Distribution of CD133 reveals glioma stem cells self-renew through symmetric and asymmetric cell divisions.

Malignant gliomas contain a population of self-renewing tumorigenic stem-like cells; however, it remains unclear how these glioma stem cells (GSCs) self-renew or generate cellular diversity at the single-cell level. Asymmetric cell division is a proposed mechanism to maintain cancer stem cells, yet the modes of cell division that GSCs utilize remain undetermined. Here, we used single-cell analyses to evaluate the cell division behavior of GSCs. Lineage-tracing analysis revealed that the majority of GSCs were generated through expansive symmetric cell division and not through asymmetric cell division. The majority of differentiated progeny was generated through symmetric pro-commitment divisions under expansion conditions and in the absence of growth factors, occurred mainly through asymmetric cell divisions. Mitotic pair analysis detected asymmetric CD133 segregation and not any other GSC marker in a fraction of mitoses, some of which were associated with Numb asymmetry. Under growth factor withdrawal conditions, the proportion of asymmetric CD133 divisions increased, congruent with the increase in asymmetric cell divisions observed in the lineage-tracing studies. Using single-cell-based observation, we provide definitive evidence that GSCs are capable of different modes of cell division and that the generation of cellular diversity occurs mainly through symmetric cell division, not through asymmetric cell division.

Engulfment genes cooperate with ced-3 to promote cell death in Caenorhabditis elegans.

Genetic studies have identified over a dozen genes that function in programmed cell death (apoptosis) in the nematode Caenorhabditis elegans. Although the ultimate effects on cell survival or engulfment of mutations in each cell death gene have been extensively described, much less is known about how these mutations affect the kinetics of death and engulfment, or the interactions between these two processes. We have used four-dimensional-Nomarski time-lapse video microscopy to follow in detail how cell death genes regulate the extent and kinetics of apoptotic cell death and removal in the early C. elegans embryo. Here we show that blocking engulfment enhances cell survival when cells are subjected to weak pro-apoptotic signals. Thus, genes that mediate corpse removal can also function to actively kill cells.

Interaction between the C. elegans cell-death regulators CED-9 and CED-4.

Programmed cell death (apoptosis) is an evolutionarily conserved process used by multicellular organisms to eliminate cells that are not needed or are potentially detrimental to the organism. Members of the Bcl-2 family of mammalian proteins are intimately involved in the regulation of apoptosis, but, their precise mechanism of action remains unresolved. In Caenorhabditis elegans, the Bcl-2 homologue CED-9 prevents cell death by antagonizing the death-promoting activities of CED-3, a member of the Caspase family of death proteases, and of CED-4, a protein with no known mammalian homologue. Here we show that CED-9 interacts physically with CED-4. Mutations that reduce or eliminate CED-9 activity also disrupt its ability to bind CED-4, suggesting that this interaction is important for CED-9 function. Thus, CED-9 might control C. elegans cell death by binding to and regulating CED-4 activity. We propose that mammalian Bcl-2 family members might control apoptosis in a similar way through interaction and regulation of CED-4 homologues or analogues.

Identification of essential nucleotides in an upstream repressing sequence of Saccharomyces cerevisiae by selection for increased expression of TRK2.

The TRK2 gene in Saccharomyces cerevisiae encodes a membrane protein involved in potassium transport and is expressed at extremely low levels. Dominant cis-acting mutations (TRK2D), selected by their ability to confer TRK2-dependent growth on low-potassium medium, identified an upstream repressor element (URS1-TRK2) in the TRK2 promoter. The URS1-TRK2 sequence (5'-AGCCGCACG-3') shares six nucleotides with the ubiquitous URS1 element (5'-AGCCGCCGA-3'), and the protein species binding URS1-CAR1 (URSF) is capable of binding URS1-TRK2 in vitro. Sequence analysis of 17 independent repression-defective TRK2D mutations identified three adjacent nucleotides essential for URS1-mediated repression in vivo. Our results suggest a role for context effects with regard to URS1-related sequences: several mutant alleles of the URS1 element previously reported to have little or no effect when analyzed within the context of a heterologous promoter (CYC1) [Luche, R.M., Sumrada, R. & Cooper, T.G. (1990) Mol. Cell. Biol. 10, 3884-3895] have major effects on repression in the context of their native promoters (TRK2 and CAR1). TRK2D mutations that abolish repression also reveal upstream activating sequence activity either within or adjacent to URS1. Additivity between TRK2D and sin3 delta mutations suggest that SIN3-mediated repression is independent of that mediated by URS1.