Restriction fragment length polymorphism in sheep at the growth hormone locus is the result of variation in gene number

Do some viruses use growth hormone, prolactin and their receptors to facilitate entry into cells?: Episodic evolution of hormones and receptors suggests host-virus arms races; related placental lactogens may provide protective viral decoys

The molecular evolution of pituitary growth hormone and prolactin in mammals shows two unusual features: episodes of markedly accelerated evolution and, in some species, complex families of related proteins expressed in placenta and resulting from multiple gene duplications. Explanations of these phenomena in terms of physiological adaptations seem unconvincing. Here, I propose an alternative explanation, namely that these evolutionary features reflect the use of the hormones (and their receptors) as viral receptors. Episodes of rapid evolution can then be explained as due to "arms races" in which changes in the hormone lead to reduced interaction with the virus, and subsequent changes in the virus counteract this. Placental paralogues of the hormones could provide decoys that bind viruses, and protect the foetus against infection. The hypothesis implies that the extensive changes introduced into growth hormone, prolactin and their receptors during the course of mammalian evolution reflect viral interactions, not endocrine adaptations.

Polymorphism and association of growth hormone gene with growth traits in Sirohi and Barbari breeds of goat

AIM

The aim was to study the polymorphism of exon 2 and exon 3 of growth hormone (GH) gene, to test the polymorphic variants for Hardy-Weinberg equilibrium and to investigate association of these polymorphisms with chest girth and paunch girth in Sirohi and Barbari breeds of goat.

MATERIALS AND METHODS

A total of 80 kids involving forty each of Sirohi and Barbari breeds of goat were included in the study. A good quality genomic DNA isolated from the whole blood using standard protocol were used for polymerase chain reaction (PCR) amplification and products obtained on restriction digestion of amplicon with enzyme HaeIII were separated on 2% agarose gel, and documented in a gel doc system. The chest girth and paunch girth of kids at birth and weekly intervals up to 4 weeks of age and subsequently at 2 months, 3 months and 6 months of age were recorded. Allele frequency and genotype distribution of polymorphism were tested for Hardy-Weinberg equilibrium by program me Genepop package. Association between different genetic variants on chest girth and paunch girth were analyzed by least squares analysis employing suitable statistical model.

RESULTS

The PCR product of genomic DNA isolated from kids of Sirohi and Barbari breeds of goat on digestion with the restriction enzyme HaeIII revealed two genotypic variants viz., AB and BB. None of the two breeds was in Hardy-Weinberg equilibrium for these variants. The least squares analysis of variance revealed non-significant effect of GH genotype and breed × genotype interaction on chest girth and paunch girth from birth to 180 days of age. The effect of breed was highly significant (p<0.01) at all ages.

CONCLUSION

The present study showed that both the breeds were polymorphic at the exon 2 and exon 3 loci of GH gene under study with respect to HaeIII restriction endonuclease. None of the breeds was in Hardy-Weinberg equilibrium for this region of GH gene. In the present study, no significant association between GH genotype and chest girth and paunch girth could be established but comparatively higher chest girth and paunch girth were observed for AB genotype across the breeds.

The sheep growth hormone gene polymorphism and its effects on milk traits

Growth hormone (GH) is encoded by the GH gene, which may be single copy or duplicate in sheep. The two copies of the sheep GH gene (GH1/GH2-N and GH2-Z) were entirely sequenced in one 106 ewes of Sarda breed, in order to highlight sequence polymorphisms and investigate possible association between genetic variants and milk traits. Milk traits included milk yield, fat, protein, casein and lactose percentage. We evidenced 75 nucleotide changes. Transcription factor binding site prediction revealed two sequences potentially recognised by the pituitary-specific transcription factor POU1FI at the GH1/GH2-N gene, which were lost at the promoter of GH2-Z, which might explain the different tissues of expression of GH1/GH2-N (pituitary) and GH2-Z (placenta). Significant differences in milk traits were observed among genotypes at polymorphic loci only for the GH2-Z gene. Sheep with homozygote genotype ss748770547 CC had higher fat percentage (P < 0·01) than TT. SNP ss748770547 was part of a potential transcription factor binding site for C/EBP alpha (CCAAT/Enhancer Binding Protein), which is involved in the regulation of adipogenesis and adipoblast differentiation. SNP ss748770547, located in the GH2-Z gene 5′ flanking region, may be a causal mutation affecting milk fat content. These findings might contribute to the knowledge of the sheep GH locus and might be useful in selection processes in sheep.

