Birth control for centrioles

In This Issue In This Issue Birth control for centrioles mnis centriolus e centriolo—every centriole comes from a centriole. This statement underlies the standard model of centrosome duplication, in which daughter centrioles that will form the foundation of a new centrosome must be patterned on some kind of template provided by a mother centriole. On page 1171, Khodjakov et al. now demonstrate that vertebrate cells are fully capable of assembling centrioles de novo, overturning this long-held belief and suggesting a different function for the mother centrioles. A few specialized cell types, such as clam zygotes and rabbit blastomeres, previously have been shown to form centrioles de novo, but these examples were thought to be exceptions. The new work argues otherwise. The authors arrested CHO cells in S phase, and then destroyed their centrosomes with a laser. O Signaling clusters caught in the act iochemical studies have provided a detailed accounting of the molecules present in the T cell receptor (TCR) complex during T cell activation, but relatively little is known about the maturation and dynamic composition of these complexes. Now Bunnell et al., reporting on page 1263, have developed a novel assay that allows them to visualize B the formation of these complexes in live cells. The authors dropped live Jurkat leukemic T cells onto coverslips coated with anti-TCR antibodies, and then tracked chimeric signaling proteins as they associated with and dissociated from signaling complexes. TCR-signaling complexes develop within 15 s, and undergo dynamic assembly and disassembly throughout the process of contact formation. Initial clustering of the TCRs does not require phosphotyrosine-dependent interactions, but the formation of a functional signaling complex does. A lipid raft marker does not localize to the complexes, a result that should fan the controversy surrounding raft function in signaling. Signaling complexes assemble soon after TCR ligation. transformation. On page 1183, Dupuis-Williams et al. used a different model system to analyze the function of ␧-tubulin, which specifically associates with centrosomes in human cells. The authors cloned the ␧-tubulin gene of Paramecium , and found that it is required to stabilize the microtubule triplets that assemble into basal bodies in the protozoan. ᭿ Centrioles can form de novo. In this system, a loose cloud of peri-centriolar material (PCM) forms, and within 24 h this PCM cloud becomes more compact, correlating with the appearance of new centrioles. The formation of the PCM clouds does not require microtubules, but …