Effects of nonglycosylated and glycosylated prolactin on basal and gonadotropin-stimulated steroidogenesis in chicken ovarian follicles

In galliformes, the circulating isoform of prolactin (PRL) significantly changes during different reproductive states. However, the role of the major isoform (glycosylated PRL [G-PRL]) in ovarian steroidogenesis is unknown. The present study aimed to compare the effects of nonglycosylated (NG-) and G-PRL on basal and gonadotropin-stimulated estradiol (E₂) and progesterone (P₄) production in granulosa cells or follicular walls of chicken of different size class follicles. In the initial experiment, granulosa cells of preovulatory F3-F1 and prehierarchical 6- to 8-mm follicles were incubated for 24 h with different concentrations of NG- or G-PRL (0, 1, 10, 100, or 1,000 ng/mL). In the subsequent experiments, these categorized granulosa cells and follicular walls of prehierarchical 4-6, 2-4, and <2-mm follicles were incubated for 24 h in the absence and presence of 10-ng/mL FSH or LH, or in combination with different concentrations of NG- or G-PRL (10, 100, or 1,000 ng/mL). We observed that lower levels of NG-PRL induced (P < 0.05) E₂ and P₄ secretion in granulosa cells of either preovulatory or prehierarchical follicles, but at higher levels, this effect was reduced. In contrast, G-PRL promoted (P < 0.05) basal E₂ and P₄ secretion in preovulatory granulosa cells but was inhibitory (P < 0.05) in prehierarchical granulosa cells. Results obtained by real-time quantitative PCR (qPCR) demonstrated that these effects were mediated through modulation of the expression of StAR, CYP11A1, CYP19A1, and 3β-HSD. Furthermore, G-PRL was less potent than NG-PRL in inhibiting FSH- or LH-stimulated E₂ and P₄ production in granulosa cells of preovulatory follicles, whereas NG-PRL enhanced (P < 0.05) but G-PRL reduced (P < 0.05) FSH-induced P₄ production in those of prehierarchical follicles. In follicular walls from each group of prehierarchical 4-6, 2-4, and <2-mm follicles, NG- and G-PRL had both stimulatory and inhibitory influences on the actions of FSH on E₂ and P₄ secretion, but both suppressed (P < 0.05) LH-induced E₂ and P₄ secretion except for the synergistic effects of LH and G-PRL on P₄ secretion by follicular walls of the follicles of 4-6 mm. Taken together, these results suggest that both NG- and G-PRL are biologically active in regulating basal and gonadotropin-stimulated E₂ and P₄ production in chicken ovarian follicles. However, their effects are different depending on the concentration, the type of gonadotropin (FSH or LH), and the stage of follicle development.

423 PRODUCTION OF CLONED PIGS EXPRESSING APOLIPOPROTEIN E-SPECIFIC SMALL HAIRPIN (shRNA)

Apolipoprotein E (apo E) is a known risk factor for developing premature atherosclerosis and Alzheimer’s syndrome. The aim of this study was to create a pig model with reduced apo E levels using RNA interference (RNAi) and somatic cell nuclear transfer (SCNT) technologies. Three synthetic small interfering RNA targeting the porcine apo E mRNA were designed, and the knockdown efficiency was assessed in cultured porcine granulosa cells by real-time PCR. The observed apo E knockdown efficiency ranged from 45 to 82% compared with control cells, indicating the targeted degradation of apoE mRNA.A small hairpin RNA (shRNA) expressing vector was constructed in PRNAT.U6.Neo (Genscript Corp., Piscataway, NJ, USA) based on the most effective apo E RNAi sequence under the control of polymerase III (U6) promoter, and then introduced into fetal porcine fibroblast cells. Clones were selected by neomycin treatment and green fluorescent protein (GFP) expression. SCNT was performed using IVM oocytes collected from prepubertal gilts. Oocyte maturation and activation and embryo culture were performed as previously described (Nascimento et al. 2009 Reprod. Domest. Anim. in press). Embryos were cultured in vitro for 5 to 6 days, briefly exposed to fluorescent light to confirm GFP expression, and then surgically transferred into the uterus of recipient gilts. The recipient gilts were synchronized by daily oral administration of altrenogest (20 mg day-1; Regu-Mate®, Intervet, Millsboro, MD, USA) for 12 or 13 days, followed by 1000 IU of eCG injected in the last day of altrenogest treatment and 500 IU of hCG 72 h later. Pregnancy diagnosis was performed by ultrasonography at Day 20 to 25 after embryo transfer, and parturition was induced by injecting PGF2? (10 mg of dinoprost tromethamine; Lutalyse®, Pfizer Canada Inc., Montreal, QC, Canada) at Day 115 of pregnancy. Rates of cleavage (74.7%) and development to the blastocyst stage (37.2%) were comparable with that of embryos reconstructed with nontransfected cells from the same cell line. A total of 309 embryos were transferred to 5 recipients, of which 3 became pregnant and farrowed. Seven live and 1 stillborn piglets were delivered naturally. The presence of the introduced plasmid and the expression of the GFP transgene tag were confirmed by PCR in placental and umbilical tissues of all the piglets. Six cloned pigs have survived after weaning and exhibit no obvious morphological defects. The status of apo E gene expression is currently under investigation. Supported by a NSERC Discovery Grant to VB.

Association of a marker in the vitamin D receptor gene with Marek's disease resistance in poultry

Vitamin D is an important immunomodulator that mediates its effect via a nuclear receptor. In this study, we analyzed 3 uncorrelated genetic markers (tag single nucleotide polymorphisms) in the vitamin D receptor gene for association with Marek's disease (MD) resistance. The database consisted of 400 commercial White Leghorn chickens that had been vaccinated with herpes turkey virus and challenged by intraperitoneal injection of the virulent MD virus RB1B. Viral titers in feather tips were determined at weekly intervals for 8 wk, mortality was recorded, and necropsy analyses preformed on all chickens. The 3 genotypes defined by 1 of the markers were associated with significant differences in the viral load (integration of the viral titer over time; P = 3 x 10(-4)). The effect was additive, with the 2 homozygotes differing by a factor of 2. The ranking of the genotypes by viral load, frequency of MD lesions, mortality, and bursal atrophy were consistent. There was no effect on the tissue distribution of MD lesions. The degree of MD resistance in the 9 genotypes defined by the 3 tag single nucleotide polymorphisms was proportional to the frequency of major histocompatibility complex class II-positive peripheral blood leukocytes that had been previously measured in uninfected chickens in a different database.

