The Role of Protein Phosphatase 4 in Regulating Microtubule Severing in the Caenorhabditis elegans Embryo

Xue Han; José-Eduardo Gomes; Cheryl L. Birmingham; Lionel Pintard; Asako Sugimoto; Paul E. Mains

doi:10.1534/genetics.108.096016

$MEI-1, the catalytic subunit of the Caenorhabditis elegans “katanin” microtubule-severing complex, is required for meiotic spindle formation. However, MEI-1 must be inactivated after the completion of meiosis to allow formation of the first mitotic spindle. Recent work demonstrated that post-meiotic MEI-1 undergoes ubiquitin-dependent degradation mediated by two independent pathways. Here we describe another level of MEI-1 regulation involving the protein phosphatase 4 (PP4) complex. The PP4 R1 regulatory subunit p rotein p hosphatase f our r egulatory subunit 1 ( ppfr-1 ) was identified in an RNA interference (RNAi) screen for suppressors of a mei-1(gf) allele that is refractory to post-meiotic degradation. RNAi to the PP4 catalytic subunit PPH-4.1 or to the α4 regulatory PPFR-4 also suppressed lethality of ectopic MEI-1. These results suggest that PP4(+) activates MEI-1, and therefore loss of PP4 decreases ectopic MEI-1( gf ) activity. PPH-4.1 and MEI-1 co-immunoprecipitate with one another, indicating that the PP4 complex likely regulates MEI-1 activity directly rather than through an intermediate. The ppfr-1 mutant has subtle meiotic defects indicating that PPFR-1 also regulates MEI-1 during meiosis. MBK-2 is the only kinase known to phosphorylate MEI-1 and triggers post-meiotic MEI-1 degradation. However, genetic interactions between PP4 and mbk-2 were not consistent with an antagonistic relationship between the phosphatase and kinase. Additionally, reducing PP4 in mei-1(gf) did not change the level or localization of post-meiotic MEI-1. Thus, by making use of a genetic background where MEI-1 is ectopically expressed, we have uncovered a third mechanism of MEI-1 regulation, one based on phosphorylation but independent of degradation. The redundant regulatory pathways likely contribute in different ways to the rapid and precise post-meiotic inactivation of MEI-1 microtubule-severing activity. Footnotes ↵ 1 Present address: Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. ↵ 2 Present address: Integran Technologies, 1 Meridian Rd., Toronto, ON M9W 4Z6, Canada. Communicating editor: K. K emphues Received September 9, 2008. Accepted December 15, 2008. Copyright © 2009 by the Genetics Society of America Related articles Issue Highlights : ISSUE HIGHLIGHTS Genetics March 2009 181 : NP Full Text Full Text (PDF)$

The Role of Protein Phosphatase 4 in Regulating Microtubule Severing in the Caenorhabditis elegans Embryo

Han, Xue; Gomes, José-Eduardo; Birmingham, Cheryl L.; Pintard, Lionel; Sugimoto, Asako; Mains, Paul E.

Follow Genetics , Volume 181 (3): 933 Genetics Society of America – Mar 1, 2009