Ontogenesis of triiodothyronine nuclear receptors in three skeletal muscles in male and female chicks

Research progress on regulating factors of muscle fiber heterogeneity in poultry: a review

Control of meat quality traits is an important goal of any farm animal production, including poultry. A better understanding of the biochemical properties of muscle fiber properties that drive muscle development and ultimately meat quality constitutes one of the major challenging topics in animal production and meat science. In this paper, the existing classification methods of skeletal muscle fibers in poultry were reviewed and the relationship between contractile and metabolic characteristics of muscle fibers and poultry meat quality was described. Finally, a comprehensive review of multiple potential factors affecting muscle fiber distribution and conversion is presented, including breed, sex, hormones, growth performance, diet, muscle position, exercise, and ambient temperature. We emphasize that knowledge of muscle fiber typing is essential to better understand how to control muscle characteristics throughout the life cycle of animals to better manage the final quality of poultry meat.

Avian adjustments to cold and non-shivering thermogenesis: whats, wheres and hows

Avian cold adaptation is hallmarked by innovative strategies of both heat conservation and thermogenesis. While minimizing heat loss can reduce the thermogenic demands of body temperature maintenance, it cannot eliminate the requirement for thermogenesis. Shivering and non-shivering thermogenesis (NST) are the two synergistic mechanisms contributing to endothermy. Birds are of particular interest in studies of NST as they lack brown adipose tissue (BAT), the major organ of NST in mammals. Critical analysis of the existing literature on avian strategies of cold adaptation suggests that skeletal muscle is the principal site of NST. Despite recent progress, isolating the mechanisms involved in avian muscle NST has been difficult as shivering and NST co-exist with its primary locomotory function. Herein, we re-evaluate various proposed molecular bases of avian skeletal muscle NST. Experimental evidence suggests that sarco(endo)plasmic reticulum Ca²⁺ -ATPase (SERCA) and ryanodine receptor 1 (RyR1) are key in avian muscle NST, through their mediation of futile Ca²⁺ cycling and thermogenesis. More recent studies have shown that SERCA regulation by sarcolipin (SLN) facilitates muscle NST in mammals; however, its role in birds is unclear. Ca²⁺ signalling in the muscle seems to be common to contraction, shivering and NST, but elucidating its roles will require more precise measurement of local Ca²⁺ levels inside avian myofibres. The endocrine control of avian muscle NST is still poorly defined. A better understanding of the mechanistic details of avian muscle NST will provide insights into the roles of these processes in regulatory thermogenesis, which could further inform our understanding of the evolution of endothermy among vertebrates.

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds.

Reprint of "Avian thyroid development and adaptive plasticity" [Gen. Comp. Endocrinol. 147, 93-101]

Precocial and altricial modes of avian development are characterized by different degrees of maturation and physiological capabilities at hatching. In precocial birds, thyroid function and its control are well developed during the latter part of incubation and hatchlings exhibit metabolic responses to cooling and relatively mature sensory and locomotor capabilities. In altricial birds, thyroid function shows little maturation until after hatch as also is the case for thermoregulatory, sensory, and motor functions. This review describes the patterns of precocial and altricial thyroid development, their hypothalamic-pituitary control, extrathyroidal control of hormone activation and deactivation, and target tissue effects during development. Our knowledge is greatest for precocial galliform birds although the organismal picture of thyroid development has been investigated in several altricial avian species.

Avian thyroid development and adaptive plasticity

Precocial and altricial modes of avian development are characterized by different degrees of maturation and physiological capabilities at hatching. In precocial birds, thyroid function and its control are well developed during the latter part of incubation and hatchlings exhibit metabolic responses to cooling and relatively mature sensory and locomotor capabilities. In altricial birds, thyroid function shows little maturation until after hatch as also is the case for thermoregulatory, sensory, and motor functions. This review describes the patterns of precocial and altricial thyroid development, their hypothalamic-pituitary control, extrathyroidal control of hormone activation and deactivation, and target tissue effects during development. Our knowledge is greatest for precocial galliform birds although the organismal picture of thyroid development has been investigated in several altricial avian species.

