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 fertil ization. The granulosa cell DNA obtained from each follicle was subjec ted to the PCR, to amplify a highly polymorphic region of the X-linked human androgen receptor gene, after digestion by the methylation-sens itive HpaII restriction endonuclease, thereby achieving exclusive ampl ification of the inactive allele. Seventeen of 65 informative follicle s (26 +/- 5%) were comprised of granulosa cells exhibiting inactivatio n 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 find ings: 1) approximately one fourth of all follicles contain a truly mon oclonal granulosa cell population; 2) the granulosa cells of a given f ollicle 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 granu losa cell complement of a given follicle have the same X chromosome in activated by chance. We favor the latter explanation and conclude that the granulosa cell cohort of mature human follicles is oligoclonal.