Academic literature on the topic 'Tyrosine. Chickens'

The biological activity of natural chicken gastrins isolated from the "antrum"-like region of the chicken gut have been studied on gastric secretion in chickens, turkeys, and rats, pancreatic secretion in turkeys and rats, and gallbladder contraction in chickens and guinea pigs. Natural chicken gastrin was shown to be approximately 85% sulfated on the tyrosine that occurs at position 7 from the COOH-terminus. In both avian and mammalian systems, chicken gastrins were found to be potent stimulants of acid secretion but were virtually inactive as stimulants of pancreatic secretion and gallbladder contraction. Peptides with the COOH-terminal tetrapeptide amide of CCK and a sulfated tyrosine at position 7 from the COOH-terminus are usually potent stimulants of pancreas and gallbladder. However, although chicken gastrin has a CCK-like structure, it has a gastrin-like spectrum of biological actions. A proline immediately adjacent to the sulfated tyrosine may produce a steric effect that lowers the activity of chicken gastrin on pancreas and gallbladder. Evidently, then, the factors that determine specificity of action of CCK and gastrin are different in birds and mammals.

The measurement of o-tyrosine levels in poultry meat is a potential method for postirradiation dosimetry of poultry. The validity of using o-tyrosine for this purpose has not yet been established. As part of the validation process, the o-tyrosine content in unirradiated chicken meat, the radiation dose response curve, and the effects of postirradiation storage on o-tyrosine levels are examined. In 18 individual samples, the mean background level of o-tyrosine was 0.18 ± 0.11 ppm (wet weight, 70% moisture), and the most frequent background level (60% of the cases) was between 0.05 and 0.15 ppm (wet weight, 70% moisture). In pooled samples of 10 chickens, the mean background level was 0.12 ± 0.03 ppm (wet weight, 70% moisture). The levels were not significantly affected by storage at 5°C (7 d) or by freezing the sample. The radiation dose response curve was linear within the dose range studied (0 to 10 kGy), with a slope of 0.127 ± 0.003 ppm (wet weight)/kGy. Although there was some variation in the intercept (0.132 ± 0.013), the slope was the same in all samples tested. Postirradiation storage at either 4 or 8°C until spoilage did not affect the levels of o-tyrosine. These data indicate that o-tyrosine level may be useful for determining the absorbed dose in chicken meat gamma-irradiated to doses greater than 0.6 kGy. Further validation studies are continuing.

A high affinity polyclonal antibody specific for phosphotyrosyl residues has been used in immunoblotting experiments to survey developing embryonic chicken tissues for the presence and characteristics of tyrosine phosphorylated proteins. Proteins phosphorylated on tyrosine were found to be present in all the embryonic tissues examined, including heart, thigh, gizzard, intestine, lung, liver, kidney, brain, and lens, from 7 to 21 d of development in ovo, but were greatly reduced or absent in the same tissues taken from adult chickens. A limited number of major tyrosine phosphorylated proteins were seen in all the tissues examined and they ranged in molecular mass from 35 to 220 kD. Most of the tissues contained proteins phosphorylated on tyrosine with apparent molecular masses of 120, 70, 60, and 35 kD, suggesting that the substrates of tyrosine protein kinases in different tissues may be related proteins. One-dimensional peptide mapping of the 120- and 70-kD protein bands indicated a close structural relationship among the phosphotyrosine-containing proteins of 120 kD, and similarly among those of 70 kD, from the different tissues.

On the basis of analysis of cDNA clones of alpha-tubulin RNAs expressed during spermiogenesis in chickens, we report the identification of a novel alpha-tubulin which is expressed exclusively in chicken testes. Comparison of its sequence with those previously determined not only demonstrates that the encoded polypeptide is significantly divergent from other alpha-tubulins but also supports the hypothesis that alpha-tubulin isotypes are distinguished by a carboxy-terminal variable region sequence and, to a lesser extent, by a domain near the amino terminus. Since essentially all previously known alpha-tubulins undergo a unique cycle of removal and posttranslational readdition of a tyrosine residue at the extreme carboxy terminus, the presence in this testes alpha-tubulin of a very divergent carboxy terminus that does not contain an encoded tyrosine raises the possibility that this polypeptide does not participate in the usual cycle of tyrosination/detyrosination.

