Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Programmed elimination of cells by caspase-independent cell extrusion in C. elegans


The elimination of unnecessary or defective cells from metazoans occurs during normal development and tissue homeostasis, as well as in response to infection or cellular damage1. Although many cells are removed through caspase-mediated apoptosis followed by phagocytosis by engulfing cells2, other mechanisms of cell elimination occur3, including the extrusion of cells from epithelia through a poorly understood, possibly caspase-independent, process4. Here we identify a mechanism of cell extrusion that is caspase independent and that can eliminate a subset of the Caenorhabditis elegans cells programmed to die during embryonic development. In wild-type animals, these cells die soon after their generation through caspase-mediated apoptosis. However, in mutants lacking all four C. elegans caspase genes, these cells are eliminated by being extruded from the developing embryo into the extra-embryonic space of the egg. The shed cells show apoptosis-like cytological and morphological characteristics, indicating that apoptosis can occur in the absence of caspases in C. elegans. We describe a kinase pathway required for cell extrusion involving PAR-4, STRD-1 and MOP-25.1/-25.2, the C. elegans homologues of the mammalian tumour-suppressor kinase LKB1 and its binding partners STRADα and MO25α. The AMPK-related kinase PIG-1, a possible target of the PAR-4–STRD-1–MOP-25 kinase complex, is also required for cell shedding. PIG-1 promotes shed-cell detachment by preventing the cell-surface expression of cell-adhesion molecules. Our findings reveal a mechanism for apoptotic cell elimination that is fundamentally distinct from that of canonical programmed cell death.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Cells with apoptotic morphology are shed from C. elegans embryos lacking caspase activity.
Figure 2: Cells that are shed from ced-3 -mutant embryos are normally fated to die early during wild-type embryogenesis.
Figure 3: The LKB1 homologue PAR-4 and the AMPK-related kinase PIG-1 are required for cell shedding from ced-3 embryos.
Figure 4: Shed cells lack cell-adhesion molecules that are inappropriately expressed in pig-1 mutants, possibly because of impaired endocytosis.


  1. Fuchs, Y. & Steller, H. Programmed cell death in animal development and disease. Cell 147, 742–758 (2011)

    Article  CAS  Google Scholar 

  2. Reddien, P. W. & Horvitz, H. R. The engulfment process of programmed cell death in Caenorhabditis elegans . Annu. Rev. Cell Dev. Biol. 20, 193–221 (2004)

    Article  CAS  Google Scholar 

  3. Yuan, J. & Kroemer, G. Alternative cell death mechanisms in development and beyond. Genes Dev. 24, 2592–2602 (2010)

    Article  CAS  Google Scholar 

  4. Rosenblatt, J., Raff, M. C. & Cramer, L. P. An epithelial cell destined for apoptosis signals its neighbors to extrude it by an actin- and myosin-dependent mechanism. Curr. Biol. 11, 1847–1857 (2001)

    Article  CAS  Google Scholar 

  5. Ellis, H. M. & Horvitz, H. R. Genetic control of programmed cell death in the nematode C. elegans . Cell 44, 817–829 (1986)

    Article  CAS  Google Scholar 

  6. Abraham, M. C., Lu, Y. & Shaham, S. A morphologically conserved nonapoptotic program promotes linker cell death in Caenorhabditis elegans . Dev. Cell 12, 73–86 (2007)

    Article  CAS  Google Scholar 

  7. Shaham, S., Reddien, P. W., Davies, B. & Horvitz, H. R. Mutational analysis of the Caenorhabditis elegans cell-death gene ced-3 . Genetics 153, 1655–1671 (1999)

    CAS  PubMed  PubMed Central  Google Scholar 

  8. Wu, Y. C., Stanfield, G. M. & Horvitz, H. R. NUC-1, a Caenorhabditis elegans DNase II homolog, functions in an intermediate step of DNA degradation during apoptosis. Genes Dev. 14, 536–548 (2000)

    CAS  PubMed  PubMed Central  Google Scholar 

  9. Shaham, S. Identification of multiple Caenorhabditis elegans caspases and their potential roles in proteolytic cascades. J. Biol. Chem. 273, 35109–35117 (1998)

    Article  CAS  Google Scholar 

  10. Sulston, J. E. & Horvitz, H. R. Post-embryonic cell lineages of the nematode, Caenorhabditis elegans . Dev. Biol. 56, 110–156 (1977)

