Studies On Germinal Vesicle Chromatin Configuration Of Rabbit Oocytes

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 during follicular growth; however,no such ring was observed in goat oocytes. 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 ,maturation and atresia of rabbit oocytes were studied using methods that allow a clearer visualization of both the nucleolus and the chromatin after Hoechst33342 staining. On the basis of the degree of condensation and distribution, the GV chromatin of rabbit oocytes was classified into five configurations:NSN:diffuse chromatin throughout the nucleus, with nucleoli nonsurrounded by chromatin;N:net-like chromatin throughout the nucleus, with nucleoli surrounded by chromatin;LCC(loosely condensed chromatin): chromatin condensed into loose clumps with an irregular outline throughout the nucleus, nucleoli surrounded by chromatin;TCC(tightly condensed chromatin): chromatin condensed into dense clumps with an regular outline throughout the nucleus or near the nuclear envelope, nucleoli surrounded by chromatin;SCC(singly condensed chromatin): chromatin condensed into a single clump, nucleoli disappeared. The results are as follows:1.Compared with other species, the perinucleolar chromatin ring of rabbit oocytes appeared in the primordial follicles.2.With follicular growth,diffuse chromatin condensed gradually, NSN disappeared,N,LCC,TCC began to emerge and were the dominant configuration of≤0.4,0.7-1.0,and≥1.1mm follicular oocytes respectively. The low proportions of SCC appeared only in the large follicular oocytes.3. During maturation in vivo, most of the oocytes were synchronized at the LCC configuration before GVBD.During maturation in vitro,both LCC and TCC were able to GVBD directly and the maturation dynamics of TCC advanced than LCC.4.The LCC configuration might represent a healthy state, whereas TCC and SCC might be indicative of atresia.5.The NSN and N configurations were juvenile chromatin patterns without meiotic competence;LCC gained the meiotic competence but didn't acquire the full developmental competence;TCC gained the full meiotic competence and developmental competence.