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An attempt at intracytoplasmic sperm injection of frozen-thawed minke whale (Balaenoptera bonaerensis) oocytes

  • Masatsugu Asada (a1), Hong Wei (a1), Rie Nagayama (a1), Masafumi Tetsuka (a1), Hajime Ishikawa (a2), Seiji Ohsumi (a2) and Yutaka Fukui (a1)...

Little is known about the characteristics of fertilisation events in minke whales. Cryopreserved minke whale oocytes and spermatozoa do not fertilise in a standard IVF. This study was conducted to investigate the pronucleus formation ability of cryopreserved minke whale oocytes and their subsequent development following intracytoplasmic sperm injection (ICSI). In experiment 1, frozen-thawed minke whale immature oocytes were cultured for in vitro maturation (IVM) in a maturation medium (TCM199) supplemented with either porcine follicle stimulating hormone (pFSH)/estradiol-17β(E2) or pregnant mare's serum gonadotropin (PMSG)/human chorionic gonadotropin (hCG). After 120 h of IVM, oocyte survival was examined before ICSI, and showed no significant difference in morphological normality (24-36%) between the two IVM media. Two-cell embryos (two oocytes from 21 sperm-injected oocytes) were obtained when the maturation medium was supplemented with pFSH/E2 or PMSG/hCG. In experiment 2, cryopreserved maturing oocytes were investigated for the effects of repeat-culture (2 h or 24 h) on survival before ICSI. Pronuclear formation and development were examined for the effects of sperm pretreatment with dithiothreitol (DTT) and oocyte activation with ethanol at ICSI. A frequency of 49-69% of frozen-thawed maturing oocytes was used for ICSI. Although oocyte activation did not produce a significant difference in survival, pronucleus formation and embryonic development, 2- and 4-cell cleaved oocytes were observed after injection of sperm pretreated with DTT.

Corresponding author
All correspondence to: Yutaka Fukui, Laboratory of Animal Genetics and Reproduction, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan. Tel: +81 155 49 5415. Fax: +81 155 49 5462. e-mail:
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  • ISSN: 0967-1994
  • EISSN: 1469-8730
  • URL: /core/journals/zygote
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