Germinal vesicle chromatin configurations of bovine oocytes

Abstract

A common feature in the configuration of germinal vesicle (GV) chromatin in most species is that diffuse chromatin condenses into a perinucleolar ring during follicular growth; however, no such ring was observed in goat oocytes. Reports on whether bovine GV chromatin condenses into a perinucleolar ring are controversial. Besides, it is not known whether the perinucleolar ring in an oocyte represents a step toward final maturation or atresia. Changes in GV chromatin configurations during growth and maturation of bovine oocytes were studied using a new method that allows a clearer visualization of both the nucleolus and the chromatin after Hoechst and chromomycin A(3) staining. On the basis of the degree of condensation and distribution, the GV chromatin of bovine oocytes were classified into five configurations: NSN with diffuse chromatin in the whole nuclear area, N with condensed netlike chromatin, C with clumped chromatin, SN with clumped chromatin surrounding the nucleoli, and F with floccular chromatin near the nucleoli and near the nuclear envelope. Most of the oocytes were at the NSN stage in the <1.4-mm follicles, but the NSN pattern disappeared completely in follicles larger than 1.5mm. The SN pattern began to emerge in 1.5-mm follicles, and the number of SN oocytes increased while the number of oocytes with N and C configurations decreased with follicular growth. During maturation in vivo, while the number of N, C, and SN oocytes decreased, that of the F oocytes increased and reached maximum at 51h post prostaglandin injection. After that, the number of F oocytes decreased significantly because of germinal vesicle breakdown (GVBD). During maturation in vitro, GV chromatin configurations changed in a similar manner as during maturation in vivo. Fewer oocytes were at N, C, and SN stages, but more were at F and GVBD stages in the atretic than in the healthy follicles. Serum starvation slowed the F-GVBD transition of the in vitro maturing oocytes. More oocytes were of the SN or C configuration when ovaries were transported at 45-40 degrees C than at 35-30 degrees C. Most of the heated oocytes were blocked at the SN stage during in vitro maturation. It is concluded that (i) bovine GV chromatin condenses into a perinucleolar ring during follicular growth; (ii) bovine oocytes were synchronized at the F stage before GVBD; (iii) oocyte GV chromatin configurations were affected by serum starvation, high temperature, and follicular atresia.

Modifications in chromatin morphology and organization during sheep oogenesis

“…However, differently to the mouse, the SN configuration did not represent the more advanced configuration toward ovulation, since medium and preovulatory antral follicles developed a new pattern of GV organization where the condensed chromatin appeared localized partly around the nucleolus and partly close to the nuclear envelope (SNE pattern). Recently, similar observations were reported from Liu et al (2006) in bovine fully grown oocytes before GVBD suggesting that the ruminants have more in common with each other than with different mammalian species (mouse, pig).…”

“…Many reports linked a highly condensed chromatin to an inactive transcriptional form of chromatin that precedes the meiotic competence (De La Fuente, 2006;Liu et al, 2006;Zuccotti et al, 2005). A growing body of evidence indicates that the chromatin structure together with DNA methylation mutually reinforce the transcriptionally repressive states of DNA (Fuks et al, 2003;Tamaru and Selker, 2001).…”

Morphologic indicators predict the stage of chromatin condensation of human germinal vesicle oocytes recovered from stimulated cycles

“…Because the GV chromatin condensation stage previously has been related to oocyte quality in IVM, transcriptional activity, and nuclear, cytoplasmic, and genomic competence (4,11,14), our next objective is to determine whether this new predictive GVoocyte classification is related to meiotic and cytoplasm competence.…”

Spontaneous in vitro maturation and artificial activation of human germinal vesicle oocytes recovered from stimulated cycles

“…A cohort can include mature metaphase II (MII) oocytes, which usually have reproductive potential, and immature oocytes, which are discarded from IVF protocols. Immature oocytes also vary in their chromatin configuration (9)(10)(11)(12)(13)(14)(15)(16), ability to progress to meiosis (9,10,17), and cytoplasmic and developmental competence (10,13,18,19).…”