Interactions between genes involved in growth and muscularity in pigs: IGF-2, myostatin, ryanodine receptor 1, and melanocortin-4 receptor

One-step base editing in multiple genes by direct embryo injection for pig trait improvement

The precise and simultaneous acquisition of multiple beneficial alleles in the genome is in great demand for the development of elite pig breeders. Cytidine base editors (CBEs) that convert C:G to T:A have emerged as powerful tools for single-nucleotide replacement. Whether CBEs can effectively mediate C-to-T substitution at multiple sites/loci for trait improvement by direct zygote injection has not been verified in large animals. Here, we determined the editing efficiency of four CBE variants in porcine embryonic fibroblast cells and embryos. The findings showed that hA3A-BE3-Y130F and hA3A-eBE-Y130F consistently resulted in increased base-editing efficiency and low toxic effects in embryonic development. Further, we verified that using a one-step approach, direct zygote microinjection of the CBE system can generate pigs harboring multiple point mutations. Our process resulted in a stop codon in CD163 and myostatin (MSTN) and introduced a beneficial allele in insulin-like growth factor-2 (IGF2). The pigs showed disrupted expression of CD163 and MSTN and increased expression of IGF2, which significantly improved growth performance and infectious disease resistance. Our approach allows immediate introduction of multiple mutations in transgene-free animals to comprehensively improve economic traits through direct embryo microinjection, providing a potential new route to produce elite pig breeders.

Identification of novel genes significantly affecting growth in catfish through GWAS analysis

Growth is the most important economic trait in aquaculture. Improvements in growth-related traits can enhance production, reduce costs and time to produce market-size fish. Catfish is the major aquaculture species in the United States, accounting for 65% of the US finfish production. However, the genes underlying growth traits in catfish were not well studied. Currently, the majority of the US catfish industry uses hybrid catfish derived from channel catfish female mated with blue catfish male. Interestingly, channel catfish and blue catfish exhibit differences in growth-related traits, and therefore the backcross progenies provide an efficient system for QTL analysis. In this study, we conducted a genome-wide association study for catfish body weight using the 250 K SNP array with 556 backcross progenies generated from backcross of male F1 hybrid (female channel catfish × male blue catfish) with female channel catfish. A genomic region of approximately 1 Mb on linkage group 5 was found to be significantly associated with body weight. In addition, four suggestively associated QTL regions were identified on linkage groups 1, 2, 23 and 24. Most candidate genes in the associated regions are known to be involved in muscle growth and bone development, some of which were reported to be associated with obesity in humans and pigs, suggesting that the functions of these genes may be evolutionarily conserved in controlling growth. Additional fine mapping or functional studies should allow identification of the causal genes for fast growth in catfish, and elucidation of molecular mechanisms of regulation of growth in fish.

The MC4R c.893G>A mutation: a marker for growth and leanness associated with boar taint odour in Belgian pig breeds

Since surgical castration of male piglets without anaesthesia is under heavy societal pressure, finding a sustainable solution to reduce boar taint has become urgent. One way to circumvent this animal welfare violation is raising entire male pigs whilst selecting against the tainted phenotype through marker-assisted selection. Since slaughtering at a lower weight is often suggested to reduce boar taint, selection using a marker for that trait could be a promising strategy. Therefore, in this study a melanocortin 4 receptor (MC4R) mutation, frequently described in different pig breeds as marker for fat content, weight gain and feed intake, was examined in relation to boar taint in pig breeds used in Belgian pig farms. Although results suggest an association between this mutation and a boar taint odour score assigned by experts, no association was found between the mutation and the concentration of the individual chemical boar taint components androstenone, skatole and indole.

Prenatal programming of obesity in a swine model of leptin resistance: modulatory effects of controlled postnatal nutrition and exercise

The main role of early nutritional programming in the current rise of obesity and associated diseases is well known. However, translational studies are mostly based in postnatal food excess and, thus, there is a paucity of information on the phenotype of individuals with prenatal deficiencies but adequate postnatal conditions. Thus, we assessed the effects of prenatal programming (comparing descendants from females fed with a diet fulfilling 100 or only 50% of their nutritional requirements for pregnancy) on gene expression, patterns of growth and fattening, metabolic status and puberty attainment of a swine model of obesity/leptin resistance with controlled postnatal nutrition and opportunity of exercise. Maternal restriction was related to changes in the relationships among gene expression of positive (insulin-like growth factors 1 and 2) and negative (myostatin) regulators of muscle growth, with negative correlations in gilts from restricted pregnancies and positive relationships in the control group. In spite of these differences, the patterns of growth and fattening and the metabolic features during juvenile growth were similar in control gilts and gilts from restricted pregnancies. Concomitantly, there was a lack of differences in the timing of puberty attainment. However, after reaching puberty and adulthood, females from restricted pregnancies were heavier and more corpulent than control gilts, though such increases in weight and size were not accompanied by increases in adiposity. In conclusion, in spite of changes in gene expression induced by developmental programming, the propensity for higher weight and adiposity of individuals exposed to prenatal malnutrition may be modulated by controlled food intake and opportunity of physical exercise during infant and juvenile development.

