65 Moderate body weight loss and one-carbon metabolite supplementation in early gestation beef heifers alters the fetal Longissimus dorsi transcriptome.

Abstract Moderate body weight (BW) loss occurs naturally throughout production cycles and is detrimental to fetal growth and development. Supplementing one-carbon metabolites may alleviate improper fetal development. The objective of this study was to determine the effects of early gestation nutrient restriction and one-carbon metabolite (OCM) supplementation on fetal skeletal muscle gene expression. Angus-cross heifers (n = 72) were subjected to estrus synchronization and bred to a single sire using female-sexed semen. At breeding, heifers were stratified by BW in a 2 × 2 factorial: fed to gain 0.45 kg/d (CON) or lose 0.23 kg/d (RES) BW and to receive corn carrier with OCM supplement (+OCM) or without (−OCM) from d 0 to 63 of gestation. The OCM supplement consisted of vitamin B12 (20 mg/wk) and folate (320 mg/wk) injections and dietary rumen-protected methionine (7.4 g/d) and choline (44.4 g/d). Pregnancy was determined on d 35 of gestation using transrectal ultrasonography, resulting in 31 pregnant heifers across treatments. On d 63 of gestation, heifers were slaughtered and the uterus was excised for fetal dissection. Fetal Longissimus dorsi (LD) tissue was collected into RNAlater and stored at -80℃. Total RNA was extracted and after quality control, sequenced on the Illumina NovaSeq 6000 platform. After quality control, reads were mapped to the ARS-UCD1.2 reference genome using STAR. Differential gene expression was analyzed using DESeq2 (log2FC ≥ |1| and P ≤ 0.05). Pathway analysis was conducted using ShinyGO at nGenes ≥ 2 and FDR ≤ 0.10. There were 148 differentially expressed genes (DEG) in RES+OCM vs. CON−OCM, and ABC transporters pathway was enriched. Among the DEG, MAT1, EPYC, and PANX3 have roles in bone development and function, and were downregulated ≥ 4-fold in RES+OCM. There were 62 DEG in RES+OCM vs. CON+OCM, and 63 DEG in RES+OCM vs. RES−OCM. Interestingly, the Tyrosine metabolism pathway was enriched in both the RES+OCM vs. CON+OCM and RES+OCM vs. RES−OCM contrasts, and cytosolic DNA-sensing pathways was enriched in the RES+OCM vs. RES−OCM comparison. Tyrosine metabolism has essential roles in catecholamine and thyroid hormone synthesis. No other pathways were enriched among the remaining contrasts. There were 61 DEG in RES−OCM vs. CON+OCM. There were 121 genes in RES−OCM vs. CON−OCM. MATN1 and EPYC were downregulated > 4-fold in RES−OCM. There were 92 DEG in CON−OCM vs. CON+OCM. HSPA6 is involved in the cellular response to heat stress and was upregulated more than 2-fold in CON−OCM. Our results suggest that moderate BW loss and one-carbon metabolite supplementation affect the fetal LD transcriptome. In fact, pathway analysis suggests supplementation of one-carbon metabolites in moderate BW loss heifers during early gestation affects gene expression in pathways associated with fetal growth and development, and biological function.