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Suresh Jesuthasan

Publications and source records attributed to Suresh Jesuthasan.

10 recordsLinked to original sources
PubMed2005

The recombination activation gene 1 (Rag1) is expressed in a subset of zebrafish olfactory neurons but is not essential for axon targeting or amino acid detection.

BACKGROUND: Rag1 (Recombination activation gene-1) mediates genomic rearrangement and is essential for adaptive immunity in vertebrates. This gene is also expressed in the olfactory epithelium, but its function there is unknown. RESULTS: Using a transgenic zebrafish line and immunofluorescence, we show that Rag1 is expressed and translated in a subset of olfactory sensory neurons (OSNs). Neurons expressing GFP under the Rag1 promoter project their axons to the lateral region of the olfactory bulb only, and axons with the highest levels of GFP terminate in a single glomerular structure. A subset of GFP-expressing neurons contain Galphao, a marker for microvillous neurons. None of the GFP-positive neurons express Galphaolf, Galphaq or the olfactory marker protein OMP. Depletion of RAG1, by morpholino-mediated knockdown or mutation, did not affect axon targeting. Calcium imaging indicates that amino acids evoke chemotopically organized glomerular activity patterns in a Rag1 mutant. CONCLUSION: Rag1 expression is restricted to a subpopulation of zebrafish olfactory neurons projecting to the lateral olfactory bulb. RAG1 catalytic activity is not essential for axon targeting, nor is it likely to be required for regulation of odorant receptor expression or the response of OSNs to amino acids.

Amino Acids↗
PubMed2005

Esrom, an ortholog of PAM (protein associated with c-myc), regulates pteridine synthesis in the zebrafish.

Zebrafish esrom mutants have an unusual combination of phenotypes: in addition to a defect in the projection of retinal axons, they have reduced yellow pigmentation. Here, we investigate the pigment phenotype and, from this, provide evidence for an unexpected defect in retinal neurons. Esrom is not required for the differentiation of neural crest precursors into pigment cells, nor is it essential for cell migration, pigment granule biogenesis, or translocation. Instead, loss of yellow color is caused by a deficiency of sepiapterin, a yellow pteridine. The level of several other pteridines is also affected in mutants. Importantly, the cofactor tetrahydrobiopterin (BH4) is drastically reduced in esrom mutants. Mutant retinal neurons also appear deficient in this pteridine. BH4-synthesizing enzymes are active in mutants, indicating a defect in the regulation rather than production of enzymes. Esrom has recently been identified as an ortholog of PAM (protein associated with c-myc), a very large protein involved in synaptogenesis in Drosophila and C. elegans. These data thus introduce a new regulator of pteridine synthesis in a vertebrate and establish a function for the Esrom protein family outside synaptogenesis. They also raise the possibility that neuronal defects are due in part to an abnormality in pteridine synthesis.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Mutation in the delta-subunit of the nAChR suppresses the muscle defects caused by lack of Dystrophin.

Normal motility of the zebrafish embryo requires a large number of gene loci, many of which have human orthologues implicated in myasthenias and other myopathies. We have identified a mutation in the zebrafish that abolishes body motility. Embryos have narrower myofibrils and lack clusters of nicotinic acetylcholine receptors (nAChRs) on the surface of the somitic muscle. We mapped the mutation to the delta-subunit of the nAChR, showing this mutant to be a new allele of the previously named sofa potato (sop). The mutant allele carries a missense mutation in the extracellular domain altering the cysteine at position 150 to an arginine. The delta-subunit is expressed in all striated muscles in embryonic and early larval stages together with the alpha1, beta1, epsilon, and gamma-subunits of nAChR. In contrast to mammals that show switching from the gamma embryonic to the adult epsilon-subunit, the two subunits are coexpressed in zebrafish embryos. We, furthermore, demonstrated that the sop/delta-nAChR mutation is a suppressor of the myopathy caused by lack of Dystrophin. The myofiber detachment phenotype of Dystroglycan-deficient embryos was not suppressed, suggesting that Dystrophin and Dystroglycan play distinct roles in muscle formation and maintenance of muscle integrity.

Animals↗
PubMed2004

Formation of the retinotectal projection requires Esrom, an ortholog of PAM (protein associated with Myc).

Visual system development is dependent on correct interpretation of cues that direct growth cone migration and axon branching. Mutations in the zebrafish esrom gene disrupt bundling and targeting of retinal axons, and also cause ectopic arborization. By positional cloning, we establish that esrom encodes a very large protein orthologous to PAM (protein associated with Myc)/Highwire/RPM-1. Unlike motoneurons in Drosophila highwire mutants, retinal axons in esrom mutants do not arborize excessively, indicating that Esrom has different functions in the vertebrate visual system. We show here that Esrom has E3 ligase activity and modulates the amount of phosphorylated Tuberin, a tumor suppressor, in growth cones. These data identify a mediator of signal transduction in retinal growth cones, which is required for topographic map formation.

