Evaluating the effects of a single copy of a mutation in the myostatin gene (c.*1232G>A) on carcass traits in crossbred lambs

Genome wide association studies for carcass traits measured by video image analysis in crossbred lambs

This is the first UK genome wide association study investigating potential links between Video Image Analysis (VIA) carcass traits and molecular polymorphisms in crossbred sheep. Phenotypic and genotypic data were collected from two crossbred lamb populations: Texel x Scotch Mule (TxSM, n = 2330) and Texel x Lleyn (TxL, n = 3816). Traits measured included live weights at birth, eight weeks and weaning (∼15 weeks). VIA-predicted traits included total weights and weights of fat, muscle and bone in the whole carcass and primal (hind leg, saddle, shoulder) regions. Within-breed heritabilities estimated for the VIA traits ranged from 0.01 to 0.70, indicating potential for inclusion of some traits in breeding programmes. The two crossbred populations differed in SNPs associated with different traits. Two SNPs on chromosomes two (s74618.1) and eight (s68536.1), respectively, reached genome-wise significance for TxSM, explaining <1% of trait variance, for whole carcass fat and muscle weights, hind leg and saddle fat weights and shoulder bone weights. For TxL, four SNPs reached genome-wise significance, on chromosome two for hind leg muscle weight (OAR2_117,959,202 and OAR2_11804335), on chromosome 10 for whole carcass bone weight (OAR19_8,995,957.1), and on chromosome 19 for weaning weight (s40847.1), each explaining <1% of trait genetic variation. Differences in apparent genetic control of carcass traits may be influenced by the lambs' cross-breed, but also by management decisions affecting environmental variance and trait definitions, which should be understood in order to define protocols for incorporation of carcass traits into (cross)breeding programmes. IMPLICATIONS: Combining VIA-measured carcass traits with conventional production traits in a breeding programme could potentially improve the production and product quality of meat sheep. Phenotypes for VIA traits could be collected relatively easily if VIA machines were present at all abattoir sites. The current study and future Genome Wide Association Studies may help to identify potentially informative molecular markers, that explain large proportions of the genetic variance observed in VIA-measured carcass traits. Including this information in the estimation of breeding values could increase the accuracy of prediction, increasing the potential rate of genetic improvement for product quality. This study confirms the polygenic architecture of the investigated carcass traits, with a small number of molecular markers that each explain a small amount of genetic variation. Further studies across breed types are recommended to further test and validate molecular markers for traits related to lamb carcass quality, as measured by video image analysis.

The comparative results of myostatin introgression from donor Texel to recipient Ramlıç sheep with the aspects of growth, pre-, and post-slaughter carcass traits in the second backcross generation

The aim of the study was to evaluate the growth, body and ultrasonic measurements and some carcass traits of purebred Ramlıç, Texel and crossbred (87.5 % Ramlıç and 12.5 % Texel) lambs in a marker-assisted introgression (MAI) project. The effects of some environmental factors such as genotype, sex, birth type, dam age, weaning age, and birth weight on growth, ultrasound measurements, and carcass traits were significant (P<0.05). There were no significant differences between pure Ramlıç and its myostatin carrier (+/-) and non-carrier (-/-) second backcrosses (BC2) for birth weight, daily live weight gain, and weaning weight. The BC2 genotype (+/-) was statistically caught up with pure Ramlıç for wither height, body length, and rump width. Differences in the longissimus muscle depth indicated that the BC2 (+/-) genotypes tended to be better for both pure Ramlıç and Texel lambs. Texel lambs were superior to Ramlıç in the aspect of some carcass characteristics such as leg length, cold right-half carcass weight, foreleg weight in the left-half carcass, and muscle weight in the left leg. BC2 (+/-) lambs were in the middle of both breeds for the traits. BC2 lambs carrying myostatin did not vary from Ramlıç morphologically. The new type of Ramlıç was also closer to Texel in the aspect of carcass characteristics. In this connection, improvement of indigenous breeds could be achieved by MAI without changing the essential characteristics. For the summary, please visit http://www.mustafatekerli.com (last access: 14 June 2022).

Optimized Cas9:sgRNA delivery efficiently generates biallelic MSTN knockout sheep without affecting meat quality

BACKGROUND

CRISPR/Cas9-based genome-editing systems have been used to efficiently engineer livestock species with precise genetic alterations intended for biomedical and agricultural applications. Previously, we have successfully generated gene-edited sheep and goats via one-cell-stage embryonic microinjection of a Cas9 mRNA and single-guide RNAs (sgRNAs) mixture. However, most gene-edited animals produced using this approach were heterozygotes. Additionally, non-homozygous gene-editing outcomes may not fully generate the desired phenotype in an efficient manner.

