Centrosome misorientation reduces stem cell division during ageing

Asymmetric division of adult stem cells generates one self- renewing stem cell and one differentiating cell, thereby maintaining tissue homeostasis. A decline in stem cell function has been proposed to contribute to tissue ageing, although the underlying mechanism is poorly understood. Here we show that changes in the stem cell orientation with respect to the niche during ageing contribute to the decline in spermatogenesis in the male germ line of Drosophila. Throughout the cell cycle, centrosomes in germline stem cells ( GSCs) are oriented within their niche and this ensures asymmetric division. We found that GSCs containing misoriented centrosomes accumulate with age and that these GSCs are arrested or delayed in the cell cycle. The cell cycle arrest is transient, and GSCs appear to re- enter the cell cycle on correction of centrosome orientation. On the basis of these findings, we propose that cell cycle arrest associated with centrosome misorientation functions as a mechanism to ensure asymmetric stem cell division, and that the inability of stem cells to maintain correct orientation during ageing contributes to the decline in spermatogenesis. We also show that some of the misoriented GSCs probably originate from dedifferentiation of spermatogonia.University of Michigan ; March of Dimes Basil O'Conner Starter Scholar Research Award ; Searle Scholar Program ; NIH [P01 DK53074, R01GM072006]We thank C. Gonzalez, D. McKearin, N. Rusan, M. Peifer and the Bloomington Stock Center for fly stocks; R. Lehmann, C. Field and the Developmental Studies Hybridoma Bank for antibodies; M. Kiel and D. Nakada for help with X-ray irradiation; and S. Morrison and T. Mahowald for comments on the manuscript. This research was supported by a University of Michigan start-up fund, March of Dimes Basil O'Conner Starter Scholar Research Award and the Searle Scholar Program (to Y.M.Y.), and NIH grants P01 DK53074 (to M.T.F.) and R01GM072006 (to A.J.H.).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62879/1/nature07386.pd

Determination of the number of wounded nucleons in Pb+Pb collisions at 158 A GeV/c

The charged particle multiplicity distributions measured by two experiments, WA97 and NA57, in Pb+Pb collisions at 158 A GeV/c have been analyzed in the framework of the wounded nucleon model (WNM). We obtain a good description of the data within the centrality range of our samples. This allows us to make use of the measured multiplicities to estimate the number of wounded nucleons of the collision

Study of the production of strange and multi-strange particles in lead-lead interactions at the CERN SPS: the NA57 experiment

The NA57 experiment studies the production of strange and multi-strange baryons and antibaryons in ultrarelativistic nucleus-nucleus collisions at the SPS. The main aim of NA57 is to investigate the behaviour of the enhancement of the production of particles with strangeness \s\=1,2,3 in nucleus-nucleus collisions at the variation of the energy and of the centrality of the collision defined e.g. as the number of participant nucleons. We shall recall the main features of the experimental set-up, and we shall illustrate the collected data samples and the status of their analysis

Experiment NA57 at the CERN SPS

Experiment NA57 studies the production of strange and multi-strange baryons and antibaryons in ultrarelativistic nucleus-nucleus collisions at the SPS. The principal aim of NA57 is to investigate the existence of an onset for the strangeness enhancement effect at the variation of the energy and centrality (i.e. number of participants) of the nucleus-nucleus collisions. The experiment was successfully installed and commissioned in 1997

Determination of the number of wounded nucleons in Pb + Pb collisions at 158 A GeV/c

The charged particle multiplicity distributions measured with the WA97 and the NA57 multiplicity detectors in Pb + Pb collisions at 158 A GeV/c have been analyzed in the framework of the Wounded Nucleon Model (WNM). We obtain a good description of the data within the centrality range of our samples. This allows us to make use of the measured multiplicities tc, estimate the number of wounded nucleons of the collision