Sequence polymorphisms at the growth hormone GH1/GH2-N and GH2-Z gene copies and their relationship with dairy traits in domestic sheep (Ovis aries)

The purpose was to analyze the growth hormone GH1/GH2-N and GH2-Z gene copies and to assess their possible association with milk traits in Sarda sheep. Two hundred multiparous lactating ewes were monitored. The two gene copies were amplified separately and each was used as template for a nested PCR, to investigate single strand conformation polymorphism (SSCP) of the 5'UTR, exon-1, exon-5 and 3'UTR DNA regions. SSCP analysis revealed marked differences in the number of polymorphic patterns between the two genes. Sequencing revealed five nucleotide changes at the GH1/GH2-N gene. Five nucleotide changes occurred at the GH2-Z gene: one was located in exon-5 (c.556G > A) and resulted in a putative amino acid substitution G186S. All the nucleotide changes were copy-specific, except c.*30delT, which was common to both GH1/GH2-N and GH2-Z. Variability in the promoter regions of each gene might have consequences on the expression level, due to the involvement in potential transcription factor binding sites. Both gene copies influenced milk yield. A correlation with milk protein and casein content was also evidenced. These results may have implications that make them useful for future breeding strategies in dairy sheep breeding.

Taql growth hormone gene polymorphism and milk production traits in Holstein-Friesian cattle

The positive effect of administration of growth hormone (GH) on milk production and its presence in selected dairy cattle lines of higher GH concentrations prompted an examination of the presence of restriction fragment length polymorphism (RFLP) in the growth hormone gene using the enzyme Taq/ and to investigate associations between this polymorphism and milk production traits. Blood was sampled from 251 Italian Holstein-Friesian cows. Three fragment bands, arbitrarily denoted A, B and E, of 6·2, 5·2 and 1·9 kilobase (kb), respectively, were observed. Their combinations exhibited six patterns, AA, AB, ABE, AE, BB and BE with frequencies of 64·5, 24·3, 2·4, 6·8, 1·4 and 0·4%, respectively. The statistical analysis was performed using linear mixed animal models. The results indicated an effect of the GHgene polymorphic Taq/restriction fragment on 305-day productions of milk, fat and protein; the low frequency pattern AE showed productions inferior to those for AA or AB patterns. Effect estimates of AA, AB and AE were, respectively, 200 (s.e. 215), 218 (s.e. 267) and -910 (s.e. 380) kg for milk production, 7·75 (s.e. 7·98), 16·10 (s.e. 9·79) and -22·14 (s.e. 14·42) kg for fat production, and 6·78 (s.e. 6·21), 8·57 (s.e. 7·58) and -20·74 (s.e. 11·14) kg for protein production. The average substitution effect estimates of E were -891 (s.e. 278), -26·56 (s.e. 10·16) and -24·50 (s.e. 9·43) kg for milk, fat and protein yields, respectively. In conclusion, these results suggest that the E fragment deserves further designed and specific study.

Mammalian genome projects reveal new growth hormone (GH) sequences. Characterization of the GH-encoding genes of armadillo (Dasypus novemcinctus), hedgehog (Erinaceus europaeus), bat (Myotis lucifugus), hyrax (Procavia capensis), shrew (Sorex araneus), ground squirrel (Spermophilus tridecemlineatus), elephant (Loxodonta africana), cat (Felis catus) and opossum (Monodelphis domestica)

