Clonal analysis of chimaeric mouse ovaries using DNA in situ hybridization

Analysis of chimaeric mouse ovaries using DNA in situ hybridization was undertaken to (i) investigate the morphogenesis of follicular cell clonal expansion, (ii) evaluate whether the different cell populations within the ovary are derived from the same or unrelated progenitor cells and (iii) estimate the number of progenitor cells giving rise to the different types of ovarian cell. Chimaeras were produced by aggregation of eight-cell morulae from normal mice and those transgenic for the beta-globin gene. Chimaeric blastocysts were transferred to pseudopregnant hosts and the ovaries of resultant adult offspring were prepared for in situ hybridization using a digoxigenin-labelled cDNA probe to the beta-globin gene. Results showed that follicles are constructed by the non-random, radial proliferation of granulosa cell clones, which form long, thin, unbranched columns across the follicle wall. Qualitative and quantitative studies revealed that both peripheral and central granulosa cells are derived from the same progenitor cells. Phenotypic differences may therefore be due to positional cues within the follicle rather than being cell lineage dependent. It is suggested that granulosa cells and germinal epithelium may be partly derived from the same progenitor cells and that theca externa is probably derived from interstitial tissue. However, results from this study did not support the contention that theca interna and theca externa-interstitial tissue have the same origin, and it is suggested that the former cell type may exist in an undifferentiated state from early stages of follicle development. Furthermore, granulosa and germinal epithelium appear to be derived from different progenitor cells from either theca interna or theca externa-interstitial cells.(ABSTRACT TRUNCATED AT 250 WORDS)