions had little or no effect on transcript levels or the production of full-length transcripts, whereas sense L1 insertions reduced transcript levels from several-fold to more than 10-fold. A bioinformatic analysis of all mouse L1s shows a approximately 2-fold under-representation of L1s in introns when compared with bulk genomic DNA, and, within introns, a further approximately 2-fold under-representation of sense when compared with antisense L1s. Interestingly, there is no evidence for orientation-specific positive or negative selection within any subregions of the L1 element. These data suggest that L1s have evolved to present the host transcriptional machinery with a minimally disruptive profile in the antisense orientation such that antisense intronic L1s often escape purifying negative selection.

Animals↗

PubMed2006

Ca2+-activated Cl- current from human bestrophin-4 in excised membrane patches.

Bestrophins are a newly discovered family of Cl(-) channels, some members of which are activated by intracellular Ca(2+). So far, all studies were carried out with whole-cell recordings from plasmid-transfected cultured cells, so it is unclear whether Ca(2+) activates bestrophin through a metabolic mechanism or in a more direct way. We report here experiments that addressed this question with excised, inside-out membrane patches. We chose human bestrophin-4 (hBest4) for heterologous expression because it gave particularly large Cl(-) currents when expressed, thus allowing detection even in excised membrane patches. hBest4 gave a negligible Cl(-) current in a Ca(2+)-free solution on the cytoplasmic (bath) side, but produced a Cl(-) current that was activated by Ca(2+) in a dose-dependent manner, with a K(1/2) of 230 nM. Thus, Ca(2+) appears to activate the bestrophin Cl(-) channel without going through a freely diffusible messenger or through protein phosphorylation. Because the activation and deactivation kinetics were very slow, however, we cannot exclude the involvement of a membrane-associated messenger.

Animals↗

PubMed2006

The role of Frizzled3 and Frizzled6 in neural tube closure and in the planar polarity of inner-ear sensory hair cells.

In the mouse, Frizzled3 (Fz3) and Frizzled6 (Fz6) have been shown previously to control axonal growth and guidance in the CNS and hair patterning in the skin, respectively. Here, we report that Fz3 and Fz6 redundantly control neural tube closure and the planar orientation of hair bundles on a subset of auditory and vestibular sensory cells. In the inner ear, Fz3 and Fz6 proteins are localized to the lateral faces of sensory and supporting cells in all sensory epithelia in a pattern that correlates with the axis of planar polarity. Interestingly, the polarity of Fz6 localization with respect to the asymmetric position of the kinocilium is reversed between vestibular hair cells in the cristae of the semicircular canals and auditory hair cells in the organ of Corti. Vangl2, one of two mammalian homologs of the Drosophila planar cell polarity (PCP) gene van Gogh/Strabismus, is also required for correct hair bundle orientation on a subset of auditory sensory cells and on all vestibular sensory cells. In the inner ear of a Vangl2 mutant (Looptail; Lp), Fz3 and Fz6 proteins accumulate to normal levels but do not localize correctly at the cell surface. These results support the view that vertebrates and invertebrates use similar molecular mechanisms to control a wide variety of PCP-dependent developmental processes. This study also establishes the vestibular sensory epithelium as a tractable tissue for analyzing PCP, and it introduces the use of genetic mosaics for determining the absolute orientation of PCP proteins in mammals.

Animals↗

PubMed2006

Axonal growth and guidance defects in Frizzled3 knock-out mice: a comparison of diffusion tensor magnetic resonance imaging, neurofilament staining, and genetically directed cell labeling.