    Article  CAS  Google Scholar 

  11. Sulston, J. E., Schierenberg, E., White, J. G. & Thomson, J. N. The embryonic cell lineage of the nematode Caenorhabditis elegans . Dev. Biol. 100, 64–119 (1983)

    Article  CAS  Google Scholar 

  12. Potts, M. B. & Cameron, S. Cell lineage and cell death: Caenorhabditis elegans and cancer research. Nature Rev. Cancer 11, 50–58 (2011)

    Article  CAS  Google Scholar 

  13. Buechner, M. Tubes and the single C. elegans excretory cell. Trends Cell Biol. 12, 479–484 (2002)

    Article  CAS  Google Scholar 

  14. Abdus-Saboor, I. et al. Notch and Ras promote sequential steps of excretory tube development in C. elegans . Development 138, 3545–3555 (2011)

    Article  CAS  Google Scholar 

  15. Cordes, S., Frank, C. A. & Garriga, G. The C. elegans MELK ortholog PIG-1 regulates cell size asymmetry and daughter cell fate in asymmetric neuroblast divisions. Development 133, 2747–2756 (2006)

    Article  CAS  Google Scholar 

  16. Ou, G., Stuurman, N., D’Ambrosio, M. & Vale, R. D. Polarized myosin produces unequal-size daughters during asymmetric cell division. Science 330, 677–680 (2010)

    Article  ADS  CAS  Google Scholar 

  17. Shackelford, D. B. & Shaw, R. J. The LKB1–AMPK pathway: metabolism and growth control in tumour suppression. Nature Rev. Cancer 9, 563–575 (2009)

    Article  CAS  Google Scholar 

  18. Lizcano, J. M. et al. LKB1 is a master kinase that activates 13 kinases of the AMPK subfamily, including MARK/PAR-1. EMBO J. 23, 833–843 (2004)

    Article  CAS  Google Scholar 

  19. Boudeau, J. et al. MO25α/β interact with STRADα/β enhancing their ability to bind, activate and localize LKB1 in the cytoplasm. EMBO J. 22, 5102–5114 (2003)

    Article  CAS  Google Scholar 

  20. Zeqiraj, E., Filippi, B. M., Deak, M., Alessi, D. R. & van Aalten, D. M. F. Structure of the LKB1-STRAD-MO25 complex reveals an allosteric mechanism of kinase activation. Science 326, 1707–1711 (2009)

    Article  ADS  CAS  Google Scholar 

  21. Narbonne, P., Hyenne, V., Li, S., Labbé, J.-C. & Roy, R. Differential requirements for STRAD in LKB1-dependent functions in C. elegans . Development 137, 661–670 (2010)

    Article  CAS  Google Scholar 

  22. Labouesse, M. Epithelial junctions and attachments. WormBook 13, 1–21 (2006)

    Google Scholar 

  23. Kinchen, J. M. et al. A pathway for phagosome maturation during engulfment of apoptotic cells. Nature Cell Biol. 10, 556–566 (2008)

    Article  CAS  Google Scholar 

  24. Singhvi, A. et al. The Arf GAP CNT-2 regulates the apoptotic fate in C. elegans asymmetric neuroblast divisions. Curr. Biol. 21, 948–954 (2011)

    Article  CAS  Google Scholar 

  25. D’Souza-Schorey, C. & Chavrier, P. ARF proteins: roles in membrane traffic and beyond. Nature Rev. Mol. Cell Biol. 7, 347–358 (2006)

    Article  Google Scholar 

  26. D’Souza-Schorey, C. Disassembling adherens junctions: breaking up is hard to do. Trends Cell Biol. 15, 19–26 (2005)

    Article  Google Scholar 

  27. Potten, C. S. Stem cells in gastrointestinal epithelium: numbers, characteristics and death. Phil. Trans. R. Soc. Lond. B 353, 821–830 (1998)

    Article  CAS  Google Scholar 

  28. Watson, A. J. M., Duckworth, C. A., Guan, Y. & Montrose, M. H. Mechanisms of epithelial cell shedding in the mammalian intestine and maintenance of barrier function. Ann. NY Acad. Sci. 1165, 135–142 (2009)

