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

Abstract

The 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.

Spindle morphology changes between meiosis and mitosis driven by CK2 regulation of the Ran pathway

“…Overexpression of HSET (kinesin-14) in mouse oocytes elongated spindles, making them more mitotic-like (Bennabi et al, 2018) and expression of mutant INCENP in Drosophila oocytes led to ectopic aster formation in proximity to the spindle (Colombié et al, 2008) suggesting these factors may also contribute to the spindle morphology change. A recent preprint demonstrated that inhibition of the Mos-MAPK pathway led to a shift in spindle morphology to mitotic-like, with astral microtubules, in starfish oocytes (Avilov et al, 2023 Preprint) suggesting this signaling pathway, which is active in meiosis but inactivated by degradation of Mos at fertilization (Dupré et al, 2011), may be part of the upstream control.…”