BOVINE SYNEPITHELIOCHORIAL PLACENTATION IS A BARRIER TO FETAL MICROCHIMERISM

Abstract

The diversity in placental structure and functional attributes have co-evolved with the biodiversity in eutherian mammals. Synepitheliochorial placentation is the most recent evolutionary innovation observed in cows, characterized by binucleate trophoblast giant cells and fetal-maternal hybrid cells at the intact fetal-maternal placental interface of placentomes. The non-invasive trophoblast cells, unlike those found in species with hemochorial and endotheliochorial placentation, maintain the structural integrity of the maternal endometrium, limiting access of fetal cells and its content to the uterine epithelium in cows. However, the accessibility of fetal cells and/or their DNA to maternal circulation and solid organs during gestation and/or parturition results in a condition known as fetal microchimerism. It has been reported to occur in humans, rodents, sheep, cattle, non-human primates, and dogs irrespective of differences in placentation types among those species. This study used highly specific and sensitive end-point PCR primers to investigate transplacental leakage of fetal cells into maternal circulation in cows at gestation, parturition , and post-partum. The study did not detect any male fetal DNA in maternal circulation. Earlier works in pigs and goats have also failed to detect any transfer of fetal cells or their DNA across the placental barrier. Placental abnormalities and pathologies may facilitate transfer of fetal cells in bovine making mechanisms for such exchange physiologically unlikely.