Cell-cycle dependent localization of MELK and its new partner RACK1 in epithelial versus mesenchyme-like cells in Xenopus embryo.

Maternal Embryonic Leucine zipper Kinase (MELK) was recently shown to be involved in cell division of Xenopus embryo epithelial cells. The cytokinetic furrow of these cells ingresses asymmetrically and is developmentally regulated. Two subpopulations of xMELK, the mMELK (for "mitotic" xMELK) and iMELK ("interphase" xMELK), which differ in their spatial and temporal regulation, are detected in Xenopus embryo.

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.

ZFPIP/Zfp462 is maternally required for proper early Xenopus laevis development.

ZFPIP (Zinc Finger Pbx1 Interacting Protein) has been recently identified in our laboratory in a yeast two hybrid screen using an embryonic mouse cDNA library and PBX1 as a bait. This gene encodes a large protein (250 kDa) that contains a bipartite NLS, numerous C2H2 zinc fingers and is highly conserved amongst vertebrates. In order to address the role of ZFPIP during embryonic development, we analysed the expression pattern of the gene and performed morpholinos injections into Xenopus laevis embryos.

A mitochondrial-targeting signal is present in the non-catalytic domain of the MELK protein kinase.

MELK is a cell cycle-regulated protein kinase involved in cell cycle progression, proliferation, tumor growth and mRNA splicing. MELK is localized in the cytoplasm and the nucleus during interphase and at the cell cortex during anaphase and telophase. In this report, we show that the regulatory domain of Xenopus MELK when tagged at its C-terminus with the green fluorescent protein (GFP), co-localizes with mitochondria in Xenopus XL2 cells.

CDC25B phosphorylated by pEg3 localizes to the centrosome and the spindle poles at mitosis.

The phosphatase CDC25B is one of the key regulators that control entry into mitosis through the dephosphorylation and subsequent activation of the cyclin-dependent kinases. Here we study the phosphorylation of CDC25B at mitosis by the kinase pEg3, a member of the KIN1/PAR-1/MARK family. Using mass spectrometry analysis we demonstrate that CDC25B is phosphorylated in vitro by pEg3 on serine 169, a residue that lies within the B domain.

Cell cycle regulation of pEg3, a new Xenopus protein kinase of the KIN1/PAR-1/MARK family.

We report the characterization of pEg3, a Xenopus protein kinase related to members of the KIN1/PAR-1/MARK family. The founding members of this newly emerging kinase family were shown to be involved in the establishment of cell polarity and both microtubule dynamic and cytoskeleton organization. Sequence analyses suggest that pEg3 and related protein kinases in human, mouse, and Caenorhabditis elegans might constitute a distinct group in this family.