Polymorphisms in the promoter region of myostatin gene are associated with carcass traits in pigs

Higher average daily gain, more lean meat yield and less fat yield of porcine carcass increase selling profits for animal producers. Myostatin (MSTN), previously called GDF8, is a member of transforming growth factor-β (TGF-β) superfamily. It is a negative regulator for both embryonic development and adult homeostasis of skeletal muscle. In this study, the genotypes of the previously described SNPs MSTN g.435G>A and g.447A>G SNPs in 66 Duroc pigs, 33 Landrace pigs, 180 Duroc × Landrace (DL) pigs and 155 Duroc × Yorkshire × Landrace (DYL) pigs were determined by Taqman SNP Genotyping Assays. For Duroc and Landrace pigs, MSTN g.435GG/g.447AA individual had greater backfat thickness (p < 0.05) than g.435AA/g.447GG individual, whereas MSTN g.435AA/g.447GG had greater meat (p < 0.05) and meat percentage (p < 0.05) than g.435GA/g.447AG individual. For DL and DYL pigs, the MSTN g.435GG/g.447AA animals were greater in backfat at ultrasound 10th rib (p < 0.05) and carcass 10th rib (p < 0.01) than g.435AA/g.447GG individual. The MSTN g.435AA/g.447GG individual also had higher values than g.435GG/g.447AA for anterior-end meat (p < 0.05), posterior-end meat (p < 0.01), total meat weight (p < 0.01) and meat percentage (p < 0.01). This study confirmed evidence that MSTN g.435G>A and g.447A>G affected carcass traits in pigs. The effects of the mutated alleles were additive with the maximal effects resulting from two copies of the mutated allele. Selection for MSTN g.435A/g.447G allele is expected to increase muscle of limb and total meat production and decrease backfat thickness.

The association of genetic variations in the promoter region of myostatin gene with growth traits in Duroc pigs

Average daily gain (ADG) and feed efficiency (FE) are important factors for assessing productivity in farm animals. Myostatin (MSTN), previously called GDF8, is a member of transforming growth factor β (TGFβ) superfamily. It is a negative regulator for both embryonic development and adult homeostasis of skeletal muscle. In this study, the genotypes of MSTN g.435G > A and g.447A > G SNPs in Duroc pigs were determined. The 435GG/447AA individually had significantly higher ADG (P < 0.01), body weight at 70 d (P < 0.05) and 150 d (P < 0.01), and a lower age at 110 kg (P < 0.01) than 435AA/447GG individuals. Dose dependent genetic additive effects were found for the negative effects of the 435A/447 G allele for ADG and body weight on 70 d and 150 d. The 435A/447 G allele also increased the age at 110 kg about 1.47 and 4.53% for 1 and 2 copies, respectively. The MSTN 435 G/447A allele increased the age at 110 kg about 1.41 and 4.47% for 1 and 2 copies, respectively. Overall, the two mutated MSTN 435A/447G allele had negative effects on ADG (P < 0.01), body weight at 70 d (P < 0.05), and 150 d (P < 0.001) and increased the age at 110 kg (P < 0.001). The present study provided evidence that MSTN g.435G > A and g.447A > G affected growth in Duroc pigs. The effects of the mutated alleles were additive with the maximal effects resulting from two copies of the wild-type allele. Selection for the 435 G/447A allele is expected to increase ADG, body weight and decrease the age at 110 kg in Duroc pigs and might be used in porcine breeding programs.

