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Biomedical subjects

P D Currie

Publications and source records attributed to P D Currie.

13 recordsLinked to original sources
PubMed2000

Evolutionary origins of vertebrate appendicular muscle.

The evolution of terrestrial tetrapod species heralded a transition in locomotor strategies. While most fish species use the undulating contractions of the axial musculature to generate propulsive force, tetrapods also rely on the appendicular muscles of the limbs to generate movement. Despite the fossil record generating an understanding of the way in which the appendicular skeleton has evolved to provide the scaffold for tetrapod limb musculature, there is, by contrast, almost no information as to how this musculature arose. Here we examine fin muscle formation within two extant classes of fish. We find that in the teleost, zebrafish, fin muscles arise from migratory mesenchymal precursor cells that possess molecular and morphogenetic identity with the limb muscle precursors of tetrapod species. Chondrichthyan dogfish embryos, however, use the primitive mechanism of direct epithelial somitic extensions to derive the muscles of the fin. We conclude that the genetic mechanism controlling formation of tetrapod limb muscles evolved before the Sarcopterygian radiation.

Animals↗
PubMed2000

Slow muscle induction by Hedgehog signalling in vitro.

Muscles are composed of several fibre types, the precise combination of which determines muscle function. Whereas neonatal and adult fibre type is influenced by a number of extrinsic factors, such as neural input and muscle load, there is little knowledge of how muscle cells are initially determined in the early embryo. In the zebrafish, fibres of the slow twitch class arise from precociously specified myoblasts that lie close to the midline whereas the remainder of the myotome differentiates as fast myosin expressing muscle. In vivo evidence has suggested the Sonic Hedgehog glycoprotein, secreted from the notochord, controls the formation of slow twitch and fast twitch muscle fates. Here we describe an in vitro culture system that we have developed to test directly the ability of zebrafish myoblasts to respond to exogenous Sonic Hedgehog peptide. We find that Sonic Hedgehog peptide can control the binary cell fate choice of embryonic zebrafish myoblasts in vitro. We have also used this culture system to assay the relative activities of different Hedgehog-family proteins and to investigate the possible involvement of heterotrimeric G-proteins in Hedgehog signal transduction.

Animals↗
PubMed1999

Control of muscle cell-type specification in the zebrafish embryo by Hedgehog signalling.

The specification of different muscle cell types in the zebrafish embryo requires signals that emanate from the axial mesoderm. In previous studies we and others have shown that overexpression of different members of the Hedgehog protein family can induce the differentiation of two types of slow-twitch muscles, the superficially located slow-twitch fibres and the medially located muscle pioneer cells. Here we have investigated the requirement for Hedgehog signalling in the specification of these distinct muscle cell types in two ways: first, by characterising the effects on target gene expression and muscle cell differentiation of the u-type mutants, members of a phenotypic group previously implicated in Hedgehog signalling, and second, by analysing the effects of overexpression of the Patched1 protein, a negative regulator of Hedgehog signalling. Our results support the idea that most u-type genes are required for Hedgehog signalling and indicate that while such signalling is essential for slow myocyte differentiation, the loss of activity of one signal, Sonic hedgehog, can be partially compensated for by other Hedgehog family proteins.

Animals↗
PubMed1998

Hedgehog's escape from Pandora's box.

The Hedgehog family of secreted glycoproteins proteins plays multifarious roles during vertebrate embryogenesis. In both the Drosophila and vertebrate embryo correct deployment of Hedgehog-like proteins is critical for the generation of pattern in many tissues and organs. New evidence now reveals that genes involved in hedgehog signalling are mutated in a number of common human genetic disorders, including skin cancer and craniofacial defects. The understanding of how cells generate, receive and transduce the Hedgehog signal during development has led to the establishment of molecular paradigms for the pathogenesis of these diseases. These studies clearly illustrate that knowledge of the normal role of a gene during development is critical for generating an understanding of the disease state in which it is mutated.

Abnormalities, Multiple↗
PubMed1998

The generation and interpretation of positional information within the vertebrate myotome.

How somitic cells become restricted to the muscle fate has been investigated on a number of levels. Classical embryological manipulations have attempted to define the source of inductive signals that control the formation of the myotome. Recently, these studies have converged with others dissecting the role of secreted proteins in embryonic patterning to demonstrate a role for specific peptides in inducing individual cell types of the myotome. Collectively, these investigations have implicated the products of the Wnt, Hedgehog (Hh) and Bone morphogenetic protein (Bmp) gene families as key myogenic regulators; simultaneously controlling both the initiation of myogenesis and the fate of individual myoblasts.

Animals↗
PubMed1997

Notochord induction of zebrafish slow muscle mediated by Sonic hedgehog.

The patterning of vertebrate somitic muscle is regulated by signals from neighboring tissues. We examined the generation of slow and fast muscle in zebrafish embryos and show that Sonic hedgehog (Shh) secreted from the notochord can induce slow muscle from medial cells of the somite. Slow muscle derives from medial adaxial myoblasts that differentiate early, whereas fast muscle arises later from a separate myoblast pool. Mutant fish lacking shh expression fail to form slow muscle but do form fast muscle. Ectopic expression of shh, either in wild-type or mutant embryos, leads to ectopic slow muscle at the expense of fast. We suggest that Shh acts to induce myoblasts committed to slow muscle differentiation from uncommitted presomitic mesoderm.

Animals↗
PubMed1996

Zebrafish genetics: mutant cornucopia.

The initial characterization of mutations from the large-scale mutagenesis of the zebrafish genome has been reported. What new insights will we gain about vertebrate development from these studies?

Animals↗
PubMed1996

Induction of a specific muscle cell type by a hedgehog-like protein in zebrafish.

