The infiltration of immune cells into tissues underlies the establishment of tissue resident macrophages, and responses to infections and tumors. Yet the mechanisms immune cells utilize to negotiate tissue barriers in living organisms are not well understood, and a role for cortical actin has not been examined. Here we find that the tissue invasion of Drosophila macrophages, also known as plasmatocytes or hemocytes, utilizes enhanced cortical F-actin levels stimulated by the Drosophila member of the fos proto oncogene transcription factor family (Dfos, Kayak). RNA sequencing analysis and live imaging show that Dfos enhances F-actin levels around the entire macrophage surface by increasing mRNA levels of the membrane spanning molecular scaffold tetraspanin TM4SF, and the actin cross-linking filamin Cheerio which are themselves required for invasion. Cortical F-actin levels are critical as expressing a dominant active form of Diaphanous, a actin polymerizing Formin, can rescue the Dfos Dominant Negative macrophage invasion defect. In vivo imaging shows that Dfos is required to enhance the efficiency of the initial phases of macrophage tissue entry. Genetic evidence argues that this Dfos-induced program in macrophages counteracts the constraint produced by the tension of surrounding tissues and buffers the mechanical properties of the macrophage nucleus from affecting tissue entry. We thus identify tuning the cortical actin cytoskeleton through Dfos as a key process allowing efficient forward movement of an immune cell into surrounding tissues.
We thank the following for their contributions: The Drosophila Genomics Resource Center supported by NIH grant 2P40OD010949-10A1 for plasmids, K. Brueckner. B. Stramer, M. Uhlirova, O. Schuldiner, the Bloomington Drosophila Stock Center supported by NIH grant P40OD018537 and the Vienna Drosophila Resource Center for fly stocks, FlyBase (Thurmond et al., 2019) for essential genomic information, and the BDGP in situ database for data (Tomancak et al., 2002, 2007). For antibodies, we thank the Developmental Studies Hybridoma Bank, which was created by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the NIH, and is maintained at the University of Iowa, as well as J. Zeitlinger for her generous gift of Dfos antibody. We thank the Vienna BioCenter Core Facilities for RNA sequencing and analysis and the Life Scientific Service Units at IST Austria for technical support and assistance with microscopy and FACS analysis. We thank C.P. Heisenberg, P. Martin, M. Sixt and Siekhaus group members for discussions and T.Hurd, A. Ratheesh and P. Rangan for comments on the manuscript. A.G. was supported by the Austrian Science Fund (FWF) grant DASI_FWF01_P29638S, D.E.S. by Marie Curie CIG 334077/IRTIM. M.S. is supported by the FWF, PhD program W1212 915 and the European Research Council (ERC) Advanced grant (ERC-2015-AdG TNT-Tumors 694883). S.W. is supported by an OEAW, DOC fellowship.
Belyaeva V, Wachner S, Gridchyn I, et al. Cortical actin properties controlled by Drosophila Fos aid macrophage infiltration against surrounding tissue resistance. bioRxiv. doi:10.1101/2020.09.18.301481
Belyaeva, V., Wachner, S., Gridchyn, I., Linder, M., Emtenani, S., György, A., … Siekhaus, D. E. (n.d.). Cortical actin properties controlled by Drosophila Fos aid macrophage infiltration against surrounding tissue resistance. BioRxiv. https://doi.org/10.1101/2020.09.18.301481
Belyaeva, Vera, Stephanie Wachner, Igor Gridchyn, Markus Linder, Shamsi Emtenani, Attila György, Maria Sibilia, and Daria E Siekhaus. “Cortical Actin Properties Controlled by Drosophila Fos Aid Macrophage Infiltration against Surrounding Tissue Resistance.” BioRxiv, n.d. https://doi.org/10.1101/2020.09.18.301481.
V. Belyaeva et al., “Cortical actin properties controlled by Drosophila Fos aid macrophage infiltration against surrounding tissue resistance,” bioRxiv. .
Belyaeva V, Wachner S, Gridchyn I, Linder M, Emtenani S, György A, Sibilia M, Siekhaus DE. Cortical actin properties controlled by Drosophila Fos aid macrophage infiltration against surrounding tissue resistance. bioRxiv.
Belyaeva, Vera, et al. “Cortical Actin Properties Controlled by Drosophila Fos Aid Macrophage Infiltration against Surrounding Tissue Resistance.” BioRxiv, doi:10.1101/2020.09.18.301481.