Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2009
Publication Date: 2/1/2010
Citation: Vallet, J.L., Miles, J.R., Freking, B.A. 2010. Effect of Fetal Size on Fetal Placental Hyaluronan and Hyaluronoglucosaminidases Throughout Gestation in the Pig. Animal Reproduction Science. 118(2-4):297-309.
Interpretive Summary: During pregnancy, the pig placenta is responsible for delivery of nutrients to the developing pig fetuses. The microscopic structure of the placenta contributes to the efficiency of nutrient delivery. Specifically, the part of the placenta where sow tissues meet fetal tissues becomes highly folded, increasing the surface area of interaction which increases nutrient transfer from sow to fetus. Little is known about the folds develop. On the fetal side of the placenta, the folds are surrounded by a tissue called stroma that provides support and structure for the fetal part of the placenta. The stroma must be altered to allow fold development, thus the composition of the stroma provides clues to proteins involved in fold development. In this experiment, we demonstrated that hyaluronan, a polymer made up of glucose derived molecules, is a major component of placental stroma. Hyaluronidases are enzymes that degrade hyaluronan. We further demonstrated that hyaluronidases were present in placental tissues, and their concentrations were consistent with a role for these enzymes in placental fold development. A clear understanding of how the placenta develops during pregnancy will lead to improvements in nutrient transport from the sow to the pig fetus, which will result in increased litter size, increased piglet birth weights, and reduced perinatal and preweaning mortality of piglets.
Technical Abstract: Previous results indicated that the trophoblast-endometrial epithelial cell bilayer of porcine placenta undergoes microscopic folding during gestation, and the folded bilayer is embedded in placental stroma. We hypothesized that hyaluronan was a component of placental stroma, and that hyaluronidases played a role in bilayer folding. Gilts were unilaterally hysterectomized-ovariectomized (UHO) at 160 days of age, mated at estrus and killed on days 25, 45, 65, 85 or 105 of gestation. Placental tissues were collected to evaluate hyaluronan and hyaluronidase content. Placental hyaluronan concentration increased (P < 0.01) between day 25 and 45 of gestation, remained high throughout gestation, and was greater (P < 0.05) in the placenta of the smallest compared to the largest fetuses on day 105 of gestation. Hyaluronan was localized to placental stroma. Three cDNAs for hyaluronidase 1 (two 1379 and one 1552 bp) and one cDNA (1421 bp) for hyaluronidase 2 were cloned from day-85 placental RNA. Expression analysis indicated that the 1379 bp form of hyaluronidase 1 mRNA did not differ, the 1552 bp form increased, and the 1421 bp form of hyaluronidase 2 decreased during pregnancy. Expression of all three mRNAs was greater (P < 0.05) in placenta of the smallest compared to the largest fetuses. Zymography indicated 70 and 55 kd protein isoforms of hyaluronidase in placental tissue. Both forms increased with advancing gestation and were greater in placentas of the smallest compared to the largest fetuses (P < 0.05). These results are consistent with a role for hyaluronan and hyaluronidases in the development of the microscopic folds of the pig placenta during gestation.