Characterization of uterine epidermal growth factor during early pregnancy in pigs

Genomic research has identified a quantitative trait locus for uterine capacity, a component trait contributing to litter size, on porcine chromosome 8. The epidermal growth factor (EGF) gene, on porcine chromosome 8, may influence uterine capacity because of its growth-promoting activities. Using reverse transcription-polymerase chain reaction (PCR) and iterative screening of a porcine reproductive tissue cDNA library, 4932 bp cDNA sequence coding for porcine EGF precursor was obtained. The predicted protein sequence of the EGF precursor contained 1214 amino acids, similar to human EGF precursor (1207 amino acids, 81% identity). Curiously, the sequence of the mature peptide was less homologous between species than other regions of EGF precursor. The presence of conserved regions outside the mature peptide may suggest that these regions are functionally important. Expression of EGF mRNA in the endometrium of White crossbred gilts (n = 3 to 5 each) was determined by Northern blotting using 20 microg of total RNA from endometrium of D 10, 13, and 15 cyclic, and D 10, 13, 15, 20, 30, and 40 of pregnant gilts. A 3342 bp probe from EGF precursor was used. The bands corresponding to EGF mRNA were quantified by densitometry and results were analyzed by ANOVA. EGF mRNA expression decreased significantly from D 13 to 15 of the cycle and pregnancy (P = 0.04), and from D 30 to 40 of pregnancy (P = 0.01). These findings show that EGF mRNA expression is temporally regulated during the cycle and early pregnancy, and this pattern of gene expression may be important during early conceptus development.