Roles of MK2 in Oocyte Meiosis Figure 2. Localization of p-MK2 in mouse oocytes treated with taxol and nocodazole. (A) Oocytes cultured for 8.5 h (MI) and 12 h (MII) were incubated in M16 medium containing 10 mM taxol for 45 min and then double stained with antibodies against p-MK2 (red), a-tubulin (green), and DNA (blue). (B) Oocytes at the metaphase I stage were incubated in M16 medium containing 20 mg/ml nocodazole for 10 min (b,c) and then washed thoroughly and cultured in fresh M16 mediun for 30 min (d). Control groups were treated with DMSO (a). Then oocytes were fixed and double stained with antibodies against p-MK2 (red), a-tubulin (green), and stained for DNA (blue). Bar 20 mm. (C) Oocytes at the metaphase II stage were incubated in M16 medium containing 20 mg/ml nocodazole for 10 min (b) and then washed thoroughly and cultured in fresh M16 medium for 30 min (c). Control group was treated with DMSO(a). Then oocytes were fixed and double stained with antibodies against p-MK2 (red), a-tubulin (green), and DNA (blue). Bar 20 mm. doi:10.1371/journal.pone.0011247.g002 localized at spindle poles and kinetochores. These results suggest that the MK2-deficient oocytes contain a collapsed spindle without spindle poles. From the data above, we conclude that depletion of MK2 by morpholino injection caused meiosis progression arrest with damaged spindles and nondisjuncted chromosomes. In addition, these results were further proved by RNAi depletion of MK2 (Fig. S2). MK2 inhibitor treatment results in spindle defects and homologous chromosome nondisjunction similar to depletion of MK2 by morpholino injection CMPD1, an MK2a specific p38a inhibitor, is noncompetitive with ATP and specifically prevents the phosphorylation and activation of MK2a by p38a [41]. To further investigate the function of MK2 during oocyte maturation, the inhibitor PLoS ONE | www.plosone.org 4 June 2010 | Volume 5 | Issue 6 | e11247