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Adhesion G protein‐coupled receptors (GPCRs) are an underrepresented class of GPCRs in drug discovery. We previously developed an in vivo drug screening pipeline to identify compounds with agonist activity for Adgrg6 (Gpr126), an adhesion GPCR required for myelination of the peripheral nervous system in vertebrates. The screening assay tests for rescue of an ear defect found in adgrg6tb233c−/− hypomorphic homozygous mutant zebrafish, using the expression of versican b (vcanb) mRNA as an easily identifiable phenotype. In the current study, we used the same assay to screen a commercially available library of 1280 diverse bioactive compounds (Sigma LOPAC). Comparison with published hits from two partially overlapping compound collections (Spectrum, Tocris) confirms that the screening assay is robust and reproducible. Using a modified counter screen for myelin basic protein (mbp) gene expression, we have identified 17 LOPAC compounds that can rescue both inner ear and myelination defects in adgrg6tb233c−/− hypomorphic mutants, three of which (ebastine, S‐methylisothiourea hemisulfate, and thapsigargin) are new hits. A further 25 LOPAC hit compounds were effective at rescuing the otic vcanb expression but not mbp. Together, these and previously identified hits provide a wealth of starting material for the development of novel and specific pharmacological modulators of Adgrg6 receptor activity. [ABSTRACT FROM AUTHOR]

Live imaging in the zebrafish embryo using tissue‐specific expression of fluorescent proteins can yield important insights into the mechanisms that drive sensory organ morphogenesis and cell differentiation. Morphogenesis of the semicircular canal ducts of the vertebrate inner ear requires a complex rearrangement of epithelial cells, including outgrowth, adhesion, fusion and perforation of epithelial projections to generate pillars of tissue that form the hubs of each canal. We report the insertion sites and expression patterns of two enhancer trap lines in the developing zebrafish embryo, each of which highlight different aspects of epithelial cell morphogenesis in the inner ear. A membrane‐linked EGFP driven by smad6b regulatory sequences is expressed throughout the otic epithelium, most strongly on the lateral side of the ear and in the sensory cristae. A second enhancer trap line, with cytoplasmic EGFP driven by frizzled1 (fzd1) regulatory sequences, specifically marks cells of the ventral projection and pillar in the developing ear, and marginal cells in the sensory cristae, together with variable expression in the retina and epiphysis, and neurons elsewhere in the developing central nervous system. We have used a combination of methods to identify the insertion sites of these two transgenes, which were generated through random insertion, and show that Targeted Locus Amplification is a rapid and reliable method for the identification of insertion sites of randomly inserted transgenes. [ABSTRACT FROM AUTHOR]

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In the zebrafish embryo, expression of the prdm1 and patched1 genes in adaxial cells is indicative of their specification to give rise to slow twitch muscle fibers in response to Hedgehog (Hh) signaling. Subsets of these slow twitch muscle progenitors activate engrailed ( eng) strongly in response to high-level Hh signaling, and differentiate into muscle pioneer cells, which are important for subsequent development of the horizontal myoseptum. In addition, eng is expressed more weakly in medial fast fibers in response to lower Hh levels. Somite morphology in the lamprey, an agnathan (jawless) vertebrate, differs significantly from that of teleosts. In particular, the lamprey does not have clear epaxial/hypaxial domains, lacks a horizontal myoseptum, and does not appear to possess distinct populations of fast and slow fibers in the embryonic somite. Nevertheless, Hh is expressed in the midline of the lamprey embryo, and we report here that, as in zebrafish, homologues of patched and prdm1 are expressed in adaxial regions of the lamprey somite, and an eng homologue is also expressed in the somite. However, the lamprey adaxial region does not exhibit the same distinct adaxial cell morphology as in the zebrafish. In addition, the expression of follistatin is not excluded from the adaxial region, and eng is not detected in discrete muscle pioneer-like cells. These data suggest the presence of conserved responses to Hh signaling in lamprey somites, although the full range of effects elicited by Hh in the zebrafish somite is not recapitulated. [ABSTRACT FROM AUTHOR]