Cloning and Molecular Characterization of Porcine β-casein Gene (CNS2)

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

Simple Summary

The two non-synonymous g.11685G>A and g.11773T>C SNPs of PRLR(L2) were significantly associated with milk yield, fat%, and protein%, and mRNA and protein levels of PRL and PRLR in milk somatic cells. GT-animals had the best milk performance; however, AC-animals had inferior milk production. Thus, the selection of buffaloes with GT haplotypes may enhance milk performance in Egyptian buffaloes.

Abstract

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 β-casein gene polymorphism with milk composition traits of Egyptian Maghrebi camels (Camelus dromedarius)

The objectives of this study were to detect the polymorphism of 2126A/G SNP in the β-casein (CSN2) gene among Egyptian Maghrebi camels and to investigate the association of 2126A/G SNP genotypes, parity, lactation stage, and temperature–humidity index (THI) with the milk composition traits of Maghrebi camels. Sixty-eight hair samples were collected from three different populations of Maghrebi camels for DNA extraction. Fat, protein, total solids, solids-not-fat, and lactose percentages were determined in Maghrebi camel milk using an automatic milk analyzer device. Three different genotypes – A/A, A/G, and G/G – were identified in the 5′ flanking region of β-casein gene by using PCR-RFLP method with the A/G genotype showing the highest frequency. Association among these three genotypes with milk composition traits suggests a positive effect of A/A genotype on acidity and protein percentage. Higher protein and acidity values were observed in the milk of individuals carrying the A/A genotype. The protein percentage of this study significantly increased from the first till the fourth parity and then decreased. Fat and total solid percentages were significantly higher in the late stage of lactation, while lactose showed a decreasing trend from the early till the late stages of lactation. Fat and protein percentages were highest in the low THI class. Our results encourage the utilization of Maghrebi camel milk for cheese and butter processing at the late lactation stages of the middle parities of their productive life. Moreover, the A/G SNP of the CSN2 gene may be used as a DNA marker in selection programs for the improvement of camel milk composition. Further studies are needed in order to fully explore the variation in the chemical composition of camel milk due to the effect of CSN2 gene, parity, lactation stage, and THI factors.

Association of GHR Polymorphisms with Milk Production in Buffaloes

Simple Summary

The present study reported two missense mutations in the buffalo GHR gene: A novel (c.380G>A) and (c.836T>A) which was described in previous studies. These two single nucleotide polymorphisms (SNPs) were found to be associated with milk yield, fat %, protein %, and 305 day-milk, fat and protein yield, with higher performance for AA haplotype animals. Therefore, selection of buffaloes with AA haplotype would more likely improve milk production traits. Consequently, this would allow breeders to take more precise selection decisions, leading to significantly higher productivity and profitability within the Egyptian buffalo herds.

Abstract

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), β-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.

Characterization of a Novel Porcine CSN2 Polymorphism and Its Distribution in Five European Breeds

Simple Summary

Polymorphisms in genes encoding major milk proteins have been intensely studied, and are used, worldwide, in marker-assisted selection in dairy species: αS1-casein in goats—associated with milk protein content and flavor; κ-casein and β-lactoglobulin in cattle—associated with milk quantity and quality; bovine β-casein—associated with human health, etc. This aspect has scarcely been investigated in pigs. Using an electrophoretic technique, we previously identified a novel porcine β-casein (encoded by CSN2) polymorphism. Here, we fully characterize it at protein and DNA level, propose a genotyping protocol, and investigate its distribution in five European porcine breeds. In brief, a G/A point mutation in position 647 of the porcine CSN2 cDNA leads to an arginine/glutamine substitution in position 201 of the protein. This mutation can be typed via a StyI PCR-RFLP assay. The frequency of the G allele was 0.965 in the investigated Landrace population (number of individuals genotyped n = 67), one in the Pietrain (n = 40), 0.705 in the Large White (n = 36), 0.885 in the Bazna (n = 13), and 0.555 in the Mangalita population (n = 11). Considering that milk protein content still varies widely within (and between) porcine breeds, this and/or other similar polymorphisms may have implications for the dynamics of piglet growth during suckling.

