Regulation of MBK-2/DYRK by CDK-1 and the Pseudophosphatases EGG-4 and EGG-5 during the Oocyte-to-Embryo Transition

Abstract

DYRKs are kinases that self-activate in vitro by auto-phosphorylation of a YTY motif in the kinase domain, but their regulation in vivo is not well understood. In C. elegans zygotes, MBK-2/DYRK phosphorylates oocyte proteins at the end of the meiotic divisions to promote the oocyte-to-embryo transition. Here we demonstrate that MBK-2 is under both positive and negative regulation during the transition. MBK-2 is activated during oocyte maturation by CDK-1-dependent phosphorylation of Serine 68, a residue outside of the kinase domain required for full activity in vivo. The pseudo-tyrosine phosphatases EGG-4 and EGG-5 sequester activated MBK-2 until the meiotic divisions by binding to the YTY motif and inhibiting MBK-2’s kinase activity directly, using a novel mixed-inhibition mechanism that does not involve tyrosine dephosphorylation. Our findings link cell cycle progression to MBK-2/DYRK activation and the oocyte-to-embryo transition.

The eggshell in the C. elegans oocyte‐to‐embryo transition

“…The complex contains the phosphatase-related proteins EGG-3, EGG-4/5, and the DYRK-family kinase MBK-2 and depends on CHS-1 for localization (Cheng et al, 2009;Heighington and Kipreos, 2009;Johnston et al, 2006;Parry et al, 2009). CHS-1, EGG-3, and MBK-2 are subsequently cointernalized in zygotes, indicating membrane CHS-1 may physically associate with the EGG-3-5/MBK-2 cortical complex (Maruyama et al, 2007).…”

Fertilization and the oocyte-to-embryo transition in C. elegans

“…EGG-3, EGG-4, and EGG-5 are pseudo-phosphatases in the oocyte that regulate MBK-2 activity, a kinase known to regu-http://bmbreports.org late the oocyte-to-embryo transition (72)(73)(74)(75). EGG-3, EGG-4, and EGG-5 are considered pseudo-phosphatases because they contain an inactive protein tyrosine phosphatase (PTP) domain that lacks a key residue in the catalytic active site (72,73,76).…”

“…The localization of CHS-1 and EGG-3 are interdependent and both genes are required for the proper localization of MBK-2 in oocytes (72,74). EGG-3 binds MBK-2 and, after meiosis, co-localizes with it in the cortex of oocytes and in cytoplasmic puncta (72,74,75). EGG-3 plays a central role in spatial localization and temporal regulation of molecules that are directly involved in executing the oocyte-to-embryo transition (72)(73)(74).…”

“…Like EGG-3, EGG-4/5 binds MBK-2 and the combination of EGG-3 and EGG-4/5 localize MBK-2 to the cortex (73). EGG-4/5 uses its PTP domain to bind the phosphotyrosine in the activation loop of MBK-2, thereby inhibiting MBK-2 by blocking access to substrates and reducing catalytic activity (75). The complex begins to dissociate when EGG-3 is targeted for degradation by the ubiquitin ligase containing APC/C that is activated at meiotic anaphase I (74).…”

“…The spatial and temporal regulation of MBK-2 is just beginning to be elucidated and the pseudo-phosphatases EGG-3, EGG-4, and EGG-5 are central to this regulation. While EGG-4 and EGG-5 are partially responsible for regulating MBK-2, it is evident that there are other regulating factors that have yet to be identified (73,75).…”