Polymorphisms of the PRLR Gene and Their Association with Milk Production Traits in Egyptian Buffaloes.

Prolactin (PRL) and its receptor (PRLR) were considered as potential genetic markers for milk production and quality traits in cattle. However, little information is available regarding PRLR genetic diversity and association studies with milk traits in Egyptian water buffaloes. Therefore, the present study was conducted to search for mutations in PRLR and determine their associations with milk performance in these animals. Exon3 (E3) and E10 of PRLR were screened for polymorphisms using single strand conformation polymorphism (SSCP) and sequencing in 400 buffaloes. The associations between haplotypes and milk production (fat%, protein%, lactose%, and solid%) traits as well as mRNA and protein levels of PRL and PRLR were studied. Two single nucleotide polymorphisms (SNPs) in E10 were detected: g.11685G>A (p.Ala494Thr) and g.11773T>C (p.Val523Aal). The G and T alleles were wild (ancestral) alleles, while the A and C alleles were mutant alleles. These SNPs resulted in four haplotypes; AC, AT, GC, and GT. Buffaloes with wild GT haplotypes showed significantly higher milk yield, fat% and protein%, mRNA and protein levels of PRL and PRLR in milk somatic cells than other animals. Animals carrying mutant AC haplotype had inferior milk traits and lowest levels of associated mRNAs and proteins. With these results, we could conclude that the selection of buffaloes with wild GT haplotypes for g.11685G>A and g.11773T>C SNPs of the PRLR gene might improve the milk production traits of Egyptian water buffaloes.

Association of GHR Polymorphisms with Milk Production in Buffaloes.

For its role in the mediation of growth hormone (GH) galactopoietic effect, growth hormone receptor (GHR) was considered a functional candidate gene for milk performance in cattle. However, its genetic variation and potential effect have not been investigated in Egyptian buffaloes. This study aimed to screen GHR for polymorphisms and study their associations with milk traits in Egyptian buffaloes. Polymerase chain reaction, single-strand conformation polymorphism, and sequencing were used to identify mutations in 4 exons (E4-E6 and E8) of the GHR gene in 400 Egyptian buffaloes. No polymorphisms were found in E4, while 2 SNPs (c.380G>A/p.Arg127Lys and c.387C>T/p.Gly129) in E5, one silent mutation (c.435A>G/p.Pro145) in E6, and another missense mutation (c.836T>A/p.Phe279Tyr) in E8 were detected. The c.380G>A SNP in the extracellular domain was associated with milk yield, fat %, protein %, and 305-day milk, fat and protein yield, with higher levels in animals carrying the mutant A allele. The c.836T>A SNP in the transmembrane domain was associated with milk yield, fat %, protein %, and 305-day milk, fat and protein yield, with higher milk yield and lower fat %, protein %, fat and protein yield in the mutant A allele-animals. Interestingly, animals with the two mutant AA alleles produced higher milk yield, fat %, protein %, fat and protein yield, accompanied with upregulated expressions of GHR, GH, insulin-like growth factor 1 (IGF1), prolactin (PRL), prolactin receptor (PRLR), ß-casein (encoded by CSN2 gene), and diacylglycerol acyltransferase-1 (DGAT1) genes and proteins in milk somatic cells. Therefore, selection of Egyptian buffaloes with mutant AA haplotypes for the novel c.380G>A SNP and the well-known c.836T>A SNP could improve milk yield and quality in buffaloes.

Association of CYP19A1 gene polymorphisms with anoestrus in water buffaloes.

Cytochrome P450 aromatase (encoded by the CYP19A1 gene) regulates oestrogen biosynthesis and so plays an essential role in female fertility. We investigated the genetic association of CYP19A1 with the risk of anoestrus in Egyptian water buffaloes. A total of 651 animals (326 anoestrous and 325 cycling) were used in this case-control study. Using single-strand conformation polymorphisms and sequencing, four single nucleotide polymorphisms (SNPs) were detected; c.-135T>C SNP in the 5'UTR and three non-synonymous SNPs: c.559G>A (p. V187M) in Exon 5, c.1285C>T (p. P429S) and c.1394A>G (p. D465G) in Exon 10. Individual SNP-anoestrus association analyses revealed that genotypes (CC, AA and GG) and alleles (C, A and G) of the -135T>C, c.559G>A and c.1394A>G SNPs respectively were high risk for anoestrus. A further analysis confirmed that these three SNPs were in linkage disequilibrium. Additionally, haplotypes with two (TAG/122 and CAA/221) or three (CAG/222) risk alleles were significantly associated with susceptibility to anoestrus, lower blood levels of both oestradiol and antioxidant enzymes (superoxide dismutase, glutathione peroxidase (GPX) and catalase) and downregulated expression levels of CYP19A1, oestrogen receptor α and Gpx3 in the ovary, as well as increased serum level of malondialdehyde. This suggests the occurrence of a high incidence of oxidative ovarian damage and subsequently ovarian inactivity in buffaloes carrying risk alleles. Therefore, with this study we suggest the selection of buffaloes with protective alleles at these SNPs to improve the reproductive efficiency of the herd.

Polymorphisms of the IGF1 gene and their association with growth traits, serum concentration and expression rate of IGF1 and IGF1R in buffalo.

The insulin-like growth factor 1 (IGF1) gene is a member of the group of somatotropin axis genes that play a significant role in cell proliferation and growth of muscles. Here, we searched for polymorphisms in buffalo IGF1 and found two novel single nucleotide polymorphisms (SNPs), G64A and G280A, in the noncoding sequences of exon 1 and exon 4, respectively. Statistical analysis of different genotypes showed that the individuals with GG genotypes had significantly (P<0.05) higher body weight (BW) and average daily gain (ADG) than those with other genotypes at ages of 3-6 months in G64A SNP and 6-9 months in G280A SNP. The combined genotypes of these two SNPs produced three haplotypes, GG/GG, AG/AG, and AA/AA, which were significantly associated (P<0.0001) with BW and ADG at an age from 3 to 12 months. Buffaloes with the homozygous GG/GG haplotype showed higher growth performance than other buffaloes. The two SNPs were correlated with mRNA levels of IGF1 and IGF1 receptor (IGF1R) in semitendinosus muscle as well as with the serum concentration level of IGF1. Also, buffaloes with GG/GG haplotype showed higher mRNA and serum concentration levels. The data revealed that these two SNPs could be valuable genetic markers for selection of Egyptian buffaloes for better performance in the population.