Abstract

Here, we describe a novel porcine β-casein (CNS2) polymorphism, initially identified using the isoelectric focusing (IEF) technique, and provide its distribution in five European breeds. Porcine CSN2 cDNA samples, from sows identified using IEF as carriers of polymorphic variants, were sequenced, and based on the sequence alignments, a genotyping assay was developed. The distribution of the polymorphism was investigated by genotyping 167 sows. Population genetic indexes were computed using POPGENE32 version 1.32. Sequence alignments revealed that the mutation which caused the different β-casein IEF migration profiles was c.647G>A, a substitution located in exon 7, which modifies the amino acid from position 201 of the mature protein from arginine to glutamine. The frequency of the G allele was 0.965 in the investigated Landrace population (number of individuals genotyped n = 67), one in the Pietrain population (n = 40), 0.705 in the Large White population (n = 36), 0.885 in the Bazna population (n = 13), and 0.555 in the Mangalita population (n = 11). For all breeds, except Pietrain (monomorphic), the genotype distribution was in accordance with the Hardy–Weinberg equilibrium. Given that β-casein is the most important protein in sows’ milk, a polymorphism like the one described here may prove interesting for marker-assisted selection.

Knock-in of Enhanced Green Fluorescent Protein or/and Human Fibroblast Growth Factor 2 Gene into β-Casein Gene Locus in the Porcine Fibroblasts to Produce Therapeutic Protein

Transgenic animals have become important tools for the production of therapeutic proteins in the domestic animal. Production efficiencies of transgenic animals by conventional methods as microinjection and retrovirus vector methods are low, and the foreign gene expression levels are also low because of their random integration in the host genome. In this study, we investigated the homologous recombination on the porcine β-casein gene locus using a knock-in vector for the β-casein gene locus. We developed the knock-in vector on the porcine β-casein gene locus and isolated knock-in fibroblast for nuclear transfer. The knock-in vector consisted of the neomycin resistance gene (neo) as a positive selectable marker gene, diphtheria toxin-A gene as negative selection marker, and 5′ arm and 3′ arm from the porcine β-casein gene. The secretion of enhanced green fluorescent protein (EGFP) was more easily detected in the cell culture media than it was by western blot analysis of cell extract of the HC11 mouse mammary epithelial cells transfected with EGFP knock-in vector. These results indicated that a knock-in system using β-casein gene induced high expression of transgene by the gene regulatory sequence of endogenous β-casein gene. These fibroblasts may be used to produce transgenic pigs for the production of therapeutic proteins via the mammary glands.

The β-casein in camels: molecular characterization of the CSN2 gene, promoter analysis and genetic variability

The β-casein is the most abundant protein in camel milk and its encoding gene (CSN2) is considered in other species a 'major' gene for the presence of alleles associated to different level of expression. In the present paper, we report for the first time the characterization of the nucleotide sequence of the whole β-casein-encoding gene (CSN2) plus 2,141 bp at the 5'-flanking region in Camelus dromedarius. The promoter region and the complete cDNA are also provided for the first time in Camelus bactrianus. The gene is spread over 7.8 kb and consists of 9 exons varying in length from 24 bp (exon 5) to 519 bp (exon 7), and 8 introns from 95 bp (intron 5) to 1,950 bp (intron 1). The composite response element (CoRE) region was identified in the promoter, whereas the presence of mature microRNA sequences improves the knowledge on the factors putatively involved in the gene regulation. A total of 46 polymorphic sites have been detected. The transition g.2126A>G falls within the TATA-box of dromedary CSN2 promoter with a putative influence on the transcription factor binding activity. The frequency of the G allele is 0.35 in a population of 180 she-camels belonging to 4 different ecotypes. In the same population, a conservative SNP (g.4175C>A) was found at the codon 7 of the signal peptide, whereas a comparative analysis with a cDNA sequence available in the database evidenced a missense SNP (g.4180T(Leu)>G(Arg)) at exon 2. Four SNPs were found in the bactrian camel. The SNP c.666G>A is responsible for the amino acid change Met(201)→Ile and it represents the first missense allele at the β-casein in camels. Finally, five interspersed repeated elements were identified at intronic level, whereas the presence of putative bio-functional peptides belonging to ACE-inhibitor and anti-oxidative families confirms the potential protective role of the camel milk for the human nutrition.