Previous work has identified axonal outgrowth and/or guidance defects in the brain and spinal cord of prenatal Frizzled3 (Fz3)(-/-) mice. To systematically explore the axonal defects in Fz3(-/-) mice and to compare techniques for the global assessment of axon tracts in the developing mouse, we have analyzed wild-type and Fz3(-/-) brains using (1) diffusion tensor magnetic resonance imaging (muDTI), (2) neurofilament staining, and (3) two genetically directed neuronal labeling methods. Confirming and extending the previous work of Wang et al. (2002), we find that the following structures/tracts are absent or greatly reduced in the Fz3(-/-) brain: the anterior commissure, cerebral peduncle (corticospinal tract), corpus callosum, fornix, internal capsule (thalamocortical and corticothalamic tracts), stria medullaris, stria terminalis, and hippocampal commissure. An aberrant U-shaped fiber bundle immediately caudal to the optic tract connects the left and right sides of the Fz3(-/-) thalamus and likely represents a default pathway for thalamic axons that failed to enter the internal capsule. At embryonic day 18, labeling of cortical pyramidal cells with a yellow fluorescent protein reporter reveals widespread fragmentation of axons with no apparent loss of pyramidal cell bodies. Fragmentation likely represents one stage in the process that normally eliminates stalled or mistargeted axons. This work demonstrates the usefulness of muDTI and genetically directed neuronal labeling for the analysis of nervous system defects in the mouse.

Abnormalities, Multiple↗

PubMed2006

An evolutionary perspective on the photoreceptor damage response.

PURPOSE: To review recent advances related to the response to photoreceptor damage and to place this knowledge in an evolutionary context. DESIGN: Synthesis of published laboratory, clinical, and epidemiologic data. METHODS: The authors have synthesized the principal published findings related to the mechanism and function of the photoreceptor damage response with the goal of trying to understand the selective pressures that shaped its evolution. RESULTS: The past several years have seen considerable advances in understanding the molecular and cellular basis of the retina's response to photoreceptor damage. From their analysis of laboratory, clinical, and epidemiologic data, the authors suggest that the photoreceptor damage response may have evolved to counter the effects of retinal tears and detachment, infectious retinitis, and/or light damage. CONCLUSIONS: If the natural response to photoreceptor damage can be fully defined, it may be possible to augment desirable aspects of the damage response and/or suppress undesirable ones in the context of a wide variety of photoreceptor diseases.

Animals↗

PubMed2005

Written in our genes?

Explore the source record for details and available documents.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2005

The genomic response to retinal disease and injury: evidence for endothelin signaling from photoreceptors to glia.

Regardless of proximal cause, photoreceptor injury or disease almost invariably leads to the activation of Muller cells, the principal glial cells in the retina. This observation implies the existence of signaling systems that inform Muller cells of the health status of photoreceptors. It further suggests that diverse types of photoreceptor damage elicit a limited range of biochemical responses. Using the mouse retina, we show by microarray, RNA blot, and in situ hybridization that the genomic responses to both light damage and inherited photoreceptor degeneration involve a relatively small number of genes and that the genes activated by these two insults overlap substantially with one another and with the genes activated by retinal detachment. Among the induced transcripts, those coding for endothelin2 (Edn2) are unusual in that they are localized to photoreceptors and are also highly induced in all of the tested models of photoreceptor disease or injury. Acute light damage also leads to a >10-fold increase in endothelin receptor B (Ednrb) in Muller cells 24 h after injury. These observations suggest that photoreceptor-derived EDN2 functions as a general stress signal, that EDN2 signals to Muller cells by binding to EDNRB, and that Muller cells can increase their sensitivity to EDN2 as part of the injury response.

Animals↗

PubMed2005

The rod photoreceptor-specific nuclear receptor Nr2e3 represses transcription of multiple cone-specific genes.

