Quantitative Trait Loci and Promoter Analysis of the Bovine Butyrophilin Gene

Abstract

The butyrophilin gene (BTN1A1) has been described in all mammalian species so far investigated. BTN1A1 is a likely QTL candidate that affects an economically important trait in dairy animals because it is specifically expressed in lactating mammary tissue and the gene product BTN1A1 may function in the secretion of milk lipid. Five PCR-RFLP intragenic markers were identified. Three of the five markers are bi-allelic, however, the two 5'-most markers may be multiallelic loci. The markers were further used to conduct a QTL analysis to examine any allelic substitution effects on economically important milk production traits, namely, total protein, percent protein, total fat, percent fat, somatic cell score, herd life, and milk yield. One significant effect was detected for percent protein. Other effects were not significant, but this could possibly be due to the skewed allelic frequency distribution, or because the variable nucleotides were either intronic or coded for a conservative amino acid substitution.

The 5' flanking region of bBTN was cloned and sequenced. Computational and transient transfection assays were conducted to identify regions of bBTN that are important for its expression. A computational analysis was conducted to compare and analyze the 5' flanking region of cow, goat, human and mouse sequences. Several regions of homology were identified that code for shared binding motifs. However, neither the transcription start site (TSS) nor the other segments of similarity in the proximal promoter region were analogous to other 'milk protein genes' such as the caseins and α-lactalbumin, and other widely studied non-mammary-specific genes. Transient transfection assays in HC11 cells indicate the region from -1kb to -0.45 kb is sufficient to drive the expression of a reporter gene. bBTN appears to contain a novel set of elements that define the (TSS) and proximal promoter modules. A more incisive examination will circumscribe the major cis-acting elements.