Cell adhesion

Activation of Cdc42 by trans interactions of the cell adhesion molecules nectins through c-Src and Cdc42-GEF FRG. Fukuhara, T. et al. J. Cell Biol. 166, 393–405 (2004)

As well as mediating intercellular adhesion, the trans interactions of nectins induce Rac and Cdc42 activation, which increases the speed at which cell–cell adherens junctions form. The authors found that these immunoglobulin-like, Ca2+-independent molecules recruited Src to sites of cell–cell adhesion. Here, Src was activated and induced the formation of filopodia and lamellipodia by phosphorylating and activating the guanine nucleotide-exchange factor FRG, which, in turn, activated Cdc42.

Cell proliferation

Compensatory proliferation induced by cell death in the Drosophila wing disc requires activity of the apical cell death caspase Dronc in a nonapoptotic role. Huh, J. R., Guo, M. & Hay, B. A. Curr. Biol. 14, 1262–1266 (2004)

Up to 60% of cells in the wing discs of Drosophila melanogaster die. Despite this, the remaining cells undergo compensatory proliferation so that the adult wings develop normally. By uncoupling signals that induce cell death from the death process itself, the authors found that the activation of death signals, such as Hid, activated the caspase Dronc, which stimulated compensatory proliferation in neighbouring cells. How Dronc might carry out this non-apoptotic role is a focus for future investigation, but increased expression of the mitogen Wingless was observed in Hid-expressing regions of the wing disc.

Telomeres

Closed chromatin loops at the ends of chromosomes. Nikitina, T. & Woodcock, C. L. J. Cell Biol. 166, 161–165 (2004)

Image courtesy of Christopher L. Woodcock, University of Massachusetts, Amherst, Massachusetts, USA.

Telomeres are specialized DNA structures that 'cap' the ends of linear DNA to protect them against shortening. Telomere chromatin has been notoriously difficult to study because it is tightly embedded within the nuclear matrix. But Nikitina and Woodcock used the nuclei from chicken erythrocytes and mouse lymphocytes, which contain fewer non-histone chromosomal proteins, to prepare telomere chromatin and study its structure. Electron microscopy showed that telomere chromatin formed closed terminal loops, which correspond to 't-loop' structures in which single-stranded-DNA ends insert into duplex DNA.