GV卵子染色體重新起動分裂(染色體緻密-->鬆散), 進而引發RNA蛋白質轉錄轉譯&粒腺體重組分布決定GV卵子是否能進一步成熟至MI & MII
GV卵子較MII體積小
位於細胞核旁粒腺體數量分布影響IVM

Hum Reprod. 2015 Jun;30(6):1396-409. doi: 10.1093/humrep/dev083. Epub 2015 Apr 22.

Human cumulus-enclosed germinal vesicle oocytes from early antral follicles reveal heterogeneous cellular and molecular features associated with in vitro maturation capacity.

Sánchez F1, Romero S2, De Vos M3, Verheyen G4, Smitz J2.

Author information

Abstract

STUDY QUESTION:

Are oocyte size, chromatin remodelling, transcriptional activity and mitochondrial distribution in human immature oocytes from early antral follicles retrieved for in vitro maturation (IVM) associated with the acquisition of meiotic competence?

SUMMARY ANSWER:

Oocyte size, chromatin compaction, cessation of RNA synthesis and mitochondria rearrangement around the nucleus are associated with the oocyte's potential to resume meiosis in vitro.

WHAT IS KNOWN ALREADY:

Information on oocyte features that confer meiotic competence in human mainly derives from germinal vesicle (GV) oocytes that failed to resume meiosis following an hCG trigger after ovulation induction cycles. Characterization of cumulus-enclosed GV oocytes from small antral follicles prior to IVM provides knowledge on the initial oocyte status and suggests culture requirements in order to promote oocyte competence in vitro.

STUDY DESIGN, SIZE, DURATION:

Prospective collection of 107 oocytes immediately after retrieval (before IVM) and of 293 GV oocytes that had failed to resume meiosis (after IVM).

PARTICIPANTS/MATERIALS, SETTING, METHODS:

Human oocytes were collected from women with polycystic ovary syndrome (PCOS), receiving in total 450 IU of highly purified-hMG for IVM treatment (patients) or who donated oocytes for IVM research (donors). Oocytes at GV-stage were retrieved from follicles <10 mm (range 2-10 mm) diameter, before IVM (oocytes at retrieval) or those that failed to mature after IVM (meiotically incompetent). Oocytes were allocated for either mitochondrial staining, by incubating in mitotracker red and then fixed; or for nascent RNA staining, which was assessed by fluorescent labelling (Click-iT(®) RNA Assay). In every case, oocyte diameter was recorded and chromatin was stained after oocyte fixation. GV-stage oocytes were analysed by confocal laser-scanning microscopy and their characteristics were compared and related to their meiotic competence.

MAIN RESULTS AND THE ROLE OF CHANCE:

Analysis of oocytes at the immature GV-stage revealed that oocytes at retrieval were significantly larger than those that failed to resume meiosis after IVM (112.7 versus 109.6 µm, P < 0.0001). Oocytes assessed at retrieval showed that 50.6% had a condensed chromatin configuration (perinucleolar chromatin rim) and were consistently transcriptionally silent. This rate matched maturation rates in our current in vitro culture system (49%). However, oocytes that had not reinitiated meiosis after 30 h IVM demonstrated, apart of being smaller in diameter, significantly higher rates of dispersed or intermediate chromatin (P = 0.005). Analysis of mitochondrial distribution revealed that many oocytes at retrieval displayed mitochondrial internalization towards the nucleus (12/30) or a perinuclear mitochondrial distribution (6/30). These mitochondrial patterns were observed more rarely in GV incompetent oocytes following 30 h IVM (16/98 and 1/98, respectively).