Identification of fetal microchimerism after pregnancy in older ewes using qPCR

Authors: BROWN, ALISON - Wingate University; NILAND, ERIKA - Wingate University; Cherry, Natalie; Taylor, Joshua - Bret

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2021
Publication Date: 6/2/2021
Citation: Brown, A., Niland, E.S., Pierce, N.L., Taylor, J.B. 2021. Validation of fetal microchimerism after pregnancy in the ovine using qPCR. Translational Animal Science. 5(2). https://doi.org/10.1093/tas/txab100.
DOI: https://doi.org/10.1093/tas/txab100

Interpretive Summary: Male cells hanging out in females??? During pregnancy, cells from the fetus may cross over the placenta and enter the circulation of the mother and vice versa. This process is referred to as microchimerism. Cells from the fetus have been found to colonize in the mother’s tissues and organs decades after pregnancy has ended. Interestingly, human male fetal cells have been identified in tissues of women affected by certain autoimmune diseases. However, the exact role of fetal cells concerning health is unknown. We set out to determine, first, if fetal microchimerism occurs in sheep. Indeed, we identified male fetal DNA in the brain and liver of an older female sheep (aka, ewe). At this time, the origin of the male DNA is not known, because not only did the ewe give birth to male offspring during her lifetime, but she was born as a triplet with two male brothers. We intend to further investigate the source of microchimerism in sheep and subsequently determine if fetal male cells residing in ewes have a lifelong effect on the ewe’s general health and reproductive success.

Technical Abstract: The presence of a male littermate in-utero may impact lifetime reproductive performance in the co-sibling ewe. XY chimerism, thought to originate from a male co-twin, has been observed in ewes, and may be associated with the rare development of freemartins. Fetal ram DNA has been observed in maternal circulation during pregnancy, but it is unknown if this chimerism persists after parturition. The objective of this study was to determine if fetal male cells were present in soft tissues of older ewes and if so, does the occurrence differ with lifetime offspring sex ratio. Eight Rambouillet ewes approximately seven years-old and having given birth to at least 71% female (n = 4) or 82% males (n = 4) were tested. DNA was extracted from 10 different tissues from each ewe (n = 80). In triplicate, real-time PCR (qPCR) was used to identify the presence of the SRY gene in each sample. Using an SRY primer pair, male DNA was identified in the brain (between 1.25ng / µL and 125 pg / µL) and liver (between 125 and 12.5 pg / µL) from a ewe that had given birth to two males during her lifetime. If any additional male fetal DNA was present, it was below the detectable limits. This ewe was also born with two male co-siblings, thus the origin (sibling or offspring) of the male DNA is not known. These data indicated that fetal cell transfer in sheep is possible, but did not detect an association of frequency of fetal microchimerism with sex ratio of lifetime offspring.