On the basis of analysis of cDNA clones of alpha-tubulin RNAs expressed during spermiogenesis in chickens, we report the identification of a novel alpha-tubulin which is expressed exclusively in chicken testes. Comparison of its sequence with those previously determined not only demonstrates that the encoded polypeptide is significantly divergent from other alpha-tubulins but also supports the hypothesis that alpha-tubulin isotypes are distinguished by a carboxy-terminal variable region sequence and, to a lesser extent, by a domain near the amino terminus. Since essentially all previously known alpha-tubulins undergo a unique cycle of removal and posttranslational readdition of a tyrosine residue at the extreme carboxy terminus, the presence in this testes alpha-tubulin of a very divergent carboxy terminus that does not contain an encoded tyrosine raises the possibility that this polypeptide does not participate in the usual cycle of tyrosination/detyrosination.

The aim of this study was to evaluate the effects of high ambient temperature (HT) and orotic acid supplementation on the plasma and muscle metabolomic profiles in broiler chickens. Thirty-two 14-day-old broiler chickens were divided into four treatment groups that were fed diets with or without 0.7% orotic acid under thermoneutral (25 ± 1 °C) or cyclic HT (35 ± 1 °C for 8 h/day) conditions for 2 weeks. The chickens exposed to HT had higher plasma malondialdehyde concentrations, suggesting an increase in lipid peroxidation, which is alleviated by orotic acid supplementation. The HT environment also affected the serine, glutamine, and tyrosine plasma concentrations, while orotic acid supplementation affected the aspartic acid, glutamic acid, and tyrosine plasma concentrations. Untargeted gas chromatography–triple quadrupole mass spectrometry (GC-MS/MS)-based metabolomics analysis identified that the HT affected the plasma levels of metabolites involved in purine metabolism, ammonia recycling, pyrimidine metabolism, homocysteine degradation, glutamate metabolism, urea cycle, β-alanine metabolism, glycine and serine metabolism, and aspartate metabolism, while orotic acid supplementation affected metabolites involved in pyrimidine metabolism, β-alanine metabolism, the malate–aspartate shuttle, and aspartate metabolism. Our results suggest that cyclic HT affects various metabolic processes in broiler chickens, and that orotic acid supplementation ameliorates HT-induced increases in lipid peroxidation.

ABSTRACT The effects of the recessive and sex-linked dw gene on insulin sensitivity and liver insulin receptors were compared in normal (Dw-dw) and dwarf (dw-dw) brother or half-brother chickens. At 3·5 weeks of age, following an overnight fast, exogenous insulin (0–6·9 nmol/kg body weight) was slightly but significantly more hypoglycaemic in dwarf chickens. At 4 weeks of age, following an oral glucose load (2 g/kg), glucose tolerance was the same in both genotypes, whereas plasma insulin levels were greatly decreased in dwarf chickens. At 5 weeks of age, plasma concentrations of glucose and insulin were the same in both genotypes in the fasting state and decreased in the fed state in dwarf chickens. In liver membranes prepared from fasted chickens, insulin binding was increased in dwarf chickens, while the affinity of insulin receptors and the insulin-degrading activity of the membranes were the same in both genotypes. Following solubilization with Triton X-100, liver receptors were successively purified on lentil then wheat germ lectins. Autophosphorylation of the β-subunit did not differ between either the genotype or the nutritional (fed or fasted) state. In the basal state (in the absence of insulin) the tyrosine kinase activity of the receptor towards artificial substrate poly(Glu,Tyr)4:1 was significantly decreased in dwarf chickens by fasting. However, the change in tyrosine kinase activity of the receptor in response to insulin was similar, irrespective of the genotype and the nutritional state. Therefore, the slight increase in insulin sensitivity observed in vivo in dwarf chickens is accounted for, at least partly, by a slight increase in liver insulin receptor number, but not by a change in the kinase activity of liver insulin receptors. In addition, post-insulin receptor kinase events and/or GH-dependent counter-regulatory mechanisms may superimpose and increase the insulin sensitivity of dwarf chickens. Journal of Endocrinology (1990) 126, 67–74

