Studies On Germinal Vesicle Chromatin Configuration Of Golden Hamster Oocytes

There are more evidences showing that variouse stages of antral follicular oocytes before in vitro maturation first reflected on the chromatin configuration of the nucleus,may account for the observed flaw of in vitro maturation system. The configuration of germinal vesicle (GV) chromatin has been studied and found correlated with the developmental competence of oocytes. A common feature in the configuration of GV chromatin in most species studied is that the diffuse chromatin condenses into a perinucleolar ring with oocyte development. Studies have shown that this modification occurs coincidently with the acquisition of meiotic competence, and that it reflects a greater potential for normal embryo development. The golden hamster is an excellent model animal for many research fields. It represents an attractive species for studies ranging from reproductive physiology, oncology, genetics and virology. Until now, no report of configuration of GV chromatin of golden hamster oocytes is seen. In order to investigate the relationships between the configuration of GV chromatin and developmental competence of golden hamster oocytes, this study was conducted.The oocytes were obtainned from 6-week-old golden harmsters under three treatments: (1) non-hormone treatment; (2) PMSG treatment; (3) PMSG and hCG combined treatment. The oocytes at GV stage were collected according to their diameters by two methods: small oocytes (≤120μm) were collected by digestion, and large oocytes (>120μm) were collected by a syringe to stab the surface of follicle. The collected oocytes were denuded of cumulus cells with 0.1% hyaluronidase, and stainned by 10 mg/ml of Hoechst 33342 for 10 min. The oocytes were then placed on glass slides and squashed with coverslips to visualize GVs under UV. The results are as follows:1. Five types of GV chromatin configurations were observed in golden hamster oocytes according to the degree of condensation and distribution and they were: GV1 (diffuse chromatin throughout the nucleus); GV2 (chromatin condensed into clumps, with nucleoli nonsurrounded by chromatin); GV3 (condensed chromatin formed 2-4 clumps and can be detected near the nuclear envelope, nucleoli surrounded by chromatin); GV4 (the nucleolus was enveloped completely by condensed chromatin); GV5 (chromatin condensed into large clump, nuclear envelope and nucleoli disappeared) ;2. With oocyte growth, diffuse chromatin condensed gradually, GV1 stage disappears gradually and GV3 to GV5 stages begin to appear;3. The GV3 stage is the dominant configuration when oocyte diameters are larger than 100μm;4. GV1 and GV2 stages disappear gradually after PMSG and hCG treaments. Both PMSG and hCG can increase the extent of chromatin condense;5. Configurations of GV chromatin in most of the oocytes matured in vivo were synchronized at the GV3 before GVBD; and configurations of GV chromatin in oocytes matured in vitro were synchronized at GV3 and GV4 before GVBD; and GV3 is the dominant;6. The GV1 and GV2 configurations were juvenile chromatin patterns without meiotic competence; GV3 and GV4 gained the meiotic competence; GV3 gained the full meiotic competence.