Genetic regulation of meat production by embryonic muscle formation - a review

Analysis of mRNA and lncRNA Expression Profiles of Breast Muscle during Pigeon (Columbalivia) Development

The breast muscle is essential for flight and determines the meat yield and quality of the meat type in pigeons. At present, studies about long non-coding RNA (lncRNA) expression profiles in skeletal muscles across the postnatal development of pigeons have not been reported. Here, we used transcriptome sequencing to examine the White-King pigeon breast muscle at four different ages (1 day, 14 days, 28 days, and 2 years old). We identified 12,918 mRNAs and 9158 lncRNAs (5492 known lncRNAs and 3666 novel lncRNAs) in the breast muscle, and 7352 mRNAs and 4494 lncRNAs were differentially expressed in the process of development. We found that highly expressed mRNAs were mainly related to cell-basic and muscle-specific functions. Differential expression and time-series analysis showed that differentially expressed genes were primarily associated with muscle development and functions, blood vessel development, cell cycle, and energy metabolism. To further predict the possible role of lncRNAs, we also conducted the WGCNA and trans/cis analyses. We found that differentially expressed lncRNAs such as lncRNA-LOC102093252, lncRNA-G12653, lncRNA-LOC110357465, lncRNA-G14790, and lncRNA-LOC110360188 might respectively target UBE2B, Pax7, AGTR2, HDAC1, Sox8 and participate in the development of the muscle. Our study provides a valuable resource for studying the lncRNAs and mRNAs of pigeon muscles and for improving the understanding of molecular mechanisms in muscle development.

circTAF8 Regulates Myoblast Development and Associated Carcass Traits in Chicken

Recent studies have shown that circular RNAs (circRNAs) play important roles in skeletal muscle development. CircRNA biogenesis is dependent on the genetic context. Single-nucleotide polymorphisms in the introns flanking circRNAs may be intermediate-inducible factors between circRNA expression and phenotypic traits. Our previous study showed that circTAF8 is an abundantly and differentially expressed circRNA in leg muscle during chicken embryonic development. Here, we aimed to investigate circTAF8 function in muscle development and the association of the SNPs in the circTAF8 flanking introns with carcass traits. In this study, we observed that overexpression of circTAF8 could promote the proliferation of chicken primary myoblasts and inhibit their differentiation. In addition, the SNPs in the introns flanking the circTAF8 locus and those associated with chicken carcass traits were analyzed in 335 partridge chickens. A total of eight SNPs were found associated with carcass traits such as leg muscle weight, live weight, and half and full-bore weight. The association analysis results of haplotype combinations were consistent with the association analysis of a single SNP. These results suggest that circTAF8 plays a regulatory role in muscle development. These identified SNPs were found correlated with traits to muscle development and carcass muscle weight in chickens.

Association of MyoD1 Gene Polymorphisms with Meat Quality Traits in Domestic Pigeons (Columba livia)

Myogenic differentiation 1 (MyoD1) belongs to the MyoD family and plays a key role in myogenesis and consequently, in determining muscle fiber characteristics. In this study, single nucleotide polymorphisms (SNPs) in the exons of MyoD1 were identified in 200 domestic pigeons (Columba livia) by direct DNA sequencing, and the association between MyoD1 polymorphisms and meat quality traits was analyzed. We found four novel variations (A2967G, G3044A, A3164C, and C3311G) in exon 3. The SNP A2967G is a synonymous mutation, while the other 3 SNPs are located in the 3' untranslated region. The analysis revealed 3 genotypes, in which allele A was the predominant allele in the SNP A2967G, while allele B was the predominant allele in the SNPs G3044A and A3164C. The mutations A2967G and G3044A were significantly associated with meat quality traits in pigeon. Pigeons with AA or AB genotypes had higher breast muscle concentrations of inosinic acid and intramuscular fat than those of BB genotype. Moreover, these 2 SNPs had significant effects on MyoD1 mRNA expression. The SNPs A2967G and G3044A were organized into 4 haplotypes, which formed 7 diplotypes. Association analysis showed that the diplotypes were not significantly associated with meat quality traits. Our results implied that associations do exist between MyoD1 gene polymorphisms and meat quality traits in domestic pigeons, and the AA and AB genotypes could be applied as genetic markers in marker-aid pigeon breeding.

