Basal body timing

ggregation of ␥-tubulin, pericentrin, and myosin II (GPM) precedes de novo basal body assembly, according to a report from Kim et al. on page 719. The number of basal bodies formed is controlled by the duration of ␥-tubulin phosphorylation. Until now, it has not been clear whether basal body and centriole formation occurred before or after clouds of pericentriolar material take shape. To answer that question, the researchers turned to Naegleria gruberi , which start life with amoeboid shapes but differentiate into swimming flagellates when food becomes scarce. During differentiation, the cells assemble basal bodies de novo, providing scientists with a window into the process. The researchers knew that after the cells are transferred to a dilute buffer, ␥-tubulin and pericentrin concentrate together in the cell. The percentage of cells with a concentrated region of ␥-tubulin is maximal at 40 min, but no poly-merized microtubules are visible. Basal bodies are assembled from the ␥-tubulin concentration ‫ف‬ 60 min after initiation. This situation resembles what others have seen in animal cells during de novo centriole formation. Now, Kim et al. find that in vitro purified GPM from 40-min cells was competent to nucleate microtubules, but GPM from cells before or after this time was not. Phosphorylation of ␥-tubulin correlated with the competency. When the team inhibited dephosphorylation of GPM in vivo, cells ended up with multiple pairs of flagella—suggest-ing that dephosphorylation of ␥-tubulin is required to limit the number of new basal bodies. The team doesn't yet know what regulates phosphorylation of ␥-tubulin, but they are looking. They have also started using electron micros-copy to study the GPM aggregates, which can reach 2 ␮ m in diameter, to find out just what's hidden in the cloud. A Prolonging phosphorylation of ␥-tubulin results in multiple basal bodies. Interleukins drive the cell cycle ytokines control the number of lymphocytes in the body. Too many cytokines can lead to lymphoma; an absence to immunodeficiency. And while it is broadly known that cytokines, like IL-3 and IL-7, block apoptosis, it is less well-recognized that they promote cell proliferation. On page 755, Khaled et al. show that cytokines promote cycling by inhibiting the effects of the stress protein p38 MAP kinase and activating Cdc25A. Withdrawal of IL-3 or IL-7 from either primary lymphocytes or cytokine-dependent cell lines induces apoptosis in 24 to 36 hours. However, cell cycle arrest starts within the first 8 hours. The team …