RESULTS

We report the optimization of a Cas9 mRNA-sgRNA delivery system to efficiently generate homozygous myostatin (MSTN) knockout sheep for improved growth and meat production. Firstly, an sgRNA selection software (sgRNAcas9) was used to preliminarily screen for highly efficient sgRNAs. Ten sgRNAs targeting the MSTN gene were selected and validated in vitro using sheep fibroblast cells. Four out of ten sgRNAs (two in exon 1 and two in exon 2) showed a targeting efficiency > 50%. To determine the optimal CRISPR/Cas9 microinjection concentration, four levels of Cas9 mRNA and three levels of sgRNAs in mixtures were injected into sheep embryos. Microinjection of 100 ng/μL Cas9 mRNA and 200 ng/μL sgRNAs resulted in the most improved targeting efficiency. Additionally, using both the highly efficient sgRNAs and the optimal microinjection concentration, MSTN-knockout sheep were generated with approximately 50% targeting efficiency, reaching a homozygous knockout efficiency of 25%. Growth rate and meat quality of MSTN-edited lambs were also investigated. MSTN-knockout lambs exhibited increased body weight and average daily gain. Moreover, pH, drip loss, intramuscular fat, crude protein, and shear force of gluteal muscles of MSTN-knockout lambs did not show changes compared to the wild-type lambs.

CONCLUSIONS

This study highlights the importance of in vitro evaluation for the optimization of sgRNAs and microinjection dosage of gene editing reagents. This approach enabled efficient engineering of homozygous knockout sheep. Additionally, this study confirms that MSTN-knockout lambs does not negatively impact meat quality, thus supporting the adoption of gene editing as tool to improve productivity of farm animals.

Identification of polymorphisms in the MSTN and ADRB3 genes associated with growth and ultrasound carcass traits in Kajli sheep

The aim of this investigation was to find single nucleotide polymorphisms (SNPs) in the myostatin (MSTN) and the beta-3 adrenergic receptor (ADRB3) genes associated with growth and ultrasound carcass traits in Kajli sheep. The five growth traits were birth weight (BWT-EBV), 120-day weight (120DWT-EBV), 180-day weight (180DWT-EBV), 270-day weight (270DWT-EBV), and 365-day weight (365DWT-EBV). The three ultrasound carcass traits were width (WLD) and depth of longissimus dorsi (DLD) and back fat thickness (BFT). The analysis of the MSTN sequence revealed one non-synonymous substitution (c.197T > A) in exon 1, one single nucleotide substitution (c.373 + 18G > T) in intron 1, and one synonymous substitution (c.861T > A) in exon 3. However, there were four single nucleotide synonymous substitutions (c.130C > T, c.294C > G, c.579G > T, and c.654C > G) in exon 1 of the ADRB3 gene. All the SNPs in the MSTN gene, except for c.373 + 18G > T, were in Hardy-Weinberg Equilibrium (HWE). Conversely, none of the SNPs found in ADRB3 were in HWE. Two of the MSTN SNPs (c.197T > A and c.373 + 18G > T) had significant associations with all evaluated growth and ultrasound carcass traits. The SNPs c.130C > T and c.294C > G in ADRB3 were significantly associated with 180DWT-EBV. Collectively, these findings indicate that several SNPs in the studied genes were significantly related to growth and carcass traits in Kajli sheep.

Myostatin regulates fatty acid desaturation and fat deposition through MEF2C/miR222/SCD5 cascade in pigs

Myostatin (MSTN), associated with the “double muscling” phenotype, affects muscle growth and fat deposition in animals, whereas how MSTN affects adipogenesis remains to be discovered. Here we show that MSTN can act through the MEF2C/miR222/SCD5 cascade to regulate fatty acid metabolism. We generated MSTN-knockout (KO) cloned Meishan pigs, which exhibits typical double muscling trait. We then sequenced transcriptome of subcutaneous fat tissues of wild-type (WT) and MSTN-KO pigs, and intersected the differentially expressed mRNAs and miRNAs to predict that stearoyl-CoA desaturase 5 (SCD5) is targeted by miR222. Transcription factor binding prediction showed that myogenic transcription factor 2C (MEF2C) potentially binds to the miR222 promoter. We hypothesized that MSTN-KO upregulates MEF2C and consequently increases the miR222 expression, which in turn targets SCD5 to suppress its translation. Biochemical, molecular and cellular experiments verified the existence of the cascade. This novel molecular pathway sheds light on new targets for genetic improvements in pigs.

