Fos regulates macrophage infiltration against surrounding tissue resistance by a cortical actin-based mechanism in Drosophila

Abstract

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. Both the filamin and the tetraspanin enhance the cortical activity of Rho1 and the formin Diaphanous and thus the assembly of cortical actin, which is a critical function since expressing a dominant active form of Diaphanous can rescue the Dfos macrophage invasion defect. In vivo imaging shows that Dfos enhances 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 properties of the macrophage nucleus from affecting tissue entry. We thus identify strengthening the cortical actin cytoskeleton through Dfos as a key process allowing efficient forward movement of an immune cell into surrounding tissues.

Macrophage mitochondrial bioenergetics and tissue invasion are boosted by an Atossa‐Porthos axis in Drosophila

“…These macrophages not only resolve infections, but also influence development and homeostasis (Bunt et al , 2010 ; Buck et al , 2016 ; Caputa et al , 2019 ; Riera‐Domingo et al , 2020 ). To reach places where they are needed to enable proper development, some macrophages follow guidance cues and invade the extended germband between the closely apposed ectoderm and mesodermal tissues, moving against the resistance of surrounding tissues (Siekhaus et al , 2010 ; Ratheesh et al , 2018 ; Valoskova et al , 2019 ; Belyaeva et al , 2022 ). Importantly, the rate‐limiting step for this tissue invasion is the infiltration of the pioneer macrophage, a process affected both by the properties of the surrounding tissues (Ratheesh et al , 2018 ) as well as macrophages themselves (Valoskova et al , 2019 ; Belyaeva et al , 2022 ).…”

“…To reach places where they are needed to enable proper development, some macrophages follow guidance cues and invade the extended germband between the closely apposed ectoderm and mesodermal tissues, moving against the resistance of surrounding tissues (Siekhaus et al , 2010 ; Ratheesh et al , 2018 ; Valoskova et al , 2019 ; Belyaeva et al , 2022 ). Importantly, the rate‐limiting step for this tissue invasion is the infiltration of the pioneer macrophage, a process affected both by the properties of the surrounding tissues (Ratheesh et al , 2018 ) as well as macrophages themselves (Valoskova et al , 2019 ; Belyaeva et al , 2022 ). Here we identify a previously uncharacterized pathway that induces concerted metabolic and mitochondrial reprogramming to support the higher energy levels needed for pioneer cell invasion through changes in translation and metabolic enzyme expression.…”

The macrophage genetic cassette inr/dtor/pvf2 is a nutritional status checkpoint for developmental timing

“…Drosophila macrophages express nutritional sensors, such as nuclear receptors and the insulin receptor, and are a source of secreted factors including cytokines and growth factors that can mediate adaptive responses of local or distant tissues in response to external or internal cues [23, 24, 44]. We thus designed a targeted knock-down screen for genes encoding secreted factors and nutrient-sensing receptors that are expressed in larval macrophages before the onset of pupation (96 hours AEL) [45] ( Fig. S2, S3 ), testing their role in the timing of pupation and ecdysone production.…”

Emerging concepts on the mechanical interplay between migrating cells and microenvironment in vivo

“…This forces cells to use strategies to mechanically adapt to such challenges. During macrophage invasion of the germ band, macrophages prepare for the challenging migration through the restrictive environment by forming a protective actin cortex ( Belyaeva et al, 2022 ). This protective shell is required for proper macrophage migration, and it shields the migrating macrophage nucleus from mechanical stress during confinement.…”