The hypothalamic-pituitary-thyroid axis and the female reproductive system

Increasing evidence derived from experimental and clinical studies suggests that the hypothalamic-pituitary-thyroid axis (HPT) and the hypothalamic-pituitary-ovarian axis (HPO) are physiologically related and act together as a unified system in a number of pathological conditions. The suggestion that specific thyroid hormone receptors at the ovarian level might regulate reproductive function, as well as the suggested influence of estrogens at the higher levels of the HPT axis, seems to integrate the reciprocal relationship of these two major endocrine axes. Both hyper- and hypothyroidism may result in menstrual disturbances. In hyperthyroidism the most common manifestation is simple oligomenorrhea. Anovulatory cycles are very common. Increased bleeding may also occur, but it is rare. Hypothyroidism in girls can cause alterations in the pubertal process; this is usually a delay, but occasionally it can result in pseudo-precocious puberty. In mature women hypothyroidism usually is associated with abnormal menstrual cycles characterized mainly by polymenorrhea, especially anovulatory cycles, and an increase in fetal wastage.

Thyroid development in relation to the development of endothermy in the red-winged blackbird (Agelaius phoeniceus)

We investigated the development of thyroid function during the transition to endothermy in red-winged blackbirds (Agelaius phoeniceus). Thermoregulatory capabilities of blackbirds improve markedly over their relatively short nestling period (10-12 days), with the most striking improvements occurring between days 6 and 8. We hypothesized that the development of endothermy in these birds is dependent in part on the development of thyroid function. We assessed thyroid development by measuring changes in thyroid gland histology and plasma concentrations of thyroxine (T4) and triiodothyronine (T3) during the nestling period. To gain insight into the role of thyroid maturation in the context of thermoregulation, we compared plasma thyroid hormone profiles in nestlings exposed to cold temperatures to those maintained at thermoneutral temperatures. The overall size of the thyroid (as cross-sectional area) increased during nestling development, with the fastest growth occurring just before the development of endothermy. By day 8, it reached the size typical of that in adults. Follicular cell height of the thyroid glands increased in nestlings up to day 6 and then decreased for the rest of the nestling period. The mean area of individual follicles increased up to day 8 of nestling life and then decreased. Individual nestlings were capable of strong endothermic responses at 7 to 8 days of age and had significantly decreased plasma T4 concentrations following cold exposure, suggesting increased T4 to T3 deiodination to maintain the plasma concentrations of the more metabolically active T3. The patterns of plasma T4 and T3 during nestling development were consistent with those of nestlings of other altricial species of birds that have been studied. Overall, the patterns of thyroid development observed were consistent with the hypothesis that the functional development of the thyroid is critical to the development of endothermic capabilities and that thyroid hormones play a role in endothermic responses to cold temperatures.

Myosin isoform transitions in four rabbit muscles during postnatal growth

Four rabbit muscles (i.e. semimembranosus proprius, psoas major, biceps femoris and longissimus lumborum), differing in their fibre type composition in the adult, were investigated during postnatal development. Muscle samples were taken at 1, 7, 14, 21, 28, 35, 49 and 77 days of age. Complementary techniques were used to characterize myosin heavy chain (MHC) isoform transitions, i.e. SDS-PAGE, immunocytochemistry and conventional histochemistry. Good accordance was found between electrophoretic and immunocytochemical techniques. Our results show that rabbit muscles were phenotypically immature at birth. At 1 day of age, perinatal isoform represented 70-90% of the total isoform content of the muscles. Two generations of myofibres could be observed on the basis of their morphology and reaction to specific antibodies. In all muscles, primary fibres expressed slow MHC. In contrast, secondary generation of fibres never expressed slow MHC in future fast muscles, while half of them expressed slow MHC in the future slow-twitch muscle, the semimembranosus proprius. During the postnatal period, all muscles displayed a transition from embryonic to perinatal MHC isoforms, followed by a transition from perinatal to adult MHC isoforms. These transitions occured mainly during the first postnatal month. The embryonic isoform was no longer expressed after 14 days, except in longissimus where it disappeared after 28 days. On the contrary, large differences were found in the timing of disappearance of the perinatal isoform between the four muscles. The perinatal isoform disappeared between 28 and 35 days in semimembranosus proprius and 35 and 49 days in psoas and biceps femoris. Interestingly, the perinatal isoform was still present in 6% of the fibres in longissimus at 77 days, the commercial slaughter age, denoting a great delay in the maturation. Fate of each generation of fibres differed between muscles.