Ren, Xiao et al. identify a mechanism by which myostatin regulates adipogenesis, using myostatin-knockout pigs. Myostatin deficiency upregulates MEF2C that binds to the promoter of miR222. miR222 in turn downregulates stearoyl-CoA desaturase 5. This study provides potential targets that can be engineered to generate a new pig variety that has high leanness while maintaining its high intramuscular fat content.

Variants in myostatin and MyoD family genes are associated with meat quality traits in Santa Inês sheep

Myostatin and MyoD family genes play vital roles in myogenesis and this study aimed to identify association of variants in MyoD1, MyoG, MyF5, MyF6, and MSTN genes with meat traits in Santa Inês sheep. A dataset with 44 variants and records of seven meat traits in 192 lambs (pH0, pH24, a*, b*, L*, tenderness assessed by shear force, and water-holding capacity) was used. Single-locus and haplotype association analyses were performed, and the significance threshold was established according to Bonferroni's method. Single-locus analysis revealed two associations at a Bonferroni level, where the variant c.935-185C > G in MyoD1 had an additive effect (-4.31 ± 1.08 N) on tenderness, while the variant c.464 + 185G > A in MyoG had an additive effect (-2.86 ± 0.64) on a*. Additionally, the haplotype replacement GT>AC in MSTN was associated with pH0 (1.26 ± 0.31), pH24 (1.07 ± 0.27), a* (-1.40 ± 0.51), and tenderness (3.83 ± 1.22 N), while the replacement GT > AG in MyoD1 was associated with pH0 (1.43 ± 0.26), pH24 (1.25 ± 0.22), b* (-1.06 ± 0.39), and tenderness (-4.13 ± 1.16 N). Our results have demonstrated that some variants in MyoG, MyF6, MyoD1, and MSTN can be associated with physicochemical meat traits in Santa Inês sheep.

Effects of Intronic SNPs in the Myostatin Gene on Growth and Carcass Traits in Colored Polish Merino Sheep

Myostatin acts as a negative regulator of muscle growth; therefore, its role is important with regard to animal growth and meat production. This study was undertaken with the objective to detect polymorphisms in the first intron and c.*1232 position of the MSTN gene and to analyze effects of the detected alleles/genotypes on growth and carcass traits in Colored Polish Merino sheep. In total, 23 traits were analyzed, i.e., seven describing lamb growth and 16 carcass traits. Single nucleotide polymorphisms (SNPs) in the first intron and the c.*1232 position were identified using polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) and PCR-restriction fragment length polymorphism (PCR-RFLP) methods, respectively. The MIXED procedure of the SAS software package was used to analyze allelic and genotypic effects of the MSTN gene on growth and carcass traits. Polymorphisms were only detected in the first intron of the MSTN gene. All investigated sheep were monomorphic G in the c.*1232 position. The MSTN genotype was found to have significant effect on body weight at 2nd day of life (BW2) and loin and fore shank weights. Significant allelic effects were detected with respect to BW2, scrag, leg, fore, and hind shank weights. These results suggest that polymorphisms in the first intron of the MSTN gene are relevant with respect to several carcass traits and BW2 in Colored Polish Merino sheep.

Genotypic and allelic effects of the myostatin gene (MSTN) on carcass, meat quality, and biometric traits in Colored Polish Merino sheep

The aim of this study was to identify polymorphisms in the first intron and c.*1232G>A position of the MSTN gene and analyze associations between the detected alleles/genotypes and carcass, meat quality, and biometric traits in Colored Polish Merino sheep. We analyzed 44 traits using the MIXED procedure of the SAS software. Five alleles (MSTN-A, MSTN-B, MSTN-C, MSTN-E and MSTN-E1) were detected. Significant genotypic effects were detected with regard to chest depth (live lamb) and fat depth over ribs, drip loss, subjective meat flavor and color, whereas significant allelic effects were found for chest depth (live lamb), pre-slaughter weight, hot carcass weight, cold carcass dressing out, leg depth (carcass), eye of loin width and area, intramuscular fat (IMF) content, water-holding capacity, and subjective meat tenderness, flavor and color. The results suggest MSTN gene polymorphisms may be considered a genetic marker of carcass quality, meat quality, and biometric traits in sheep.

The effects of the myostatin g+6723G>A mutation on carcass and meat quality of lamb

This study evaluated the effects of the myostatin g+6723G>A mutation on carcass and meat quality traits of lamb (AA: n=5; AG: n=8; GG: n=9). Dressing percentage was positively affected by the mutation with homozygotes for the mutation having the highest yield. Regarding carcass composition, there was a significant increase in the proportional weights of the loin and hindquarter muscles. Objective meat quality traits of the M. longissimus lumborum (LL) and M. semimembranosus (SM) were not significantly affected. For the SM, toughness (shear force and compression) tended to be lowest for homozygotes for the mutation. The myostatin g+6723G>A mutation did not affect sensory meat quality traits of grilled steaks for the LL, but resulted in a significant improvement in eating quality for the SM. Given the number of animals in this study, the robustness of the outcome of this study with regard to the effects on meat quality and its causes requires further investigation.

