CLONAL ANALYSIS OF CHIMERIC MOUSE OVARIES USING DNA IN-SITU HYBRIDIZATION

Analysis of chimaeric mouse ovaries using DNA in situ hybridization wa s undertaken to (i) investigate the morphogenesis of follicular cell c lonal expansion, (ii) evaluate whether the different cell populations within the ovary are derived from the same or unrelated progenitor cel ls and (iii) estimate the number of progenitor cells giving rise to th e different types of ovarian cell. Chimaeras were produced by aggregat ion of eight-cell morulae from normal mice and those transgenic for th e beta-globin gene. Chimaeric blastocysts were transferred to pseudopr egnant hosts and the ovaries of resultant adult offspring were prepare d for in situ hybridization using a digoxigenin-labelled cDNA probe to the beta-globin gene. Results showed that follicles are constructed b y the non-random, radial proliferation of granulosa cell clones, which form long, thin, unbranched columns across the follicle wall. Qualita tive and quantitative studies revealed that both peripheral and centra l granulosa cells are derived from the same progenitor cells. Phenotyp ic differences may therefore be due to positional cues within the foll icle rather than being cell lineage dependent. It is suggested that gr anulosa cells and germinal epithelium may be partly derived from the s ame progenitor cells and that theca externa is probably derived from i nterstitial tissue. However, results from this study did not support t he contention that theca interna and theca externa-interstitial tissue have the same origin, and it is suggested that the former cell type m ay exist in an undifferentiated state from early stages of follicle de velopment. Furthermore, granulosa and germinal epithelium appear to be derived from different progenitor cells from either theca interna or theca externa-interstitial cells. Evidently, all types of ovarian cell , including the somatic cells of individual follicles, are derived fro m more than one progenitor cell.