Human germ cell formation in xenotransplants of induced pluripotent stem cells carrying X chromosome aneuploidies

Induced pluripotent stem cells (iPSCs) offer opportunity for insight into the genetic requirements of the X chromosome for somatic and germline development. Turner syndrome is caused by complete or partial loss of the second sex chromosome; while more than 90% of Turner cases result in spontaneous fetal loss, survivors display an array of somatic and germline clinical characteristics. Here, we derived iPSCs from Turner syndrome and control individuals and examined germ cell development as a function of X chromosome composition. We analyzed gene expression profiles of derived iPSCs and in vitro differentiated cells by single cell qRT-PCR and RNA-seq. We whoed that two X chromosomes are not necessary for reprogramming or pluripotency maintenance. Genes that escape X chromosome inactivation (XCI) between control iPSCs and those with X chromosome aneuploidies revealed minimal expression differences relative to a female hESC line. Moreover, when we induced germ cell differentiation via murine xenotransplantation of iPSC lines into the seminiferous tubules of busulfan-treated mice, we observed that undifferentiated iPSCs, independent of X chromosome composition, when placed within the correct somatic environment, are capable of forming early germ cells in vivo. Results indicate that two intact X chromosomes are not required for germ cell formation; however, clinical data suggest that two sex chromosomes are required for maintenance of human germ cells.