Effects of a Novel p.A41P Mutation in the Swine Myogenic factor 5(MYF5) Gene on Protein Stabilizing, Muscle Fiber Characteristics and Meat Quality

Myogenic factor 5 (MYF5) plays an important role in regulating skeletal muscle fiber characteristics, consequently affecting meat production and quality. We identified a novel p.A41P mutation in exon1 of the porcine MYF5 gene by direct sequencing. The mutation was predicted to be destabilizing in protein structure based on the resultant amino acid substitution. We estimated the significant substitution effect of p.A41P on the energy stabilization of Myf5 protein structure. Then, we demonstrated that the mutation in Yorkshire population significantly affected muscle fiber type I composition (p<0.05), loin-eye area of lean meat content (p<0.05) and filter-fluid uptake of meat quality (p<0.01). Furthermore, dominant effects significantly influenced total muscle fiber number (p<0.05). This study suggests that the novel p.A41P mutation in porcine MYF5 may be a valuable genetic marker to affect the muscle fiber characteristics and consequently improve meat production quality and quantity.

Effects of variation in porcine MYOD1 gene on muscle fiber characteristics, lean meat production, and meat quality traits

Three single nucleotide polymorphisms (SNPs) in the porcine MYOD1 gene were used for association analysis and haplotype construction to evaluate the effects of their substitution. Four hundred and three pigs of Yorkshire and Berkshire breeds were used. The mRNA expression levels of MYOD1 were examined. The g.489C>T and g.1264C>A SNPs were significantly associated with several muscle fiber characteristics, the loin eye area, and lightness. Particularly, animals having hetero-genotypes of both sites showed good performance both in lean meat production and meat quality traits. The results of haplotype substitution were similar to the associations of individual SNPs. Moreover, the 2 SNPs had significant effects on mRNA expression. Therefore, the g.489C>T and g.1264C>A SNPs in MYOD1 may be meaningful DNA markers that can be used for improving important porcine economic traits.

A novel polymorphism of the myogenin gene is associated with body measurement traits in native Chinese breeds

Using PCR-SSCP and DNA sequencing technology, we examined the association of single nucleotide polymorphisms (SNPs) in the bovine MyoG gene with body measurement traits in 779 individuals of six native Chinese cattle breeds, namely Luxi, Luxi × Simmental crossbred, Nanyang, Xia'nan, Jiaxian red, and Qinchuan. A novel SNP, T314C, was detected. Allelic frequencies of MyoG-T/C in the six breeds were 0.8308/0.1692, 0.8774/0.1226, 0.8021/0.1979, 0.8209/0.1791, 0.8630/0.1370, 0.8044/0.1956, respectively. Least squares analysis revealed a significant (P < 0.05) association of the MyoG SNP with rump length in four breeds (Luxi, Xia'nan, Jiaxian red, and Qinchuan), with hucklebone width in three breeds (Luxi × Simmental crossbred, Nanyang and Xia'nan), with waist height in two breeds (Luxi × Simmental crossbred and Nanyang) and with body length in the Luxi breed. We conclude that the MyoG SNP has potential as a genetic marker for economically relevant body measurement traits in native Chinese cattle breeds.

Polymorphisms of MRF4 and H-FABP genes association with growth traits in Qinchuan cattle and related hybrids

PCR-RFLP was applied to analyse polymorphisms within the MRF4 and heart fatty acid-binding protein (H-FABP) gene for correlation studies with growth traits in three-month-old Qinchuan (QQ), Qinchuan × Limousin (LQ) and Qinchuan × Red Angus (AQ) cattle. The results showed that 874 bp PCR products of MRF4 digested with XbaI and 2,075 bp PCR products of H-FABP digested with HaeIII were polymorphic in the three populations. Moreover, the frequencies of allele A at MRF4 locus and allele B at H-FABP locus in the QQ, AQ, and LQ populations were 0.8358/0.8888/0.8273 and 0.8358/0.7500/0.8195 respectively. Allele A at MRF4 locus and allele B at H-FABP locus were dominant in the three populations. No statistically significant differences in growth traits were observed among the genotypes of the all three populations at H-FABP locus. However, the association of MRF4 polymorphism with growth traits was then determined in all three populations. The body weight, withers height, heart girth and height at hip cross of individuals with genotype AA were higher than those with genotype AB or BB (P < 0.05). Therefore, we suggest that the MRF4 gene may function in the control or expression of growth traits, particularly body weight, withers height, heart girth and height at hip cross.

