A functional analysis of MELK in cell division reveals a transition in the mode of cytokinesis during Xenopus development.

MELK is a serine/threonine kinase involved in several cell processes, including the cell cycle, proliferation, apoptosis and mRNA processing. However, its function remains elusive. Here, we explored its role in the Xenopus early embryo and show by knockdown that xMELK (Xenopus MELK) is necessary for completion of cell division. Consistent with a role in cell division, endogenous xMELK accumulates at the equatorial cortex of anaphase blastomeres. Its relocalization is highly dynamic and correlates with a conformational rearrangement in xMELK. Overexpression of xMELK leads to failure of cytokinesis and impairs accumulation at the division furrow of activated RhoA - a pivotal regulator of cytokinesis. Furthermore, endogenous xMELK associates and colocalizes with the cytokinesis organizer anillin. Unexpectedly, our study reveals a transition in the mode of cytokinesis correlated to cell size and that implicates xMELK. Collectively, our findings disclose the importance of xMELK in cytokinesis during early development and show that the mechanism of cytokinesis changes during Xenopus early development.