Proteomics

Nucleolar proteome dynamics. Andersen, J. S. et al. Nature 433, 77–83 (2005)

Using mass-spectrometry-based organellar proteomics and stable-isotope labelling, Mann, Lamond and colleagues quantitatively analysed the proteome of human nucleoli. By monitoring 489 endogenous nucleolar proteins, they showed that the nucleolar proteome varies considerably over time in response to changes in cellular growth conditions. They therefore “...conclude that there is no unique, complete proteome for the nucleolus, or probably for any other organelle, but rather an overlapping set of proteomes that are relevant to different cell states or conditions.”

Mitosis

Stabilization of microtubule dynamics at anaphase onset promotes chromosome segregation. Higuchi, T. & Uhlmann, F. Nature 433, 171–176 (2005)

Microtubules (MTs) form the bipolar mitotic spindle, which captures chromosomes during metaphase and segregates chromosomes during anaphase. At the onset of anaphase, the highly dynamic MTs become more stable, and the authors showed that the phosphatase Cdc14, which is activated by separase at the onset of anaphase, is required for this. Without Cdc14, MTs remain dynamic, and this interferes with the transport of chromosomes towards the spindle poles and with spindle elongation.

Signalling

EGF receptor signaling regulates pulses of cell delamination from the Drosophila ectoderm. Brodu, V., Elstob, P. R. & Gould, A. P. Dev. Cell 7, 885–895 (2004)

The authors studied the separation of oenocyte precursors from the ectoderm of developing Drosophila melanogaster embryos and report an example of oscillatory cell behaviour. The precursors delaminate in discrete, well-separated bursts of three. The epidermal growth factor receptor (EGFR) ligand Spitz specifies the final number of delamination pulses, but has only a permissive role in generating pulses. Before delamination, several EGFR targets, some of which might underlie pulse generation, are switched on in the three cells.

Cytoskeleton

TSC2 modulates actin cytoskeleton and focal adhesion through TSC1-binding domain and the Rac1 GTPase. Goncharova, E. et al. J. Cell Biol. 167, 1171–1182 (2004)

Tuberosis sclerosis complex (TSC) protein-1 and -2 regulate protein translation and cell growth, but are also implicated in cell motility. Goncharova et al. found that TSC2 regulates stress-fibre disassembly and focal-adhesion remodelling through its TSC1-binding domain by Rac1 activation and subsequent Rho inhibition. The TSC1-binding domain, however, is not needed for TSC2 to regulate the ribosomal protein S6 or DNA synthesis.