Association of RYR1 and MYOG Genotype with Carcass and Meat Quality Traits in Grower-finisher Pigs

The study involved 110 hybrid grower-finisher pigs from Polish Large White x Polish Landrace sows sired by Pietrain breed boars and their crossbreds with the 990 line and Duroc. The aim of the study was to determine an association of the polymorphism of RYR1, myogenin (MYOG) genes and carcass meatiness level with carcass slaughter value and meat quality traits in hybrid pigs. Better meat quality was found in pigs of CC genotype at locus RYR1 than in those of CT genotype, with a similar carcass slaughter value and meat chemical composition. No significant differences were found in meat traits (carcass slaughter value) and quality between AA and AB genotypes at locus MYOG. Similarly, no significant differences were found between carcass meatiness ranges adopted in meat quality and its chemical composition, except for water holding capacity, which was higher in pigs with ⪬ 54% meatiness than in those with > 54%. Moreover, interaction was found between carcass meatiness range and RYR1 genotype in relation to backfat thickness and intramuscular fat content, as well as a connection between carcass meatiness range and MYOG genotype in relation to water-soluble protein content. The results indicate the need to continue selection work towards the elimination of allele T RYR1 gene’s in pedigree herds to improve meat quality in fatteners.

Associations of the variation in the porcine myogenin gene with muscle fibre characteristics, lean meat production and meat quality traits

Pig breeding is aimed at improving lean meat production ability as well as meat quality, and muscle fibre characteristics may be important for enhancing these traits. Therefore, new molecular markers have been demanded for selecting lean meat production ability and meat quality in live animals. Myogenin belongs to the MyoD gene family, and is a candidate gene responsible for muscle fibre characteristics. We identified a new single nucleotide polymorphism (SNP) site in the 5' upstream region of the myogenin gene (nucleotides C and T). A total of 252 pigs of three breeds were genotyped by polymerase chain reaction-restriction fragment length polymorphism using BspCNI. Additionally, they were genotyped for the previously detected MspI site in the 3'-flanking region (alleles A and B). The CCBB diplotype had the highest frequency over breeds, followed by TCBB and CCAB. The other diplotypes were not found in studied pigs. Association analysis performed for the markers found that the TCBB diplotype has desirable effects on the total number of fibres (p < 0.002), fibre cross-sectional area (p < 0.06), and loin eye area (p < 0.001) than the other diplotypes. Moreover, the diplotype had the highest muscle pH value (p < 0.07) and all meat quality traits were near the upper limit of the normal range as a reddish pink, firm and non-exudative (RFN) pork. Therefore, we suggest that selection for the myogenin diplotypes could improve total muscle fibre number, size and lean meat production ability with good meat quality.

Impact of MYOD family genes on pork traits in Large White and Landrace pigs

Porcine myogenic differentiation genes (MYOD) family play a key role in growth and muscle development and are therefore considered as candidate genes for meat production traits. The objective of the study was to investigate the polymorphisms at four loci belonging to the MYOD genes family and analyse their associations with variation in meat production traits in Czech pig breeds. To verify the associations between the polymorphisms and the selected meat traits, altogether 254 pigs, including full- and half-sibs, of Large White and Landrace breeds were tested. The studied meat characteristics were weight of neck, loin, shoulder and ham, lean meat content (LMC), backfat thickness, intramuscular fat (IMF), remission, dry matter content and test daily gain. Statistically significant associations were observed between MYOG gene and fat and neck weight, and between MYF5 gene and IMF and LMC. High significant differences were observed between genotypes AA and AB of MYOD1 in IMF and between genotypes AB and BB of MYF5 in loin weight.

