Validation of fetal microchimerism after pregnancy in the ovine using qPCR

Fetal microchimerism has been detected in maternal tissues of humans and rodents during and after pregnancy. Studies focusing on fetal DNA transfer to maternal tissues in domestic animals are limited, especially in sheep. Fetal ram DNA was observed in the maternal circulation during pregnancy, but it is not known if this chimerism persists in soft tissues after parturition. The objectives of this exploratory study were to: 1) determine if male fetal DNA is detectable in soft tissues of mature ewes after parturition and if so, determine if detection repeatability differed with lifetime offspring sex ratio and 2) determine if male fetal DNA was present in soft tissues of yearling (primiparous) ewes shortly after parturition. Eight mature (open, non-lactating) and 8 yearling (primiparous, periparturient) Rambouillet ewes were used. Mature ewes (5- to 7-yr old) had given birth to primarily 82% males (n = 4) or 71% female (n = 4) over a lifetime. Yearling ewes had birthed either a singleton male (n = 4) or female (n = 4) lambs. DNA was extracted from 10 and 11 different soft tissues from the mature and yearling ewes, respectively. Real-time PCR (qPCR) was used to identify the presence of the SRY gene in each tissue sample. Male DNA was detected in the brain and liver from one mature open ewe that had given birth to two males and six females during her lifetime. In younger ewes that gave birth to a ram lamb, male DNA was observed in the thyroid of one ewe and the pancreas and brain of a second ewe. Male DNA was detected in the ovary of one ewe that had given birth to a female lamb. Based on these data, we suggest fetal microchimerism in soft maternal tissues is possible in sheep and may remain after pregnancy has ended. The detection repeatability of male fetal DNA was not associated with sex ratio of lifetime offspring. Male DNA was observed in maternal soft tissues collected shortly after parturition. The greater detection of fetal male DNA found in younger ewes shortly after parturition may be due to not having enough time for fetal DNA clearance to occur. Future studies are warranted to further study XY chimerism in maternal tissues of the ewe and its potential role in ovine physiology.