Constitutive heterochromatin and micronucleoli in the human oocyte at the diplotene stage.

In the diplotene stage of the human oocyte, the processes of elaboration of the nucleolar material are amplified. The principal nucleoli are more voluminous but their relations with the secondary constrictions and the satellites of the D and G chromosomes are not modified. Numerous micronucleoli, frequently to the number of 15-20 this stage. The most remarkable point is their association to various segments of constitutive heterochromatin: centromeric regions, secondary constrictions of the C9 and probably of the A1 and E16. These observations reveal that the human oocyte at the diplotene stage shows an amplification of the ribosomal cistrons. This phenomenon is homologous, to a more reduced scale, of this described from the inferior vetebrates. Besides, the role of heterochromatin in the synthesis of nucleolar material without the intervention of the classic nucleolar organizers is suggested.