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. 2010 Feb 23;20(4):333-8.
doi: 10.1016/j.cub.2009.12.032. Epub 2010 Feb 4.

Cell-nonautonomous regulation of C. elegans germ cell death by kri-1

Shu Ito  1 , Sebastian Greiss, Anton Gartner, W Brent Derry
Affiliations

Cell-nonautonomous regulation of C. elegans germ cell death by kri-1

Shu Ito et al. Curr Biol. .

Abstract

Programmed cell death (or apoptosis) is an evolutionarily conserved, genetically controlled suicide mechanism for cells that, when deregulated, can lead to developmental defects, cancers, and degenerative diseases. In C. elegans, DNA damage induces germ cell death by signaling through cep-1/p53, ultimately leading to the activation of CED-3/caspase. It has been hypothesized that the major regulatory events controlling cell death occur by cell-autonomous mechanisms, that is, within the dying cell. In support of this, genetic studies in C. elegans have shown that the core apoptosis pathway genes ced-4/APAF-1 and ced-3/caspase are required in cells fated to die. However, it is not known whether the upstream signals that activate apoptosis function in a cell-autonomous manner. Here we show that kri-1, an ortholog of KRIT1/CCM1, which is mutated in the human neurovascular disease cerebral cavernous malformation, is required to activate DNA damage-dependent cell death independently of cep-1/p53. Interestingly, we find that kri-1 regulates cell death in a cell-nonautonomous manner, revealing a novel regulatory role for nondying cells in eliciting cell death in response to DNA damage.

