Browsing by Author "Llewellyn, Lynda"
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- Analysis of the Sox gene family in the european sea bass (Dicentrarchus labrax)Publication . Galay-Burgos, M.; Llewellyn, Lynda; Mylonas, Constantinos C.; Canario, Adelino V. M.; Zanuy, Silvia; Sweeney, Glen E.Sox (SRY-related genes containing a HMG box) genes encode a family of transcription factors that are involved in a variety of developmental processes including sex determination. Twenty Sox genes are present in the genomes of humans and mice, but far less is known about the Sox gene family in other vertebrate types. We have obtained clones representing the HMG boxes of twelve Sox genes from European sea bass (Dicentrarchus labrax), a fish species whose farming is complicated by a heavily skewed sex ratio, with between 70% and 99% of offspring typically being male. The cloned Sox genes are members of the SoxB, SoxC, SoxE and SoxF groups. Sequence analysis shows that some of the clones represent genes duplicated in sea bass with respect to the mammalian Sox gene family.
- Characterization of a sea bream (Sparus aurata) thyroid hormone receptor-ß clone expressed during embryonic and larval developmentPublication . Nowell, M. A.; Power, Deborah; Canario, Adelino V. M.; Llewellyn, Lynda; Sweeney, Glen E.A clone encoding thyroid hormone receptor-b (TR-b) was isolated from a sea bream (Sparus aurata) ovary cDNA library. Sea bream (sb)TR-b is closely related to its counterparts from other vertebrates and, like them, preferentially binds T3 rather than T4. However, the putative sbTR-b protein contains a nine-amino-acid insert that is also present in the corresponding proteins from flounder and salmon but absent in TR-bs from zebrafish and terrestrial vertebrates. Semiquantitative RT–PCR analysis showed that sbTR-b transcripts begin to accumulate during gastrulation and increase markedly in quantity up to the period around hatch (ca. 40 h postfertilization) before declining slightly. In adult tissues, TR-b mRNA was present in approximately equal quantities in heart, intestine, brain, kidney, skeletal muscle, liver, and gill. The significance of the relatively strong expression of TR-b during sea bream embryogenesis is discussed.
- Cloning and characterisation of a fish aldolase B genePublication . Llewellyn, Lynda; Ramsurn, Vimi P.; Sweeney, Glen E.; Wigham, Trevor; Santos, Cecilia; Power, DeborahA full length cDNA clone representing an aldolase mRNA was isolated from a sea bream (Sparus aurutu) liver cDNA library. Sequencing of this clone revealed it to encode a 364 amino acid protein with 74% amino acid identity to human aldolase B and slightly lower similarity to human aldolase A and C. In view of the sequence data and of Northern blot analysis showing strong expression of a 1.6 kb transcript in liver it was concluded that the cloned gene represents aldolase B. This clone represents the first aldolase gene to be sequenced from any fish species thus providing new data on the evolution of the vertebrate aldolase gene family.
- Cloning and expression of an elongation factor-1α in sea bream ( Sparus aurata ) larvae and adult tissuePublication . Nowell, M. A.; Power, Deborah; Guerreiro, P. M.; Llewellyn, Lynda; Ramsurn, Vimi P.; Wigham, Trevor; Sweeney, Glen E.A clone encoding the polypeptide elongation factor EF-1a was isolated from a complementary DNA library prepared from sea bream (Spartus aurata) larvae 1 to 10 days after hatching. The deduced amino acid sequence is between 82% and 95% similar to EF-1a in other animal species. EF-1a messenger RNA is present at low abundance in sea bream embryos prior to gastrulation, but at around 15 hours postfertilization, there is a 10-fold increase in transcript levels. This increase presumably reflects midblastula transition in this species. In adult sea bream, EF-1a appeared to have a relatively uniform distribution across all the tissues analyzed.
- Cloning and sequencing of a full-length sea bream (Sparus aurata) beta-actin cDNAPublication . Santos, Cecilia; Power, Deborah; Kille, Peter; Llewellyn, Lynda; Ramsurn, Vimi P.; Wigham, Trevor; Sweeney, Glen E.A full-length cDNA clone encoding beta-actin (b-actin) was isolated from a sea bream (Sparus aurata) liver cDNA library. Sequencing of this clone reveals an open reading frame encoding a 375 amino acid protein that shares a high degree of conservation to other known actins. The sea breamb-actin sequence showed 98% identity to carp and human b-actin and 95% and 94% identity to sea squirt and Dictyostelium cytoplasmic actins, respectively.