The work analyzes qualitative and quantitative amino acid composition of broiler meat for diet enrichment nanotracelement feed additive «Mikrostymulin». It was founded that poultry muscle in control and experimental groups contain such essential amino acids, as threonine, valine, isoleucine, leucine, phenylalanine, lysine, methionine, and tryptophan tsystin. Research the quality of the essential amino–acids showed the presence of aspartic acid, serine, glycine, tyrosine, alanine, glutamic acid, proline, histidine, arginine and oxyproline.It was established that the use of «Mikrostymulin» increases the content of amino acids in meat of broiler chickens. In muscles of broiler chickens in the 1st research group, have beenadded «Mikrostymulin» in a dose of 1 ml/dm³ of water, the amount of essential amino acids and replacement tends to increase at chest and hip muscles, compared with the contro group.. Obviously, this can be explained by improved assimilation of food and stimulating the synthesis of amino acids under the influence of the components of the feed additive. In chickensof the 2nd research group,they received «Mikrostymulin» at a dose of 10 ml/dm³ water, it was registered a tendency to increase essential amino acids in the pectoral muscles, but in the femoral – it was tendency to decrease. In chickens of the 3 rd research group, they received«Mikrostymulin» at a dose of 20 ml/dm³ water, it was registered a tendency to reduce the amount of essential amino acids in the chest and thigh muscles. Number of essential amino–acids in chicken pectoral muscle in the 2 nd experimental group also increased slightly, and in the3 rd – reduced slightly, but in the femoral muscles they decreased slightly in the 2 nd and 3 rd experimental groups compared to control group.It is proved that the use of nanotracelement feed additive «Mikrostymulin» in a dose of 1 ml / dm³ of water improves the quality and increases the biological value of meat.

After insulin binding, insulin receptors (IR) phosphorylate the insulin receptor substrate 1 (IRS-1) on specific motifs and thereby initiate insulin action. The interaction between IR and IRS-1 and their expression were studied in vivo in two target tissues (muscle and liver) in chickens, a species that is insulin resistant. To induce extreme changes in plasma insulin levels, chickens were subjected to three different nutritional states (ad libitum fed, fasted for 48 h, and refed for 30 min after 48-h fast). Liver membrane IR number was significantly increased in fasted compared with fed chickens. This upregulation of IR number was concomitant with the an enhanced expression of IR mRNA as determined by reverse transcription-polymerase chain reaction. In leg muscle, IR mRNA was not altered by the nutritional state. Using specific antibodies directed toward human IR, anti-phosphotyrosines, or mouse IRS-1, we demonstrated that IR and IRS-1 are associated in vivo in liver and muscles. Tyrosine phosphorylation of liver IR and IRS-1 were significantly decreased by prolonged fasting and restored by 30-min refeeding. These alterations were not observed in muscle. Fasting increased IRS-1 mRNA expression in liver but not in muscle. These results are the first evidence showing that chicken liver and muscle express IRS-1. Therefore, the chicken insulin resistance is not accounted for by the lack of IRS-1. The differences observed for the regulation of IR and IRS-1 messengers and phosphorylation between liver and muscle in response to alterations of the nutritional state remain to be explained.

