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Teresa Nicolson

Publications and source records attributed to Teresa Nicolson.

14 recordsLinked to original sources
PubMed2007

Large-scale mapping of mutations affecting zebrafish development.

BACKGROUND: Large-scale mutagenesis screens in the zebrafish employing the mutagen ENU have isolated several hundred mutant loci that represent putative developmental control genes. In order to realize the potential of such screens, systematic genetic mapping of the mutations is necessary. Here we report on a large-scale effort to map the mutations generated in mutagenesis screening at the Max Planck Institute for Developmental Biology by genome scanning with microsatellite markers. RESULTS: We have selected a set of microsatellite markers and developed methods and scoring criteria suitable for efficient, high-throughput genome scanning. We have used these methods to successfully obtain a rough map position for 319 mutant loci from the Tübingen I mutagenesis screen and subsequent screening of the mutant collection. For 277 of these the corresponding gene is not yet identified. Mapping was successful for 80 % of the tested loci. By comparing 21 mutation and gene positions of cloned mutations we have validated the correctness of our linkage group assignments and estimated the standard error of our map positions to be approximately 6 cM. CONCLUSION: By obtaining rough map positions for over 300 zebrafish loci with developmental phenotypes, we have generated a dataset that will be useful not only for cloning of the affected genes, but also to suggest allelism of mutations with similar phenotypes that will be identified in future screens. Furthermore this work validates the usefulness of our methodology for rapid, systematic and inexpensive microsatellite mapping of zebrafish mutations.

Animals↗
PubMed2005

Duplicated genes with split functions: independent roles of protocadherin15 orthologues in zebrafish hearing and vision.

In the sensory receptors of both the eye and the ear, specialized apical structures have evolved to detect environmental stimuli such as light and sound. Despite the morphological divergence of these specialized structures and differing transduction mechanisms, the receptors appear to rely in part on a shared group of genes for function. For example, mutations in Usher (USH) genes cause a syndrome of visual and acoustic-vestibular deficits in humans. Several of the affected genes have been identified, including the USH1F gene, which encodes protocadherin 15 (PCDH15). Pcdh15 mutant mice also have both auditory and vestibular defects, although visual defects are not evident. Here we show that zebrafish have two closely related pcdh15 genes that are required for receptor-cell function and morphology in the eye or ear. Mutations in pcdh15a cause deafness and vestibular dysfunction, presumably because hair bundles of inner-ear receptors are splayed. Vision, however, is not affected in pcdh15a mutants. By contrast, reduction of pcdh15b activity using antisense morpholino oligonucleotides causes a visual defect. Optokinetic and electroretinogram responses are reduced in pcdh15b morpholino-injected larvae. In electron micrographs, morphant photoreceptor outer segments are improperly arranged, positioned perpendicular to the retinal pigment epithelium and are clumped together. Our results suggest that both cadherins act within their respective transduction organelles: Pcdh15a is necessary for integrity of the stereociliary bundle, whereas Pcdh15b is required for alignment and interdigitation of photoreceptor outer segments with the pigment epithelium. We conclude that after a duplication of pcdh15, one gene retained an essential function in the ear and the other in the eye.

Animals↗
PubMed2005

Fishing for key players in mechanotransduction.

The senses of touch and hearing involve transduction of mechanical stimuli into electrical signals. The search for components of the transduction apparatus in mechanosensory neurons has benefited greatly from genetic approaches using both invertebrates and vertebrates. A consensus model has emerged that includes extracellular and intracellular structural components arranged around a central mechanically gated channel. In the sensory hair cell of the inner ear, the extracellular structural component thought to have a key role in opening the transduction channel is the tip link. Although elusive for decades, recent studies have yielded candidates for both the transduction channel and the tip link in hair cells.

Animals↗
PubMed2005

The genetics of hearing and balance in zebrafish.

The zebrafish is an excellent model system for studying the molecular basis of inner ear development and function. The eggs develop ex utero and the ear is transparent for the first few weeks of life. Forward genetic screens and antisense technology have helped to elucidate the signaling pathways and molecules required for inner ear development and function. This review addresses the most recent advances in our understanding of how the ear forms and discusses the molecules in hair cells that are essential for sensing sound and movement in the zebrafish.

Animals↗
PubMed2004

Mutated otopetrin 1 affects the genesis of otoliths and the localization of Starmaker in zebrafish.

Otoliths in bony fishes and otoconia in mammals are composite crystals consisting of calcium carbonate and proteins. These biominerals are part of the gravity and linear acceleration detection system of the inner ear. Mutations in otopetrin 1 have been shown to result in lack of otoconia in tilted and mergulhador mutant mice. The molecular function of Otopetrin 1, a novel protein that contains ten predicted transmembrane domains, however, has remained elusive. Here we show that a mutation in the orthologous gene in zebrafish is responsible for the complete absence of otoliths in backstroke mutants. We examined the localization of Starmaker, a secreted protein that is highly abundant in otoliths in backstroke mutants. Starmaker protein accumulated within cells of the otic epithelium, indicating a possible defect in secretion. Our data suggest that Otopetrin 1 in zebrafish may be involved in the protein trafficking of components required for formation of biominerals in the ear.

