In female mammalian cells, one of the two X chromosomes is inactivated to compensate for gene-dose effects, which would be otherwise doubled compared with that in male cells. In somatic lineages in mice, the inactive X chromosome can be of either paternal or maternal origin, whereas the paternal X chromosome is specifically inactivated in placental tissue. In human somatic cells, X inactivation is mainly random, but both random and preferential paternal X inactivation have been reported in placental tissue. To shed more light on this issue, we used PCR to study the methylation status of the polymorphic androgen-receptor gene in full-term human female placentas. The sites investigated are specifically methylated on the inactive X chromosome. No methylation was found in microdissected stromal tissue, whether from placenta or umbilical cord. Of nine placentas for which two closely apposed samples were studied, X inactivation was preferentially maternal in three, was preferentially paternal in one, and was heterogeneous in the remaining five. Detailed investigation of two additional placentas demonstrated regions with balanced (1:1 ratio) preferentially maternal and preferentially paternal X inactivation. No differences in ratio were observed in samples microdissected to separate trophoblast and stromal tissues. We conclude that methylation of the androgen receptor in human full-term placenta is specific for trophoblastic cells and that the X chromosome can be of either paternal or maternal origin.

*Dosage Compensation, Genetic, *Trophoblasts, DNA Methylation, Female, Humans, Male, Placenta/cytology/metabolism, Pregnancy, Receptors, Androgen/*genetics/metabolism, Research Support, Non-U.S. Gov't
hdl.handle.net/1765/9079
American Journal of Human Genetics
Erasmus MC: University Medical Center Rotterdam

Looijenga, L.H.J, Gillis, A.J.M, Verkerk, A.J.H.M, van Putten, W.L.J, & Oosterhuis, J.W. (1999). Heterogeneous X inactivation in trophoblastic cells of human full-term female placentas. American Journal of Human Genetics. Retrieved from http://hdl.handle.net/1765/9079