Retinol-Binding Protein: A Major Secretory Product of the Pig Conceptus1

Abstract

Pig conceptuses and endometrial explants recovered from gilts between Days 10 and 15 of pregnancy were cultured in leucine-deficient or methionine-deficient medium supplemented with 3H-leucine or 35S-methionine, respectively, for 30 h. Conceptus and endometrial tissues from Day 15 of pregnancy were fixed in Bouin's fixative for immunocytochemistry and light microscopy. Conceptus culture medium from Day 15 of pregnancy was pooled, dialyzed, and fractionated by anion exchange and gel filtration chromatography. A family of 3-5 low molecular weight (Mr) acidic (Mr = 19,000-22,000; pI = 5.6-6.5) 3H-leu-labeled proteins were isolated and identified by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), electroblotting, and fluorography. The two major proteins (pCSP-1 and pCSP-2) were excised from a polyvinylidene difluoride transfer membrane, and NH2-terminal amino acids were sequenced. One peptide was sequenced through 33 amino acids and the second, which shared 100% homology, was sequenced through 22 amino acids. Analysis of the larger sequence indicated that it shared 93.9% and 90.9% homology with the first 33 amino acids of human and rabbit plasma retinol-binding protein (RBP), respectively. Analyses of culture medium from pig conceptus incubations by 2D-PAGE and immunoprecipitation with rabbit anti-human RBP serum indicated that immunoreactive RBP was produced between Days 10 and 15 of pregnancy and was present in Day 30 allantoic fluid. Western blotting of enriched fractions of Day 15 conceptus RBP followed by immunostaining indicated that five isoforms of radiolabeled RBP were present. Immunoreactive RBP was detected in trophectoderm and yolk sac of conceptuses and endometrial surface and glandular epithelium at Day 15 of pregnancy. Results from this study demonstrate that pig conceptuses secrete RBP prior to onset of conceptus elongation and throughout the peri-implantation period, which suggests that RBP and associated retinoids influence conceptus development.

Expression of retinol‐binding protein messenger RNA and retinoic acid receptors in preattachment bovine embryos

“…RT-PCR is a very sensitive technique and is capable of detecting low abundance transcripts that may be beyond the detection power of in situ hybridization depending on the signal to noise ratio in the in situ assay. Similarly, RBP has been shown to be actively secreted by the day 13 elongated sheep conceptus (Liu et al, 1992) and the elongated pig conceptus (Harney et al, 1990). Transcripts for RBP have been localized to the inner cell mass and trophectoderm of the elongating pig conceptus (Trout et al, 1991).…”

Candidate gene analysis for loci affecting litter size and ovulation rate in swine.

“…Yelich et al (1997) stated that most embryonic death losses occur between d 10 and 18 of gestation, concurrent with trophoblast elongation and secretion of estrogen by the conceptus. Retinolbinding protein 4, a major protein produced by the conceptus, may have a role in trophoblast elongation (Harney et al, 1990). It also enhances gene expression of transforming growth factor β via retinoic acid receptors (Yelich et al, 1997).…”

Within-litter variation in birth weight: impact of nutritional status in the sow

“…Moreover, sows on vitamin A-deficient diets did not experience a reduction in fetal survival and growth at Day 30 of pregnancy , perhaps due to a compensatory increase in the abundance of retinol binding protein (RBP) (Antipatis et al, 2008). Since pig conceptuses secrete RBP prior to onset of elongation and throughout the peri-implantation period, RBP could be an important component of the uterine secretions for early embryonic development (Harney et al, 1990;Schweigert et al, 1999). Thus, elevated levels of RBP in gilts deficient in vitamin A can account for positive outcomes of piglets having low within-litter variation in birth weight.…”