This study addresses one genetic regulatory mechanism that establishes the distinct identities of rod and cone photoreceptors. Previous work has shown that mutations in either humans or mice in the gene coding for photoreceptor-specific nuclear receptor Nr2e3 cause a progressive retinal degeneration characterized by increased numbers of short-wave cones. In the present work, we have examined the cellular and developmental pattern of Nr2e3 protein localization in mammals and fish, identified an optimal Nr2e3 DNA-binding site using cycles of binding to recombinant Nr2e3, characterized the transcriptional activity of wild type and one of the disease-associated point mutations in Nr2e3 in transfected cells, and characterized the transcriptional defects in the naturally occurring Nr2e3 mutant (rd7) mouse. These experiments indicate that in the mature vertebrate retina Nr2e3 is expressed exclusively in rods, that expression of Nr2e3 is one of the earliest events in the pathway of rod-specific photoreceptor development, and that Nr2e3 functions, either directly or indirectly, as a repressor of cone-specific genes in rod photoreceptor cells.

Amino Acid Sequence↗

PubMed2004

Quantitative analysis of neuronal morphologies in the mouse retina visualized by using a genetically directed reporter.

An alkaline phosphatase (AP) reporter has been used to visualize detailed morphologies for all major classes of retinal neurons in the adult mouse. The analysis was performed on retinas in which AP expression was activated by Cre-mediated DNA recombination in a small fraction of cells. Recombination was controlled pharmacologically and, to a first approximation, appears to have occurred randomly. The morphologies of 794 inner retinal neurons have been analyzed by measuring arbor area, stratification level, and neurite branching patterns. When analyzed in this multidimensional parametric space, the cells can be clustered into subgroups by visual inspection and by using the Ward's and K-means algorithms. One application of this cell morphology data set and cluster analysis is as a standard for comparison with the retinas of genetically altered mice. This work illustrates the utility and feasibility of genetically directed marking methods for large-scale surveys of neuronal morphology.

Alkaline Phosphatase↗

PubMed2004

Proteolytic shedding of the extracellular domain of photoreceptor cadherin. Implications for outer segment assembly.

Photoreceptor cadherin (prCAD) is a distinctive cadherin family member that is concentrated at the base of rod and cone outer segments and is required for their structural integrity. During retinal development, prCAD localizes to the site of the future outer segment before rhodopsin or other phototransduction proteins. In vivo, prCAD undergoes a single proteolytic cleavage that releases the ectodomain as a soluble fragment. The C-terminal fragment containing the transmembrane and cytosolic domains remains associated with the outer segment. In rds(-/-) retinas, in which outer segment assembly is severely disrupted because of the absence of retinal degeneration slow (RDS)/peripherin, an essential outer segment structural protein, the level of prCAD is increased, whereas the levels of other outer segment proteins are decreased relative to wild type retinas. Additionally, the ratio of intact:cleaved prCAD polypeptides is increased in rds(-/-) retinas. These data imply that prCAD ectodomain cleavage is an integral part of the outer segment assembly process, and they further suggest that outer segment assembly might be driven, at least in part, by the near irreversibility of proteolysis.

Amino Acid Sequence↗

PubMed2004

Frizzled6 controls hair patterning in mice.

Hair whorls and other macroscopic hair patterns are found in a variety of mammalian species, including humans. We show here that Frizzled6 (Fz6), one member of a large family of integral membrane Wnt receptors, controls macroscopic hair patterning in the mouse. Fz6 is expressed in the skin and hair follicles, and targeted deletion of the Fz6 gene produces stereotyped whorls on the hind feet, variable whorls and tufts on the head, and misorientation of hairs on the torso. Embryo chimera experiments imply that Fz6 acts locally to control or propagate the macroscopic hair pattern and that epithelial cells rather than melanocytes are the source of Fz6-dependent signaling. The Fz6 phenotype strongly resembles the wing-hair and bristle patterning defects observed in Drosophila frizzled mutants. These data imply that hair patterning in mammals uses a Fz-dependent tissue polarity system similar to the one that patterns the Drosophila cuticle.

Amino Acid Sequence↗

PubMed2004

Vascular development in the retina and inner ear: control by Norrin and Frizzled-4, a high-affinity ligand-receptor pair.