The notochord plays a central role in vertebrate development, acting as a signalling source that patterns the neural tube and somites. In in vitro assays, the secreted protein Sonic hedgehog mimics the inducing effects of notochord on both presomitic mesoderm and neural plate explants of amniote embryos, suggesting that both patterning activities of the notochord may be mediated by this protein in vivo. In zebrafish, however, mutants with disrupted notochord development lack a specific muscle cell type, the muscle pioneers, although they retain the ability to induce neural differentiation, raising the possibility that neural tube and somite patterning may be mediated by distinct signals. Here we describe a new member of the hedgehog family, echidna hedgehog, that is expressed exclusively in the notochord and has the ability to rescue the differentiation of muscle pioneer cells in mutants with no notochord. Moreover, we show that a combination of ectopic echidna hedgehog and sonic hedgehog expression induces supernumary muscle pioneers in wild-type embryos, suggesting that both signals act sequentially to pattern the developing somites.

Amino Acid Sequence↗
PubMed1994

Structure and expression of the gene encoding phosphofructokinase (PFK) in Drosophila melanogaster.

The gene from Drosophila melanogaster that encodes phosphofructokinase has been isolated and its structure and expression characterized. Southern blots of genomic DNA, comparison of multiple clones, and in situ hybridization to salivary gland chromosomes indicate that the Drosophila genome contains a single copy of the gene which encodes phosphofructokinase (PFK) that is located at cytogenetic position 46D/E on the polytene map. Analysis of the gene structure reveals a single coding region that spans 6.5 kilobase pairs and is composed of eight exons and seven introns. Three developmentally regulated transcripts are generated through the use of alternative polyadenylation sites. Transcription initiation occurs at a single site. The pattern of transcript accumulation during development is similar to other genes of Drosophila which encode enzymes of the glycolytic pathway. Deficiency analysis of the 46D/E region has identified a lethal complementation group associated with reduced PFK activity, thereby establishing the vital role of PFK function in Drosophila.

Amino Acid Sequence↗
PubMed1994

Structure, expression and duplication of genes which encode phosphoglyceromutase of Drosophila melanogaster.

We report here the isolation and characterization of genes from Drosophila that encode the glycolytic enzyme phosphoglyceromutase (PGLYM). Two genomic regions have been isolated that have potential to encode PGLYM. Their cytogenetic localizations have been determined by in situ hybridization to salivary gland chromosomes. One gene, Pglym78, is found at 78A/B and the other, Pglym87, at 87B4,5 of the Drosophila polytene map. Pglym78 transcription follows a developmental pattern similar to other glycolytic genes in Drosophila, i.e., substantial maternal transcript deposited during oogenesis; a decline in abundance in the first half of embryogenesis; a subsequent increase in the second half of embryogenesis which continues throughout larval life; a decline in pupae and a second increase to a plateau in adults. This transcript has been mapped by cDNA and genomic sequence comparison, RNase protection, and primer extension. Using similar analyses transcripts of Pglym87 could not be detected. Pglym78 has two introns which interrupt the coding region, while the Pglym87 gene lacks introns. This and other features support a model of retrotransposition mediated gene duplication for the origin of Pglym87. The apparent absence of a complete, intact coding frame and transcript suggest that Pglym87 is a pseudogene. However, retention of reading frame and codon bias suggests that Pglym87 may retain coding function, or may have been inactivated recently, substantially after the time of duplication, or that the molecular evolution of Pglym87 is unusual. Similarities of the unusual molecular evolution of Pglym87 and other proposed pseudogenes are discussed.

Amino Acid Sequence↗
PubMed1993

Intragenic dominant suppressors of glp-1, a gene essential for cell-signaling in Caenorhabditis elegans, support a role for cdc10/SWI6/ankyrin motifs in GLP-1 function.

The glp-1 gene product mediates cell-cell interactions required for cell fate specification during development in Caenorhabditis elegans. To identify genes that interact with glp-1, we screened for dominant suppressors of two temperature-sensitive glp-1 alleles and recovered 18 mutations that suppress both germline and embryonic glp-1 phenotypes. These dominant suppressors are tightly linked to glp-1 and do not bypass the requirement for a distal tip cell, which is thought to be the source of a signal that is received and transduced by the GLP-1 protein. Using single-strand conformation polymorphism (SSCP) analysis and DNA sequencing, we found that at least 17 suppressors are second-site intragenic revertants. The suppressors, like the original glp-1(ts) mutations, are all located in the cdc10/SWI6/ankyrin domain of GLP-1. cdc10/SWI6/ankyrin motifs have been shown to mediate specific protein-protein interactions in other polypeptides. We propose that the glp-1(ts) mutations disrupt contact between GLP-1 and an as yet unidentified target protein(s) and that the dominant suppressor mutations restore appropriate protein-protein interactions.

Amino Acid Sequence↗
PubMedDate not supplied

Morphogenesis and evolution of vertebrate appendicular muscle.

Two different modes are utilised by vertebrate species to generate the appendicular muscle present within fins and limbs. Primitive Chondricthyan or cartilaginous fishes use a primitive mode of muscle formation to generate the muscle of the fins. Direct epithelial myotomal extensions invade the fin and generate the fin muscles while remaining in contact with the myotome. Embryos of amniotes such as chick and mouse use a similar mechanism to that deployed in the bony teleost species, zebrafish. Migratory mesenchymal myoblasts delaminate from fin/limb level somites, migrate to the fin/limb field and differentiate entirely within the context of the fin/limb bud. Migratory fin and limb myoblasts express identical genes suggesting that they possess both morphogenetic and molecular identity. We conclude that the mechanisms controlling tetrapod limb muscle formation arose prior to the Sarcopterygian or tetrapod radiation.

Animals↗