Sperm-borne phospholipase C zeta-1 ensures monospermic fertilization in mice

Abstract

Sperm entry in mammalian oocytes triggers intracellular Ca2+ oscillations that initiate resumption of the meiotic cell cycle and subsequent activations. Here, we show that phospholipase C zeta 1 (PLCζ1) is the long-sought sperm-borne oocyte activation factor (SOAF). Plcz1 gene knockout (KO) mouse spermatozoa fail to induce Ca2+ changes in intracytoplasmic sperm injection (ICSI). In contrast to ICSI, Plcz1 KO spermatozoa induced atypical patterns of Ca2+ changes in normal fertilizations, and most of the fertilized oocytes ceased development at the 1–2-cell stage because of oocyte activation failure or polyspermy. We further discovered that both zona pellucida block to polyspermy (ZPBP) and plasma membrane block to polyspermy (PMBP) were delayed in oocytes fertilized with Plcz1 KO spermatozoa. With the observation that polyspermy is rare in astacin-like metalloendopeptidase (Astl) KO female oocytes that lack ZPBP, we conclude that PMPB plays more critical role than ZPBP in vivo. Finally, we obtained healthy pups from male mice carrying human infertile PLCZ1 mutation by single sperm ICSI supplemented with Plcz1 mRNA injection. These results suggest that mammalian spermatozoa have a primitive oocyte activation mechanism and that PLCζ1 is a SOAF that ensures oocyte activation steps for monospermic fertilization in mammals.

Mouse strain‐dependent egg factors regulate calcium signals at fertilization

“…Ca 2+ oscillations at fertilization are initiated by a sperm‐specific phospholipase C (PLC), PLCζ, a soluble protein that is released from the sperm head after sperm–egg plasma membrane fusion (Hachem et al, 2017; Nozawa et al, 2018; Saunders et al, 2002). The first Ca 2+ transient is a result of PLCζ‐mediated generation of inositol trisphosphate (IP 3 ) and IP 3 ‐mediated Ca 2+ release from the endoplasmic reticulum (ER) via the IP 3 receptor (IP 3 R; Miyazaki et al, 1992).…”

“…Characteristics of these Ca 2+ oscillations are linked experimentally to the success of preimplantation embryo development, implantation, and measures of offspring health (Bernhardt et al, 2018;Ducibella et al, 2002;Ozil et al, 2005Ozil et al, , 2006. Ca 2+ oscillations at fertilization are initiated by a sperm-specific phospholipase C (PLC), PLCζ, a soluble protein that is released from the sperm head after sperm-egg plasma membrane fusion (Hachem et al, 2017;Nozawa et al, 2018;Saunders et al, 2002). The first Ca 2+ transient is a result of PLCζ-mediated generation of inositol trisphosphate (IP 3 ) and IP 3 -mediated Ca 2+ release from the endoplasmic reticulum (ER) via the IP 3 receptor (IP 3 R; Miyazaki et al, 1992).…”

Toward the understanding of biology of oocyte life cycle in Xenopus Laevis: No oocytes left behind

“…The molecular details of the sperm‐egg interaction and subsequent egg activation in X laevis are different from those in mammalian species. In mice, gamete interaction and fusion are shown to be mediated by the sperm protein IZUMO1 and the egg/oocyte proteins CD9 and Juno; sperm‐dependent activation of eggs is mediated by phospholipase Cζ that is introduced from fertilizing sperm into the egg cytoplasm . The latter mechanism is named as “sperm factor mechanism” while the mechanism inferred in X laevis is named as “membrane contact mechanism.” The difference between the mechanisms of egg fertilization and activation in frogs and mammals is intriguing, considering that cellular and molecular details of oogenesis, ovulation, and maturation (eg, regulation of meiosis; coordinated actions of MPF, MAPK, and CSF) in mouse and X laevis are similar, as studied so far.…”

Ion channels and signaling pathways used in the fast polyspermy block

“…It is possible that the same signaling mechanisms are used to activate the fast and slow blocks in X. laevis. In mammals, the slow block is activated by a spermderived PLCζ (Hachem et al, 2017;Nozawa, Satouh, Fujimoto, Oji, & Ikawa, 2018;Saunders et al, 2002). Although PLCζ is also expressed in pufferfish eggs and testes from the teleost fish medaka (Coward et al, 2011;Ito et al, 2008), a gene encoding PLCζ has not been annotated in genomes for X. laevis or any other frog (Hammond et al, 2017;Hellsten et al, 2010;Session et al, 2016;Sun et al, 2015).…”