ESPE Yearbook of Paediatric Endocrinology

Brief summary: This in vitro study reports that fully potent oocytes were generated from pluripotent stem cells of the tail of a sexually mature male mouse. These oocytes were able to give rise to offspring after fertilization.

A particular challenge in the care of DSD patients in adulthood is the optimization of fertility potential. Fertility outcome is significantly reduced in all types of DSD depending on the underlying etiology as well as the severity of the condition. When considering fertility potential, it is also important not to assume heterosexual orientation and to be open-minded about the many ways in which fertility can be achieved for individuals. Notably, it should not be assumed that an individual’s gametes must match his or her gender to discuss biological fertility potential. Advancing technology and innovative thinking may enable future fertility for individuals with DSD currently considered to be infertile.

In such an attempt, Murakami K, et al. converted the sex of ES and iPS cells (embryonic stem cells and induced Pluripotent stem cells) by removing the Y chromosome and duplicating the X chromosome. Knocking-in of DsRed reporter into the X chromosome by CRISPR-Cas9 system facilitated the generation of sex-converted ES and iPS cells that embody maternally uniparental disomy of the X chromosome. Uniparental disomy of X chromosome can be caused by unequal segregation of the X chromosomes into daughter cells, a similar machinery would be effective for generating XX ES cells from XO ES cells, but such segregation is quite rare. Fluorescence-activated cell sorting (FACS) followed by fluorescence in situ hybridization (FISH) sorted XX ES clones and DNA sequencing confirmed that XX ES cells were euploid, without any large insertions or deletions. These sex-converted XX ES and iPS cells then underwent germ cell differentiation and oocyte production in differentiation, growth, and maturation cultures in the reconstituted ovary, making it possible to analyze the effect of uniparental disomy in oogenesis. lUniparental maternal disomy of the X chromosome had no effect on oocyte development or gene expression. XX iPS cell-derived oocytes were capable of fertilization with wild-type sperm by in vitro fertilization, and development to two-cell embryos which were transferred to pseudopregnant mice and consequently gave rise to pups. Furthermore, offspring were generated from a single male iPS line via sex conversion in vitro. These results were the gold standard evidence of the proper function of oocytes from the sex-converted PS cells.

Using similar chromosomal alteration techniques Murakami K, et al. successfully eradicated trisomy 16, a model of Down’s syndrome, in iPS cells. This study provides insights that could ameliorate infertility caused by sex or autosomal chromosome disorders, or 46,XY DSD, and opens the possibility of bipaternal reproduction. Nevertheless, a major concern seems a need for detailed monitoring for other conditions related to uniparental disomy and chromosomal rearrangements before human applications.