Meat Quality Characteristics And Transcriptome And Metabolome Analysis Of Hu Sheep And Southdown×Hu F₁ Sheep

The demand of consumers for high-quality mutton is increasing.Hybridization can improve meat quality and is widely used in sheep production.However,little is known about the molecular mechanisms underlying the formation of meat quality in hybrid sheep.Hu sheep,as a unique breed of multiparous sheep in China,has early sexual maturity and perennial oestrus,and is often used as a hybrid female parent.Due to its strong feed utilization ability and excellent meat quality,Southdown sheep is often used as a hybrid male parent for meat sheep.In this study,Southdown sheep and Hu sheep were hybridized,and six 6-month-old Hu sheep and six Southdown×Hu F₁ sheep under the same feeding and management conditions were selected for slaughter.Slaughtering performance,muscle fiber characteristics,and mutton nutritional quality,edible quality,and processing quality were measured.Through the comprehensive analysis of transcriptome and metabolomics of longissimus dorsi muscle of Hu sheep and Southdown×Hu F₁ sheep,the effect of hybrid production on meat quality was explored.The main research results are as follows:（1）Slaughter performance,meat quality characteristics and muscle fiber characteristics of Hu Sheep and Southdown×Hu F₁ sheep.Southdown×Hu F₁sheep compared with Hu sheep,the live weight（62.68 kg vs 53.32 kg）,carcass weight（34.34kg vs 29.65 kg）,net meat weight（14.55 kg vs 12.57 kg）,eye muscle area（27.69 cm² vs19.40 cm²）,cook loss（67.30%vs 63.82%）,protein content（21.88%vs 20.87%）,essential amino acid content（8.09%vs 7.87%）,total amino acid content（20.15%vs19.62%）,polyunsaturated fatty acid content（32.81 mg/100 g vs 27.24 mg/100 g）polyunsaturated fatty acid/saturated fatty acid content（PUFA/SFA;1.49 vs 1.03）and muscle fiber density（625.33 number/mm² vs 469.33 number/mm²）were significantly increased（P<0.05）.Southdown×Hu F₁sheep compared with Hu sheep,back fat thickness（2.80 mm vs 4.41 mm）,carcass fat content（GR;4.54 mm vs 7.26 mm）,shear force（41.05 N vs 52.52 N）,cholesterol content（50.80 mg/100 g vs 59.70 mg/100 g）,saturated fatty acid content（22.13 mg/100 g vs 26.62 mg/100 g）,muscle fiber diameter（37.59μm vs 40.58μm）and muscle fiber cross-sectional area（1447.62μm² vs 1677.63μm²）were significantly decreased（P<0.05）.（2）Transcriptome analysis of Longissimus dorsi muscle of Hu Sheep and Southdown×Hu F₁ sheep.A total of 538 differentially expressed genes（DEGs）were detected in the longissimus dorsi muscle of Hu Sheep and Southdown×Hu F₁ sheep（P<0.05）,of which 473 were upregulated and 65 were downregulated.These DEGs were significantly enriched in cytokine-cytokine receptor interaction,adipokine signaling pathways,amino acid metabolism,and muscle growth and development pathways（P<0.05）.METTL21C,ACE,HDC,AOC1,POMC,ACSBG2,ACSL6 and PPARGC1A were associated with muscle growth and meat quality.The reliability of transcriptome sequencing data was verified by quantitative real time polymerase chain reaction（q RT-PCR）.（3）Metabolomics analysis of Longissimus dorsi muscle of Hu Sheep and Southdown×Hu F₁ sheep.In gas chromatography-mass spectrometry（GC-MS）and liquid chromatography-mass spectrometry（LC-MS）metabolomics analysis,a total of166 differential metabolites（DMs）were detected in the Southdown×Hu F₁ sheep compared to Hu sheep（P<0.05）,of which 104 were upregulated and 62 were downregulated.These DMs were significantly enriched in protein digestion and absorption,glycolysis/gluconeogenesis,amino acid metabolism and m TOR signaling pathway（P<0.05）.（4）Combined transcriptomic and metabolomics analysis and functional verification of key gene METTL21C.Through joint analysis of transcriptome and metabolomics,it was found that there were|correlation|>0.5 DEGs and DMs in the pathways of arginine and proline metabolism,histidine metabolism,tryptophan metabolism,and neuroactive ligand receptor interaction.Among them,the key candidate gene METTL21C was strongly positively correlated with carnosine,a meat quality related metabolite（correlation>0.6,P<0.05）.Lamb myoblasts were isolated using type IV collagenase method,and myoblast identification was performed using indirect immunofluorescence detection of muscle derived marker factors DESMIN,MYOD1,and PAX7.The results showed that the myoblast separation effect was good and the purity was high.During the proliferation phase,overexpression of METTL21C inhibited the expression of cell proliferation marker factor PAX7 and myogenic regulatory factors（MYF5,MYOD1,and MYOG）,and inhibited myoblast proliferation;Interference with METTL21C promoted the expression of PAX7 and myogenic regulatory factors,and promoted myoblast proliferation.During the differentiation phase,overexpression of METTL21C promoted the expression of myogenic regulatory factors and promoted myoblast differentiation;Interference with METTL21C inhibited the expression of myogenic regulatory factors and inhibited myoblast differentiation.In summary,this study analyzed the slaughter performance,meat quality characteristics,muscle fiber characteristics,and DEGs and DMs in the longissimus dorsi of Hu sheep and Southdown×Hu F₁ sheep,and validated the key candidate gene METTL21C at the cellular level.It comprehensively analyzed the effects of hybridization on meat quality and growth of sheep,providing a theoretical basis for sheep hybrid production.