Expression patterns of the prolactin receptor gene in chicken lymphoid tissues during embryogenesis and posthatch period

Prolactin (PRL) is a pituitary hormone with multiple homeostatic roles among vertebrates. Although it has mainly been studied in relation to its role during the initiation and maintenance of incubation behavior in avian species, it has also been shown to act on the immune system. In this study, levels of PRL receptor (PRLR) mRNA were quantified by real-time PCR, and tissue expression was localized by in situ hybridization in primary and secondary lymphoid organs. Prolactin receptor was shown to be expressed in the bursa follicles, thymus lobules, and splenic pulp at all stages of development examined. Levels of PRLR expression were consistently higher in the bursa of Fabricius when compared with other lymphoid organs, suggesting that PRL acts primarily on bursal development. Furthermore, levels of PRLR mRNA appeared to fluctuate during embryogenesis, with a significant increase observed at embryonic day 19 in the bursa, at 7 d of age in the thymus, and on hatching day in the spleen. Thus, PRL might play an important role during the development of the immune system in chickens.

Ontogenesis of the Expression of Prolactin Receptor Messenger Ribonucleic Acid During Late Embryogenesis in Turkeys and Chickens

Changes in circulating levels of prolactin (PRL) and tissue content of PRL receptor (PRLR) messenger RNA (mRNA) in the liver, pancreas, kidney, and gonads (testis/ovary) were measured in turkey and chicken embryos from embryonic day (ED) 21 or ED15, respectively, to 1 d after hatch by real-time PCR. There were no differences between the sexes in chickens or turkeys. Both species had very similar patterns of PRL release and expression of PRLR mRNA, and no major differences were observed between turkey or chicken embryos. Plasma levels of PRL increased from low levels during the last week of embryonic development and were at significantly higher levels (about 4-fold) by 1 d after hatch. Similarly, in all tissues the content of PRLR mRNA was minimal at the outset and increased to reach maxima about the time of hatch. In both species, the highest levels of transcript were observed in the kidney followed by the gonad, liver, and pancreas. The tissue content of PRLR was correlated (0.6 to 0.8 dependent on the tissue) to circulating levels of PRL, which suggested that PRL may be associated with an increase in its receptor number around the time of hatch. Because levels of PRL and tissue content of PRLR mRNA increased around the time of hatch, this suggests that these tissues may be targets for PRL and may be involved in the physiologic changes occurring in embryos around the time of hatching.

Development of a real-time (Q) PCR assay to measure variation in expression of prolactin receptor mRNA in the hypothalamus and pituitary gland during late embryogenesis in turkeys and chickens

Changes in levels of PRLR mRNA in the pituitary gland and hypothalamus of chickens and turkeys from embryonic day (ED) 15 and ED21 to 1 day post-hatch, respectively, were measured by real-time PCR. In both species, PRLR mRNA increased from low levels during the last week of ED to reach maxima at the peri-hatch period. Similarly, circulating levels of PRL also increased during this interval and were highly correlated with levels of the PRLR mRNA in both the pituitary gland and hypothalamus. This suggests that PRL was up-regulating its receptor. In support of this, stimulation of the turkey pituitary gland with VIP on ED24 resulted in a 4- and 3-fold increase in PRL and PRLR, respectively. Since VIP had no direct effect on the levels of PRLR transcript in the hypothalamus, it is likely that VIP is acting indirectly through increased PRL to up-regulate the number of receptors.

Ornithine decarboxylase: haplotype structure and trait associations in White Leghorn chickens

Sequence analysis of 4,230 bp of the 3' end of the ornithine decarboxylase gene of 20 chickens from a noninbred White Leghorn strain revealed a total of 62 polymorphisms. Of these 61% were transitions, 24% were transversions, and 16% were deletions or insertions. Despite the high number of polymorphisms, only 3 haplotypes were present among the 40 alleles analyzed. Based on the genetic distances between haplotypes they segregated early during domestication of the chicken. Ornithine decarboxylase is a pivotal enzyme in regulating the synthesis of polyamines, cations that are important regulators of cell division, differentiation, and apoptosis. Variants of ornithine decarboxylase are, therefore, expected to affect many different traits. Association analyses between genotypes and the major egg production traits in female chickens of the same strain revealed significant effects on the onset of sexual maturity, BW at sexual maturity, eggshell thickness (a measure of calcium deposition), and residual feed consumption (a measure of the metabolic rate). Further, comparisons of the genotypes indicated that the 3 haplotypes differ in their phenotypic properties. Our results show that variations in a gene that is ubiquitously expressed in all cells of an organism may nevertheless contribute to distinct phenotypic properties of the organism as a whole.

Alleles of cytosolic phosphoenolpyruvate carboxykinase (PEPCK): trait association and interaction with mitochondrial PEPCK in a strain of White Leghorn chickens

White Leghorn chickens from a nonselected closed population were typed for two RFLP located in the 3' end of the gene coding for cytosolic phosphoenol-pyruvate carboxykinase (PEPCK-C), a major control gene of gluconeogenesis. The two RFLP gave rise to three alleles (or haplotype classes), thus defining six genotypes. Feed efficiency (FE) and residual feed consumption (RFC) varied significantly among the genotypes and indicated that all three haplotypes differed from each other. FE is the ratio between feed consumption and egg mass produced, whereas RFC is the feed consumption after correcting for BW and egg production. There was significant interaction between PEPCK-C genotypes and mitochondrial PEPCK (PEPCK-M) genotypes defined by a single RFLP. The latter enzyme catalyzes the same reaction but is located in the matrix of the mitochondria and is encoded by a different nuclear gene. Interaction was evident from an analysis of the egg weight and egg specific gravity in the early phase of egg laying. It was such that the effect of the variation in one gene depended entirely on the genotype of the second gene. In addition, significant genotypic disequilibria were observed between two of the three alleles of PEPCK-C and between one of these alleles and the two RFLP alleles of PEPCK-M. This finding indicates variations of genes in the gluconeogenesis pathway may affect feed utilization and egg production traits, as well as reproductive fitness.

The dynamics of the genotype-phenotype association

The integrity of an organism is maintained by networks of interacting genes. Such networks predict that genetic variants affect phenotypes in a nonadditive fashion. That is, the effect of an allelic variation in one gene is dependent on the variations in other genes. We summarize the analyses of a series of genes in a White Leghorn strain that support the existence of such gene networks: 1) genes are pleiotropic, 2) genes affect trait correlations, 3) genes affect trait distributions in a nonadditive fashion, 4) genes interact with each other, and 5) genes are at linkage disequilibrium, even when located on different chromosomes. The latter observation indicated that certain gene combinations lead to reduced reproductive fitness. Each candidate genes we analyzed segregated for multiple alleles that affected production traits. This finding was surprising, even for a strain with a large effective population size. The shapes of trait distributions appear to be a better descriptor of gene effects than measures of central tendency. Despite this complexity, it is feasible to conduct DNA-based selection, starting from any of several different genes that affect a trait. Gene networks may be altered in many different ways to improve a particular phenotype, but networks may differ in their effects on other traits.

