Differences in resistance against osmotic challenge among C57BL/6, DBA/2 and their hybrid mice metaphase II (MII) stage oocytes.

Abstract

Oocytes of B6D2F1 (BDF1) mice are often used as recipients for intracytoplasmic sperm injection because of their cell membrane resistance against capillary penetration. It is assumed that oocytes of BDF1 mice have superior traits because of their hybrid vigour. However, the mechanisms of hybrid vigour are unclear. In this study, we focused on the membrane resistance of MII stage oocytes against changes in extracellular osmotic pressure. As a result, MII stage oocytes of inbred C57BL/6 and DBA/2 mice showed high tolerance in either a hypertonic or a hypotonic environment. Conversely, MII stage oocytes of hybrid BDF1 and D2B6F1 mice showed high tolerance in both hypertonic and hypotonic environments. Therefore, it is considered that MII stage oocytes of hybrid mice have superior traits than those of inbred mice. Our findings demonstrated that the hybrid vigour exists in the form of resistance to extracellular osmotic environment in hybrid MII stage oocytes.