Qun Zhao, M.E. Davis¹ , and H.C. Hines
The Ohio State University Department of Animal Sciences
Abstract
The Pit-1 is a pituitary specific transcription factor that helps regulate the expression of growth hormone (GH). Therefore, the Pit-1 gene was chosen to be a candidate gene for growth traits in beef cattle. Growth traits, which are under the control of multiple genes, are economically important traits in livestock. Detecting genetic variations in the Pit-1 gene and relating them to growth traits could be helpful in development of marker-assisted selection (MAS) programs in animal breeding. Experimental animals used in this research were Angus beef cattle, which were divergently selected for high versus low blood serum insulin-like growth factor-I (IGF-I) concentration, starting in 1989. Three polymorphisms, including one single strand conformation polymorphism (SSCP) detected in intron 5, one MspI polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in intron 2, and a PCR-RFLP HinfI polymorphism (Woollard et al., 1994) in exon 6, were studied. The intron 5 SSCP was examined in 185 cattle, the exon 6 HinfI RFLP in 416 cattle, and the intron 2 MspI RFLP in 80 cattle. We found genotypes AB and BB with frequencies of 0.09 and 0.91, respectively, for the intron 5 polymorphism. No AA individuals were found in this sample. For the HinfI RFLP, genotypic frequencies of 0.11, 0.45 and 0.44 were observed for CC, CD, and DD, respectively. Finally, three genotypes, EE, EF, and FF, were detected with frequencies of 0.16, 0.48, and 0.36, respectively, for the MspI RFLP. The associations of the polymorphisms with growth traits were also analyzed using the General Linear Model (GLM) procedure in the Statistic Analysis System (SAS). For each polymorphism, a linear model was fitted for birth weight, weaning weight, preweaning gain, on-test weight, off-test weight, weight at day 28 and d 56 of the 140-day postweaning test, and IGF-I concentration. For the intron 5 SSCP, no significant associations between the genotypes and these growth traits were found. A moderate association of genotypes with weight at day 56 was found (P = 0.08), with genotype AB having a higher day 56 weight. Therefore, allele A could be associated with superior day 56 weight. Significant associations were found between the HinfI genotypes and birth weight (P = 0.03) and pre-weaning gain (P = 0.01). Therefore, this Pit-1 polymorphism appears to affect growth traits in Angus beef cattle and may be a candidate for use in MAS. The MspI polymorphism was not found to be significantly related to any of these traits. Further study of these polymorphisms in a larger sample is warranted.