Genetic variability of the cytosolic phosphoenolpyruvate carboxykinase gene in white leghorn chickens

Phosphoenolpyruvate carboxykinase (PEPCK) is a key regulatory enzyme of gluconeogenesis. Genetic variations in this gene may therefore affect a wide variety of traits, including tumor growth that is heavily dependent on glucose metabolism. We have previously shown the gene coding for the mitochondrial form of PEPCK (PEPCK-M) segregates for markers that are collected with resistance to Marek's disease. In this communication we analyze the genetic variability of PEPCK-C, the gene which codes for the cytosolic form of PEPCK. A 3,792-bp segment of 5'-region of the PEPCK-C gene (position -1723 to 2069) was sequenced in four individuals from eight different strains of White Leghorn chickens (a total of 64 genomes). A total of 19 single nucleotide polymorphisms (SNP) were identified. Neither deletions nor insertions were present. The most frequent SNP were transitions (79%), and in most cases the ancestral allele coincided with CpG dinucleotides (10-fold excess after correcting for dinucleotide frequencies). A gene tree was constructed assuming maximal parsimony. It led to the delineation of 6 haplotypes (combination of alleles). Two of the SNP coincided with RFLP detectable by the restriction enzymes AciI and BstEII, respectively. Based on this analysis we can now identify individuals with the evolutionary most distant PEPCK-C haplotypes, establish strains of these haplotypes, and analyze trait associations and epistasis with other genes.

Molecular cloning of chicken vasoactive intestinal polypeptide receptor complementary DNA, tissue distribution and chromosomal localization

Chicken vasoactive intestinal polypeptide receptor (VIPR) cDNA was cloned by the reverse transcription-polymerase chain reaction method using primers designed on the basis of other species of VIPR cDNA. The cDNA obtained was sequenced by the dideoxy-mediated chain-termination method. Of the 2227 nucleotides that were sequenced, 84, 855, and 1338 bases represent the 5'-untranslated region (UTR), the 3'-UTR, and the open reading frame that predicts a peptide of 446 amino acids. The cDNA of the chicken VIPR shows 65% and 60% homologies to human cDNA of VIP1 and VIP2 receptors, respectively. The clone had the expected similarity to highly conserved features of the other G protein-coupled receptors (GPCRs) such as six cysteine residues that are functionally important in the VIPR subfamily. In addition, the seven potential membrane-spanning domains characteristic of the family B group III GPCR superfamily and highly conserved motif within the third cellular loop between transmembrane regions 5 and 6. Northern blot hybridization analysis in this study indicated mRNA expression of VIPRs in the various tissues of the chicken. Strong signal was detected in the brain and anterior pituitary gland. High levels of VIPR mRNA in the brain was consistent with VIP-binding experiments and with the function of VIP in the brain as a neuroendocrine factor or neurotransmitter. Expression of VIPR was detected in the anterior pituitary gland of chick embryos. The expression of VIPR mRNA in the chick anterior pituitary gland may indicate a regulatory function of VIP on prolactin (PRL) production or PRL cell proliferation during embryogenesis. Chicken VIPR shows high homology with mammalian type I VIPR but, in some part, possesses similarity of amino acid sequence. Expression of VIPR in various tissues supports diverse functions for VIP in the chicken.

Comparative FISH mapping on Z chromosomes of chicken and Japanese quail

Using direct R-banding fluorescence in situ hybridization, we assigned five functional genes-growth hormone receptor (GHR), prolactin receptor (PRLR), spleen tyrosine kinase (SYK), aldolase B (ALDOB), and muscle skeletal receptor tyrosine kinase (MUSK)-to the chicken Z chromosome. SYK and MUSK were newly localized to the chicken Z chromosome in this study. GHR and PRLR were situated close to each other on the short arm of the chicken Z chromosome, as are their counterparts on human chromosome 5. SYK, MUSK, and ALDOB, which have been mapped to human chromosome 9, were localized to the long arm of the chicken Z chromosome. Thus, the present results indicate the presence of conserved synteny between the chicken Z chromosome and human chromosomes 5 and 9. Using the same method, four of the genes (GHR, PRLR, ALDOB, and MUSK) were assigned to the Japanese quail Z chromosome. The locations of these four Z-linked genes were conserved between chicken and Japanese quail. The results support the notion that the avian Z chromosome and the mammalian X chromosome did not evolve from a common ancestral linkage group.

Cytogenetic mapping of 31 functional genes on chicken chromosomes by direct R-banding FISH

Using direct R-banding fluorescence in situ hybridization, we determined the location of 31 functional genes on chicken chromosomes. Replication R-banded chromosomes were obtained by synchronizing splenocyte cultures with excessive thymidine, followed by BrdU treatment. Thirty-one functional genes were directly localized to banded chicken chromosomes using genomic DNA and cDNA fragments as probes. The possibility of conserved linkage homology between chicken and human chromosomes was demonstrated for seven chicken chromosome regions (1p, 1q, 2q, 4p, 4q, and 5q).

Trait association of a genetic marker near the IGF-I gene in egg-laying chickens

The insulin-like growth factor I (IGF-I) gene was screened for genetic variants associated with trait means and trait correlations. Analysis of an unselected randomly mated White Leghorn population revealed a PstI restriction fragment length polymorphism (RFLP) in the 5' region of the gene which segregated at a frequency of 0.83 for the PstI(+) allele (presence of a PstI restriction site). A comparison of the three genotypic classes revealed that the PstI(-/-) genotype was associated with a significantly lower egg weight measured in three different time periods, while the PstI(+/-) genotype was significantly associated with a higher eggshell weight estimated from the egg weight and egg specific gravity. For eggshell weight, the effect was age dependent and significant only for the last two periods of egg laying. No genotype associations were found for body weight, feed consumption, and egg laying rates. Significant dominance effects of the IGF-I genotype were observed for two of the egg weight measurements and three of the eggshell weight estimates. Partial correlation analyses in the two most frequent genotypic classes, PstI(+/+) and PstI(+/-), revealed the presence of a regulatory loop between feed consumption, body weight, egg weight, and the rate of egg laying. Several aspects of this regulatory loop were different between the two genotypic classes. In particular, for the PstI(+/+) genotype, feed consumption was positively associated with egg weight, while there was no significant association for the PstI(+/-) genotype. Further, the degree of association of body weight with egg weight decreased with age in the genotypic class PstI(+/-), while it was constant for the PstI(+/+) genotype. The results indicated that the marker in the IGF-I gene was not only associated with changes in some trait means, but also with changes in the stability of the coordination between feed intake, body weight, and egg production traits.

