Secreted Phosphoprotein 1 Expression in Endometrium and Placental Tissues of Hyperprolific Large White and Meishan Gilts

Increased litter size and within-litter uniformity in birth weight would improve pig reproductive efficiency. This study compared the location and gene and protein expression of secreted phosphoprotein 1 in placental and uterine tissues supplying a normally-sized and the smallest fetus carried by Hyperprolific Large White and Meishan gilts on Days 41-42 of pregnancy. Immunohistochemistry and in situ hybridization showed that the protein and gene encoding secreted phosphoprotein 1 were located in the glandular and luminal epithelium of the endometrium and in the placenta. Secreted phosphoprotein 1 protein levels were higher in glandular epithelium, luminal epithelium and placenta from Meishan gilts compared to corresponding tissues from Hyperprolific Large White gilts. Reverse transcription quantitative PCR demonstrated secreted phosphoprotein 1 mRNA levels were higher in endometrium, but not placenta, from Meishan compared to Hyperprolific Large White gilts. In Hyperprolific Large White gilts secreted phosphoprotein 1 protein levels were higher in glandular epithelium and placenta surrounding small fetuses than corresponding tissues supplying normal-sized fetuses. Similarly, in Meishan gilts secreted phosphoprotein 1 protein levels were higher in luminal epithelium surrounding small compared to normal-sized fetuses. Within Hyperprolific Large White, but not Meishan, gilts secreted phosphoprotein 1 mRNA was higher in endometrium surrounding the normal-sized fetus than the control fetus. The contradictory relationship between fetal size and secreted phosphoprotein 1 protein and mRNA in the Hyperprolific Large White is intriguing and may reflect breed differences in post-translational modification. The striking breed differences in secreted phospoprotein 1 expression, suggest that SPP1 may be associated with placental efficiency.