Phosphoproteomics identifies targets of Mos-MAPK regulating translation and spindle organization in oocyte meiosis

Abstract

AbstractThe Mos kinase is a constitutive activator of the ERK/MAPK pathway exclusively expressed during oocyte meiosis, mediating key meiotic functions across animal species. While a few of its downstream effectors have been studied in some detail, molecular targets under the control of Mos-MAPK have not yet been identified systematically. Here, we combined live-cell microscopy of starfish oocytes to characterize the cellular phenotypes caused by Mos-MAPK inhibition with phosphoproteomic analysis of synchronous oocyte populations at key transitions. This revealed a large set of proteins involved in regulation of translation through the CPE-element binding protein CPEB to be controlled by Mos-MAPK. Our data indicate that cyclin B is the main target of this regulation to drive the second meiotic division. A second large group of phospho-proteins we found to be controlled by Mos-MAPK are regulators of the actin and microtubule cytoskeleton, in particular regulators of centrosomal microtubule nucleation. Indeed, we show that Mos-MAPK inhibition increases the size of microtubule asters and promotes separation of spindle poles in meiotic anaphase, i.e turning meiotic spindles mitotic-like. Together, here we identified core molecular modules controlled by Mos-MAPK driving key meiotic functions, haploidization and the asymmetric polar body divisions. These molecular modules are highly conserved and are thus likely to be involved in reproductive processes across species including humans. In addition, our work may help understand disease mechanisms when Mos is expressed erroneously, acting as an oncogene.