Finding genes for economically important traits: Brahman cattle puberty

Abstract

Abstract. Age at puberty is an important component of reproductive performance in beef cattle production systems. Brahman cattle are typically late-pubertal relative to Bos taurus cattle and so it is of economic relevance to select for early age at puberty. To assist selection and elucidate the genes underlying puberty, we performed a genome-wide association study (GWAS) using the BovineSNP50 chip (~54 000 polymorphisms) in Brahman bulls (n = 1105) and heifers (n = 843) and where the heifers were previously analysed in a different study. In a new attempt to generate unbiased estimates of singlenucleotide polymorphism (SNP) effects and proportion of variance explained by each SNP, the available data were halved on the basis of year and month of birth into a calibration and validation set. The traits that defined age at puberty were, in heifers, the age at which the first corpus luteum was detected (AGECL, h 2 = 0.56 AE 0.11) and in bulls, the age at a scrotal circumference of 26 cm (AGE26, h 2 = 0.78 AE 0.10). At puberty, heifers were on average older (751 AE 142 days) than bulls (555 AE 101 days), but AGECL and AGE26 were genetically correlated (r = 0.20 AE 0.10). There were 134 SNPs associated with AGECL and 146 SNPs associated with AGE26 (P < 0.0001). From these SNPs, 32 (~22%) were associated (P < 0.0001) with both traits. These top 32 SNPs were all located on Chromosome BTA 14, between 21.95 Mb and 28.4 Mb. These results suggest that the genes located in that region of BTA 14 play a role in pubertal development in Brahman cattle. There are many annotated genes underlying this region of BTA 14 and these are the subject of current research. Further, we identified a region on Chromosome X where markers were associated (P < 1.00E-8) with AGE26, but not with AGECL. Information about specific genes and markers add value to our understanding of puberty and potentially contribute to genomic selection. Therefore, identifying these genes contributing to genetic variation in AGECL and AGE26 can assist with the selection for early onset of puberty.

Emerging role of PLAG1 as a regulator of growth and reproduction

“…Interestingly, a number of GWASs have shown that sequence variants in the PLAG1 chromosomal region in cattle are associated not only with the growth-and reproduction-related traits discussed above but also with circulating IGF1 concentrations. The Q variant, which is associated with increased body size and higher PLAG1 expression, correlates to lower IGF1 levels in the blood and later onset of puberty (Fortes et al 2012a,b, 2013b, Hawken et al 2012. Other reproduction-related traits, such as plasma inhibin levels at 4 months of age, plasma luteinizing hormone (LH) levels following GnRH challenge at 4 months, and sperm quality, showed no obvious associations with the PLAG1 region (Fortes et al 2012b(Fortes et al , 2013b.…”

“…Bovine QQ genotypes, which show a higher expression of PLAG1, are significantly associated with lower circulating IGF1 levels in the animals (Fortes et al 2012a,b, 2013b, Hawken et al 2012. It is generally accepted that IGF1, be it of peripheral or central origin, affects the onset of puberty, which in endocrinological terms equates to the re-activation of the GnRH neurons after adolescence (DiVall et al 2010, Wolfe et al 2014.…”

“…While a role for PLAG1 in human fertility is yet to be established, GWASs have found links between puberty onset and PLAG1 (or chromosome 14) polymorphisms in cattle (Fortes et al 2012a,b, 2013a,b,c, Hawken et al 2012, Bolormaa et al 2015. A number of genetic markers for the onset of puberty mapped to the PLAG1-containing region on chromosome 14 in Brahman cows (determined as the age at which the first corpus luteum was detected) and bulls (determined as scrotal circumference or age at a scrotal circumference of 26 cm) (Fortes et al 2012a,b, 2013b, Hawken et al 2012.…”

“…A number of genetic markers for the onset of puberty mapped to the PLAG1-containing region on chromosome 14 in Brahman cows (determined as the age at which the first corpus luteum was detected) and bulls (determined as scrotal circumference or age at a scrotal circumference of 26 cm) (Fortes et al 2012a,b, 2013b, Hawken et al 2012. Interestingly, a number of GWASs have shown that sequence variants in the PLAG1 chromosomal region in cattle are associated not only with the growth-and reproduction-related traits discussed above but also with circulating IGF1 concentrations.…”

Initiation of Puberty in Heifers

“…Nonetheless, it has been reported that age of puberty in bulls, based on attainment of a critical SC, is correlated with age at puberty in female offspring. 50 One explanation of the conflicting data may be that heterosis has a significant effect on the percentage of heifers reaching puberty by 368 days, 410 days, and 452 days, with the greatest effect at the younger age. 51…”