Browsing by Author "Nowell, M. A."
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- 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 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.
- 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.