Lack of association between allelic status and myostatin content in lambs with the myostatin g+6723G>A allele

Lambs with the myostatin (MSTN) g+6723G>A mutation have a greater muscle mass, which is believed to be associated with reduced myostatin protein abundance. This experiment was designed to determine if differences in allelic frequency of the MSTN g+6723G>A mutation affected abundance of myostatin protein from birth to 24 wk of age. A Poll Dorset cross White Suffolk ram (MSTN A/G) was mated to 35 White Suffolk cross Border Leicester cross Merino ewes (MSTN A/G, n=21, and MSTN G/G, n=14). The progeny of these matings delivered 44 lambs with MSTN A/A (n=9), MSTN A/G (n=21), and MSTN G/G (n=14) genotypes. At approximately 1, 4, and 12 wk of age, a biopsy sample was collected and a blood sample was taken to measure the abundance of myostatin protein in muscle and plasma. At approximately 24 wk of age, the wether lambs were slaughtered to determine carcass characteristics and muscle samples were taken from the bicep femoris. The abundance of mature myostatin protein in muscle from 1 wk old lambs was less (P=0.05) in MSTN A/A and MSTN A/G compared with MSTN G/G lambs. However, at 4 and 24 wk the MSTN A/A lambs had a greater (P=0.04) abundance of myostatin protein compared with the MSTN A/G and MSTN G/G lambs. The abundance of mature myostatin did not differ between genotypes in plasma but the myostatin protein did increase as the lambs aged. At slaughter the MSTN A/A wether lambs had greater dressing percentages (P=0.04), shortloin (P=0.01), topside (P<0.001), and round (P=0.01) weights but did not differ in final BW or HCW (P>0.05). The MSTN A/A lambs had more muscle fibers (P=0.02) in the cross-section of LM between the 12th and 13th rib. The MSTN A/A lambs also had greater lean (P=0.002), less fat (P=0.009), and reduced organ (heart, liver, spleen, and kidneys) mass as determined by computed tomography scanning than MSTN G/G lambs. The results of this study demonstrated that lambs homozygous for the MSTN g+6723G>A mutation have changes in carcass characteristics (dressing and total lean), organ weights, and muscle fiber number. This may be due to reduced myostatin protein early in utero, but after 4 wk of age there was no difference in the abundance of mature myostatin protein in muscle or plasma among MSTN A/A, MSTN A/G, and MSTN G/G genotypes.

Genes contributing to genetic variation of muscling in sheep

Selective breeding programs aiming to increase the productivity and profitability of the sheep meat industry use elite, progeny tested sires. The broad genetic traits of primary interest in the progeny of these sires include skeletal muscle yield, fat content, eating quality, and reproductive efficiency. Natural mutations in sheep that enhance muscling have been identified, while a number of genome scans have identified and confirmed quantitative trait loci (QTL) for skeletal muscle traits. The detailed phenotypic characteristics of sheep carrying these mutations or QTL affecting skeletal muscle show a number of common biological themes, particularly changes in developmental growth trajectories, alterations of whole animal morphology, and a shift toward fast twitch glycolytic fibers. The genetic, developmental, and biochemical mechanisms underpinning the actions of some of these genetic variants are described. This review critically assesses this research area, identifies gaps in knowledge, and highlights mechanistic linkages between genetic polymorphisms and skeletal muscle phenotypic changes. This knowledge may aid the discovery of new causal genetic variants and in some cases lead to the development of biochemical and immunological strategies aimed at enhancing skeletal muscle.

Effect of an exon 1 mutation in the myostatin gene on the growth traits of the Bian chicken

Myostatin (MSTN), or growth and differentiation factor 8 (GDF8), is a member of the transforming growth factor (TGF)-β superfamily. This family functions as a negative regulator of skeletal muscle development and growth in mammals. Single-nucleotide polymorphisms in exon 1 of the Bian chicken myostatin gene were detected by polymerase chain reaction-restriction fragment length polymorphism. A mutation (c.234G>A) in exon 1 was found. Female Bian chickens of genotypes AA and GA had significantly higher body weights than those of genotype GG (P < 0.05 or P < 0.01) from 6 to 18 weeks of age. These results suggested that the mutation c.234G>A in exon 1 could be used as a genetic marker for Bian chicken growth traits.