Incomplete retinal vascularization occurs in both Norrie disease and familial exudative vitreoretinopathy (FEVR). Norrin, the protein product of the Norrie disease gene, is a secreted protein of unknown biochemical function. One form of FEVR is caused by defects in Frizzled-4 (Fz4), a presumptive Wnt receptor. We show here that Norrin and Fz4 function as a ligand-receptor pair based on (1) the similarity in vascular phenotypes caused by Norrin and Fz4 mutations in humans and mice, (2) the specificity and high affinity of Norrin-Fz4 binding, (3) the high efficiency with which Norrin induces Fz4- and Lrp-dependent activation of the classical Wnt pathway, and (4) the signaling defects displayed by disease-associated variants of Norrin and Fz4. These data define a Norrin-Fz4 signaling system that plays a central role in vascular development in the eye and ear, and they indicate that ligands unrelated to Wnts can act through Fz receptors.

Animals↗

PubMed2004

An outer segment localization signal at the C terminus of the photoreceptor-specific retinol dehydrogenase.

Photoreceptor retinol dehydrogenase (prRDH) is a membrane-associated cytosolic protein that localizes to the outer segments (OS) of rods and cones. Here, we demonstrate that the C-terminal 16 amino acids of prRDH confer membrane association as well as cone and rod OS targeting on a linked green fluorescent protein. Membrane association in transfected 293 cells and in transgenic Xenopus photoreceptors is mediated by fatty acylation at one or more evolutionarily conserved cysteines within the prRDH C-terminal tail. In bovine OS, native prRDH is similarly acylated, and hydrolysis of this linkage releases the protein from the membrane. Efficient OS localization requires both membrane association and the prRDH sequence. (V/I)XPX at the extreme C terminus, which closely resembles the C-terminal sequence that targets opsin/rhodopsin to the OS. Taken together, these data imply that the C-terminal. (V/I)XPX sequence is a general OS localization signal that can function in the context of both integral and peripheral membrane proteins. This strategy for OS localization resembles those used for protein localization to mitochondria, peroxisomes, endosomes, and endoplasmic reticulum; in each case, a short N- or C-terminal sequence is shared among structurally diverse proteins that are targeted to the same subcellular destination.

Alcohol Oxidoreductases↗

PubMed2004

Proximal and distal sequences control UV cone pigment gene expression in transgenic zebrafish.

The molecular basis of cone photoreceptor-specific gene expression is largely unknown. In this study, we define cis-acting DNA sequences that control the cell type-specific expression of the zebrafish UV cone pigment gene by transient expression of green fluorescent protein transgenes following their injection into zebrafish embryos. These experiments show that 4.8 kb of 5'-flanking sequences from the zebrafish UV pigment gene direct expression specifically to UV cones and that this activity requires both distal and proximal sequences. In addition, we demonstrate that a proximal region located between -215 and -110 bp (with respect to the initiator methionine codon) can function in the context of a zebrafish rhodopsin promotor to convert its specificity from rod-only expression to rod and UV cone expression. These experiments demonstrate the power of transient transgenesis in zebrafish to efficiently define cis-acting regulatory sequences in an intact vertebrate.

5' Untranslated Regions↗

PubMed2003

Anterior-posterior guidance of commissural axons by Wnt-frizzled signaling.

Commissural neurons in the mammalian dorsal spinal cord send axons ventrally toward the floor plate, where they cross the midline and turn anteriorly toward the brain; a gradient of chemoattractant(s) inside the spinal cord controls this turning. In rodents, several Wnt proteins stimulate the extension of commissural axons after midline crossing (postcrossing). We found that Wnt4 messenger RNA is expressed in a decreasing anterior-to-posterior gradient in the floor plate, and that a directed source of Wnt4 protein attracted postcrossing commissural axons. Commissural axons in mice lacking the Wnt receptor Frizzled3 displayed anterior-posterior guidance defects after midline crossing. Thus, Wnt-Frizzled signaling guides commissural axons along the anterior-posterior axis of the spinal cord.

Animals↗