Asymmetry-defective oligodendrocyte progenitors are glioma precursors.

Postnatal oligodendrocyte progenitor cells (OPC) self-renew, generate mature oligodendrocytes, and are a cellular origin of oligodendrogliomas. We show that the proteoglycan NG2 segregates asymmetrically during mitosis to generate OPC cells of distinct fate. NG2 is required for asymmetric segregation of EGFR to the NG2(+) progeny, which consequently activates EGFR and undergoes EGF-dependent proliferation and self-renewal. In contrast, the NG2(-) progeny differentiates. In a mouse model, decreased NG2 asymmetry coincides with premalignant, abnormal self-renewal rather than differentiation and with tumor-initiating potential. Asymmetric division of human NG2(+) cells is prevalent in non-neoplastic tissue but is decreased in oligodendrogliomas. Regulators of asymmetric cell division are misexpressed in low-grade oligodendrogliomas. Our results identify loss of asymmetric division associated with the neoplastic transformation of OPC.

Asymmetric localization of the adaptor protein Miranda in neuroblasts is achieved by diffusion and sequential interaction of Myosin II and VI.

The adaptor protein Miranda plays a pivotal role in the asymmetric cell division of neuroblasts by asymmetrically segregating key differentiation factors. Miranda localization requires Myosin VI and Myosin II. The apical-then-basal localization pattern of Miranda detected in fixed tissue, and the localization defects in embryos lacking Myosin VI, suggest that Miranda is transported to the basal pole as a Myosin VI cargo. However, the mode and temporal sequence of Miranda localization have not been characterized in live embryos. Furthermore, it is unknown whether Miranda and PON, a second adaptor protein required for asymmetric protein localization, are both regulated by Myosin II. By combining immunofluorescence studies with time-lapse confocal microscopy, we show that Miranda protein forms an apical crescent at interphase, but is ubiquitously localized at prophase in a Myosin-II-dependent manner. FRAP analysis revealed that Miranda protein reaches the basal cortex by passive diffusion throughout the cell, rather than by long-range Myosin VI-directed transport. Myosin VI acts downstream of Myosin II in the same pathway to deliver diffusing Miranda to the basal cortex. PON localization occurs mainly along the cortex and requires Myosin II but not Myosin VI, suggesting that distinct mechanisms are employed to localize different adaptor proteins during asymmetric cell division.

The lipolytic proteome of mouse adipose tissue.

Hydrolysis of triacylglycerols and cholesteryl esters is a key event in energy homeostasis of animals. However, many lipolytic activities still await their molecular identification. Here we report on a novel tool for concomitant analysis of lipases in complex proteomes. Fluorescent activity tags mimicking lipid substrates were used to label the proteome of mouse adipose tissue. Analysis by two-dimensional gel electrophoresis and LC-MS/MS led to the identification of all known intracellular lipases as well as a number of novel candidates. One of them was recently shown to be involved in triacylglycerol mobilization in adipocytes and therefore named adipose triglyceride lipase. Functional characterization of expressed enzymes demonstrated that lipolytic and esterolytic activities could be well discriminated. Thus our results show the first map of the lipolytic proteome of mouse adipose tissue and demonstrate the general applicability of our method for rapid profiling and identification of lipolytic activities in complex biological samples.

The Drosophila caspase DRONC is required for metamorphosis and cell death in response to irradiation and developmental signals.

Cell death is essential for eliminating excess cells during development as well as removing damaged cells. While multiple conserved apoptosis pathways involving different cascades of caspases, which are cysteine proteases, have been identified, their regulation in the context of a developing organism is not very well understood. Expression of the Drosophila caspase-9 homolog, DRONC, can be induced by ecdysone, a steroid hormone, which induces metamorphosis. To elucidate the functional role of DRONC during metamorphosis and for cell death during development we have generated and analyzed two loss-of-function alleles of DRONC. We report that DRONC is required for developmentally induced neuroblast cell death and apoptosis in response to X irradiation. DRONC mutants show reduced pupariation even in the presence of high levels of ecdysone and impaired cell death of larval midgut. The levels of ecdysone-inducible transcripts such as E75A and Reaper (Rpr) are normal in the absence of DRONC, suggesting that DRONC acts downstream of these genes. In addition, Reaper and Grim, but not Hid induced apoptosis is sensitive to a reduction of DRONC levels. Our study places DRONC at a central point of convergence for multiple cell death pathways and for the ecdysone pathway regulating metamorphosis.