The differentiation of melanocytes from multipotential neural crest cells is an ideal system for studying the processes underlying lineage determination in development. Tyrosinase is a key enzyme in melanin biosynthesis and the activation of the tyrosinase gene is characteristic of differentiated melanocytes. In order to study the mechanisms underlying activation of melanocyte-specific genes during differentiation in chick embryos, a chicken genomic DNA library was screened for tyrosinase-encoding sequences using a mouse tyrosinase cDNA probe. Two identical hybridising clones were identified. Restriction mapping and sequencing revealed that both clones contained a 4.3 kb genomic DNA fragment, CTYR4.3, that included 2125 nt of the 5' flanking region, the first exon and part of the first intron of the chicken tyrosinase gene. The 5' flanking sequence of CTYR4.3, which is the most extensive to be reported for a lower vertebrate tyrosinase gene to date, was analysed further using computer-aided homology searches and primer extension. Alignment of the promoter sequences of CTYR4.3 with those of the human, mouse, quail and turtle tyrosinase genes revealed two evolutionary conserved regions. These regions may be functionally significant as they contain regulatory elements previously reported to play a role in melanocyte-specific expression of the tyrosinase gene in mammals. These include an initiator region and an associated SP1-binding site, the M-box and an upstream enhancer element, TDE. In addition, other potential transcription factor binding motifs were identified, including an AP-1-binding site, a UV-responsive element and glucocorticoid-responsive elements. Although several TATA box motifs were identified, they were situated more than 200 bp upstream of the transcription start sites mapped by primer extension analysis and therefore are unlikely to function as TFIID-binding sites. Transcription initiation appears to occur at heterogeneous start sites, and given the absence of a functional TATA box, may be mediated via the conserved initiator region and SP1-binding site. To test the ability of the 5' flanking sequence of CTYR4.3 to drive transcription and to begin to assess the functional significance of the various conserved elements, transient transfection assays were carried out. Constructs were generated in which 2.1 kb, 1.1 kb, 0.5 kb and 0.2 kb fragments of the 5' flanking sequence were linked to a luciferase reporter gene. These constructs were introduced into cultures of chicken retinal pigment epithelial cells (RPE), immortalised quail neural crest cells (MQTNC), and human liver cells (Hep G2) by calcium phosphate-mediated transfection. Transfections with all constructs resulted in luciferase activities significantly greater than those that were observed with the promoterless luciferase construct, thus confirming that the 5' flanking sequence of CTYR4.3 does possess promoter activity. However, the level of expression from the various constructs differed markedly in the different cell types. In the tyrosinase-negative Hep G2 cells, low levels of expression were observed with all constructs. In the tyrosinase-positive RPE cells, a high level of luciferase activity was obtained specifically with the smallest (0.2 kb) promoter construct. Since the 0.2 kb promoter fragment does not include the conserved initiator region, SP1-binding site, or M-box, the role of these elements in tissue-specific transcription initiation of the chicken tyrosinase gene is now questionable. These results suggest the existence of transcription regulatory mechanisms that are unique to avians and possibly other lower vertebrates. In contrast to the results obtained for RPE cells, the highest luciferase activity was obtained with the full length 2.1 kb promoter construct in the immortalised quail neural crest-derived cells. These results may have developmental significance since they suggest that the chicken tyrosinase gene promoter is regulated differently in RPE cells and neural crest-derived cells.