Quantification of prolactin messenger ribonucleic acid, pituitary content and plasma levels of prolactin, and detection of immunoreactive isoforms of prolactin in pituitaries from turkey embryos during ontogeny

The content of prolactin mRNA as well as total prolactin content and type of isoforms of prolactin were measured in single pituitary glands from turkey embryos and poults. Levels of mRNA and pituitary content of prolactin remained low until 5 days before hatching, while plasma concentrations remained low until 2 days before hatching. Levels of prolactin mRNA then increased until the day of hatch, stayed stable during the 3 first days of age, and significantly increased until 2 wk of age. Similar changes were observed in pituitary content and plasma levels of prolactin. Two immunoreactive bands of apparent molecular masses of 24 and 27 kDa, corresponding to the nonglycosylated and glycosylated form of prolactin, respectively, were visualized on Western blots. In pituitary glands from embryos at 22 days of incubation, 31.5% of the protein was glycosylated, whereas in embryos at 27 days of incubation and poults at 1 and 7 days of age, 48.6%, 48.0%, and 56. 0% of prolactin was glycosylated, respectively. The results indicate that the increases in the synthesis and the release of prolactin occur mainly around and after the time of hatching in the turkey embryo. Higher percentages of glycosylated isoforms were associated with increasing levels of total prolactin in the pituitary gland. Thus, the synthesis of prolactin and its post-translational modifications may be important factors involved in the physiologic changes occurring around the time of hatching.

In vitro release of isoforms of prolactin from pituitary glands of turkey hens at different physiological stages

To study the in vitro release of PRL isoforms, anterior pituitary glands from medium white turkeys at various physiological stages were stimulated by cVIP in a perifusion system. Pituitaries were cut into hemi-pituitaries after collection and placed into separate perifusion chambers. Medium (M199) was continuously perifused through the system and pituitaries were stimulated with cVIP (10(-7) M). Total PRL content was monitored by RIA and, the ratio of immunoreactive PRL isoforms in the perifusate was estimated by Western blotting. After exposure to X-ray film for autoradiography, the relative intensity of the bands was analyzed by densitometry. All the perifused pituitaries responded to cVIP stimulation by increasing the release of PRL. Two immunoreactive bands with relative molecular weights of 24 and 27 kDa were detected by Western blotting. The immunoreactive band corresponding to the glycosylated isoforms of PRL (27 kDa) was predominant in samples from egg-laying and incubating hens and the band corresponding to the nonglycosylated isoform (24 kDa) was predominant in samples from out-of-lay and molting stages. No changes in the ratio of isoform released were detected during cVIP stimulation. Our data clearly show that glycosylated and nonglycosylated PRL isoforms are released by the pituitary gland in vitro in the same relative proportion that was previously observed in pituitary extracts and thus are likely to reflect the secreted forms of PRL in the blood during various physiological stages. In addition, the PRL-releasing activity of VIP does not affect the ratio of isoforms secreted by the pituitary gland in vitro.

Changes in levels of immunoreactive prolactin isoforms during a reproductive cycle in turkey hens

Changes in the ratio between immunoreactive isoforms of prolactin using Western blotting and in the total prolactin content using radioimmunoassay were measured in pituitary glands from turkey hens at different physiological stages. The type of glycosylation (N- or O-linked carbohydrates) was determined using endoglycosidase digestion (N-glycosidase F, O-glycosidase, and neuraminidase). Low levels of prolactin were observed in pituitary glands from sexually immature, out-of-lay, and molting hens. Higher levels were present during the egg-laying period and the highest levels were detected in hens which expressed incubation behavior. Two immunoreactive bands of apparent molecular weights of 24 and 27 kDa were visualized on Western blots, corresponding to the nonglycosylated and glycosylated forms of prolactin, respectively. In pituitary glands from incubating turkey hens, about 70% of the prolactin was glycosylated (27-kDa isoforms), whereas about 60% was glycosylated in immature and in hens during the first egg-laying period. In pituitaries from out-of-lay and molting hens the percentage of glycosylated prolactin was 38 and 33%, respectively. Thus, higher percentages of glycosylated isoforms (27 kDa) were associated with high levels of total prolactin and lower percentages were associated with low levels of prolactin content in the pituitary gland. Digestion of the isoforms with N-glycosidase F resulted in a single band with an apparent molecular weight of 24 kDa. Partial deglycosylation was achieved using neuraminidase, whereas digestion with O-glycosidase had no apparent effect on the isoforms. Thus it appears that the glycosylated isoforms of prolactin have N-linked carbohydrates containing sialic acid.

Markers within the regulatory region of the growth hormone receptor gene and their association with milk-related traits in Holsteins

We studied sequence variations in the regulatory region of the bovine growth hormone receptor gene. A polymerase chain reaction (PCR)-based method for detecting AluI, AccI, and StuI restriction fragment length polymorphisms (RFLPs) in the 5' flanking region of the bovine growth hormone receptor gene was developed and tested for association with milk-related traits in Holstein bulls. Allele frequencies of the polymorphisms in two groups of Holstein progeny-tested bulls born from 1950 to 1970 and in the 1980s, respectively, were estimated. The allele frequency of the AluI(-) allele was 0.63 and 0.42 in the bulls from 1950 to 1970 and in the 1980s, respectively. The frequency of the StuI(-) allele was 0.14 and 0.07 in the two respective bull groups. Allele frequency for AccI(-) allele was about 0.22 in both bull groups. The differences in allele frequencies for the AluI polymorphism in the two bull groups were significantly different (P < or = .005). The AluI(+/+) bulls had a higher estimated breeding value (EBV) for fat (P < or = .016) than AluI(-/-) bulls. The average effect of allele substitution for the AluI polymorphism was +/- 8 for fat EBV. The AluI polymorphism could be further evaluated for use in marker-assisted selection in dairy cattle.

Mitochondrial PEPCK: a highly polymorphic gene with alleles co-selected with Marek's disease resistance in chickens

The gene coding for the mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M), a pivotal component in gluconeogenesis from lactate via the Cori cycle, was highly polymorphic in strains of egg-type chickens (White Leghorn) of different origins. Based on MspI restriction fragment polymorphisms a total of seven alleles could be distinguished. The allele frequencies were determined in six pairs of strains derived from different genetic base populations. Each pair consisted of two strains which differed in their susceptibility to Marek's disease (MD), a virus-induced neoplastic disease. The frequency of the most common haplotype (M2) was consistently higher in the susceptible strains than in the corresponding resistant strains (P < 0.05, Wilcoxon signed-ranks test), indicating that the observed differences were not due to random genetic drift. This result suggests that PEPCK-M may be a candidate gene which contains genetic variants affecting MD susceptibility. Variations in gluconeogenesis may affect the interplay between proliferation of neoplasia and host metabolism.

