Volume 9 Issue 7, July 2007

The irreversibility of cell-cycle transitions is commonly thought to derive from the irreversible degradation of certain regulatory proteins. We argue that irreversible transitions in the cell cycle (or in any other molecular control system) cannot be attributed to a single molecule or reaction, but that they derive from feedback signals in reaction networks. This systems-level view of irreversibility is supported by many experimental observations.

Degradation of the MYC oncoprotein through site-specific phosphorylation and recognition by the ubiquitin ligase Fbw7 is central for controlling cell growth and tumorigenesis. New work adds another layer of complexity by showing that the deubiquitinating enzyme Usp28 'piggybacks' on the nuclear isoform of the ligase and stabilizes MYC, thus explaining the selective degradation of MYC in the nucleolus.

As legends go, when Alexander the Great crossed the Land of Darkness searching for the elixir of life, he encountered only desert. Thousands of years later, is it too optimistic to think that scientists have finally found the secret to a longer life? A recent study suggests that p63 may be key, at least for many epithelial stem cells.

Bacterial protein secretion is an important process necessary for adhesion, motility, communication, nutrient acquisition, and virulence. Secretion is energy intensive and time sensitive, so it needs to be tightly regulated. Recent work indicates that threonine phosphorylation can provide this control.

Two recent studies in Drosophila demonstrate that overexpression of proteins required for centriole duplication can not only induce centriole over-duplication in cells containing centrioles, but can also drive de novo centriole assembly in unfertilized eggs that initially lack centrioles. These studies offer a new perspective on the mechanisms that control centriole duplication.

Specification of the axon and dendrites is a critical step in the development of a neuron and requires the asymmetric organization of the cell. A possible link between the extrinsic and intrinsic pathways that drive axon specification has been made with the finding that Dishevelled acts downstream of Wnt5a to activate the PAR6–aPKC–PAR3 pathway.