Mammalian growth hormone (GH) sequences have been shown previously to display episodic evolution: the sequence is generally strongly conserved but on at least two occasions during mammalian evolution (on lineages leading to higher primates and ruminants) bursts of rapid evolution occurred. However, the number of mammalian orders studied previously has been relatively limited, and the availability of sequence data via mammalian genome projects provides the potential for extending the range of GH gene sequences examined. Complete or nearly complete GH gene sequences for six mammalian species for which no data were previously available have been extracted from the genome databases-Dasypus novemcinctus (nine-banded armadillo), Erinaceus europaeus (western European hedgehog), Myotis lucifugus (little brown bat), Procavia capensis (cape rock hyrax), Sorex araneus (European shrew), Spermophilus tridecemlineatus (13-lined ground squirrel). In addition incomplete data for several other species have been extended. Examination of the data in detail and comparison with previously available sequences has allowed assessment of the reliability of deduced sequences. Several of the new sequences differ substantially from the consensus sequence previously determined for eutherian GHs, indicating greater variability than previously recognised, and confirming the episodic pattern of evolution. The episodic pattern is not seen for signal sequences, 5' upstream sequence or synonymous substitutions-it is specific to the mature protein sequence, suggesting that it relates to the hormonal function. The substitutions accumulated during the course of GH evolution have occurred mainly on the side of the hormone facing away from the receptor, in a non-random fashion, and it is suggested that this may reflect interaction of the receptor-bound hormone with other proteins or small ligands.

Pituitary and placental ovine growth hormone variants differ in their receptor-binding ability and in their biological properties

The wild-type (WT) GH2-N ovine growth hormone (oGH) and duplicated GH2-Z genes differ in their open reading frame by two nonsynonymous substitutions, predicting a two-amino-acid difference in their product (G9R/G63S). Three recombinant oGH muteins: G9R, G63S and G9R/G63S, were prepared by site-directed mutagenesis of the WT oGH gene, expressed in E. coli, refolded and purified as monomers with over 98% homogeneity. Gel-filtration experiments with WT oGH and the three muteins indicated formation of 1:2 complexes with oGH receptor extracellular domain (oGHR-ECD). Interactions of oGHR-ECD with the WT and the muteins were studied by surface plasmon resonance. Kinetics constants calculated using a two-site model predicted that G9R/G63S has the highest affinity to oGHR-ECD, WT oGH the lowest, and G9R and G63S have intermediate affinities. These relative affinities were further investigated by radioreceptor assay with EC50 values were the lowest for G9R/G63S, highest for WT oGH, and intermediate for G9R and G63S. Bioactivity of the WT oGH and oGH muteins was determined by proliferation assay with FDC-P1-3B9 cells stably transfected with rabbit GHR. Relative proliferation rates of cells in cultures treated with the WT, G63S, G9R or G9R/G63S variants were 100%, 183%, 259% and 498%, respectively. In COS-7 transfected with oGHR, LHRE-TK-luciferase and beta-galactosidase plasmids G9R/G63S showed 18% higher activity than WT oGH (P<0.001). Thus the product of the oGH duplicated copy has higher affinity for GHR and higher somatogenic activity. As the GH2-Z gene copy is expressed in the placenta, allelic differences at the oGH locus may influence feto-placental development.

Polymorphism of the growth hormone gene of red deer (Cervus elaphus)

In mammals, pituitary growth hormone (GH) is usually encoded by a single gene, but in some caprine ruminants there are two GH genes, and higher primates have a cluster of at least 5 GH-like genes. We have previously shown that in several artiodactyls (chevrotain, giraffe, and hippopotamus) there are two GH gene sequences, differing by 5-21 nucleotides (nt), but whether these arise from two distinct gene loci is unclear. We report here that in the red deer (Cervus elaphus) also there are two main GH gene sequences (designated A and B) differing at about 23 nt. Investigation of DNA from a number of individual animals demonstrated that this variation was due to allelic polymorphism, with individuals carrying either the A-type or the B-type sequence, or both. A- and B-type sequences showed some variation between individuals. The overall difference between the A and B sequences is substantial-greater than that between the GH gene sequences of three distinct bovine species, Bos taurus (ox), Bos indicus (zebu) and Bos grunniens (yak). The biological significance of the presence of two markedly differing GH gene sequences in red deer is not clear, but it is notable that several of the differences between the A and B sequences occur in the 5' upstream region, which may be associated with differences in gene expression.