Prevention of incubation behavior expression in turkey hens by active immunization against prolactin

The consequences of active immunization against prolactin on expression of incubation, reproductive performance and hormonal profiles were evaluated in turkey hens. Hens were injected weekly for 4 wk starting 8 wk before being submitted to a stimulatory photoperiod and 3 times thereafter at intervals of 4 to 5 wk. The hens were injected i.d. with 0.5 mL of a mixture diluted half in Freund's adjuvant. The mixture was prediluted in .9% saline and contained 100 micrograms of a fusion protein (GST-tPRL), GST, oPRL or vehicle. The results indicate that active immunizations with GST-tPRL or oPRL both induce production of specific prolactin antibodies. The onset of egg production was unaffected but higher egg production was observed for the GST-tPRL immunized hens. No GST-tPRL immunized hens expressed incubation behavior, whereas 20 to 30% of hens in the other experimental groups did so. Apparent hyperprolactinemia was detected by RIA for the GST-tPRL immunized groups starting before photostimulation and lasting until Week 10 of egg production but not in other groups. No significant differences were observed in either plasma LH or estradiol concentrations of immunized and nonimmunized turkey hens. In conclusion, both GST-tPRL or oPRL induced the production of antibodies against prolactin in turkey hens. However, only active immunization using GST-tPRL induced higher antibody titers as well as full prevention of incubation behavior expression. Such a pharmacological approach is of great practical interest, although its uses need to be carefully evaluated under commercial conditions.

Analysis of the β-lactoglobulin locus using the grand-daughter design in the Canadian Holstein population

A total of 185 informative sons from nine heterozygous grandsires were used to study the associations of alleles A and B of the β-LG locus and milk production using the granddaughter design. The average informativeness of the β-LG locus for the nine heterozygous grandsires was 61%. The β-LG locus was found to be significantly associated with milk protein percentage (P ≤ 0.05) across families and (P ≤ 0.01) in one family. The A allele was associated with higher protein percentage EBV (0.096%) than the B allele in that family. There was no association between β-LG and other production traits (milk, fat and protein yields and, fat and percentages). The β-LG locus has a potential use in marker-assisted selection. However, since the association between markers and a given trait is not found in all families, within-family marker selection might be more appropriate due to linkage disequilibrium. Key words: β-lactoglobulin, Canadian Holstein, milk production traits, granddaughter design

A genetic marker in the growth hormone receptor gene associated with body weight in chickens

A genomic clone spanning 16 kb of the GH receptor gene was mapped and used as a probe for identifying restriction fragment length polymorphisms (RFLPs) in chickens. Several strains of meat-type and egg laying chickens were found to segregate for an HindIII RFLP located in the intron preceding exon 4. The polymorphic HindIII site overlapped with a poly(A) signal. Association of the HindIII RFLP with traits was analyzed in a random-bred White Leghorn strain in three generations using either selective or random genotyping. Both methods revealed significant association of the HindIII+ allele (presence of the poly(A) signal) with an increased juvenile body weight (130 days of age). In two meat-type strains divergently selected for size of the abdominal fat pad, the HindIII+ allele was coselected with leanness. The results indicate the presence of a genetic variant of the GH receptor gene which affects growth and abdominal fat deposition and which is relatively frequent in egg laying as well as in meat-type chickens.

Evidence for a genetic variation in the mitochondrial genome affecting traits in White Leghorn chickens

A mitochondrial Mspl RFLP which was coselected with Marek's disease (MD) resistance in White Leghorn chickens was mapped to the NADH subunit IV. The RFLP was due to a transition, resulting in the change of the low-usage threonine triplet ACT (Mspl- allele) to the high usage triplet ACC (Mspl+ allele). Trait association studies within an unselected strain revealed that the Mspl- allele whose frequency was reduced in MD resistant strains was associated with high body weight and high egg specific gravity (a measure of eggshell thickness). Analysis at three different time points indicated a significant interaction between the mitochondrial genotype and the growth hormone genotype in early but not in late adulthood. The analysis indicates that mitochondrial variants may contribute to phenotypic variation in chickens and that such contributions may be dependent on the genetic background.

Restriction fragment length polymorphisms at the ornithine decarboxylase locus associated with milk protein yield in Holsteins

Marker-assisted selection may provide the opportunity to make significant genetic gains in the improvement of economically important traits in livestock (Soller & Beckmann, 1983; Smith & Simpson, 1986). Implementation of this approach will first require identification of candidate genes or anonymous gene markers associated with the traits of interest. Candidate genes are those with a known relationship between physiological or biochemical processes and an economically important trait. In dairy cattle, genes associated with mammary gland growth, development and function are excellent candidate genes for milk production traits.

The polyamines are low molecular mass polycations that influence cell proliferation and growth (Tabor & Tabor, 1984; Pegg, 1986). Ornithine decarboxylase (ODC, EC 4.1.1.17) catalyses the conversion of ornithine to putrescine, the rate-limiting step in polyamine biosynthesis (Pegg, 1986). The level of ODC is induced in quiescent cells exposed to a wide variety of stimuli such as growth hormone, corticosteroids, testosterone and growth factors (Tabor & Tabor, 1984). There is ample evidence that growth factors influence morphogenesis and differentiation of the mammary gland (Imagawa et al. 1994). Trophic hormones that are associated with lactation, such as prolactin and growth hormone, are also required to induce differentiation of bovine mammary epithelial cells (Huynh et al. 1991; Flint & Gardner, 1994), and both mitogenic and lactogenic effects of prolactin, insulin and hydrocortisone appear to be mediated through the polyamine pathway (Rillema et al. 1977; Bedford & Zadworny, 1990; Golden & Rillema, 1993). Strange et al. (1992) have shown that ODC is involved in synthesis of a milk component; ODC has elevated expression in the lactating mammary gland, which declines sharply after weaning. It is therefore possible that particular variants of ODC could be associated with increased mammary gland function and thus influence milk related traits.

The objectives of the present study were to estimate allelic frequencies of ODC polymorphisms in Holstein bulls and to evaluate further the genotypic effects of ODC variants on milk production traits.

Association of endogenous viral genes with quantitative traits in chickens selected for high egg production and susceptibility or resistance to Marek's disease

1. The association of endogenous viral (ev) genes with quantitative traits in 2 genetically distinct sets of White Leghorn strains were investigated. Strain S had been selected for susceptibility to Marek's disease (MD) whereas strain K had been selected for resistance to MD and high egg production and egg weight. 2. In all, 8 ev genes were typed. Ev10, ev19 and 'newB' occurred exclusively in strain S, 'newA' occurred only in strain K, and ev1, ev3, ev6 and ev8 occurred in both strains. 3. Whereas ev6 and ev8 were associated with reduction in egg production rate in strain S, in strain K, the presence of ev3 was associated with increased group specific antigen. 4. The genetic background of the chicken strain may play a role in the way certain ev genes affect traits. 5. It was thought that the position of ev genes on the chromosome may be important and their association with traits of economic importance make them potential genetic markers for uncovering quantitative trait loci.