Amino Acid Sequence↗
PubMed2004

Myosin VI is required for structural integrity of the apical surface of sensory hair cells in zebrafish.

Unconventional myosins have been associated with hearing loss in humans, mice, and zebrafish. Mutations in myosin VI cause both recessive and dominant forms of nonsyndromic deafness in humans and deafness in Snell's waltzer mice associated with abnormal fusion of hair cell stereocilia. Although myosin VI has been implicated in diverse cellular processes such as vesicle trafficking and epithelial morphogenesis, the role of this protein in the sensory hair cells remains unclear. To investigate the function of myosin VI in zebrafish, we cloned and examined the expression pattern of myosin VI, which is duplicated in the zebrafish genome. One duplicate, myo6a, is expressed in a ubiquitous pattern during early development and at later stages, and is highly expressed in the brain, gut, and kidney. myo6b, on the other hand, is predominantly expressed in the sensory epithelium of the ear and lateral line at all developmental stages examined. Both molecules have different splice variants expressed in these tissues. Using a candidate gene approach, we show that myo6b is satellite, a gene responsible for auditory/vestibular defects in zebrafish larvae. Examination of hair cells in satellite mutants revealed that stereociliary bundles are irregular and disorganized. At the ultrastructural level, we observed that the apical surface of satellite mutant hair cells abnormally protrudes above the epithelium and the membrane near the base of the stereocilia is raised. At later stages, stereocilia fused together. We conclude that zebrafish myo6b is required for maintaining the integrity of the apical surface of hair cells, suggesting a conserved role for myosin VI in regulation of actin-based interactions with the plasma membrane.

Alternative Splicing↗
PubMed2004

gemini encodes a zebrafish L-type calcium channel that localizes at sensory hair cell ribbon synapses.

L-type Ca2+ channels (LTCCs) drive the bulk of voltage-gated Ca2+ entry in vertebrate inner ear hair cells (HCs) and are essential for mammalian auditory processing. LTCC currents have been implicated in neurotransmitter release at the HC afferent active zone, the ribbon synapse. It is likely that LTCCs play a direct role in vesicle fusion; however, the subcellular localization of the channels in HCs has not been fully resolved. Via positional cloning, we show that mutations in a zebrafish LTCC encoding gene, cav1.3a, underlie the auditory-vestibular defects of gemini (gem) circler mutants. gem homozygous receptor mutant HCs display normal cell viability, afferent synaptogenesis, and peripheral innervation, yet exhibit strongly reduced extracellular potentials (approximately 50% of wild-type potentials). Apical FM1-43 uptake, however, is unaffected in gem mutant HCs, suggesting that mechanotransduction channels are functional. Using a Gem-specific antibody, we show that the bulk of Gem/Ca(v)1.3a immunoreactivity in HCs is restricted to basally located focal spots. The number and location of focal spots relative to nerve terminals, and their remarkable ring-shaped structure, which is reminiscent of synaptic dense bodies, are consistent with Gem/Ca(v)1.3a channels clustering at HC ribbon synapses.

Amino Acid Sequence↗
PubMed2004

Mutations in cadherin 23 affect tip links in zebrafish sensory hair cells.

Hair cells have highly organized bundles of apical projections, or stereocilia, that are deflected by sound and movement. Displacement of stereocilia stretches linkages at the tips of stereocilia that are thought to gate mechanosensory channels. To identify the molecular machinery that mediates mechanotransduction in hair cells, zebrafish mutants were identified with defects in balance and hearing. In sputnik mutants, stereociliary bundles are splayed to various degrees, with individuals displaying reduced or absent mechanotransduction. Here we show that the defects in sputnik mutants are caused by mutations in cadherin 23 (cdh23). Mutations in Cdh23 also cause deafness and vestibular defects in mice and humans, and the protein is present in hair bundles. We show that zebrafish Cdh23 protein is concentrated near the tips of hair bundles, and that tip links are absent in homozygous sputnik(tc317e) larvae. Moreover, tip links are absent in larvae carrying weak alleles of cdh23 that affect mechanotransduction but not hair bundle integrity. We conclude that Cdh23 is an essential tip link component required for hair-cell mechanotransduction.

Alleles↗
PubMed2004

A family of acid-sensing ion channels from the zebrafish: widespread expression in the central nervous system suggests a conserved role in neuronal communication.

