Coordinate activation of maternal protein degradation during the egg-to-embryo transition in C. elegans.

The transition from egg to embryo occurs in the absence of transcription yet requires significant changes in gene activity. Here, we show that the C. elegans DYRK family kinase MBK-2 coordinates the degradation of several maternal proteins, and is essential for zygotes to complete cytokinesis and pattern the first embryonic axis. In mbk-2 mutants, the meiosis-specific katanin subunits MEI-1 and MEI-2 persist during mitosis and the first mitotic division fails. mbk-2 is also required for posterior enrichment of the germ plasm before the first cleavage, and degradation of germ plasm components in anterior cells after cleavage. MBK-2 distribution changes dramatically after fertilization during the meiotic divisions, and this change correlates with activation of mbk-2-dependent processes. We propose that MBK-2 functions as a temporal regulator of protein stability, and that coordinate activation of maternal protein degradation is one of the mechanisms that drives the transition from symmetric egg to patterned embryo.