Bovine ornithine decarboxylase gene: cloning, structure and polymorphisms

Bovine ornithine decarboxylase (ODC) genomic clones were isolated from a bacteriophage lambda DASH genomic library. A total of 9452 bp sequence was determined which covers the entire sequence of the bovine ODC gene. Sequence analysis showed that the bovine ODC gene consisted of 12 exons which encode a protein identical to that inferred from a bovine ODC cDNA. Comparison of the structure and nucleotide sequence of the bovine, human and mouse ODC genes revealed that the gene was highly conserved. Primer extension analysis demonstrated that the transcription start point of bovine ODC mRNA was located 378 bp upstream from the A residue in the translation initiation codon. The 5'-untranslated region (UTR) of ODC mRNA was highly G + C rich, particularly in its 5'-most portion, and computer predictions suggested a very stable secondary structure for this region, with an overall free energy of formation of -134.4 kcal/mol. Conserved sequences and potential promoter elements including a TATA box, a possible CCAAT element, SP1 ranscription factor binding sites (GC boxes) and cAMP response elements (CRE) were identified in the 5'-flanking region of the gene. Two polymorphic restriction sites, a TaqI and a MspI, were mapped to the ODC gene and PCR-based methods for detection of the 2 polymorphisms were developed.

Genetic variability in white leghorns revealed by chicken liver expressed sequence tags

A total of 92 expressed sequence tags from chicken liver (CLEST) were searched for homology with known genes. Among the CLEST, 29% had no sequence similarities with known genes, 34% showed sequence similarity to rRNA, 9% to mitochondrial genes, 23% to known nuclear genes, and 5% to human expressed sequence tags. Among the nuclear CLEST (excluding rRNA), clones with sequence similarity to aldolase B were represented four times, whereas all the other clones represented unique genes. The presence of MspI and TaqI restriction fragment length polymorphisms (RFLP) associated with CLEST were analyzed by bulk Southern blotting in 16 strains of White Leghorn chickens derived from five different genetic bases. No RFLP were observed with rRNA CLEST and a single MspI RFLP was observed with mitochondrial CLEST. The nuclear CLEST with sequence similarity to known nuclear genes were grouped into two classes on the basis of their involvement in intermediary metabolism. Among the nine genes coding for metabolic enzymes, all but one were polymorphic at MspI and/or TaqI sites in at least one of the strains, whereas among the other genes six of nine were polymorphic. The average frequency of clones revealing RFLP per cDNA clone and restriction enzyme for the two classes were 0.7 and 0.3, respectively. The analysis indicated that in White Leghorns, RFLP markers in the vicinity of nuclear CLEST are relatively frequent. Further, RFLP in the vicinity of genes coding for metabolic enzymes were significantly more frequent than near genes coding for other proteins.

Trait association of genetic markers in the growth hormone and the growth hormone receptor gene in a White Leghorn strain

Alleles of the growth hormone (GH) gene and GH receptor (GHR) gene were analyzed for association with juvenile body weight (HBWT), age at first egg (AFE), the hen-day rate of egg production (HDR), egg specific gravity (SPG), and egg weight (EWT) in a strain of White Leghorns. The particular strain segregated at near equal frequencies for two GH alleles defined by differences at three restriction fragment length polymorphisms (RFLP) and for two GHR alleles defined by a single RFLP. The GH genotype was significantly associated with AFE (P < or = 0.04) as well as HDR from 274 to 385 d (P < or = 0.04) and 386 to 497 d (P < or = 0.0003). The GHR genotype (haploid in female chickens) had trends for association with HBW (P < or = 0.06) and HDR from AFE to 273 d (P < or = 0.07). The effects on the egg quality traits SPG and EWT were not significant. Regression analysis revealed that HDR was associated negatively with AFE and positively with HBWT. The slope of the regression line of HDR on AFE varied with the GH genotype, with the effect that the differences in HDR between GH genotypes was relatively small in chickens with early AFE and large in chickens with late AFE. Similarly, the slope of the regression of HDR on HBWT varied between GHR genotypes, with the result that the effect of the GHR genotype on HDR in chickens with low HBWT was opposite to its effect in chickens with high HBWT. The complex relationship between genotypes and traits may reflect gene interaction and indicates that simple models based on additive gene effects may not be adequate for the dissection of the genetic architecture of quantitative traits.

Prevention of the expression of incubation behaviour using passive immunisation against prolactin in turkey hens (Meleagris gallopavo)

The efficacy of injecting antibodies raised against turkey prolactin to prevent the expression of incubation behaviour has been investigated in turkey hens. Medium white turkey hens (n = 15 x 2) were injected three times weekly for 4 consecutive weeks starting on week 5 of egg production. The hens were injected im with a volume of 1 mL per injection for the 1st week and 0.5 mL thereafter, of normal rabbit serum or serum containing antibodies raised against turkey prolactin (Guémené et al, 1994a). None of the 15 passively immunised hens expressed incubation behaviour, whereas, more than half (53%) of the control hens did express it. Plasma prolactin concentrations observed in the two groups presented comparable profiles until week 9 and from week 19 of egg production onward. Differences were, therefore, observed from week 10 until week 17 with the non immunised hens showing higher plasma prolactin concentrations than the immunised ones. This difference was related to the presence of incubating hens in the control group. A higher percentage of non immunised hens disrupted egg production during the course of the study and consequently immunised hens laid more eggs than the control ones. No change in plasma LH and oestradiol concentrations can be related to the immunisation procedure. We conclude that prevention of incubation behaviour can be achieved using passive immunisation against prolactin, prevention which resulted in more egg production under our experimental protocol.

DNA polymorphisms in the chicken growth hormone gene: response to selection for disease resistance and association with egg production

Analysis of the growth hormone (GH) gene in 12 strains of White Leghorn chickens revealed restriction fragment length polymorphisms (RFLPs) at three MspI sites and at a SacI site. Based on linkage disequilibrium analysis, they gave rise to eight different alleles (i.e. combinations of RFLPs), with five occurring at frequencies above 5% in at least one strain. Pairs of GH-RFLPs were at near maximal linkage disequilibrium, suggesting either a lack of recombination or the presence of selection pressure during evolution of the GH gene. Allele frequencies were determined in 12 non-inbred strains derived from three different genetic bases. These strains had been selected either for an array of egg production traits, resistance to Marek's disease or resistance to avian leukosis. Selection for disease resistance was consistently correlated with an increase in the frequency of one of the alleles. One strain segregated for only two alleles, which differed by three RFLPs. Analysis of variance in this strain indicated that the GH allele co-selected with resistance was associated with a delayed onset of ovulation but a higher persistency of ovulation as age progressed, resulting in an overall increase of egg production by 15% (age at first egg to 497 days). The resistance-associated GH allele was dominant for the onset of ovulation and recessive for the persistency of egg production. There was no significant effect of the GH genotype on juvenile body weight, egg weight or egg specific gravity.

