425 Altering methyl donors to beef heifers during the periconceptual period impacts fetal muscle transcript abundance
Authors: Hauxwell Kathlyn M , Cushman Robert A , Caton Joel S S , Da Diniz Wellison Jarles Silva , Keel Brittney N , Ward Alison K , Lindholm-Perry Amanda K , Snider Alexandria P , Freetly Harvey C , Dahlen Carl R , Amat Samat , Neville Bryan W , Thorson Jennifer F , Oliver William T , Miles Jeremy R , Crouse Matt S 
Published: September 2024

Abstract
New findings in developmental programming show an increased importance of methyl donor availability; however, effects of changing methyl donor concentration on the fetal transcriptome have yet to be identified. Differential gene expression (DEG) was used to determine the impact of maternal supplementation of methionine (MET), an obligate methyl donor, and guanidinoacetic acid (GAA), a methyl donor consumer, during the periconceptual period on bovine fetal development. MARC II heifers [n = 80; initial body weight (BW) = 346 ± 8.28 kg] receiving the same mixed ration and targeting the same gain (0.68 kg/d) were assigned to one of four treatments totaling 100 g/d of supplement with a ground corn carrier: MET (10 g/d), GAA (40 g/d), MET+GAA (10 g/d Met + 40 g/d GAA), and only ground corn carrier for control (CON). Supplementation began 63 d before breeding and concluded 63 d after breeding. Heifers pregnant with male offspring (CON, n = 10; MET, n = 8; GAA, n = 7; MET+GAA, n = 10) were slaughtered on d 63 of gestation. Transcript abundance was measured using RNA-Seq from extracted total RNA of fetal hindlimb samples (n = 35). The DEG analysis identified 227 upregulated and 121 downregulated genes from MET vs CON, 483 upregulated and 40 downregulated genes from GAA vs CON, and 672 upregulated and 34 downregulated genes from MET+GAA vs CON treated heifers (P ≤ 0.05). We identified 315 upregulated and 114 downregulated genes from MET vs GAA, 202 upregulated and 204 downregulated genes from GAA vs MET+GAA, and 35 upregulated and 133 downregulated genes from MET vs MET+GAA treated heifers (P ≤ 0.05). Over-representation analysis of DEGs highlighted immune response pathways that were found amongst the GAA vs CON, MET vs GAA, and GAA vs MET+GAA comparisons. Genes associated with cell inflammatory and immune response, including CD14, Toll-like receptor (TLR) 6, CD86, and TLR8, were upregulated in the GAA treatment. The TLR genes regulate expression of several pro-inflammatory cytokines, whereas CD genes are responsible for cell inflammatory response. Both are important for regulation of lipopolysaccharide (LPS)-binding protein, which plays a subsequent role in immune recognition when bound with LPS, resulting in genes from these families being recognized as markers for inflammatory response in beef cattle. Between MET vs CON and MET+GAA vs CON comparisons, 15 pathways including skeletal system development, alpha-amino acid catabolic process, and acylglycerol catabolic processes were shared. The FABP1 gene was upregulated in both aforementioned comparisons and has an integral role in transport and metabolism of fatty acids within cattle. Providing supplementation of methyl donors to the maternal environment results in over-representation of fetal muscle genes acting on immune response as well as fatty acid and amino acid metabolism. USDA is an equal opportunity provider and employer.