STUDIES OF X CHROMOSOME INACTIVATION IN THE HUMAN PLACENTA
The question of random or preferential X chromosome inactivation in the early differentiating tissues of the human placenta has not been satisfactorily answered. Our study analyzed X-linked glucose-6-phosphate dehydrogenase (G6PD) variants in placentae from 20 male and 300 female term infants to ascertain the source of previously reported maternal enzyme contamination and to compare activites of the maternally and paternally derived X chromosomes in fresh female placental tissues and fibroblasts cultured from them, with the following findings: (1) karyotypes of cultured amnion, chorion, and villi from males showed no contaminating maternal (46XX) cells. G6PD analysis of tissues revealed decidual remnants adhering to the chorion laeve to be the source of maternal enzyme. (2) Screening of 300 female placentae and maternal blood and/or decidua yielded 37 cases in which the infant and placenta were heterozygous for G6PD (AB) and the mother homozygous (8 AA, 29 BB), thus identifying parental sources of the enzyme alleles. Ultraviolet spectrophotometry revealed considerable G6PD activity, even though little enzyme was seen in most amnion and chorion with cellulose acetate electrophoresis. In the cases in which G6PD was measurable on electrophoresis, the amnion and chorion revealed preferential X('M) activity (p < .05). It was not possible to remove all contaminating fetal blood from villi, so activities of X('P) and X('M) in this tissue were not compared. To remove erythrocytes and extend the amount of informative material, amnion, chorion, and villi were cultured and the resultant fibroblasts electrophoresed. Cultured cells showed significant (p < .05, p < .02, p < .001, respectively) preferential expression of the maternally derived allele irrespective of the enzyme variant involved. It is thus proposed that in humans, tissues derived from those earliest to differentiate within the blastula exhibit preferential activity of the maternally derived X chromosome. ^
HARRISON, KATHLEEN WILKE, "STUDIES OF X CHROMOSOME INACTIVATION IN THE HUMAN PLACENTA" (1982). ETD Collection for Fordham University. AAI8219246.