title: Expression of patched, prdm1 and engrailed in the lamprey somite reveals conserved responses to Hedgehog signaling.
abstract: 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.
authors.affiliation: Department of Biomedical Science, MRC Centre for Developmental and Biomedical Genetics, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Hammond
authors.forename: Sarah
authors.initials: S
authors.lastname: Baxendale
authors.forename: David W
authors.initials: DW
authors.lastname: McCauley
authors.forename: Philip W
authors.initials: PW
authors.lastname: Ingham
authors.forename: Tanya T
authors.initials: TT
authors.lastname: Whitfield
mesh_terms: D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D018076:DNA, Complementary / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D050437:Genes, Developmental / Q000235:genetics*; D053823:Hedgehog Proteins / Q000378:metabolism*; D017403:In Situ Hybridization; D007798:Lampreys / Q000196:embryology* / Q000378:metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D010802:Phylogeny; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000235:genetics*; D019170:Somites / Q000033:anatomy & histology / Q000378:metabolism*; D029961:Zebrafish Proteins
chemical_list: D018076:DNA, Complementary; D053823:Hedgehog Proteins; D008565:Membrane Proteins; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011956:Receptors, Cell Surface; D029961:Zebrafish Proteins; C491715:ptch1 protein, zebrafish