Developmental Genetics Program, Helen and Martin Kimmel Center for Stem Cell Biology, Skirball Institute of Biomolecular Medicine, Department of Pathology, New York University School of Medicine, New York, NY 10016, USA.
Development (Impact Factor: 6.46). 03/2012; 139(5):859-70. DOI: 10.1242/dev.074047
Coupling of stem/progenitor cell proliferation and differentiation to organismal physiological demands ensures the proper growth and homeostasis of tissues. However, in vivo mechanisms underlying this control are poorly characterized. We investigated the role of ribosomal protein S6 kinase (S6K) at the intersection of nutrition and the establishment of a stem/progenitor cell population using the C. elegans germ line as a model. We find that rsks-1 (which encodes the worm homolog of mammalian p70S6K) is required germline-autonomously for proper establishment of the germline progenitor pool. In the germ line, rsks-1 promotes cell cycle progression and inhibits larval progenitor differentiation, promotes growth of adult tumors and requires a conserved TOR phosphorylation site. Loss of rsks-1 and ife-1 (eIF4E) together reduces the germline progenitor pool more severely than either single mutant and similarly to reducing the activity of let-363 (TOR) or daf-15 (RAPTOR). Moreover, rsks-1 acts in parallel with the glp-1 (Notch) and daf-2 (insulin-IGF receptor) pathways, and does not share the same genetic dependencies with its role in lifespan control. We show that overall dietary restriction and amino acid deprivation cause germline defects similar to a subset of rsks-1 mutant phenotypes. Consistent with a link between diet and germline proliferation via rsks-1, loss of rsks-1 renders the germ line largely insensitive to the effects of dietary restriction. Our studies establish the C. elegans germ line as an in vivo model to understand TOR-S6K signaling in proliferation and differentiation and suggest that this pathway is a key nutrient-responsive regulator of germline progenitors.
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"For example, it will be of interest to challenge the model under conditions that interfere with glp-1 activity and/or cell cycle progression. In addition, the impact on gonadogenesis and Development • Advance article cell dynamics of mutations affecting cell size could be studied in silico (Arur et al., 2009; Korta et al., 2012). Finally, the modeling approach described here could be applied to other developmental systems, such as intestinal organoids (Sato et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: The C. elegans germ line is an outstanding model system to study the control of cell division and differentiation. While many of the molecules that regulate germ cell proliferation and fate decisions have been identified, how these signals interact with cellular dynamics and physical forces within the gonad remains poorly understood. We therefore developed a dynamic, 3D in silico model of the C. elegans germ line, incorporating both the mechanical interactions between cells and the decision-making processes within cells. Our model successfully reproduces key features of the germ line during development and adulthood, including a reasonable ovulation rate, correct sperm count, and appropriate organization of the germ line into stably maintained zones. The model highlights a previously overlooked way in which germ cell pressure may influence gonadogenesis, and also predicts that adult germ cells may be subject to mechanical feedback on the cell cycle akin to contact inhibition. We provide experimental data consistent with the latter hypothesis. Finally, we present cell trajectories and ancestry recorded over the course of a simulation. The novel approaches and software described here link mechanics and cellular decision-making, and are applicable to modeling other developmental and stem cell systems.
"The results are shown in Fig. 7A, and clearly sustain the concept that MTH inhibits the phosphorylation of p70S6 kinase. Fig. 7B shows the involvement of p70S6 kinase on the cell cycle  , and demonstrates that MTH treatment of K562 cells leads to an increase of G1-phase cells, Fig. 7. Effects of MTH on p70S6 kinase and cell cycle. (A) Western blotting analysis was performed on protein extracts obtained from K562 cells treated with 30 nM MTH for the indicated length of time, using p70 and p-p70 (Thr389) monoclonal antibody. "
"There is abundant evidence for the coupling of proliferation and cell cycle progression to the nutrient environment and pH alteration , , . We demonstrated that the exposure to the experimental group harvesting media (with relatively low nutrients or no pH buffer system) triggers p53-mediated cell cycle arrest and represses the expression of cyclin E1, eventually leading to the reduction of S-phase entry (Fig. 1D,E). "
[Show abstract][Hide abstract] ABSTRACT: Various solutions are utilized widely for the isolation, harvesting, sorting, testing and transplantation of neural stem cells (NSCs), whereas the effects of harvesting media on the biological characteristics and repair potential of NSCs remain unclear. To examine some of these effects, NSCs were isolated from cortex of E14.5 mice and exposed to the conventional harvesting media [0.9% saline (Saline), phosphate-buffered saline (PBS) or artificial cerebrospinal fluid (ACSF)] or the proliferation culture medium (PCM) for different durations at 4°C. Treated NSCs were grafted by in situ injection into the lesion sites of traumatic brain injury (TBI) mice. In vitro, harvesting media-exposed NSCs displayed time-dependent reduction of viability and proliferation. S phase entry decreased in harvesting media-exposed cells, which was associated with upregulation of p53 protein and downregulation of cyclin E1 protein. Moreover, harvesting media exposure induced the necrosis and apoptosis of NSCs. The levels of Fas-L, cleaved caspase 3 and 8 were increased, which suggests that the death receptor signaling pathway is involved in the apoptosis of NSCs. In addition, exposure to Saline did not facilitate the neuronal differentiation of NSCs, suggesting that Saline exposure may be disadvantageous for neurogenesis. In vivo, NSC-mediated functional recovery in harvesting media-exposed NSC groups was notably attenuated in comparison with the PCM-exposed NSC group. In conclusion, harvesting media exposure modulates the biological characteristics and repair potential of NSCs after TBI. Our results suggest that insight of the effects of harvesting media exposure on NSCs is critical for developing strategies to assure the successful long-term engraftment of NSCs.