In vitro maturation of human preovulatory oocytes reconstructed by germinal vesicle transfer

To describe a micromanipulation-electrofusion procedure for transferring germinal vesicles (GVs) between immature human oocytes.

Pilot study to assess oocyte maturation after an invasive micromanipulation procedure.

Research laboratory at a university medical center.

Immature oocytes were discarded from intracytoplasmic sperm injection (ICSI)-IVF cycles of patients 23-48 years of age.

Initially, GV removal and transfer were performed on the same oocyte; these "self-reconstructed" oocytes were then cultured in vitro for up to 50 hours and examined periodically for maturation as judged by the extrusion of the first polar body. In a second study, GVs from oocytes of "old" patients (>38 years old) were successfully transferred into enucleated immature oocytes of "young" patients (<31 years old).

Extrusion of the first polar body was monitored in "reconstructed" and control oocytes; karyotypes also were analyzed at meiosis II.

From 48 oocytes from old patients, 12 GVs were successfully removed, transferred, and fused into previously enucleated oocytes from young patients. After in vitro culture, 7 of these "reconstructed" oocytes matured to meiosis II, a maturation rate not significantly different from that observed in nonmanipulated controls. A normal, second meiotic metaphase chromosome complement was observed in 4 of 5 reconstructed oocytes.

Normal meiosis can occur after the transfer of a GV into an enucleated host oocyte. Germinal vesicle transfer may be a valuable research procedure that generates cell models to characterize the cytoplasmic-nuclear interplay for cell cycle regulation, maturation, and fertilization in the human oocyte; it also may be a potentially attractive alternative to oocyte donation.