Changes in expression of the prolactin and growth hormone gene during different reproductive stages in the pituitary gland of turkeys

The changes in levels of prolactin (PRL) and growth hormone (GH) in plasma and the pituitary gland and their transcripts were measured in turkey hens at different physiological stages by radioimmunoassay and dot blot hybridization analysis, respectively. The levels of tPRL mRNA in the pituitary gland increased from those of the immature group to the egg-laying group, reaching a maximum during the incubation and a minimum during the moulting stages. Changes in pituitary levels of PRL and PRL mRNA followed a similar trend and consequently were highly correlated (r2 = 0.83), whereas a significant but lower correlation was observed between circulating and pituitary levels (r2 = 0.62). Less significant changes were measured for tGH mRNA, with maximum and minimum levels measured in the pituitaries of egg-laying and non-laying hens, respectively. These data suggest that although changes in concentration of PRL are correlated with the reproductive stage of the turkey hen, coordinate changes in levels of GH are not.

Sequence variations in the bovine growth hormone gene characterized by single-strand conformation polymorphism (SSCP) analysis and their association with milk production traits in Holsteins

Sequence variations in the bovine growth hormone (GH) gene were investigated by single strand conformation polymorphism (SSCP) analysis of seven amplified fragments covering almost the entire gene (2.7 kb). SSCPs were detected in four of these fragments and a total of six polymorphisms were found in a sample of 128 Holstein bulls. Two polymorphisms, a T-->C transition in the third intron (designated GH4.1) and an A-->C transversion in the fifth exon (designated GH6.2), were shown to be associated with milk production traits. GH4.1c/GH4.1c bulls had higher milk yield than GH4.1c/GH4.1t (P < or = 0.005) and GH4.1t/GH4.1t (P < or = 0.0022) bulls. GH4.1c/GH4.1c bulls had higher kg fat (P < or = 0.0076) and protein (P < or = 0.0018) than GH4.1c/GH4.1t bulls. Similar effects on milk production traits with the GH6.2 polymorphism were observed with the GH6.2a allele being the favorable allele. The average effects of the gene substitution for GH4.1 and GH6.2 are similar, with +/-300 kg for milk yield, +/-8 kg for fat content and +/-7 kg for protein content per lactation. The positive association of GH4.1c and GH6.2a with milk production traits may be useful for improving milk performance in dairy cattle.

Molecular cloning, tissue distribution, and expression of the prolactin receptor during various reproductive states in Meleagris gallopavo

The primary sequence of the prolactin receptor (PRL-R) in turkeys was deduced from a cDNA clone isolated from a kidney cDNA library and from a polymerase chain reaction (PCR) product. The open reading frame of the turkey PRL-R (tPRL-R) predicted an 831-amino acid protein composed of a leader peptide, an extracellular domain, a single transmembrane domain, and an intracellular domain. The extracellular domain contained two homologous repeat units with 63% amino acid sequence identity to each other. Each repeat unit contained all of the conserved cysteine pairs and a WSXWS motif found in mammalian PRL-Rs. A tPRL-R transcript with a molecular size of about 3000 nucleotides was identified by Northern blot analysis. The tPRL-R transcripts were detected in all 26 tissues examined using reverse transcriptase PCR (RT-PCR). The pituitary gland, hypothalamus, crop sac, duodenum, and gizzard were found to express the highest levels of tPRL-R among the 26 tissues. The expression levels of tPRL-R in 17 tissues were compared using semi-quantitative RT-PCR in nonphotostimulated, laying, out-of-lay, incubating, and maternal hens, and male birds. In most tissues examined there was no obvious relationship between blood levels of PRL, reproductive states, and estimated concentrations of the receptor mRNA. In the pituitary gland and hypothalamus, plasma levels of PRL and levels of tPRL-R transcript were inversely correlated. In the hypothalamus, increasing blood levels of PRL were associated with decreasing levels of the receptor transcript (p < or = 0.05), whereas the opposite was observed in the pituitary gland (p < or = 0.05). These findings support the hypothesis that PRL itself may participate in the neuroendocrine control of incubation behavior through actions on both the hypothalamus via a short-loop feedback mechanism and the pituitary gland via autocrine and/or paracrine effects.

Sequence analysis of the β-lactoglobulin locus in Holsteins identifies two new restriction fragment lengtn polymorphisms

The polymerase chain reaction (PCR) was used to amplify and clone a region from the β-lactoglobulin (β-LG) locus that spanned exons IV and V (849 bp). The DNA was amplified from both AA and BB homozygous individuals and sequenced. Sequence analysis revealed that the intervening intron was 673 bp and that three nucleotide substitutions differentiated the A and B forms of β-LG. One of these substitutions was associated with the amino acid substitution (aspartic acid or glycine in the A and B variants, respectively), and the other two which were not reported previously were present in the intron sequence. These nucleotide substitutions resulted in restriction fragment length polymorphisms (RFLPs) that could be used to genotype individuals. The new restriction sites in the intron would result in a more accurate genotyping of the β-LG gene. Animals with B genotype were positive for the presence of two HaeIII restriction endonuclease sites, and type A animals were negative. Animals could also be genotyped on the basis of a polymorphism at a NlaIV restriction site. Genotyping of a random sample of 129 cows and 99 bull calves in Quebec revealed a frequency of 0.66 for the B allele. A comparison between bulls in current use by the artificial insemination industry (n = 114) and from the earliest years of the industry (n = 70) revealed frequencies of 0.58 and 0.56, respectively. Thus, it is unlikely that the sire selection program has affected the allelic frequency. Key words: β-lactoglobulin, Holsteins, DNA sequence, polymorphisms

A MspI polymorphism in the bovine ornithine decarboxylase gene and its possible association with selection for milk production in Holstein bulls

A polymerase chain reaction (PCR)-based method for detection of a MspI-restriction fragment length polymorphism (RFLP) in the bovine ornithine decarboxylase gene was developed, and the allele frequencies of the polymorphism in two groups of Holstein bulls representing progeny-tested bulls during the 1950s-1960s and 1980s, respectively, were estimated. The frequencies of the MspI(-) allele ere 0.229 and 0.077 and that of MspI(+) were 0.771 and 0.923 in the progeny-tested bulls of the 1950s-1960s and 1980s, respectively. The difference in allele frequencies between the two groups was statistically significant (P < 0.005). Genetic drift could be responsible for the changes in allele frequencies; however, it could also be possible that selection for milk production was associated with the changes of the allele frequencies in the two bull populations.