- Cloning, characterisation and expression of the apolipoprotein A-I gene in the sea bream (Sparus aurata)Publication . Llewellyn, Lynda; Ramsurn, Vimi P.; Wigham, Trevor; Sweeney, Glen E.; Power, DeborahA full length cDNA clone representing apolipoprotein A-I was isolated from a sea bream (Sparus aurata) liver library. The clone encodes a 261 amino acid protein which shows highest amino acid identity (38%) with salmon apolipoprotein A-I. Northern blot analysis showed strong expression of a 1.4 kb transcript in liver with lower expression in intestine. Expression of apolipoprotein A-I in intestine was markedly reduced by treatment with triiodothyronine (T3). ß 1998 Elsevier Science B.V. All rights reserved.
- Expression of thyroid hormone receptor during early development of the sea bream (Sparus aurata)Publication . Llewellyn, Lynda; Ramsurn, Vimi P.; Sweeney, Glen E.; Wigham, Trevor; Power, DeborahThe thyroid hormones thyroxine (T4) and triiodothyronine (T3) are crucial to many aspects of vertebrate growth, development, and metabolism. They act through intracellular receptor proteins which act directly on target genes. Although the role of thyroid hormones in fish, especially in early development, is not well understood, thyroid hormones are passed to eggs by broodfish during spawning and are implicated in fish development.1,2 Sea bream (Sparus aurata) aquaculture has grown rapidly in importance in the European Community, particularly in southern Portugal. However, its further development is hindered by the high larval mortality rate and incidence of malformations. This work investigates the significance of thyroid hormones in sea bream development by cloning the thyroid hormone receptor (TR) and analyzing its expression during larval development.
- Thyroid hormone receptor expression during metamorphosis of Atlantic halibut (Hippoglossus hippoglossus)Publication . Galay-Burgos, M.; Power, Deborah; Llewellyn, Lynda; Sweeney, Glen E.Flatfish such as the Atlantic halibut (Hippoglossus hippoglossus) undergo a dramatic metamorphosis that transforms the pelagic, symmetric larva into a benthic, cranially asymmetric juvenile. In common with amphibian metamorphosis, flatfish metamorphosis is under endocrine control with thyroid hormones being particularly important. In this report we confirm that tri-iodothyronine (T3) levels peak at metamorphic climax during halibut metamorphosis. Moreover we have isolated cDNA clones of TR and TR genes and confirmed the presence in halibut of two TR isoforms (representing the products of distinct genes) and two TR isoforms (generated from a single gene by alternative splicing). Real time PCR was used to assess expression of these genes during metamorphosis. TR shows the most dramatic expression profile, with a peak occurring during metamorphic climax.
- Thyroid hormones in growth and development of fishPublication . Power, Deborah; Llewellyn, Lynda; Faustino, M.; Nowell, M. A.; Björnsson, Björn Thrandur; Einarsdóttir, Ingibjörg E.; Canario, Adelino V. M.; Sweeney, Glen E.The thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3) are products of the thyroid gland in all vertebrates. Their role in early development and metamorphosis is well established in mammals and amphibians, respectively, and recently several studies in fish have highlighted the importance of THs during flatfish metamorphosis. THs are present in high quantities in fish eggs and are presumably of maternal origin. During embryogenesis the concentration of T4 and T3 in the eggs decrease until endogenous production starts. Thyroid hormone receptors (TR) have been isolated from several teleosts and in common with tetrapods two receptor isoforms have been identified, TRα and TRβ. Both the receptors are expressed in early embryos and larvae of the Japanese flounder (Paralichthys olivaceus), zebrafish (Danio rerio) and seabream (Sparus aurata) although a different temporal pattern is apparent. The role of THs and TRs in fish embryogenesis, larval development and during metamorphosis will be discussed.
- Thyroid hormones in sea bream larval developmentPublication . Power, Deborah; Llewellyn, Lynda; Faustino, M.; Nowell, M. A.; Björnsson, Björn Thrandur; Einarsdóttir, Ingibjörg E.; Canario, Adelino V. M.; Sweeney, Glen E.The thyroid hormones (TH), thyroxine (T4) and triiodothyronine (T3) are a product of the thyroid gland in all vertebrates. The hormones are pluripotent and in vertebrates are involved in growth, differentiation, metamorphosis, reproduction and metabolism. THs are secreted from the thyroid gland, circulate bound to thyroid hormone-binding proteins and exert their biological effects by binding to specific nuclear receptors which then act directly on target genes. Studies into the role of TH in early development and metamorphosis are largely restricted to mammals and amphibians, although recently several studies in fish have established the importance of TH during flatfish metamorphosis. The involvement of TH during early dovelopment in fish is uncertain although eggs contain significant quantities of THs presumably derived from broodstock.