Biomedical subjects

Darren W Logan

Publications and source records attributed to Darren W Logan.

6 recordsLinked to original sources

PubMed2006

Olfactory mucosa-expressed organic anion transporter, Oat6, manifests high affinity interactions with odorant organic anions.

We have characterized the expression of organic anion transporter 6, Oat6 (slc22a20), in olfactory mucosa, as well as its interaction with several odorant organic anions. In situ hybridization reveals diffuse Oat6 expression throughout olfactory epithelium, yet olfactory neurons laser-capture microdissected from either the main olfactory epithelium (MOE) or the vomeronasal organ (VNO) did not express Oat6 mRNA. These data suggest that Oat6 is expressed in non-neuronal cells of olfactory tissue, such as epithelial and/or other supporting cells. We next investigated interaction of Oat6 with several small organic anions that have previously been identified as odortype components in mouse urine. We find that each of these compounds, propionate, 2- and 3-methylbutyrate, benzoate, heptanoate, and 2-ethylhexanoate, inhibits Oat6-mediated uptake of a labeled tracer, estrone sulfate, consistent with their being Oat6 substrates. Previously, we noted defects in the renal elimination of odortype and odortype-like molecules in Oat1 knockout mice. The finding that such molecules interact with Oat6 raises the possibility that odorants secreted into the urine through one OAT-mediated mechanism (Eraly et al., JBC 2006) are transported through the olfactory mucosa through another OAT-mediated mechanism. Oat6 might play a direct or indirect role in olfaction, such as modulation of the availability of odorant organic anions at the mucosal surface for presentation to olfactory neurons or facilitation of delivery to a distal site of chemosensation, among other possibilities that we discuss.

Animals↗

PubMed2006

Regulation of pigmentation in zebrafish melanophores.

In comparison with the molecular genetics of melanogenesis in mammals, the regulation of pigmentation in poikilothermic vertebrates is poorly understood. Mammals undergo morphological colour change under hormonal control, but strikingly, many lower vertebrates display a rapid physiological colour change in response to the same hormones. The recent provision of extensive genome sequencing data from teleost zebrafish, Danio rerio, provides the opportunity to define the genes and proteins mediating this physiological pigment response and characterise their function biologically. Here, we illustrate the background adaptation process in adults and larvae and describe a novel assay to visualize and directly quantify the rate of zebrafish melanophore pigment translocation in unprecedented detail. We demonstrate the resolution of this assay system; quantifying the zebrafish melanophore response to melanin-concentrating and melanocyte-stimulating hormones. Furthermore, we investigate the intracellular signalling downstream of hormone stimulation and the biomechanical processes involved in zebrafish pigment translocation, confirming the importance of cyclic adenosine monophosphate (cAMP) as a mediator of pigment translocation and finding intact microtubules are essential for both melanin dispersion and aggregation in zebrafish, but that microfilament disruption affects aggregation only. In conclusion, we propose these data establish the zebrafish as an experimental model for studying both physiological colour change and the molecular basis of pigment translocation.

Actin Cytoskeleton↗

PubMed2005

Epistatic interactions between modifier genes confer strain-specific redundancy for Tgfb1 in developmental angiogenesis.

Tgfbm1 (chromosome 5, P = 8 x 10(-5)) and Tgfbm3 (chromosome 12, P = 6 x 10(-11)) were identified as loci that modify developmental angiogenesis of Tgfb1 -/- mice. Congenic mice validated these loci and demonstrated epistatic interaction between them. The novel locus, Tgfbm3, encompasses approximately 22 genes, colocalizes with both tumor susceptibility and atherosclerosis susceptibility loci, and is enriched in genes regulating cell growth and morphogenesis. The use of gene knockout and/or transgenic mice that predispose to a complex trait, such as vascular development/angiogenesis, facilitates the identification of modifiers by simplifying genetic analysis. Identification of genes that modify response to lack of transforming growth factor beta1 (TGFbeta1) will enhance the understanding of TGFbeta1 action in vivo and may help predict which patients would respond well to anti-TGFbeta therapy. Identification of angiogenesis-modifying genes may provide new targets for angiogenesis therapies and analysis of polymorphisms therein may contribute to assessment of risk for diseases involving angiogenesis.

Animals↗

PubMed2004

Large-scale analysis of gene structure in rhodopsin-like GPCRs: evidence for widespread loss of an ancient intron.

The G-protein-coupled receptors (GPCRs) are a large superfamily of seven transmembrane domain-spanning proteins that mediate signal transduction by activation of G-proteins. Mammalian GPCR genes are reputed to be largely intron-deficient, but there have been no reports of using genome-wide analyses of gene structure to investigate this. Using complete genome sequences, we analysed the intron content of over 850 members of the rhodopsin-like GPCR subfamily (family A G-protein-coupled receptor or GPCR-A) in four species. We find that mouse and human GPCR-As have a large and significant reduction in intron number compared to the rest of their genome. In contrast, invertebrate GPCR-As have an intron repertoire similar to, or slightly greater than, the rest of their genome, suggesting that the reduced intron content in mammals is due to widespread intron loss. Furthermore, we provide a specific example of intron loss through analysis of an intron that is conserved in position and phase within a phylogenetically diverse range of GPCR-As within six vertebrate and invertebrate species. Together, these two lines of evidence provide compelling evidence for the widespread loss of introns during the evolution of the mammalian GPCR-A family.

Animals↗

PubMed2003

The structure and evolution of the melanocortin and MCH receptors in fish and mammals.

Zebrafish are an excellent genetic model system for studying developmental and physiological processes. Pigment patterns in zebrafish are affected by mutations in three types of chromatophores. The behavior of these cells is influenced by alpha-melanocyte-stimulating hormone (alphaMSH) and melanin-concentrating hormone (MCH). Mammals have five alphaMSH receptors (melanocortin receptors) and one or two MCH receptors. We have identified the full complement of melanocortin and MCH receptors in both zebrafish and the pufferfish, Fugu. Zebrafish have six melanocortin receptors, including two MC5R orthologues, while Fugu, lacking MC3R, has only four. We also demonstrate that Fugu and zebrafish have two and three MCHR genes, respectively. MC2R and MC5R are physically linked in all species examined. Unlike other species, we find the Fugu genes contain introns, one of which is in a conserved location and is probably ancestral. We also detail the differential expression of the zebrafish genes throughout development.

Animals↗

PubMed2003

Sequence characterization of teleost fish melanocortin receptors.

Zebrafish are an excellent model system for studying the function of melanocortins in developmental and physiological processes, not least because there are a considerable number of mutant lines in which pigment patterns are affected. The behavior of fish melanophores is influenced by alpha-melanocyte-stimulating hormone (alpha-MSH) and melanin-concentrating hormone (MCH). We have used a rapid assay for alpha-MSH and MCH function using melanophores present on single zebrafish scales. By in silico analysis, we have identified the full complement of melanocortin receptors in both zebrafish and the pufferfish, FUGU: Mammals have five such receptors. Zebrafish have six melanocortin receptors, including two MC5R orthologues, whereas Fugu, lacking MC3R, has only four. We have confirmed the sequences of these 10 genes and show the comparison of the amino acid sequences of the encoded proteins with the orthologous receptor in other vertebrates.

Amino Acid Sequence↗