MAP Kinase Inactivation Is Required Only for G2–M Phase Transition in Early Embryogenesis Cell Cycles of the StarfishesMarthasterias glacialisandAstropecten aranciacus

Abstract

Downregulation of MAP kinase is a universal consequence of fertilization in the animal kingdom. Here we show that oocytes of the starfishes Astropecten aranciacus and Marthasterias glacialis complete meiotic maturation and form a pronucleus when treated with 1-methyladenine and then complete DNA replication and arrest at G2 if not fertilized. Release of G2 by fertilization or a variety of parthenogenetic treatments is associated with inactivation of MAP kinase. Prevention of MAP kinase inactivation by microinjection of Ste11-DeltaN, a constitutively active budding yeast MAP kinase kinase kinase, arrests fertilized eggs at G2 in either the first or the second mitotic cell cycle, in a dose-dependent manner. G1 arrest is never observed. Conversely, inactivation of MAP kinase by microinjection of the MAP kinase-specific phosphatase Pyst-1 releases mature starfish oocytes from G2 arrest. The role of MAP kinase in arresting cell cycle at various stages in oocytes of different animal species is discussed.

Inactivation of MAPK in mature oocytes triggers progression into mitosis via a Ca2+-dependent pathway but without completion of S phase

“…We, however, believe they might have detected DNA repair. Our results also corroborate those obtained in Xenopus egg extracts (Abrieu et al, 1997) and oocytes of the starfish M. glacialis and A. aranciacus (Picard et al, 1996;Fisher et al, 1998), but contradict those reported for the starfish A. pectinifera (Tachibana et al, 1997). However, the phosphatase XCL100, used by the latter group to inactivate MAP kinase, might act upstream of DNA synthesis on a target other than ERK and, although injection of constitutively active MEK repressed the initiation of DNA synthesis following fertilization, 30% of these eggs did escape G1 arrest and developed until G2 (Tachibana et al, 1997;Abrieu et al, 1997).…”

“…Five batches treated with PD98059 and five batches treated with U0126 gave a few eggs that underwent NEB even after injection with Ca The very opposite hypothesis has been proposed recently by Philipova et al, who suggest that a rise in ERK activity occurring after fertilization is required for S phase (Philipova et al, 2005a). First, the authors detected an ERK protein that is not active in unfertilized eggs, which contradicts the wellestablished view that "downregulation of MAP kinase is a universal consequence of fertilization in the animal kingdom" (Fisher et al, 1998). Philipova's view could be explained if two types of ERK were expressed in the sea urchin egg.…”

“…On the contrary, in oocytes of the starfish M. glacialis and A. aranciacus, MAPK inactivation was neither required for premature DNA replication after the first meiotic cell cycle nor for DNA replication after completion of meiotic maturation (Picard et al, 1996). In those species, the calcium ionophore A23187 could inactivate ERK in oocytes arrested at G2 without inducing DNA synthesis (Fisher et al, 1998).…”

Protein kinase A and protein kinase Cα/PPP1CC2 play opposing roles in the regulation of phosphatidylinositol 3-kinase activation in bovine sperm

“…Towards the end of the capacitation, phospho-PRKCA undergoes dephosphorylation, and both PRKCA and PPP1CC2 are degraded, allowing the PRKA-mediated PI3K phosphorylation/ activation to occur (Fig. 8), and the activated PI3K can function in the acrosome reaction (Fisher et al 1998, Jungnickel et al 2007. The degradation of PRKCA/ PPP1CC2, which along with PI3K phosphorylation were capacitation-and PRKA-dependent processes, was possibly mediated by the ubiquitin/proteasome pathway, pointing to an additional role for PRKA in regulating this signaling pathway.…”

“…PI3K is implicated in many biological processes, including cell survival, cell growth, cell movement and adhesion, protein synthesis, and cytoskeletal rearrangements. A role for PI3K has been suggested in sperm functions during sperm capacitation and the acrosome reaction (Fisher et al 1998, Etkovitz et al 2007, Jungnickel et al 2007. It was also shown that the PI3K catalytic and regulatory subunits are present in sperm (Jungnickel et al 2007), and the PI3K catalytic subunit inhibitor wortmannin (WT) inhibited PI3K and PIP 3 production in bovine sperm (Etkovitz et al 2007).…”