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Unexpected requirement for ELMO1 in clearance of apoptotic germ cells in vivo

Abstract

Apoptosis and the subsequent clearance of dying cells occurs throughout development and adult life in many tissues. Failure to promptly clear apoptotic cells has been linked to many diseases1,2,3. ELMO1 is an evolutionarily conserved cytoplasmic engulfment protein that functions downstream of the phosphatidylserine receptor BAI1, and, along with DOCK1 and the GTPase RAC1, promotes internalization of the dying cells4,5,6,7. Here we report the generation of ELMO1-deficient mice, which we found to be unexpectedly viable and grossly normal. However, they had a striking testicular pathology, with disrupted seminiferous epithelium, multinucleated giant cells, uncleared apoptotic germ cells and decreased sperm output. Subsequent in vitro and in vivo analyses revealed a crucial role for ELMO1 in the phagocytic clearance of apoptotic germ cells by Sertoli cells lining the seminiferous epithelium. The engulfment receptor BAI1 and RAC1 (upstream and downstream of ELMO1, respectively) were also important for Sertoli-cell-mediated engulfment. Collectively, these findings uncover a selective requirement for ELMO1 in Sertoli-cell-mediated removal of apoptotic germ cells and make a compelling case for a relationship between engulfment and tissue homeostasis in vivo.

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Figure 1: Disrupted seminiferous tubule architecture in ELMO1-deficient mice.
Figure 2: Requirement for ELMO1 in apoptotic cell clearance in vivo and in vitro.
Figure 3: ELMO1 functions in Sertoli-cell-mediated apoptotic germ cell clearance.
Figure 4: BAI1 participates as an engulfment receptor in Sertoli-cell-mediated engulfment.

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Acknowledgements

We thank T. Turner, K. Tung and members of the Ravichandran and Lysiak groups for suggestions. We also thank L. Haney, A. C. Tosello-Trampont, J. Kim and S. Clugston for technical assistance. This work was supported by funding from the National Institutes of Health (to K.S.R. and J.J.L.) and the American Cancer Society (to M.R.E.). K.S.R. is a Bill Benter fellow of the American Asthma Foundation.

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The project was designed and the experiments planned by J.J.L., K.S.R and M.R.E. M.R.E. generated the Elmo1 knockout mice and performed and analysed most of the experiments in this study. S.Z. carried out the experiments using ELMO–GFP constructs. R.I.W. performed all of the immunohistochemistry, Sertoli cell extraction and sperm counts. M.A.R. performed the microbubble uptake experiments. I.J.J. performed the phagocytosis assays on non-Sertoli cells. D.P. performed phagocytosis assays and synthesized and characterized BAI1-TSR. Caenorhabditis elegans mismigration analysis using Elmo1 transgenes was conducted by J.M.K. J.Z. assisted with immunoblotting and quantitative PCR studies of Sertoli cells. J.J.L. performed intratesticular injections. M.R.E., K.S.R. and J.J.L. wrote the manuscript with input from the co-authors.

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Correspondence to Jeffrey J. Lysiak or Kodi S. Ravichandran.

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The authors declare no competing financial interests.

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Elliott, M., Zheng, S., Park, D. et al. Unexpected requirement for ELMO1 in clearance of apoptotic germ cells in vivo. Nature 467, 333–337 (2010). https://doi.org/10.1038/nature09356

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