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Figures

Figure 1
Figure 1
kri-1 Is Required for DNA Damage-Induced Germ Cell Death Specifically (A) The conserved genetic pathway regulating cell death in mammals and C. elegans. Sensors and transducers relay DNA damage signals to CEP-1/p53, which transcriptionally activates one or more BH3-only genes to promote apoptosis. (B) Wild-type animals fed control(RNAi) (black) or kri-1(RNAi) (white) were subjected to ionizing radiation (IR) at 20°C, and germ cell apoptosis was quantified 24 hr later. Data represent mean ± standard error of the mean (SEM) of three independent experiments and at least 55 germlines in total per strain per condition. ∗p < 0.05 versus wild-type. See Table S1 for full list of p values. (C) Synchronized wild-type (black), cep-1(lf) (gray), and kri-1(ok1251) (white) young adult animals were treated with increasing doses of IR, and germ cell apoptosis was scored as above. Data represent mean ± SEM of at least three independent experiments and at least 50 germlines in total per strain per condition. ∗p < 0.05 versus wild-type. (D) Embryos at the indicated developmental stages were scored for apoptosis with Nomarski optics in wild-type (black), cep-1(lf) (gray bars), and kri-1(ok1251) (white) animals. Data represent mean ± SEM of three independent experiments and at least 45 embryos in total per strain per stage. (E) Apoptosis was scored in wild-type animals (black), a strain with a wild-type copy of kri-1 in trans to the hDf9 deficiency (gray), and ok1251 in trans to hDf9 (white) treated with IR as above. Data represent mean ± SEM of at least four independent experiments and at least 25 germlines in total per strain per condition. ∗p < 0.05 versus wild-type; °p < 0.01 between kri-1(ok1251)/hDf9 and +/hDf9. See also Figure S1.
Figure 2
Figure 2
kri-1 Functions Downstream of the Checkpoint Genes but Upstream of ced-9 (A) Synchronized hermaphrodites at the fourth larval stage (L4) were treated with IR, and the number of nuclei per unit area in the mitotic region of the germline was quantified 24 hr later at 20°C. The mitotic region and nuclei have been outlined for clarity. Representative images from three independent experiments are shown. (B) RNA was isolated by TRIzol from synchronized wild-type (black), cep-1(lf) (gray), and kri-1(0) (white) mutants, and egl-1 transcript levels were measured by quantitative real-time PCR. Data represent mean ± SEM of three independent experiments. (C) Synchronized wild-type and kri-1(0) L4 animals fed control(RNAi) (Y95B8A_84.g, a nonexpressed gene) (black and white, respectively) or ced-9(RNAi) (dark gray and light gray, respectively) were subjected to IR, and germ cell death was quantified as described above. Data represent mean ± SEM of three independent experiments and at least 25 germlines in total per strain per condition. ∗p < 0.01 versus wild-type; °p < 0.05 versus kri-1(0); control(RNAi). See also Figure S2.
Figure 3
Figure 3
kri-1 Functions Independently of Known cep-1-Independent Pathways (A) Wild-type and kri-1(0) animals were immunostained with DAPI or SIR-2.1 antibodies before and after IR. The images show the pachytene region of the germline. Arrowheads indicate nuclei positive for DAPI staining but negative for SIR-2.1 protein expression. Representative images of at least three independent experiments are shown. (B) Wild-type (black), kri-1(0) (white), pmk-3(lf) (dark gray), and kri-1(0); pmk-3(lf) (light gray) animals were synchronized and scored for apoptosis as described in Figure 1B. Data represent mean ± SEM of three independent experiments and at least 50 germlines in total per strain per condition. ∗p < 0.05 versus wild-type; °p < 0.05 versus pmk-3(lf). (C) Germline apoptosis was quantified in synchronized wild-type and kri-1(0) mutants fed control(RNAi) (black and white, respectively) or daf-16(RNAi) (dark and light gray, respectively) and treated with IR as described above. Data represent mean ± SEM of four independent experiments and at least 25 germlines in total per strain per condition. ∗p < 0.01 versus wild-type; °p < 0.01 versus daf-16(RNAi). See also Figure S3.
Figure 4
Figure 4
kri-1 Regulates Germ Cell Death from Somatic Tissues by a Cell-Nonautonomous Mechanism (A) Germ cell death was quantified after treatment with IR in wild-type (black), rrf-1(lf) (light gray), and ppw-1(lf) (dark gray) L4 worms fed bacteria producing double-stranded RNA against a control gene (left panel) or kri-1 (right panel). Data represent mean ± SEM of three independent experiments and at least 35 germlines in total per strain per condition. ∗p < 0.01 versus control(RNAi); °p < 0.01 versus kri-1(RNAi). (B) GFP::KRI-1 expressed under the control of the endogenous kri-1 promoter is detectable in the pharynx (p) and intestine (i) of transgenic animals (top panel). GFP::KRI-1 is excluded from the germline in unirradiated animals (bottom left panel) and does not change localization after irradiation (bottom right panel). Representative images of at least three independent experiments are shown. (C) Apoptotic germ cells were quantified in wild-type (black), kri-1(0) (white), and a kri-1(0) strain expressing a wild-type copy of GFP::KRI-1 in the soma (dark gray). Data represent mean ± SEM of three independent experiments and at least 40 germlines in total per strain per condition. ∗p < 0.01 versus wild-type; °p < 0.01 versus kri-1(0). (D) Model depicting somatic requirement for kri-1 in promoting germ cell death in response to DNA damage. We hypothesize that there are “license to kill” factors secreted from the soma into the germline to mediate cell death. Solid lines represent known regulatory interactions; dotted lines represent hypothetical interactions.
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References

    1. Ellis H.M., Horvitz H.R. Genetic control of programmed cell death in the nematode C. elegans. Cell. 1986;44:817–829. - PubMed
    1. Hipfner D.R., Cohen S.M. Connecting proliferation and apoptosis in development and disease. Nat. Rev. Mol. Cell Biol. 2004;5:805–815. - PubMed
    1. Ahmed S., Hodgkin J. MRT-2 checkpoint protein is required for germline immortality and telomere replication in C. elegans. Nature. 2000;403:159–164. - PubMed
    1. Gartner A., Milstein S., Ahmed S., Hodgkin J., Hengartner M.O. A conserved checkpoint pathway mediates DNA damage-induced apoptosis and cell cycle arrest in C. elegans. Mol. Cell. 2000;5:435–443. - PubMed
    1. Hofmann E.R., Milstein S., Boulton S.J., Ye M., Hofmann J.J., Stergiou L., Gartner A., Vidal M., Hengartner M.O. Caenorhabditis elegans HUS-1 is a DNA damage checkpoint protein required for genome stability and EGL-1-mediated apoptosis. Curr. Biol. 2002;12:1908–1918. - PubMed

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