P. Rudas

Cloning and expression of the chicken type 2 iodothyronine 5'-deiodinase.

The type 2 iodothyronine deiodinase (D2) is critical for the intracellular production of 3,5,3′-triiodothyronine from thyroxine. The D2 mRNA of higher vertebrates is over 6 kilobases (kb), and no complete cDNA clones have been reported. Using 5′- and 3′-rapid amplification of cDNA ends and two cDNA libraries, we have cloned the 6094-base pair full-length chicken D2 cDNA. The deduced protein is ∼31 kDa and contains two in-frame UGA codons presumably encoding selenocysteine. One of these is in the highly conserved active catalytic center; the other is near the carboxyl terminus. Unusual features of the cDNA include a selenocysteine insertion sequence element ∼4.8 kb 3′ to the UGA codon in the active center and three short open reading frames in the 5′-untranslated region. The K m of D2 is ∼1.0 nm for thyroxine, and the reaction is insensitive to inhibition by 6-n-propylthiouracil. Chicken D2 is expressed as a single transcript of ∼6 kb in different brain regions and in the thyroid and lung. Hypothyroidism increases D2 mRNA in the telencephalon. Unlike in mammals, D2 mRNA and activity are expressed in the liver of the chicken, suggesting a role for D2 in the generation of plasma 3,5,3′-triiodothyronine in this species.

T-Cell subsets in blood and lymphoid tissues obtained from fetal calves, maturing calves, and adult bovine

Assessment of CD2, CD4, CD8 and gamma delta cell distribution among mononuclear cells obtained from the blood and lymphoid tissues of fetal calves, 0-150-day-old calves and adult cows was the focus of this investigation. The distributions of some of the lymphocyte subsets in peripheral blood showed variation in fetal and maturing calves as well as being markedly different from those observed in adult cows. We provide evidence that as early as 1 month prepartum, fetal calves have a full complement of at least four of the major T-cell subsets found in the normal bovine. In blood, CD2(+) were significantly higher at 1, 30 and 90 days of age, CD4(+) and CD8 cells demonstrated a peak in the fetuses that dropped below adult levels from 1 to 120 days of age, and gamma delta (+) cells were highest at birth and decreased to adult levels by 150 days of age. Except for the gamma delta (+) cells, the subsets were significantly higher in lymphoid tissues obtained from fetal and maturing calves than in the mature animals. All four subsets were significantly higher in fetal and young calf splenic tissues. No significant differences were observed in the distribution of the four subsets in thymuses assayed in this study. An interesting pattern was seen in a longitudinal study of T-cell subsets that showed 7-8 day cyclical changes in CD2 and CD4 marked cells in adult peripheral blood.

Transcriptional regulation of iodothyronine deiodinases during embryonic development

A single dose of chicken growth hormone (cGH) or dexamethasone acutely increases circulating T(3) levels in 18-day-old chicken embryos through a reduction of hepatic type III iodothyronine deiodinase (D3). The data in the present study suggest that this decrease in D3 is induced by a direct downregulation of hepatic D3 gene transcription. The lack of effect of cGH or dexamethasone on brain and kidney D3 activity, furthermore suggests that both hormones affect peripheral thyroid hormone metabolism in a tissue specific manner. Dexamethasone administration also results in an increase in brain type II iodothyronine deiodinase (D2) activity and mRNA levels that is also regulated at a transcriptional level. In contrast, however, cGH has no effect on brain D2 activity, thereby suggesting that either GH cannot pass through the blood-brain barrier in chicken or that cGH and dexamethasone regulate thyroid hormone deiodination by different mechanisms. In addition, the very short half-life of D2 and D3 (t(1/2)<1 h) in comparison with the longer half life of type I iodothyronine deiodinase (D1, t(1/2)>8 h), allows for D2 and D3 to play a more prominent role in the acute regulation of peripheral thyroid hormone metabolism than D1.

The importance of the peripheral thyroid hormone deiodination in adaptation to ambient temperature in the chicken (Gallus domesticus)

Abstract 1. 1. Evidence is obtained for a major role of thyroxine to triiodothyronine (and/or reverse-triiodothyronine) conversion in the early phase of cold and warm acclimation. 2. 2. The short term change in deiodination seems to be the first response to changes in environmental temperature, and might precede the thyrotropin release from the pituitary after mild cold exposure. 3. 3. The idea of autoregulation of thyroid hormone metabolism is discussed.

