Differential Transcriptional Activity Associated with Chromatin Configuration in Fully Grown Mouse Germinal Vesicle Oocytes1

Abstract

It was previously shown that fully grown ovarian germinal vesicle (GV) oocytes of adult mice exhibit several nuclear configurations that differ essentially by the presence or absence of a ring of condensed chromatin around the nucleolus. These configurations have been termed, respectively, SN (surrounded nucleolus) and NSN (nonsurrounded nucleolus). Work from our and other laboratories has revealed ultrastructural and functional differences between these two configurations. The aims of the present study were 1) to analyze the equilibrium between the SN and the NSN population as a function of the age of the mice and the time after hCG-induced ovulation and 2) to study the polymerase I (pol I)- and polymerase II (pol II)-dependent transcription in both types of oocytes through the detection of bromouridine incorporated into nascent RNA. We show 1) that ovarian GV oocytes exhibiting the SN-type configuration can be found as soon as 17 days after birth in the C57/CBA mouse strain and 2) that the SN:NSN ratio of ovarian GV oocytes is very low just after hCG-induced ovulation and then increases progressively with the time after ovulation. Furthermore, we demonstrate that the SN configuration correlates strictly with the arrest of both pol I- and pol II-dependent transcription in mice at any age. Finally, we show that ribosomal genes are located at the outer periphery of the nucleolus in the NSN configuration and that pol I-dependent perinucleolar transcription sites correspond to specific ultrastructural features of the nucleolus. Altogether, these results provide clear-cut criteria delineating transcriptionally active GV oocytes from those that are inactive, and confirm that the SN-type configuration is mostly present in preovulatory oocytes.

Caspase‐2L, caspase‐9, and caspase‐3 during in vitro maturation and fragmentation of the mouse oocyte

“…We have also taken into account the chromatin configuration as already described in GV oocytes (Bouniol-Baly et al, 1999;Zuccotti et al, 2002) where the chromatin may be dispersed in the nucleus (NSN) or condensed around the nucleolus (SN). The SN oocytes are considered as more ready to resume meiosis and more able to be fertilized and to have a good embryo development (for review see Lefèvre, 2008).…”

Effects of in vitro maturation of monkey oocytes on their developmental capacity

“…The enhanced incidence of condensed chromatin configuration (60 to 85%) was investigated in oocytes from small antral follicles with diameters of approximately 1 mm (Schramm et al, 1993;Zheng and Latham, unpublished data). Chromatin condensation is highly associated to the loss of transcriptional activity (Wansink et al, 1993;Aoki et al, 1997;Bouniol-Baly et al, 1999). The correlation between chromatin condensation and silencing of oocyte transcription was confirmed in the rhesus monkey in a recent study (Zheng and Ji, unpublished data).…”

Fully-mature antral mouse oocytes are transcriptionally silent but their heterochromatin maintains a transcriptional permissive histone acetylation profile

“…1e) as the first step in the transition from the NSN to the SN antral oocyte. At this stage of maturation, NSN oocytes possess a high transcriptional activity [1,4,5,11,14,17,18], their chromatin is positive to the antibodies for the acetylated form of H3, H2B and H4, whilst CHCs are seldom positive to the immunostaining. CHCs become positive during the NSN-to-SN transition.…”

“…Antral NSN oocytes are an immature form that in the ovary will acquire the SN-type of chromatin organisation before ovulation [15,24]. These morphological differences underline biological relevance as they have been correlated with changes in transcription: NSN oocytes are transcriptionally active and synthesise all classes of RNA, whereas SN oocytes become transcriptionally inactive [1,4,5,11,14,17,18]. Furthermore, whilst in vitro both types of oocytes are capable of meiosis resumption and reach the metaphase II (MII) stage, MII SN oocytes develop to term, whereas MII NSN oocytes consistently cease development at the 2-cell stage ( [9,25]; for a review see [29]).…”