Heterogeneous X inactivation in trophoblastic cells of human full-term female placentas

L H Looijenga, A J Gillis, A J Verkerk, W L van Putten, J W Oosterhuis

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59 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1445-52
Number of pages8
JournalAmerican journal of human genetics
Issue number5
Publication statusPublished - May 1999
Externally publishedYes


  • DNA Methylation
  • Dosage Compensation, Genetic
  • Female
  • Humans
  • Male
  • Placenta/cytology
  • Pregnancy
  • Receptors, Androgen/genetics
  • Trophoblasts


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