Fertilizability and chromosomal integrity of frozen-thawed Bryde's whale (Balaenoptera edeni) spermatozoa intracytoplasmically injected into mouse oocytes

Prior to attempting the in vitro production of embryos in the Bryde's whale (Balaenoputera edeni), we investigated whether spermatozoa can retain the capacity for oocyte activation and pronucleus formation as well as chromosomal integrity under cryopreservation by using intracytoplasmic sperm injection (ICSI) into mouse oocytes. Regardless of motility and viability, whale spermatozoa efficiently led to the activation of mouse oocytes (90.3–97.4%), and sperm nuclei successfully transformed into male pronucleus within activated ooplasm (87.2–93.6%). Chromosome analysis at the first cleavage metaphase (M) of the hybrid zygotes revealed that a majority (95.2%) of motile spermatozoa had the normal chromosome complement, while the percentage of chromosomal normality was significantly reduced to 63.5% in immotile spermatozoa and 50.0% in dead spermatozoa due to the increase in structural chromosome aberrations. This is the first report showing that motile Bryde's whale spermatozoa are competent to support embryonic development.