Polymorphisms in coding and regulatory regions of the porcineMYF6 andMYOG genes and expression of theMYF6 gene inm. longissimus dorsi versus productive traits in pigs

MYOG and MYF6 belong to the MyoD gene family. They code for the bHLH transcription factors playing a key role in later stages of myogenesis: differentiation and maturation of myotubes. Three SNPs in porcine MYF6 and two in porcine MYOG were analysed in order to establish associations with chosen carcass quality and growth rate traits in Polish Landrace, Polish Large White and line 990 sows. No statistically significant effect of SNP in the promoter region of the MYF6 gene on its expression measured on mRNA level was found. Associations between the genotype at the MYF6 locus and carcass quality traits appeared to be breed-dependent. The C allele in the case of SNP in the promoter region and GC haplotype in exon 1 were advantageous for right carcass side weight in Polish Landrace sows and disadvantageous for this trait in Polish Large White sows. These gene variants were also the most advantageous for loin and ham weight in sows of line 990. The mutation in exon 1 of the MYOG gene had no statistically significant association with carcass quality traits and the mutation in the 3'-flanking region had the breed-dependent effect as well. These results suggest that SNPs analysed in this study are not causative mutations, but can be considered as markers of some other, still unrevealed genetic polymorphism that influences the physiological processes and phenotypic traits considered in this study.

A new SNP in the promoter region of the porcine MYF5 gene has no effect on its transcript level in m. longissimus dorsi

Myogenic factor 5 (myf-5) is the product of the MYF5 gene, belonging to the MyoD family. This transcription factor participates in the control of myogenesis. We identified 3 new mutations in the promoter region of the gene: A65C, C580T and C613T. The aim of this study was to evaluate the influence of the A65C transversion on gene expression. The analysis was conducted on 15 Polish Large White gilts. The relative content of MYF5 mRNA in m. longissimus dorsi did not differ significantly across MYF5 genotypes (AA, AC, CC). This result suggests that the A65C transversion may not play an important role in the expression of the MYF5 gene in analysed adult muscle but it abolishes a putative binding site for two transcription factors (CDP and HSF1) and creates such a site for Sp1.

Porcine MYF6 gene: sequence, homology analysis, and variation in the promoter region

MYF6 gene codes for the bHLH transcription factor belonging to MyoD family. Its expression accompanies the processes of differentiation and maturation of myotubes during embriogenesis and continues on a relatively high level after birth, affecting the muscle phenotype. The porcine MYF6 gene was amplified and sequenced and compared with MYF6 gene sequences of other species. The amino acid sequence was deduced and an interspecies homology analysis was performed. Myf-6 protein shows a high conservation among species of 99 and 97% identity when comparing pig with cow and human, respectively, and of 93% when comparing pig with mouse and rat. The single nucleotide polymorphism (SNP) was revealed within the promoter region, which appeared to be T --> C transition recognized by a MspI restriction enzyme.

Molecular genetic and physiologic background of the growth hormone-IGF-I axis in relation to breeding for growth rate and leanness in pigs

The GH-IGF-I axis is of major importance for the regulation of body growth and composition, and cellular proliferation and differentiation processes. Selective breeding aiming to improve growth rate and/or body composition is accompanied by changes of the GH-IGF-I axis. Research aiming to elucidate the genetic and physiologic mechanism(s) underlying these changes may best use single-trait selection lines. Two such pig selection lines, one for growth rate and one for high lean content, were used in experiments to investigate the mechanisms of the GH-IGF-I axis change during selection. This contribution reviews the selection-related changes in the GH-IGF-I axis as the consequences of selection for whole body growth rate or body composition and effects on local tissue growth rate. A model explaining the observed effects and consequences for the pressure on the physiology is presented. In short, selection related demand for GH induces GH synthesis until a limit is reached. After that the pulsatile GH plasma profile changes, which may also affect expression profiles of genes regulating body composition.