Acid-sensing ion channels (ASICs) are excitatory receptors for extracellular H(+). Proposed functions include synaptic transmission, peripheral perception of pain, and mechanosensation. Despite the physiological importance of these functions, the precise role of ASICs has not yet been established. In order to increase our understanding of the physiological role and basic structure-function relationships of ASICs, we report here the cloning of six new ASICs from the zebrafish (zASICs). zASICs possess the basic functional properties of mammalian ASICs: activation by extracellular H(+), Na(+) selectivity, and block by micromolar concentrations of amiloride. The zasic genes are broadly expressed in the central nervous system, whereas expression in the peripheral nervous system is scarce. This pattern suggests a predominant role for zASICs in neuronal communication. Our results suggest a conserved function for receptors of extracellular H(+) in the central nervous system of vertebrates.

Acid Sensing Ion Channels↗
PubMed2004

The deafness gene dfna5 is crucial for ugdh expression and HA production in the developing ear in zebrafish.

Over 30 genes responsible for human hereditary hearing loss have been identified during the last 10 years. The proteins encoded by these genes play roles in a diverse set of cellular functions ranging from transcriptional regulation to K(+) recycling. In a few cases, the genes are novel and do not give much insight into the cellular or molecular cause for the hearing loss. Among these poorly understood deafness genes is DFNA5. How the truncation of the encoded protein DFNA5 leads to an autosomal dominant form of hearing loss is not clear. In order to understand the biological role of Dfna5, we took a reversegenetic approach in zebrafish. Here we show that morpholino antisense nucleotide knock-down of dfna5 function in zebrafish leads to disorganization of the developing semicircular canals and reduction of pharyngeal cartilage. This phenotype closely resembles previously isolated zebrafish craniofacial mutants including the mutant jekyll. jekyll encodes Ugdh [uridine 5'-diphosphate (UDP)-glucose dehydrogenase], an enzyme that is crucial for production of the extracellular matrix component hyaluronic acid (HA). In dfna5 morphants, expression of ugdh is absent in the developing ear and pharyngeal arches, and HA levels are strongly reduced in the outgrowing protrusions of the developing semicircular canals. Previous studies suggest that HA is essential for differentiating cartilage and directed outgrowth of the epithelial protrusions in the developing ear. We hypothesize that the reduction of HA production leads to uncoordinated outgrowth of the canal columns and impaired facial cartilage differentiation.

Amino Acid Sequence↗
PubMed2003

Control of crystal size and lattice formation by starmaker in otolith biomineralization.

The stone-like otoliths from the ears of teleost fishes are involved in balance and hearing and consist of calcium carbonate crystallites embedded in a protein framework. We report that a previously unknown gene, starmaker, is required in zebrafish for otolith morphogenesis. Reduction of starmaker activity by injection of modified antisense oligonucleotides causes a change in the crystal lattice structure and thus a change in otolith morphology. The expression pattern of starmaker, along with the presence of the protein on the growing otolith, suggest that the expression levels of starmaker control the shape of the otoliths.

Amino Acid Sequence↗
PubMed2003

Local tissue interactions across the dorsal midline of the forebrain establish CNS laterality.

The mechanisms that establish behavioral, cognitive, and neuroanatomical asymmetries are poorly understood. In this study, we analyze the events that regulate development of asymmetric nuclei in the dorsal forebrain. The unilateral parapineal organ has a bilateral origin, and some parapineal precursors migrate across the midline to form this left-sided nucleus. The parapineal subsequently innervates the left habenula, which derives from ventral epithalamic cells adjacent to the parapineal precursors. Ablation of cells in the left ventral epithalamus can reverse laterality in wild-type embryos and impose the direction of CNS asymmetry in embryos in which laterality is usually randomized. Unilateral modulation of Nodal activity by Lefty1 can also impose the direction of CNS laterality in embryos with bilateral expression of Nodal pathway genes. From these data, we propose that laterality is determined by a competitive interaction between the left and right epithalamus and that Nodal signaling biases the outcome of this competition.

Animals↗
PubMed2003

NompC TRP channel required for vertebrate sensory hair cell mechanotransduction.

The senses of hearing and balance in vertebrates rely on the sensory hair cells (HCs) of the inner ear. The central element of the HC's transduction apparatus is a mechanically gated ion channel of unknown identity. Here we report that the zebrafish ortholog of Drosophila no mechanoreceptor potential C (nompC), which encodes a transient receptor potential (TRP) channel, is critical for HC mechanotransduction. In zebrafish larvae, nompC is selectively expressed in sensory HCs. Morpholino-mediated removal of nompC function eliminated transduction-dependent endocytosis and electrical responses in HCs, resulting in larval deafness and imbalance. These observations indicate that nompC encodes a vertebrate HC mechanotransduction channel.

Amino Acid Sequence↗