Strain-specific spontaneous activation during mouse oocyte maturation

Abstract

Objective To examine whether spontaneous oocyte activation is determined by genetic differences and interacted with culture environment. Design Experimental Study. Setting Temple University School of Medicine. Animals C57BL/6, DBA/2, C3H/HeJ, and A/J strains, along with reciprocal F1 hybrid female mice (5–6 weeks). Intervention(s) 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. Result(s) 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. Conclusion(s) 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.

PLCζ is the physiological trigger of the Ca2+ oscillations that induce embryogenesis in mammals but conception can occur in its absence

“…This mode of egg activation, without Ca 2+ release, may explain the spontaneous activation observed in vivo in ovulated hamster and mouse eggs left to reside in the oviduct for extended periods of time in the absence of fertilization (Whittingham and Siracusa, 1978;Xu et al, 1997;Yanagimachi and Chang, 1961). Moreover, eggs from the C57BL/6 strain, the strain used in our studies, have been shown to have a particularly high susceptibility to spontaneous activation during in vitro maturation (Cheng et al, 2012). Thus, it is possible that a related mechanism might be responsible for the activation we observe.…”

Age-related alterations in fertilization-induced Ca2+ oscillations depend on the genetic background of mouse oocytes†

“…Interestingly, in contrast to zygotes obtained from old F1 and SWISS oocytes, zygotes from old C57BL/6 oocytes enter the 1st mitotic interphase faster than their counterparts from young oocytes. C57BL/6 oocytes have been reported as particularly prone to spontaneous parthenogenetic activation [ 68 ]. Although each C57BL/6 substrain may display different phenotype, it is possible that with age oocytes from our C57BL/6 substrain (C57BL/6Tar) become more susceptible to parthenogenetic activation, which can be reflected by the accelerated pronuclei formation.…”

Essential Role of Sperm-Specific PLC-Zeta in Egg Activation and Male Factor Infertility: An Update

“…Perhaps the atypical and delayed pattern of Ca 2+ release, observed alongside the low number of embryos and offspring, could be spontaneous activation, unrelated to Ca 2+ release, Abbreviations: ART, assisted reproductive technology; Ca 2+ , calcium; ICSI, intracytoplasmic sperm injection; InsP 3 , inositol 1,4,5-trisphosphate; PI(3)P, phosphatidylinositol 3-phosphate; PI(5P), phosphatidylinositol 5-phosphate; PIP 2 , phosphatidylinositol 4,5-bisphosphate; PLCζ, phospholipase C zeta. which is common in some strains of mice (Cheng et al, 2012), alongside with the introduction of PLCζ knockout sperm. Indeed, eggs that had been fertilized by knockout sperm also displayed multiple pronuclei, consistent with the inability of a sufficient polyspermy block (Nozawa et al, 2018).…”