Adaptor Proteins, Signal Transducing↗
PubMed2004

EphrinB2a in the zebrafish retinotectal system.

Members of the Eph-B family of receptors tyrosine kinase and their transmembrane ligands have been implicated in dorsoventral patterning of the vertebrate retinotectal projection. In the zebrafish retinotectal system, however, ephrinB2a is expressed strongly in the posterior tectum, in tectal neurons that form physical contacts with retinal ganglion cell (RGC) axons. In the gnarled mutant, where tectal neurons form ectopically in the pretectum, RGC axons stall before entering the tectum, or else are misrouted or branch aberrantly in the tectal neuropil. Ectopic expression of ephrinB2a in the anterior midbrain of wild-type embryos, with the aid of baculovirus, also inhibits RGC axon entry into the tectum. In vitro, zebrafish RGC axons are repelled by stripes of purified ephrinB2a. It is proposed that ephrinB2a may signal a subpopulation of RGC axons that they have reached their target neurons in the tectum.

Animals↗
PubMed2002

Furrow-specific endocytosis during cytokinesis of zebrafish blastomeres.

Mutations affecting endocytosis, such as those in clathrin and dynamin, unexpectedly cause defects in cytokinesis in a number of organisms. To explore the relationship between endocytosis and cytokinesis, we used the relatively large cells of the transparent zebrafish embryo. Using fluorescent markers for fluid-phase as well as plasma membrane uptake, we demonstrate that cytokinesis involves furrow-specific endocytosis. Clathrin-coated pits are visible near the furrow in ultrathin sections, while immunolabeling demonstrates that clathrin and caveolin are localized to the cleavage furrow. Hence, it is likely that both clathrin- and caveolae-mediated endocytosis occurs at the furrow during cytokinesis. Dynamin II is also localized to the furrow and may mediate furrow-specific endocytosis. Treatment of embryos with chlorpromazine or with methyl-beta-cyclodextrin, both of which inhibit endocytosis, prevents the normal completion of cytokinesis. These data suggest that furrow-specific endocytosis is an integral part of cytokinesis.

Animals↗
PubMed2002

Gene transfer into zebrafish by sperm nuclear transplantation.

A technique for fertilizing zebrafish eggs by injection of sperm nuclei is described. Eggs that cleave normally can develop into swimming larvae and give rise to fertile adults. If sperm nuclei are preincubated for 20 min with DNA encoding the green fluorescent protein, transgene expression can be detected in all cells of the embryo. The use of condensed sperm nuclei allows injection with a small bore pipette, which is critical for successful injection of the relatively small zebrafish egg. This technique enables the generation of ubiquitously expressing transgenic zebrafish directly by microinjection. Hence, experiments involving transgenic fish can be completed in days, without the need for growing and breeding founders. This technique may also be used to generate transgenic lines, as transgene expression was visible in the offspring of transgenic founders. The method described here is likely to be applicable to other teleosts, such as medaka and salmon.

Animals↗
PubMed2002

Analysis of xanthophore and pterinosome biogenesis in zebrafish using methylene blue and pteridine autofluorescence.

We have identified two simple methods to analyse xanthophore and pterinosome biogenesis in zebrafish. The first uses methylene blue (methylthionium chloride), a redox dye which specifically labels xanthophores and pterinosomes, while the second uses autofluorescence to detect pteridine levels; these methods may be used to detect the number, location and shape of xanthophores and pterinosomes. These assays were applied to two zebrafish mutants--brie and yobo--and revealed that both mutants have pterinosome biogenesis and pteridine synthesis defects. Additionally, using capillary electrophoresis, we provide evidence that sepiapterin is responsible for the yellow colour and blue-light induced fluorescence in zebrafish embryos.

Animals↗
PubMedDate not supplied

Baculovirus-mediated gene expression in zebrafish.

In an effort to misexpress genes in zebrafish, we tested the ability of baculovirus to infect and drive gene expression in embryos. By injecting virus into specific tissues and using appropriate promoters, both the location and time of gene expression could be controlled. Using a virus with 2 different promoters, LacZ and GFP could be expressed independently. The efficiency of expression appears to depend on the promoter used. As a test of this system, baculovirus was used to ectopically express ephrinB2a in the presomitic mesoderm. EphrinB2a is normally expressed in the posterior region of developing somites, and baculovirus-mediated misexpression caused abnormal somite boundary formation. Baculovirus can thus be used as a tool for gene misexpression experiments in the zebrafish, especially when localized misexpression is required late in development.

Animals↗