Presence of an additional PstI fragment in intron 1 of the chicken growth hormone-encoding gene

A previously unreported 196-bp PstI fragment was found in intron 1 of the gene encoding chicken growth hormone (cGH) when a PCR assay for an MspI restriction fragment length polymorphism was established. A pair of PCR primers was designed according to the published cGH sequence and used to amplify a fragment which contained two MspI sites, one polymorphic and another non-polymorphic. However, amplification of genomic DNA from two strains of meat-type chickens and three strains of White Leghorn chickens yielded a PCR product which was about 200 bp larger than expected. The fragment from one of the meat-type chickens was subcloned into the vector pCR-Script SK+, and sequenced. It revealed the presence of an extra fragment of 196 bp which was flanked by the PstI sites and occurred at nt +308 of the previously reported cGH sequence.

Molecular cloning of a bovine ornithine decarboxylase cDNA and its use in the detection of restriction fragment length polymorphisms in Holsteins

A cDNA coding for ornithine decarboxylase (ODC) was isolated from a bovine liver cDNA library. The clone (1758 base pairs) consisted of 5'- and 3'-untranslated regions of 185 and 187 nucleotides, respectively, and an open reading frame of 1383 nucleotides encoding an ODC protein (M(r) 51,342 daltons) of 461 amino acids. Comparison of the nucleotide and the predicted amino acid of the cDNA with other mammalian ODCs showed a very high degree of homology both at the DNA and protein levels. The bovine ODC mRNA was identified by northern blot to be a single species with a molecular size of 2.35 kilobase pairs. Primer extension analysis indicated that the 5'-untranslated region of the bovine ODC mRNA was 312 nucleotides long. Southern blot analysis of bovine genomic DNA revealed restriction fragment length polymorphisms when cleaved with restriction enzymes PstI, MspI, TaqI, and Bg/I.

Development and validation of a homologous radioimmunoassay using a biologically active recombinant turkey prolactin

1. A new homologous radioimmunoassay has been developed for the measurement of turkey prolactin. 2. A 25000 kDa purified recombinant derived turkey prolactin (rtPRL), the biological activity of which was tested using a crop sac assay, was used as immunogen for the production of rabbit antiserum. In this biological test, the rtPRL was as active as the ovinePRL. 3. The radioligand (rtPRL) was labelled with 125I and the assay allowed the detection of standard doses of rtPRL ranging from 400 pg/tube to 50 ng/tube. 4. No cross reaction with chicken luteinising hormone and recombinant chicken growth hormone was detected. 5. The within and between assay coefficients of variability were 5.0 +/- 2.7% and 16.3%, respectively. The overall mean recovery ratio was 1.01. 6. The dose-response curves obtained with serial dilution of plasma and pituitary from turkey hens at different physiological stages and from male turkeys were parallel to those obtained with standard rtPRL. 7. The measured concentration of prolactin was 5 times higher in plasma from incubating than laying turkey hens, and the pituitaries from incubating hens contained 2 and 4 times more prolactin than those of laying and out of lay hens or males, respectively. 8. To further assess the validity of the assay, we measured changes in plasma concentration of prolactin in turkeys following stimulation with chicken vasointestinal peptide (cVIP). A single injection of 1 or 10 micrograms/kg body weight of cVIP to laying hens produced a large and rapid increase in plasma prolactin. 9. This new radioimmunoassay appears to be high for the measurement of turkey prolactin.

Production and characterization of recombinant turkey prolactin

1. Recombinant turkey prolactin (rctPRL) was produced as a fusion protein in E. coli, purified by affinity chromatography followed by cleavage with thrombin. The final yield of the released rctPRL (> 90% purity) was 1-2 mg/l of bacterial culture. 2. Recombinant tPRL co-migrated with the main immunoreactive band (25 kDa) in turkey pituitary extracts and was identical to natural tPRL except for the addition of three amino acids (Gly-Ser-Ser) resulting from the cloning strategy at the amino terminal end. 3. The bioactivity of the rctPRL was equipotent to ovine PRL in a rabbit mammary explant system and in the Nb2 lymphoma mitogenic assay.

Synergism between the endogenous viral loci ev6 and ev9 in inducing immunological tolerance to avian leukosis virus

1. The course of infection by exogenous avian leukosis virus was followed in a commercial strain of White Leghorn domestic fowls by measuring viral antigen in feather pulp and egg albumin. Ten days after hatching, 2 out of 360 birds tested positive and at 286 days of age about 60% of the birds had been antigen positive at least once. 2. Among the antigen positive birds, two groups could be distinguished: those which permanently and those which transiently expressed viral antigen. Permanent antigen expression was associated with low antibody titres, while transient antigen expression was associated with high antibody titres. 3. The strain segregated for the two endogenous viral genes ev6 and ev9, both of which express endogenous viral envelope protein, and have been implicated in affecting immune-responsiveness. The antibody titre in individuals positive for both ev6 and ev9, was significantly lower than in those which had none or only one of the two ev-genes. In addition, individuals positive for both ev-genes occurred more frequently in the group permanently positive for viral antigen than in the group transiently antigen positive. 4. The results indicate that there was a strong synergism between ev6 and ev9 in reducing the antibody response to exogenous avian leukosis virus infection, perhaps by inducing immune tolerance or interfering with antibody formation.

Identification of growth hormone DNA polymorphisms which respond to divergent selection for abdominal fat content in chickens

Two strains of meat-type chickens which had been derived from the same genetic base, but were selected for high or low abdominal fat content, respectively, were analyzed for polymorphisms in the growth hormone gene (GH). A total of four DNA polymorphisms were identified, one at a SacI restriction site and three at MspI restriction sites. Restriction mapping indicated that all polymorphisms were in exons and/or introns and not in flanking regions of the gene. The incidence of GH polymorphisms was determined in 20 chickens from each strain and significant differences were observed for two of the four polymorphisms. Analysis by DNA fingerprinting using (CAC)5 as a probe indicated that the inbreeding coefficient was 0.1 in both strains and that random genetic drift was minimal. Thus, the selection for abdominal fat appears to have affected the frequency of alleles of the growth hormone gene. Whether this is the direct consequence of an altered growth hormone gene on fat metabolism or reflects linkage to an allele of a neighbouring gene remains to be determined.

Developmental expression of the prolactin gene in the chicken

Steady-state levels of prolactin (PRL) mRNA in the pituitary gland during embryonic development were determined by dot blot analyses to relate the changes with those of pituitary and plasma levels of PRL. Steady-state levels of the 1.38-kb mRNA encoding the PRL prohormone remained low until Day 18 of incubation, increased on Day 19 of incubation, and reached maximum levels on the day of hatch but decreased 1 day after hatch. Changes in both pituitary and plasma concentrations of PRL closely mimicked those changes in PRL mRNA levels. Subsequently, both the levels of the pituitary PRL mRNA and PRL remained unchanged whereas those of plasma PRL increased 7 days after hatch. The results indicate that a progressive expression of PRL gene in the pituitary gland occurs 1-2 days before the hatch and concomitant increases in plasma concentrations of prolactin may be associated with physiologic changes in pulmonary respiration and hatching.