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Rab GTPases function at all stages of the endocytic and exocytic pathways. Although it is clear that each Rab is required for specific transport events, the process by which they are recruited to distinct compartments along the membrane trafficking pathway has remained obscure. Recent data suggests that a member of the Yip family is important for the membrane recruitment of endosomal Rabs.
During cell-contact-mediated repulsion, an initially adhesive interaction between a receptor and its ligand ultimately results in a repulsive response that causes the cells to separate. Two studies looking at the case of Eph receptors and ephrins now identify a crucial role for endocytosis in this enigmatic process.
During development, tissue growth is controlled by coordinated cellular growth and apoptosis. A series of recent papers describes a newly identified Drosophila gene, hippo, that restricts excessive growth during development by both limiting cell cycle progression and promoting susceptibility to apoptosis. Therefore, hippo may coordinate the regulation of cell division and cell death.
Mammalian sperm require activation within the female reproductive tract to fertilize eggs, and bicarbonate is essential for this process in vitro. A recent study implicates the cystic fibrosis transmembrane regulator (CFTR) as a possible regulator for bicarbonate release in vivo.
The putative tumour suppressor LKB1/XEEK1 (Xenopus egg and embryo kinase 1) has been implicated in many cellular processes and signalling pathways. Now, XEEK1 is found to exist in a complex with GSK3 (glycogen synthase kinase 3) and protein kinase C ζ (PKCζ), resulting in increased Wnt signal transduction during embryonic development. This discovery positions XEEK1 as a potential intersection point for crosstalk between Wnt and other pathways.
Most cells contain two endogenous clocks, one devoted to the control of cell division and the other acting as circadian pacemaker. Although classically thought to be independent, recent findings challenge this view, as molecular components of the circadian clock directly regulate WEE1, a kinase that inhibits mitosis by inactivating Cdc2/cyclin B.