Protein phosphatase 5 is a negative regulator of separase function during cortical granule exocytosis inC. elegans

Christopher T Richie,Jill M Schumacher,Andy Golden,Tokiko Furuta,Matthew Wallenfang,Barry Chestnut,Joshua N Bembenek

doi:10.1242/jcs.073379

Abstract

Mutations in the Caenorhabditis elegans separase gene, sep-1, are embryonic lethal. Newly fertilized mutant embryos have defects in polar body extrusion, fail to undergo cortical granule exocytosis, and subsequently fail to complete cytokinesis. Chromosome nondisjunction during the meiotic divisions is readily apparent after depletion of sep-1 by RNAi treatment, but much less so in hypomorphic mutant embryos. To identify factors that influence the activity of separase in cortical granule exocytosis and cytokinesis, we carried out a genetic suppressor screen. A mutation in the protein phosphatase 5 (pph-5) gene was identified as an extragenic suppressor of sep-1. This mutation suppressed the phenotypes of hypomorphic separase mutants but not RNAi depleted animals. Depletion of pph-5 caused no phenotypes on its own, but was effective in restoring localization of mutant separase to vesicles and suppressing cortical granule exocytosis and cytokinesis phenotypes. The identification of PPH-5 as a suppressor of separase suggests that a new phospho-regulatory pathway plays an important role in regulating anaphase functions of separase.

Highlights

The maintenance of the cohesin complex that holds newly replicated sister chromatids together through metaphase and its timely dissolution at the onset of anaphase are crucial for a successful mitotic cell division
The Caenorhabditis elegans separase, sep-1, was shown to have a role in the exocytosis of specialized vesicles known as cortical granules (CGs), which occurs during the first meiotic division (Bembenek et al, 2007)
Characterization of mutant phenotypes of the novel sep-1 alleles We identified two novel alleles of the C. elegans sep-1 gene, ax110 and ax521, from a collection of mutants isolated in a temperature-sensitive embryonic lethal screen (Golden et al, 2000)

Summary

Introduction

The maintenance of the cohesin complex that holds newly replicated sister chromatids together through metaphase and its timely dissolution at the onset of anaphase are crucial for a successful mitotic cell division. The widely conserved protease, separase, cleaves the Scc ( known as Rad21) subunit of the cohesin complex, thereby allowing sister chromatids to be pulled apart towards the spindle poles at anaphase. The Caenorhabditis elegans separase, sep-1, was shown to have a role in the exocytosis of specialized vesicles known as cortical granules (CGs), which occurs during the first meiotic division (Bembenek et al, 2007). In addition to localizing to chromosomes and meiotic spindle, the SEP-1 protein can be found on CG vesicle membranes before their fusion with the plasma membrane during anaphase of meiosis I

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Conclusion