Perinatal ontogeny of porcine nuclear thyroid hormone receptors and its modulation by thyroid status

Induction of nuclear thyroid hormone receptors (TRs) represents a key point in the control of growth, development, differentiation, and metabolism of most tissues. The influence of thyroid status on the ontogeny of hepatic and skeletal muscle TRs has been investigated in perinatal pigs. Plasma concentrations of total and free 3,5,3'-triiodothyronine (T3) increased markedly from 80 days of fetal life (80 f) to 2 days of postnatal life. Test piglets obtained from sows fed a high glucosinolate rapeseed diet had lower T3 and thyroxine levels than controls at 110 f and showed a higher postnatal surge in T3. Maximal T3 binding capacity (Bmax, pmol T3/mg DNA, means +/- SE) in liver increased from 0.07 +/- 0.01 at 80 f to 0.37 +/- 0.02 at birth and then plateaued. In longissimus dorsi muscle, Bmax values were much higher than in liver and increased from 0.90 +/- 0.02 at 80 f to 1.37 +/- 0.13 at birth and then declined to 1.09 +/- 0.11 at 2 days of age. Long-term fetal hypothyroidism affected the ontogenic profile of both liver and muscle receptors but in opposite directions; Bmax values were reduced in liver but increased in muscle. Postnatally, lower muscle Bmax values occurred in parallel with transient higher levels of circulating T3. Apparent binding affinities were slightly different in liver and muscle during fetal life, and there was an effect of age in muscle. In conclusion, as far as the receptor is concerned, fetal muscle can potentially respond to thyroid hormones much earlier in development than the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of triiodothyronine on camp-dependent and camp-independent protein kinase activities in developing chick embryo liver

1. Changes in liver cytosol cAMP-dependent kinase and cAMP-independent growth-related quercetin-inhibited casein kinase activities during chick embryo development were studied. 2. Both kinase activities were found to increase continuously during the experimental period. 3. Upon treatment of embryos with triiodothyronine, an activation of cAMP-dependent kinase A and cAMP-independent casein kinase was observed which was most pronounced on days 12 and 14.

Immunocytochemical demonstration of T4 content and TSH-binding by cells of the thyroid of the developing chick embryo

The numerical densities (Nv) of immunostained thyroxine (T4)-positive cells and thyrotropin-stimulating hormone (TSH)-positive cells were determined in chick embryos on Day 5.5 through Day 11.5 and Days 5.5, 7.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, 15.5, 16.5, and 17.5, respectively. The data demonstrate that selected cells of the "prefollicular" thyroid contain T4 and bind TSH at least as early as Day 5.5. The Nv of immunocytochemically demonstrable T4-positive cells increases gradually from Day 5.5 to Day 10.5, exhibiting a statistically significant increase (P less than 0.05) between Day 10.5 and Day 11.5. Similarly, the Nv of TSH-binding cells (Nv TSH) rises slowly from Day 5.5 until Day 11.5, followed by a statistically significant (P less than 0.05) increase between Day 11.5 and Day 12.5. The peak Nv TSH value on Day 12.5 is followed by a decline (P less than 0.05) on Day 13.5, and from Day 14.5 through Day 17.5, Nv TSH values remain relatively constant. Changes in the Nv of T4-positive and TSH-binding cells over developmental time are discussed with regard to pituitary regulation of the chick embryo thyroid and the possible contribution of the yolk to circulating T4 levels.

Thyroid function in embryonic and early posthatch chickens and quail

Technological advances, especially radioimmunoassays, have led to good descriptive information about the timing and pattern of development of the thyroid gland (TG) and circulating thyroid hormone (TH). Immunocytochemical studies in combination with more traditional techniques such as gland ablation and hormone replacement have revealed the time of appearance of each hormone in the axis, the relative amounts of hormone present in each gland at different developmental stages, and a general picture of the pattern of maturation of the hypothalamic-pituitary-thyroid axis. Studies of the pituitary control of the TG remain limited by the lack of adequately specific techniques for measuring avian thyroid-stimulating hormone. Our understanding of peripheral TH dynamics is progressing as a result of iodothyronine deiodinase assays but full understanding will require more elaborate studies that adequately characterize the enzyme system(s) in each case. Molecular techniques have made powerful strides in identifying the gene responsible for producing a protein that appears to be the triiodothyronine receptor. Receptor assays have revealed the pattern of changes in receptor-binding capacities during development but have not yet revealed how binding of hormone to the receptor triggers cellular activity. Molecular genetic techniques are being used to reveal the mechanisms whereby some examples of developmental events (e.g., malic enzyme synthesis) are induced by TH. Although it is not yet possible to assess the value of molecular studies in this area for developing practical applications, these techniques are revealing the fundamental biological roles of TH in growth and development.