In vitro maturation (IVM) of human preovulatory oocytes reconstructed by germinal vesicle (GV) transfer

Objective. A micromanipulation-electrofusion procedure is described to transfer germinal vesicles (GVs) between immature human oocytes. Design. This procedure consists of the removal of a GV-containing karyoplast and its subzonal insertion, and its subsequent electrofusion into an enucleated host oocyte at the same developmental stage. The reconstructed GV oocyte is then subjected to in vitro maturation. Setting. An embryology research laboratory at a universal medical center. Patient(s). Oocytes were discarded from ICSI-IVF cycles of patients 23-48 years of age. Intervention(s). In an initial study, GV removal and transfer was performed on the same oocyte; these "self-reconstructed" oocytes were then cultured in vitro for up to 50 h and examined periodically for maturation as judged by the extrusion of the first polar body. In a second study GVs from ''old" oocytes (patients age > 38 years) were successfully transferred into enucleated immature "young" oocytes (patient age < 31 years). Main outcome measure(s). The ability to undergo normal meiotic division was evaluated between reconstructed and control group oocytes. Results. GV removal was achieved in 33/60 aged (> 38 years of age) and 28/47 young (< 31 years of age) oocytes. Nineteen GVs were transferred into young oocytes; of these, 12 fused to form a "reconstructed" oocyte. Following in vitro culture, seven reconstructed oocytes matured to meiosis stage II; this outcome was not significantly different from that of controls (9/13, chi (2) test). Four out of five reconstructed mature oocytes had a normal second meiotic metaphase complement. Conclusion(s). Normal meiosis can take place after the transfer of a GV into an enucleated host oocyte. In view of these findings, GV transfer may have several important applications in the future. First, GV transfer may be a potentially attractive alternative to whole oocyte donation. Secondly, it may also be a valuable research tool that generates the cell models needed to characterize the cytoplasmic-nuclear interplay regulating cell cycle, maturation and fertilization in the human oocyte.