Evidence for the oligoclonal origin of the granulosa cell population of the mature human follicle.

The clonality of the granulosa cell population residing in individual mature human ovarian follicles was examined by determining the pattern of X chromosome inactivation. Granulosa cells from 72 follicles were obtained from 9 patients undergoing oocyte harvest for in vitro fertilization. The granulosa cell DNA obtained from each follicle was subjected to the PCR, to amplify a highly polymorphic region of the X-linked human androgen receptor gene, after digestion by the methylation-sensitive HpaII restriction endonuclease, thereby achieving exclusive amplification of the inactive allele. Seventeen of 65 informative follicles (26 +/- 5%) were comprised of granulosa cells exhibiting inactivation of the same X chromosome. At least 1 such follicle was found in 8 of the 9 women sampled. There are 2 possible explanations for these findings: 1) approximately one fourth of all follicles contain a truly monoclonal granulosa cell population; 2) the granulosa cells of a given follicle are derived from a small number of stem cells (3 cells), such that the probability is 0.25 that all 3 stem cells producing the granulosa cell complement of a given follicle have the same X chromosome inactivated by chance. We favor the latter explanation and conclude that the granulosa cell cohort of mature human follicles is oligoclonal.