Selection for growth rate or against back fat thickness in pigs is associated with changes in growth hormone axis plasma protein concentration and mRNA level

Selection for increased growth rate or decreased back fat thickness results in concomitant changes in endocrine and metabolic status. Growth hormone (GH) changes in blood plasma concentration related to selection for growth rate and fat deposition were reported in pigs. The molecular mechanisms regulating selection-induced changes in GH plasma concentration remain largely unknown. We investigated selection-associated changes in GH axis parameters in 2 pig lines selected for increased growth rate (F-line), or decreased back fat thickness (L-line), respectively. First, we investigated selection-associated changes in GH pulse parameters. In both selection lines we found each generation a declining GH peak maximum concentration and area under the GH curve. GH pulse width was not associated with generation number. In both lines generation number was associated with a declined pulse interval, indicating that the number of pulses per day increased on average with 1 pulse per 24 h per generation. Second, plasma concentration of GH axis related Insulin-like growth factor-I (IGF-I) and insulin were investigated. Plasma IGF-I concentration was not associated with generation number in the F-line. Mean plasma insulin concentration declined each generation in both lines. Third, we investigated changes in GH and Pit-1 mRNA levels. In both selection lines GH and Pit-1 mRNA levels increased approximately 50% each generation. The high SD of the GH mRNA levels in both lines may suggest that the GH mRNA levels are pulsatile in vivo. We postulate a molecular mechanism that may explain how selection is associated with increased GH mRNA levels and GH pulse numbers, while lowering GH release per pulse.

Gender related and dexamethasone induced differences in the mRNA levels of the MRF genes in rat anterior tibial skeletal muscle

Muscle formation and postnatal growth is under the control of the muscle regulatory factors (MRF) gene family, consisting of four genes: MyoD1, myogenin, myf-5, and myf-6. Muscle mass is also known to be affected by specific drugs, like glucocorticoids. Glucocorticoids have also been characterized as muscle atrophying agents. However, glucocorticoids are also the only drugs reported to have a beneficial effect on the treatment of muscle degenerative disorders. Since muscle mass relates to gender, this may be partially caused by gender. The aim of this study is to investigate gender-related basal and dexamethasone-induced expression of the MRF genes. Gender-specific MRF mRNA levels were investigated in anterior tibial muscles of the rat. Myogenin, myf-5, and myf-6 mRNA level was significantly higher in female rats than in male rats. Since muscle mass is usually higher in males, we conclude that the development of gender-related differences in muscle mass is not primarily under the control of the mRNA levels of the MRF genes. Male rats treated with dexamethasone for 14 days (1 mg per kg body weight) showed increased levels of MyoD1, myogenin and myf-5 compared to control male rats. Female rats treated with dexamethasone showed decreased expression of myf-6 compared to control female rats. These results suggest that dexamethasone increase satellite cell-specific MRF activity in male muscle tissue, which is suggested to be associated with muscle hypertrophy, while maintenance of muscle tissue is affected in female muscle tissue. Therefore, we conclude that both basal and dexamethasone-induced MRF gene mRNA levels are regulated gender-specific.

Genetic variation in the porcine myogenin gene locus

The myogenin (MYOG) gene fulfills a key function in muscle differentiation by controlling the onset of myoblast fusion and the establishment of myofibers. In meat-producing animals like pigs and cattle, myofiber numbers have been related to growth capacity. We have characterized the porcine MYOG gene to detect genetic variation at this locus and to relate it to growth characteristics. MYOG gene fragments were isolated by PCR on genomic DNA and by screening a genomic library with a mixture of the four human MyoD cDNA fragments. Both the exons and promoter region were very similar to the human and mouse genes. Southern blot analysis of 105 unrelated pigs revealed three polymorphic MspI sites, located in the promoter region, the second intron, and at the 3' side of the gene. PCR-RFLP tests detecting four MYOG alleles were developed. PCR analysis of a panel of pig-rodent somatic cell hybrids confirmed the genetic localization of MYOG on pig Chromosome (Chr) 9. The PCR-RFLP tests and microsatellite markers on Chr 9 offer the possibility to genotype large numbers of pigs for studies of genetic linkage to meat deposition and growth characteristics.