Meiotic spindle visualization in living human oocytes

A computer-assisted polarization microscopy system (polscope) has made it possible to analyse the meiotic spindle of oocytes subjected to intracytoplasmic sperm injection (ICSI) without affecting their viability. It has been shown that the presence of a detectable birefringent meiotic spindle inside the oocyte cytoplasm of human metaphase II (MII) prepared for ICSI is an indicator of oocyte quality, such as fertilization and developmental ability. Meiotic spindle imaging has also shown that this structure, when detectable, is not always aligned with the first polar body (PB1) in fresh MII oocytes. The relationship between the degree of meiotic spindle deviation from the PB1 location and ICSI outcomes is discussed in this paper. When the meiotic spindle of in-vitro matured oocytes is analysed, it is always found to be aligned with the PB1, suggesting that the misalignment observed in the oocytes matured in vivo results from the PB1 displacement during the manipulations for the cumulus and corona removal. Furthermore, polscope analysis of meiotic spindle changes in living MII oocytes subjected to freezing and thawing procedures has shown that the current techniques of oocyte cryopreservation cause meiotic spindle destruction. The polscope system may assist in the selection of fresh and thawed oocytes for ICSI.