Episodic molecular evolution of pituitary growth hormone in Cetartiodactyla

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased substantially. As a result the sequences of higher primate and ruminant GHs differ markedly from sequences of other mammalian GHs. In order to increase knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have cloned and characterized GH genes from camel (Camelus dromedarius), hippopotamus (Hippopotamus amphibius), and giraffe (Giraffa camelopardalis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, these GH genes comprise five exons and four introns. Two very similar GH gene sequences (encoding identical proteins) were found in each of hippopotamus and giraffe. The deduced sequence for the mature hippopotamus GH is identical to that of dolphin, in accord with current ideas of a close relationship between Cetacea and Hippopotamidae. The sequence of camel GH is identical to that reported previously for alpaca GH. The sequence of giraffe GH is very similar to that of other ruminants but differs from that of nonruminant cetartiodactyls at about 18 residues. The results demonstrate that the apparent burst of rapid evolution of GH occurred largely after the separation of the line leading to ruminants from other cetartiodactyls.

Placental hormones and fetal–placental development

Production of growth promoting substances by the placenta is regulated differently from the way production of similar compounds is regulated by maternal organs in various cases. Gene duplication is one of the mechanisms that facilitated the evolution of placental specific endocrine activity. Cattle, sheep and goats, although evolutionarily related, differ significantly from each other in the way their placental growth hormone (GH) and prolactin (PRL)-like hormones have evolved. Cattle carry one copy of the GH gene and there is no evidence yet for expression of that single GH gene copy in the placenta. On the other hand, the ovine GH gene has been duplicated and both oGH copies are expressed in the placenta during early stages of gestation. Prolactin gene duplication in ruminants resulted in the formation of specific placental-expressed prolactin-related genes including the placental lactogen (PL) gene. In homologous state, ovine PL manifests PRL activity, but antagonizes GH activity. Ovine PL activity which can be mediated by PRL receptors or by hetero-dimerization of GH and PRL receptors, provide a novel regulatory mechanism for somatogenic activity dependent on the coexistence of both GH and PRL receptors in the same cells. Another mechanism for specific placental endocrine activity is silencing of the alleles through genetic imprinting. Disruption of genetic imprinting of placental genes has been proposed as one of the explanations for the loss of cloned fetuses generated by somatic cell nuclear transfer.

Cloning and characterisation of the GH gene from the common dolphin (Delphinus delphis)

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased at least 50-fold. As a result, the sequences of human and ruminant GHs differ substantially from those of other non-primate GHs. Recent molecular studies have suggested that cetaceans are closely related to artiodactyls and may be deeply nested within the artiodactyl phylogenetic tree. To extend the knowledge of GH in Cetartiodactyla (Artiodactyla plus Cetacea), we have cloned and characterised a single GH gene from the common dolphin (Delphinus delphis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, the dolphin GH gene comprises five exons and four introns. The deduced sequence for the mature dolphin GH differs from that of pig at two residues only, showing that the apparent burst of rapid evolution of GH occurred largely after the separation of cetaceans and ruminants.

Molecular evolution of growth hormone (GH) in Cetartiodactyla: cloning and characterization of the gene encoding GH from a primitive ruminant, the chevrotain (Tragulus javanicus)

In mammals the sequence of pituitary growth hormone (GH) is generally strongly conserved, indicating a slow basal rate of molecular evolution. However, on two occasions, during the evolution of primates and that of cetartiodactyls, the rate of evolution has increased dramatically (25 to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. To define further the burst of GH evolution that occurred in cetartiodactyls, the GH gene of the chevrotain (Tragulus javanicus) has been cloned and characterized by use of genomic DNA and a polymerase chain reaction technique. Two very similar gene sequences, which probably reflect allelic variation, were isolated. The deduced sequence for the mature chevrotain GH differs from that of the bovine or red deer GH at only two to three residues, and phylogenetic analysis shows that the burst of rapid evolution of GH that occurred in the Cetartiodactyla must have been completed before the divergence of the Tragulidae and the advanced ruminants (Pecora). The rate of evolution during this burst must therefore have been greater than previously estimated. In other aspects (including signal sequence, 5' upstream sequence, and synonymous substitutions in the coding sequence), the chevrotain GH gene differs considerably from the GH genes of other ruminants and here there is no evidence for the period of accelerated evolution that is seen for GH itself.

