Quantitation of ribosomal RNA genes in fetal human oocyte nuclei using rRNA: DNA hybridization in situ: Evidence for increased multiplicity

Abstract

Several experimental observations provide evidence for the existence of an amplification-type phenomenon involving the genes for ribosomal RNA (rRNA) during meiotic prophase in the human oocyte. In previous investigations multiple micronucleoli, in addition to primary nucleoli, were shown to be present in late pachytene and in diplotene human oocyte nuclei. In the present study, detailed quantitative analysis of grain counts from more than 1 000 cells following hybridization in situ indicated the presence of greater than the expected 4C number of ribosomal genes in the oocyte nuclei, most notably in these same stages. The extent of this increase over the expected 4C amount of DNA complementary to rRNA was approx. 2-fold in oocytes early in meiotic prophase and rose to approx. 4-fold in late pachytene and early diplotene oocytes. These results constitute the first evidence for the presence of extra rDNA in mammalian oocyte nuclei, the occurrence of which is clearly consistent with earlier cytological and ultrastructural observations.