To examine whether spontaneous oocyte activation is determined by genetic differences and interacted with culture environment.
Temple University School of Medicine.
C57BL/6, DBA/2, C3H/HeJ, and A/J strains, along with reciprocal F1 hybrid female mice (5–6 weeks).
Immature oocytes from different mouse strains were collected and cultured in different maturation conditions including different serum, serum replacement, bovine serum albumin (BSA) and follicle stimulation hormone (FSH).
Main Outcome Measure(s)
The emission of first polar body, pronucleus formation, meiotic arrest, spontaneous activation, and expression of maturation regulators.
Oocytes from C57BL/6 mice display a high rate of delayed first meiotic division and spontaneous activation after the first meiotic division with in vitro maturation (IVM), and the second meiosis with in vivo maturation (VVM) following superovulation. Spontaneous activation with IVM is sensitive to culture environment. Oocytes spontaneously activated during the first meiotic division with IVM have unusual paired tetrad chromosomes with slight connections at centromeres, whereas oocytes activated in vivo display haploidization from the second meiosis. Spontaneous activation is also seen in F1 hybrid oocytes, indicating a dominant trait from C57BL/6. Delayed meiosis was associated with reduced cylcin B and securin expression.
Both mouse strain and culture environment have a significant effect on the incidence of meiotic defects and spontaneous activation. Reduced expression of meiotic regulators may underlie this effect.