The physiological effects of natural variation in growth hormone gene copy number in ram lambs

The effects of natural variation in the number of copies of the growth hormone (GH) gene on growth parameters, plasma GH profiles, and the response to GHRH challenge were compared in Coopworth ram lambs from selection lines differing in body composition and GH levels. Different genotypes at the GH locus carried two, three, or four copies of the GH gene and GH secretion was studied under ad libitum feeding conditions and in the fasted state. There were no significant effects of GH genotype on any parameters of growth or body composition. Basal serum GH concentration, GH pulse frequency, and GH pulse amplitude differed significantly with selection line and fasting, but did not differ significantly between the GH genotypes. Significant differences of subtle nature were found between the GH genotypes in their responsiveness to GHRH. For the ad libitum-fed Lean selection line animals, the first GHRH challenge resulted in a higher mean maximum response for GH1/GH1 than GH2/GH2 (P < 0.05). Between the first and the second challenges there was a decrease in maximum response for the GH1/GH1 genotype and an increase for the GH2/GH2 genotype (P < 0.05 for GH genotype main effect). The differences between GH genotypes in response to GHRH challenge suggest that polymorphism in the number of GH gene copies in sheep may have physiological implications for the function of the GH axis, which may be manifested in growing lambs only under specific genotype-environment combinations.

The effects of a duplication in the ovine growth hormone (GH) gene on GH expression in the pituitaries of ram lambs from lean and fat-selected sheep lines

Growth hormone (GH) gene expression was investigated in pituitaries of 14- to 15-month-old ram lambs from flocks selected for high (fat) or low (lean) back fat depth, which were also homozygous for a single GH gene allele, heterozygous or homozygous for a duplication in the GH gene. The pituitaries of lean sheep of all three GH genotypes were significantly heavier than those of fat sheep, but there were no pituitary weight differences between GH genotypes. No significant lean-fat selection line- or GH genotype-specific differences were measured in pituitary GH concentration. However there was a significant increase (P < 0.01) in the total pituitary content of GH in lean compared with fat animals and a significant interaction between GH genotype and lean-fat selection line (P < 0.05) was noted for GH content. No significant differences were measured in the relative concentration of GH mRNA, suggesting that the ratio of GH mRNA per mg total cellular RNA remained constant across lean-fat selection line and GH genotype. We conclude that the pituitary glands of Coopworth sheep selected for low backfat depth (lean) are bigger and have an increased GH content, but appear to contain similar concentrations of GH mRNA and immunoreactive GH as the pituitaries of fat sheep. The presence of the GH gene duplication in sheep has little measurable effect on the expression and storage of GH in the pituitary.

Genetic variation in Australian Merino sheep

Variation at 22 gene loci was investigated in a flock of Australian Merino sheep using restriction fragment length polymorphism (RFLP) analysis. Polymorphism was observed at 20 loci, including loci for wool keratin, hormone and immunoglobulin light chain genes. Eleven loci yielded unambiguous genotypes suitable for population data analysis. Average heterozygosity, determined from these and two monomorphic loci, was estimated as 0.107 (SE = 0.024). Average heterozygosity excluding all monomorphic data as estimated at 0.377 (SE = 0.031), which is comparable with human RFLP heterozygosities for loci chosen in the same way that we selected sheep loci.

Sheep linkage mapping: RFLP markers for comparative mapping studies

Restriction fragment length polymorphisms (RFLPs) detected using cDNA probes for conserved genes provide an important set of markers that anchor or link syntenic groups in a range of divergent mammalian species. DNA probes from sheep, cattle, pig, human and mouse were screened against sheep DNA samples and 24 new RFLP markers for sheep were identified. Among the loci tested, 22 had a homologue that has been mapped in humans. An RFLP for fibronectin (FN1) was linked to alpha-inhibin (INHA) at a distance of 5cM. The FN1 locus has been assigned to sheep chromosome 2q41-q44 and linkage between FN1 and INHA assigns INHA to the same chromosome in sheep. In addition to the new loci reported here, 28 RFLPs have been published previously by this group and these are collated together with RFLPs published from other laboratories. RFLPs have been reported for 86 loci in sheep. Fifty-four loci have been mapped to 16 different chromosomes.

The duplicated gene copy of the ovine growth hormone gene contains a PvuII polymorphism in the second intron

PvuII restriction fragment length polymorphism (RFLP) was found at the growth hormone locus in sheep carrying the GH2 allele where the gene is duplicated. By restriction analysis and using the polymerase chain reaction we demonstrated that this RFLP is due to a mutation at the PvuII site located in the second intron of the 3' copy of the GH2 allele.