The C. elegans embryo supports both meiotic and mitotic spindles, requiring careful regulation of components specific to each spindle type. The MEI-1/katanin microtubule-severing complex is required for meiosis but must be inactivated prior to mitosis. Downregulation of MEI-1 depends on MEL-26, which binds MEI-1, targeting it for degradation by the CUL-3 E3 ubiquitin ligase complex. Here we report that other protein degradation pathways, involving the anaphase promoting complex (APC) and the MBK-2/DYRK kinase, act in parallel to MEL-26 to inactivate MEI-1. At 25 degrees all mel-26
(null) embryos die due to persistence of MEI-1 into mitosis, but at 15 degrees a significant portion of embryos hatch due to lower levels of ectopic MEI-1, suggesting that a redundant pathway also regulates MEI-1 degradation at 15 degrees . Previously the MBK-2/DYRK kinase was suggested to trigger MEL-26 mediated MEI-1 degradation. However, mbk-2
enhances the incomplete lethality of mel-26
(null) at 15 degrees , arguing that MEL-26 acts in parallel to MBK-2. APC mutants behave similarly. In mel-26
embryos, ectopic MEI-1 remains until the onset of gastrulation, but in mbk-2
; apc embryos, MEI-1 only persists through the first mitosis. We propose that mbk-2
and apc couple the initial phase of MEI-1 degradation to meiotic exit, after which MEL-26 completes MEI-1 degradation.