Alterations in Transcriptional Profile As the Result of Prenatal Heat Stress Exposure in Pigs

Gestation marks a developmental time sensitive to the epigenetic impact of environmental influences on gene expression.  Prenatal heat stress (HS) in pigs alters body composition, body temperature and metabolic profile later in life.  Study objectives were to investigate effects of prenatal exposure to HS on the transcriptional profile in pigs during the finishing growth phase. Forty-eight offspring from 14 first parity crossbred gilts were exposed to one of four environmental treatments (TNTN, TNHS, HSTN, or HSHS) in utero. TNTN and HSHS treatments were exposed to thermal neutral or HS conditions during the entire gestation, respectively. HSTN and TNHS were heat-stressed for the first or second half of gestation, respectively.  At 19 weeks of age, twelve offspring for each gestational treatment were sacrificed and liver, adipose tissue (AT), and longissimus dorsi (LD) were collected.  RNA-Seq using Illumina HiSeq produced an average of 10.7, 15.2, and 11.1 million mappable reads per library of which expression of 20, 42, and 434 transcripts were affected by gestation treatment in AT, liver and LD, respectively.  Methylation status for seven CpG positions upstream of MEF2A, a differentially expressed transcript in LD, were evaluated in the HSHS and TNTN treatments following bisulfite conversion and sequencing.  Methylation percentage at the CpG position 1937 bp upstream of exon 1 was marginally correlated (R² = 0.26, P < 0.09) to transcript abundance.  Exposure to HS during prenatal development may influence the establishment of the methylome during cellular differentiation, resulting in future alterations in transcriptional profile of specific tissues.