Partial cloning and localization of leptin and leptin receptor in the mammary gland of the Egyptian water buffalo.

Originally an overall metabolic control was attributed to the leptin hormone, which is produced mainly by the adipose tissue. Recently, leptin gene expression was demonstrated in several additional peripheral tissues. Furthermore, several isoforms of leptin receptor were found both in the central nervous system and in the peripheral tissues. Using reverse transcription and polymerase chain reaction analysis we demonstrate that leptin is expressed both in the adipose tissue and in the lactating mammary gland tissue of Egyptian water buffalo. Our results show that, short and long isoforms of leptin receptor are expressed in buffalo mammary gland tissue. We have partially cloned the buffalo leptin and its short and long isoforms of receptor, which show a high sequence homology to previously published sequences of other mammalian species especially to that of other ruminants. Localization of leptin and its receptor mRNA transcripts, as determined by in situ hybridization procedure, revealed that leptin and its receptor transcripts are expressed specifically in the alveolar epithelial cells of the mammary gland. These morphological data support that leptin could also act as an autocrine and paracrine mediator for mammary gland metabolism and as a facilitator of alveolar epithelial cell activity during lactation.

Impaired local deiodination of thyroxine to triiodothyronine in dogs with symmetrical truncal alopecia

Thyroid dysfunction causes certain dermatological alterations in dogs. Insufficient delivery of thyroid hormone to the skin may originate not only from inadequate thyroid function but also from impaired local activation of thyroxine in the target organ. Thyroid parameters and deiodination were investigated in healthy dogs (group C) and in dogs with cutaneous lesions associated with hypothyroidism (group H) or with a low-T3 syndrome (group LT). The ability of the skin to convert T4 to T3 was impaired in both groups H and LT but not in the controls. It is concluded that impaired local deiodination may contribute to skin problems in dogs.

Serum amyloid A in geese; cloning and expression of recombinant protein.

We defined the nucleotide-sequence of the full-length goose serum amyloid A and compared it to SAA sequences of the duck. The aim of this work was to clone and express recombinant goose SAA and to produce antibody against this protein: Total RNA was isolated from goose liver and used to synthesise first strand cDNA. The coding region of the goose SAA cDNA was amplified by PCR using primers corresponding to the appropriate conservative regions of duck SAA mRNA. The product was subcloned into pET-15b expression vector to result in a His•Tag® fusion protein expression. The protein was purified by affinity chromatography. Rabbits were then immunized against the recombinant purified goose SAA protein. The anti-SAA serum was tested by Western blotting. Full-length goose SAA mRNA sequence has been obtained and sequenced.

Aspects of Introducing and Writing Multimedia Lessons in Veterinary Physiology

Abstract Since 1990, the Department of Physiology and Biochemistry at the University of Veterinary Science in Budapest, Hungary, has been involved in the development of a multimedia system for teaching physiology to undergraduate veterinary students. The present paper describes the achievements and approaches during the last years, and how a Windows‐based authoring system (Guide 3.1) has allowed the student‐based introduction of ‘directed self education’, a method that very much enhances student creativity.

INTERCONNECTION BETWEEN PLASMA LEVELS OF SEX STEROIDS, THYROID HORMONES AND CORTICOSTERONE DURING THE OVULATORY-OVIPOSITION CYCLE IN THE DOMESTIC HEN

Publisher Summary This chapter discusses the interconnection among plasma levels of sex steroids, thyroid hormones, and corticosterone during the ovulatory-oviposition cycle in the domestic hen. In the experiment described in the chapter, 11 adult New Hampshire laying hens fed by laying hen concentrate and water ad libitum were used. Progesterone peak 4–6 hours prior to ovulation was definitely detectable in hens from which blood sample could be drawn 6–10 hours before the ovulation. In most of the cases, oestron and 17-oestradiol reach their maximum parallel with the progesterone. The plasma concentration of oestrogen shows not so definite synchronization as that of progesterone. In some cases, elevated testosterone level 10–12 hours before the oviposition has been found this phenomenon was however not regular. The chapter describes most characteristic changes of the sexual steroids. It is established that the progesterone plays an important and decisive role in the regulation of the ovulatory-oviposition cycle exhibiting a peak that precedes the ovulation by 4–6 hours. Testosterone, estrone, and estradiol do not take part directly in the regulation of ovulation, however, in separate cases, high testosterone levels could be detected 10–12 hours before oviposition.