Acquirement of Oocyte-activating Factor in Antarctic Minke Whale (Balaenoptera bonaerensis) Spermatogenic Cells, Assessed by Meiosis Resumption of Microinseminated Mouse Oocytes

The presence or absence of sperm-borne oocyte-activating factor (SOAF) in the Antarctic minke whale haploid spermatogenic cells was determined by assessing the meiosis resumption of microinseminated mouse oocytes. The relative capacity of mature spermatozoa from mouse, cattle and whale to resume the meiosis of BDF1 mouse oocytes was, respectively, 90.5, 84.6 and 76.5%, while nuclear changes in non-treated or buffer-injected oocytes did not occur after 90-min culture. In the whales, the late-stage elongating spermatids as well as the testicular spermatozoa triggered the meiosis resumption of mouse oocytes at similar rates (oocyte activation rates; 68.0 and 62.5%, respectively). The oocyte activating capacity of the early-stage elongating spermatids was significantly lower (25.0%), and the round spermatids did not activate mouse oocytes at all. This result suggests that the SOAF activity in the Antarctic minke whales is acquired during the early phase of spermiogenesis.