DNA polymorphisms of the Hu sheep melanocortin-4 receptor gene associated with birth weight and 45-day weaning weight

The melanocortin-4 receptor (MC4R) has important roles in regulating food intake, energy balance, and body weight in mammals. In pigs and cattle, MC4R mutations have been identified as genetic markers for growth and traits. Compared with abundant research conducted on other livestock species, little is known about mutations of the ovine MC4R gene. We investigated the effect of MC4R polymorphisms on birth weight and on 45-day weaning weight in 144 Hu sheep. Four single nucleotide polymorphisms (SNPs; g.1016 G/A, g.1240 T/C, g.1264 G/A, and g.1325 A/G) were identified in the 3ꞌ-untranslated region of Hu sheep MC4R by PCR-single-strand conformation polymorphism and DNA sequencing. A haplotype block, containing g.1240 T/C, g.1264 G/A, and g.1325 A/G, was constructed within the Hu sheep MC4R gene. Four SNPs were found to be significantly associated with 45-day weaning weight, while the haplotype block was significantly associated with birth weight. Hu sheep with the genotypes GG in g.1016 G/A or with the genotype CCAAGG in the haplotype block, had higher 45-day weaning weights. We conclude that these 4 SNPs of the MC4R gene have potential as genetic markers for early growth traits in Hu sheep.

Expression levels of candidate genes for intramuscular fat deposition in two Banna mini-pig inbred lines divergently selected for fatness traits

Intramuscular fat (IMF) content plays an important role in meat quality. Many genes involved in lipid and energy metabolism were identified as candidate genes for IMF deposition, since genetic polymorphisms within these genes were associated with IMF content. However, there is less information on the expression levels of these genes in the muscle tissue. This study aimed at investigating the expression levels of sterol regulating element binding protein-1c (SREBP-1c), diacylglycerol acyltransferase (DGAT-1), heart-fatty acids binding protein (H-FABP), leptin receptor (LEPR) and melanocortin 4 receptor (MC4R) genes and proteins in two divergent Banna mini-pig inbred lines (BMIL). A similar growth performance was found in both the fat and the lean BMIL. The fat meat and IMF content in the fat BMIL were significantly higher than in the lean BMIL, but the lean meat content was lower. The serum triacylglycerol (TAG) and free fatty acid (FFA) contents were significantly higher in the fat than in the lean BMIL. The expression levels of SREBP-1c, DGAT-1 and H-FABP genes and proteins in fat BMIL were increased compared to the lean BMIL. However, the expression levels of LEPR and MC4R genes and proteins were lower.

Mechanisms limiting body growth in mammals

Recent studies have begun to provide insight into a long-standing mystery in biology-why body growth in animals is rapid in early life but then progressively slows, thus imposing a limit on adult body size. This growth deceleration in mammals is caused by potent suppression of cell proliferation in multiple tissues and is driven primarily by local, rather than systemic, mechanisms. Recent evidence suggests that this progressive decline in proliferation results from a genetic program that occurs in multiple organs and involves the down-regulation of a large set of growth-promoting genes. This program does not appear to be driven simply by time, but rather depends on growth itself, suggesting that the limit on adult body size is imposed by a negative feedback loop. Different organs appear to use different types of information to precisely target their adult size. For example, skeletal and cardiac muscle growth are negatively regulated by myostatin, the concentration of which depends on muscle mass itself. Liver growth appears to be modulated by bile acid flux, a parameter that reflects organ function. In pancreas, organ size appears to be limited by the initial number of progenitor cells, suggesting a mechanism based on cell-cycle counting. Further elucidation of the fundamental mechanisms suppressing juvenile growth is likely to yield important insights into the pathophysiology of childhood growth disorders and of the unrestrained growth of cancer. In addition, improved understanding of these growth-suppressing mechanisms may someday allow their therapeutic suspension in adult tissues to facilitate tissue regeneration.

Frequency of DLK1 c.639C>T polymorphism and the analysis of MEG3/DLK1/PEG11 cluster expression in muscle of swine raised in Poland

DLK1--(Drosophila like element 1) is a paternally expressed gene, associated with the callipyge phenotype in sheep. In a present study we designed a new real-time PCR alleleic discrimination assay for genotyping of a silent C/T mutation (c.639C>T) in DLK1 gene in swine. The DLK1 c.639C>T mutation was highly polymorphic in all breeds analyzed and C allele was predominant in Landrace and Duroc while T allele was more frequent in Pietrain and Puławska breed. Moreover, we analyzed mRNA expression of DLK1 and adjacent genes--MEG3 and PEG11 in muscles of swines of different breeds raised in Poland. We did not observe significantly different expression of DLK1, MEG3 or PEG11 mRNA in any of analyzed breeds. We also attempted to assess the effect of DLK1 (c.639C>T) on the expression of genes in callipyge locus but did not find significant differences between animals with alternate genotypes (C/C and T/T homozygotes).