Abstract
Cluster of differentiation 4 (CD4) is the accessory protein non-covalently bound to the T cell receptor that recognizes an invariant region of MHC class II on antigen presenting cells. Its cytoplasmic tail, physically associated with a protein tyrosine kinase, is important in the activation of helper/inducer T lymphocytes. In Bos taurus, CD4 gene is located on chromosome 5 from which two isoforms are transcribed, with a different number of amino acids due to splicing of exon 7 and variation in the reading frame. The aim of this study was to investigate the sequence of the entire CD4 gene in Simmental sires to evaluate the effects of genomic variants on the indexes of the bulls for milk, fat and protein yields, as well as somatic cell score. The associations among genomic variants and indexes were analysed using the Allele and GLM procedures of SAS 9.4. The analysis indicated that only four of the thirty-one identified SNPs influenced the considered traits. Identified variants insist on coding zones and intronic sequences, where we revealed the presence of sites for transcription factors. To evaluate the existence of haplotypic effects, combinations among the four genomic variants (SNP 3, SNP 8, SNP 11 and SNP 19) were investigated. Six different haplotypic alleles were identified, but only four of them were frequent enough to allow for an evaluation of any haplotypic effect (at least six copies in the examined sample): Hap1, Hap2, Hap3 and Hap6. The analysis of associations between the selected haplotypes in the CD4 gene with milk related indexes showed that bulls with Hap2 (T-A-C-C) had better indexes for milk and protein yields (P < 0.05), whereas the presence of the Hap1 haplotype (A-G-A-T) caused a significant decrease of the index for protein yield (P < 0.05). Frequencies of the two alleles Hap1 and Hap2 (9 and 36% respectively) make them of interest for their possible inclusion in breeding schemes and support the hypothesis of considering this gene as a candidate for the improvement of milk-related traits in the Simmental breed.
Highlights
Cluster of differentiation 4 (CD4) is a single-pass transmembrane glycoprotein playing an important function in the interaction between T lymphocytes and antigen- carrying cells (König and Zhou, 2004)
The comparison of two already known sequences of bovine mRNA with the DNA fragment of 29 000 bp deriving from the genomic sequence of the Dominette bovine, suggested the use of this DNA fragment as reference basis for the study of possible variants in the CD4 gene
This study documents the occurrence of several polymorphisms in the genomic sequence of the entire CD4 gene in a sample of Simmental genomic sires
Summary
Cluster of differentiation 4 (CD4) is a single-pass transmembrane glycoprotein playing an important function in the interaction between T lymphocytes and antigen- carrying cells (König and Zhou, 2004). He et al (2011) highlighted a significant association between SNPs within CD4 gene with mastitis indicators and milk production traits. Usman et al (2016) showed a significant association between some SNPs of the CD4 gene (between exon 2 and intron 6) and the percentage of fat in milk. Zeb et al (2020) showed that four SNPs between exon 2 and exon 4 of the CD4 gene were significantly associated with clinical mastitis incidence and with annual milk yield. Evaluation (MACE) of estimated breeding values (EBV) indexes for milk, fat and protein yields, and for somatic cell score (SCS). This index allows one to obtain the genetic evaluations of the reproducers, elaborated by the various countries, in a single international evaluation. This paper documents the presence of a substantial number of polymorphisms in the CD4 gene and their significant associations on milk and protein indexes
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