Melanin, the pigment found in the eyes and coats of vertebrates, is synthesised by two main cell types: melanocytes and retinal pigment epithelial (RPE) cells. These two cell populations. which arise from distinct embryological origins, differ with respect to the rate at which they produce melanin and the ways in which they respond to melanogenic stimuli. Tyrosinase is the rate-limiting enzyme in the melanin synthesis pathway, and the regulation of tyrosinase gene expression in mammalian melanocytes has been extensively studied. In contrast, regulation oftyrosinase gene expression in RPE cells has received little attention. In the present study, the chicken tyrosinase gene promoter was used to investigate possible differences in the regulation of tyrosinase expression in melanocytes and RPE cells. Transient transfection experiments were carried out in which reporter constructs, consisting oftyrosinase promoter deletion fragments linked to a luciferase reporter gene, were introduced into melanocytes, RPE cells and a non-pigmented cell line. The following results were obtained. (1) Reporter expression obtained with the longest (2.1kb) promoter fragment was significantly higher in pigmented cells (both melanocytes and RPE cells) than in non-pigmented cells, demonstrating the pigment cell-specificity of the chicken tyrosinase promoter. (2) Reporter expression obtained with a 0.5kb promoter fragment, containing conserved core regulatory elements ( an lnr, M-box and Sp 1 binding site), was higher in melanocytes than in RPE cells. This result suggests that the core elements are sufficient for high levels of tyrosinase expression in melanocytes, but not in RPE cells. (3) Reporter activity obtained with a 248bp promoter fragment containing no elements implicated in initiating tyrosinase transcription was strikingly high in RPE cells, and very low in melanocytes. This result suggested the presence of RPE-specific regulatory elements in the tyrosinase promoter. To determine which portion of the 248bp promoter fragment contained the element(s) responsible for this RPE-specific activity, three additional deletion constructs were cloned. Transient transfection experiments with these new constructs revealed that the RPE-effect observed with the 248bp construct was a serendipitous / unfortunate experimental artefact brought about by the ligation of 203bp of proximal promoter with 45bp of distal promoter. Examination of the sequence generated by this ligation revealed the presence of an element similar to PCE-1, an element recently implicated in RPEspecific gene regulation. Factors present in RPE cells, but not in melanocytes, may bind to this element to initiate transcription. Further investigation of the mechanism mediating this RPEspecific effect could contribute to the understanding ofRPE-specific gene regulation. In conclusion, the results of the present study strongly suggest that expression of the chicken tyrosinase gene is regulated differently in RPE cells and melanocytes, and begin to identify regions in the chicken tyrosinase promoter that might be responsible for mediating such differences.

Very little is known about the molecular and genetic mechanisms controlling pigmentation within the bird kingdom. The aim therefore, of this study was to contribute towards the understanding of the genetic regulation of avian pigmentation by the cloning and characterisation of the chicken Tyrosinase-related protein (TRP) gene family. To accomplish this goal, neural crest cells from 500 black chick embryos were cultured under conditions supportive of melanocyte differentiation and proliferation. Using RNA extracted from these pigmented melanocyte cultures, a novel embryonic chick cDNA library was constructed. Screening of this library for chicken equivalents of the mammalian TRP gene family yielded more than 200 cDNA clones. After sequencing, three of these clones, 88.3, pcTRP- 1.6 and pcTRP -2. 10, were found to encode chicken Tyrosinase (Tyr), Tyrosinase-related protein-1 (Tyrp1) and Tyrosinase-related protein-2 (Tyrp2), respectively. In addition, a chicken Microphthalmia (Mi) cDNA clone (M156) was isolated using a mouse Mi cDNA probe. Comparative analyses revealed that chicken Tyr, Tyrp1 and Tyrp2 share approximately 68%, 72% and 70% amino acid sequence identity with their vertebrate orthologues. Northern blot hybridisation analysis demonstrated that the chicken TRPs are expressed in RNA from cultured retinal pigment epithelial (RPE) cells as well as in whole eye RNA. The major transcript sizes for the chicken Tyr, Tyrp1 and Tyrp2 genes are 2.5 kb, 2.3 kb and 3.5 kb, respectively. In situ hybridisation studies confirmed that both chicken Tyr and Tyrp2 genes are expressed in a pigment cell-specific fashion with signals detected in both the skin and RPE of chick embryos. Genomic Southern blot hybridisation analyses strongly suggested that all three chicken TRP genes contain several introns that are likely to be conserved within the vertebrate TRP gene family. Furthermore, the chick Tyr, Tyrp1 and Tyrp2 genes were found to span approximately 5-19 kb, 5-11 kb and 15-30 kb, respectively of the chicken genome. Comparisons between a black and white chick breed at the Tyr and Tyrp1 loci revealed no gross rearrangements at either of these loci. However, 1-2 kb alterations were observed between the same breeds at the Tyrp2 locus. The nature and significance of this alteration is not known. The cloning of the chicken Tyr, Tyrp1 and Tyrp2 cDNAs constitutes the first molecular cloning and characterisation of any avian TRP gene family. Taken together therefore, this study contributes towards the further understanding of the molecular mechanisms regulating pigmentation as well as the evolution of gene families.