Pericentrin and γ-tubulin are integral centrosome proteins that play a role in microtubule nucleation and organization. In this study, we examined the relationship between these proteins in the cytoplasm and at the centrosome. In extracts prepared from Xenopus eggs, the proteins were part of a large complex as demonstrated by sucrose gradient sedimentation, gel filtration and coimmunoprecipitation analysis. The pericentrin–γ-tubulin complex was distinct from the previously described γ-tubulin ring complex (γ-TuRC) as purified γ-TuRC fractions did not contain detectable pericentrin. When assembled at the centrosome, the two proteins remained in close proximity as shown by fluorescence resonance energy transfer. The three- dimensional organization of the centrosome-associated fraction of these proteins was determined using an improved immunofluorescence method. This analysis revealed a novel reticular lattice that was conserved from mammals to amphibians, and was organized independent of centrioles. The lattice changed dramatically during the cell cycle, enlarging from G1 until mitosis, then rapidly disassembling as cells exited mitosis. In cells colabeled to detect centrosomes and nucleated microtubules, lattice elements appeared to contact the minus ends of nucleated microtubules. Our results indicate that pericentrin and γ-tubulin assemble into a unique centrosome lattice that represents the higher-order organization of microtubule nucleating sites at the centrosome.

The developmental origin of adipose tissue and what controls its distribution is poorly understood. By linage tracing and gene expression analysis in mice, we provide evidence that mesenchymal precursors expressing Myf5—which are thought to give rise only to brown adipocytes and skeletal muscle—also give rise to a subset of white adipocytes. Furthermore, individual brown and white fats contain a mixture of adipocyte progenitor cells derived from Myf5+ and Myf5neg lineages, the number of which varies with depot location. Subsets of white adipocytes originating from both Myf5+ and Myf5neg precursors respond to β3-adrenoreceptor stimulation suggesting brite adipocytes may also have multiple origins. We additionally find that deleting PTEN with myf5-cre causes lipomatosis and partial lipodystrophy by selectively expanding the Myf5+ adipocyte lineages. Thus, the spectrum of adipocytes arising from Myf5+ precursors is broader than previously thought and differences in PI3K activity between adipocyte lineages alters body fat distribution.