CaM kinase II initiates meiotic spindle depolymerization independently of APC/C activation

Abstract

Altered spindle microtubule dynamics at anaphase onset are the basis for chromosome segregation. In Xenopus laevis egg extracts, increasing free calcium levels and subsequently rising calcium-calmodulin–dependent kinase II (CaMKII) activity promote a release from meiosis II arrest and reentry into anaphase. CaMKII induces the activation of the anaphase-promoting complex/cyclosome (APC/C), which destines securin and cyclin B for degradation to allow chromosome separation and mitotic exit. In this study, we investigated the calcium-dependent signal responsible for microtubule depolymerization at anaphase onset after release from meiotic arrest in Xenopus egg extracts. Using Ran–guanosine triphosphate–mediated microtubule assemblies and quantitative analysis of complete spindles, we demonstrate that CaMKII triggers anaphase microtubule depolymerization. A CaMKII-induced twofold increase in microtubule catastrophe rates can explain reduced microtubule stability. However, calcium or constitutively active CaMKII promotes microtubule destabilization even upon APC/C inhibition and in the presence of high cyclin-dependent kinase 1 activity. Therefore, our data demonstrate that CaMKII turns on parallel pathways to activate the APC/C and to induce microtubule depolymerization at meiotic anaphase onset.

Ion channels and transporters in cancer. 1. Ion channels and cell proliferation in cancer

“…In sea urchin oocytes for example, phosphoinositide-dependent Ca 2ϩ signals control progression through the cell cycle checkpoints at G 1 /S, G 2 /M, and mitosis exit (11, 29, 52, 144). The Ca 2ϩ -dependent regulation of the early division cycles has also been thoroughly studied in frog embryos, where the overall pattern is similar to that observed in sea urchin, although the opacity of Xenopus oocytes makes studying [Ca 2ϩ ] i with optical methods more difficult (56,92,101,124). Similar calcium transients also occur in mouse oocytes, in which however their precise functional role is still debated (7,43,62,72,82).…”

Controlling the cell cycle: The role of calcium/calmodulin-stimulated protein kinases I and II

“…66,109 Recent work has demonstrated that CaMKII regulates microtubule catastrophe during anaphase, as overexpression of a constitutively active CaMKII mutant promotes microtubule destabilization. 110 Furthermore, downregulation of CaMKIIγ in a variety of cell lines by siRNA resulted in an accumulation of prometaphase/metaphase cells, as well as cells with multipolar spindles, 67 which indicates that CaMKII is required for normal bipolar spindle formation during mitosis.…”

Cilia and cell cycle re-entry

“…Recently, it has been shown that ciliary resorption is triggered by the addition of a specific combination of growth factors, including PDGF-AA Ca 2+ /CaM-dependent protein kinase II (CaMKII). 47 CaMKII has been shown to depolymerize meiotic spindles in Xenopus egg extracts 48 and localizes at the mammalian olfactory cilia, 49,50 suggesting that the increase in Ca 2+ and subsequent activation of CaMKII at the primary cilia may participate in the dissasembly process. It is important to note that a reduction in intracellular Ca 2+ concentration resulted in abnormally long cilia in epithelial and mesenchymal cells, 51 supporting the notion that Ca 2+ directly or indirectly can regulate ciliary retraction.…”