    Article  ADS  Google Scholar 

  29. Coopersmith, C. M., O’Donnell, D. & Gordon, J. I. Bcl-2 inhibits ischemia-reperfusion-induced apoptosis in the intestinal epithelium of transgenic mice. Am. J. Physiol. 276, G677–G686 (1999)

    CAS  PubMed  Google Scholar 

  30. Hemminki, A. et al. A serine/threonine kinase gene defective in Peutz–Jeghers syndrome. Nature 391, 184–187 (1998)

    Article  ADS  CAS  Google Scholar 

  31. Brenner, S. The genetics of Caenorhabditis elegans . Genetics 77, 71–94 (1974)

    CAS  PubMed  PubMed Central  Google Scholar 

  32. Hirose, T., Galvin, B. D. & Horvitz, H. R. Six and Eya promote apoptosis through direct transcriptional activation of the proapoptotic BH3-only gene egl-1 in Caenorhabditis elegans . Proc. Natl Acad. Sci. USA 107, 15479–15484 (2010)

    Article  ADS  CAS  Google Scholar 

  33. Venegas, V. & Zhou, Z. Two alternative mechanisms that regulate the presentation of apoptotic cell engulfment signal in Caenorhabditis elegans . Mol. Biol. Cell 18, 3180–3192 (2007)

    Article  CAS  Google Scholar 

  34. Schwartz, H. T. A protocol describing pharynx counts and a review of other assays of apoptotic cell death in the nematode worm Caenorhabditis elegans . Nature Protocols 2, 705–714 (2007)

    Article  Google Scholar 

  35. Fraser, A. G. et al. Functional genomic analysis of C. elegans chromosome I by systematic RNA interference. Nature 408, 325–330 (2000)

    Article  ADS  CAS  Google Scholar 

  36. Rual, J. F. et al. Toward improving Caenorhabditis elegans phenome mapping with an ORFeome-based RNAi library. Genome Res. 14, 2162–2168 (2004)

    Article  CAS  Google Scholar 

  37. Parrish, J. Z. & Xue, D. Functional genomic analysis of apoptotic DNA degradation in C. elegans . Mol. Cell 11, 987–996 (2003)

    Article  CAS  Google Scholar 

  38. Lu, Q. et al. elegans Rab GTPase 2 is required for the degradation of apoptotic cells. Development 135, 1069–1080 (2008)

    Article  CAS  Google Scholar 

Download references


We thank Z. Zhou, T. Hirose and S. Nakano for reporter constructs; B. Castor, E. Murphy and R. Droste for determining DNA sequences; S. Dennis for screening of the deletion library; N. An for strain management; and, J. Yuan, S. Nakano, N. Paquin, C. Engert and A. Saffer for discussions. The Caenorhabditis Genetic Center, which is funded by the National Institutes of Health National Center for Research Resources (NCRR), provided many strains. S. Mitani provided grp-1(tm1956). D.P.D. was supported by post-doctoral fellowships from the Damon Runyon Cancer Research Foundation and from the Charles A. King Trust. H.R.H. is the David H. Koch Professor of Biology at the Massachusetts Institute of Technology and an Investigator at the Howard Hughes Medical Institute.

Author information

Authors and Affiliations



D.P.D. and H.R.H. designed the experiments, analysed the data and wrote the manuscript. D.P.D. and V.H. performed the experiments.

Corresponding author

Correspondence to H. Robert Horvitz.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Tables 1 -11, Supplementary Figures 1-8, legends for Supplementary Movies 1-3 (see separate files for Supplementary Movies), Supplementary References and the RNAi Construct Sequences. (PDF 9773 kb)

Supplementary Movie 1

This file contains a time-lapse movie of a developing ced-3(n3692) embryo (see Supplementary Information file for full legend). (MOV 5090 kb)

Supplementary Movie 2

This file contains a time-lapse movie of a developing pig-1(gm344) embryo (see Supplementary Information file for full legend). (MOV 2086 kb)

Supplementary Movie 3

This file contains a time-lapse movie of a developing pig-1(gm344) ced-3(n3692) embryo (see Supplementary Information file for full legend). (MOV 3778 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Denning, D., Hatch, V. & Horvitz, H. Programmed elimination of cells by caspase-independent cell extrusion in C. elegans. Nature 488, 226–230 (2012).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing