Calcium bursts allow rapid reorganization of EFhD2/Swip-1 cross-linked actin networks in epithelial wound closure

Abstract

Changes in cell morphology require the dynamic remodeling of the actin cytoskeleton. Calcium fluxes have been suggested as an important signal to rapidly relay information to the actin cytoskeleton, but the underlying mechanisms remain poorly understood. Here, we identify the EF-hand domain containing protein EFhD2/Swip-1 as a conserved lamellipodial protein strongly upregulated in Drosophila macrophages at the onset of metamorphosis when macrophage behavior shifts from quiescent to migratory state. Loss- and gain-of-function analysis confirm a critical function of EFhD2/Swip-1 in lamellipodial cell migration in fly and mouse melanoma cells. Contrary to previous assumptions, TIRF-analyses unambiguously demonstrate that EFhD2/Swip-1 proteins efficiently cross-link actin filaments in a calcium-dependent manner. Using a single-cell wounding model, we show that EFhD2/Swip-1 promotes wound closure in a calcium-dependent manner. Mechanistically, our data suggest that transient calcium bursts reduce EFhD2/Swip-1 cross-linking activity and thereby promote rapid reorganization of existing actin networks to drive epithelial wound closure.

PSC niche develops into immune-responsive blood cells capable of transdifferentiating into lamellocytes inDrosophila

“…Recent studies further revealed that the function chitinases are not exclusive to catalyze the hydrolysis of chitin producing pathogens, but also include a crucial role in bacterial infections and inflammatory diseases 54 . Interestingly our GO-term analysis not only identified the enrichment of genes involved in innate immune response but also an increased expression of genes implicated in cell-cell adhesion and septate junction assembly (Figure 3H), a special feature that we could already observe in our previous bulk RNA seq analysis of pupal hemocytes (Supplementary figure S2M, 29 . Septate junction (SJ) proteins play an essential role in regulating hematopoiesis in the Drosophila lymph gland, but might be also essential for an effective response to parasitic wasp attack 55 56 .…”

“…As previously reported 64–66 , prominent kn expression is initially found in dorsal muscle fields in the thoracic and abdominal segments of early pupae (Figure 7A), and its expression becomes restricted to segmental abdominal muscles, along the anterior-posterior border of the developing wing and in pericardial cells along the dorsal vessel in later pupal development (>16h APF-96h APF; Figure 7B, C). High-resolution spinning disc live cell imaging microscopy of 4h APF old pupae revealed migrating single kn -marked PSC cells that form polarized dynamic lamellipodial protrusions and start to redistribute from the dorsal patches of the body wall as similarly observed for plasmatocytes (Figure 7D; Supplementary movie M1) 9, 29 . kn -marked PSC cells are highly motile but much smaller as compared to hml -marked plasmatocytes, confirming that we indeed observed PSCs when focusing on small kn positive cells instead of plasmatocytes (Supplementary movies M1 and M2).…”

“…Both, embryo and lymph gland-released hemocytes mix together at the onset of pupariation and persist into the adulthood. Our recent bulk RNA analysis already revealed highly differential expression profile in pupal hemocytes compared to larvae 29 . To analyze this mixed blood cell population in more detail, we used scRNA-seq technology to dissect the cellular heterogeneity of the total blood cells in Drosophila early pupa.…”

“…We previously identified several cytoskeleton and cell motility genes upregulated in pupal hemocytes using a bulk RNA-sequencing approach 29 . Among the top50 of these genes, 37 genes showed cluster specific expression profiles (Supplementary figure S2M).…”

“…9, 27, 28 . Bulk RNA-seq gene expression analysis recently uncovered thousands of genes that are differentially expressed in pupal hemocytes compared to larvae 29 . However, whether this striking differential expression pattern of pupal hemocytes might also reflect the differentiation of new hemocyte subtypes or cell types has not yet been addressed.…”