Identification of a variant growth hormone haplotype in mice selected for high body weight

Structure of the growth hormone-encoding gene and its promoter in mice

The isolation and nucleotide sequence determination of the 5' flanking region of the mouse growth hormone (mGH)-encoding gene (mGH) is described. The mGH gene consists of five exons and four introns, as is observed in other mammalian species. The second intron in mGH is much smaller than its rat counterpart, thus being similar in size to human, bovine and porcine GH. The transcription start point was determined to be a C residue 62 bp upstream from the start codon, ATG. Analysis of 1767 bp of the 5' flanking region, with respect to putative regulatory elements, revealed a TATA box, two binding sites for growth hormone factor (GHF1), a GC box (SP1), a thyroid-response element (TRE) and a silencer (SiL) sequence motif. As expected, the mGH promoter shows a higher degree of homology with rat, as compared to the other mammalian species like pig, cattle and human, where an overall homology exists only at the proximal promoter region.

Growth hormone and insulin-like growth factor I concentrations in bulls of various growth hormone genotypes

A leucine/valine substitution at amino acid position 127 was identified by the polymerase chain reaction and restriction fragment length polymorphism in the bovine growth hormone gene. Genotyping was performed in 84 AI bulls of three different breeds, in which plasma concentrations of growth hormone (GH) and insulin-like growth factor I (IGF-1) were also measured. Gene frequencies of variants L (leucine) und V (valine) were 0.80/0.20 (Black and White), 0.90/0.10 (Brown), 0.71/0.29 (Simmental). Hormone concentrations were measured during different physiological conditions (normal feeding, fasting, realimentation) in the majority of animals. Generally, genotype LL was associated with higher concentrations of GH than LV. This difference was significant in Black and White bulls (P < 0.05). In contrast, IGF-1 concentrations were higher in LV than in LL animals. This was most pronounced in mature, realimented Simmental bulls. We conclude that the various GH alleles influence the circulating concentrations of GH and IGF-1.

The role of growth hormone in lines of mice divergently selected on body weight

An understanding of the physiological and genetic changes which determine the response to selection is critical for both evolutionary theory and to assess the application of new molecular techniques to commercial animal breeding. We investigated an aspect of physiology, growth hormone (GH) metabolism, which might a priori have been expected to play a large part in the response of mouse lines selected for high or low body weight. Disruption of endogenous GH or addition of exogenous GH had similar proportionate effects on body weight in both lines of mice (although differences in body composition arose) suggesting that neither the production of GH nor receptor sensitivity to GH had been altered as a result of selection. This supports a 'pleiotropic model' of the response to selection: that many genes with diverse metabolic roles all contribute to the divergent phenotype. This result has significant commercial implications as it suggests that artificial selection, transgenic technology and environmental manipulation may be synergistic rather than antagonistic strategies.

An analytical model for the estimation of chromosome substitution effects in the offspring of individuals heterozygous at a segregating marker locus

Use of marker genes for quantitative traits has been suggested as a supplement to selection for livestock species. Linkage relationships can be estimated by using data from offspring of a heterozygous parent, if offspring can be positively assigned segregation of one or the other of the marker alleles. In field data, some data on offspring can be characterized and used to estimate the difference in chromosome substitution effects, but other matings result in uncertain transfer of the marker alleles. In this study, an alternative estimation procedure is proposed that would allow incorporation of data on all offspring of a heterozygous parent, even those where chromosome segregation is ambiguous. If the frequency of the marker alleles is known in the population of mates of a heterozygous individual, the mean and variance of the heterozygous offspring can be used in a generalized leastsquares model to estimate the chromosome substitution effect. When gene frequencies are not known, maximum likelihood estimates can be obtained from the data for use in a conditional estimate. Monte Carlo simulations of data following the assumed genetic model were analyzed as proposed, and parameter estimates were characterized. Estimates of chromosome substitution effects were reasonable approximations of input values. Distributions of t-statistics testing the null hypothesis of no difference between marked chromosome segments were unbiased, with only slightly larger variance than expected. Addition of data from heterozygous offspring improved the efficiency of detection of chromosome substitution effects by more than four times when marker gene frequencies were low.

Structural variation around prolactin gene linked to quantitative traits in an elite Holstein sire family

Digestion of genomic DNA with the restriction endonuclease Avail disclosed a probable insertion deletion of approximately 200 base pairs (bp) near the prolactin gene. Two alleles were apparent as three distinct hybridization patterns. These alleles were statistically associated with quantitative trait loci among sons of one elite Holstein sire family. The favorable genotype was correlated with the presence of a 1.15-kb hybridization band inherited from the sire when genomic DNA was probed with a full-length cDNA for prolactin. Pedigree estimates of genetic merit among genotypes were similar, differing by only 19.3 kg for milk in ancestor merit. Comparisons of genetic estimates for quantitative yield traits in offspring of this heterozygous sire showed significant (P<0.05) differences between homozygous genotypes for predicted difference milk (PDM), predicted difference dollars (PD$), cheese yield dollars, and protein dollars. The estimated differences between homozygous genotypes for USDA Transmitting Abilities of PDM, PD$, Cheese Yield $ and Protein $ were 282.93 kg, $74.35, $48.58 and $53.67, respectively. However, the estimated breeding values from progeny ranged over 900 kg in transmitting ability for milk. Frequency of the favorable marker allele was estimated to be 0.231 in the elite cow population used as dams of sons. These results demonstrate the potential of molecular biological techniques to discriminate between individuals within a family and to predict breeding values for selection schemes.