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Oocyte spindle and embryo ploidies

From oocyte retrieval to blastocyst cryopreservation, the best timing to do fertilization is always an important issue in the IVF realm. The techniques of ICSI, or IMSI, can help the embryo technician select the sperm with the best morphology to increase the fertilization rate. After the development of spindle microscope (an modified microscope which can observe the spindle of oocyte), the question of "when to fertilize?" has emerged.

In the newly-released article of Science, the author explained the reason of higher chromosomal aneuploidy in human oocytes in comparison with the other human somatic cells, and mouse oocytes. Holubcova el al. developed a time-lapse system combing with vital stain of human oocyte to record the oocyte maturation process (from GVBD to MII).

They found that the time from GVBD (geminal vesicle breakdown) to initial chromosome congression (~16 hrs) was significantly longer than those in the other mammal meiosis (~3-5 hrs). Instead of mediating by centrosomes or MTOCs (microtubule organizing centers), the mediator in human oocyte meiosis was chromosome itself (Ran-GTP).

Lacking of centrosomes or MTOCs led spindle formation in human oocytes intrinsically unstable and error-prone, and then it made the higher aneuploid rate due to maternal origin in the following embryo propagation.

Of the application in IVF, this time-lapse video of oocyte maturation may provide the users of spindle microscope more information about the accurate timing to do the fertilization, or to cryopreserve the MII eggs.

Original article:
Zuzana Holubcova, Martyn Blayney, Kay Elder, and Melina Schuh
Science 2015;348:1143-1147.

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