title: Unraveling the complexity of Drosophila immune cells: a focus on blood cell heterogeneity, plasticity, and dynamics.
title: Entschlüsselung der Komplexität von Drosophila Immunzelle: Heterogenität, Plastizität und Dynamik von Blutzellen im Fokus.
titleType: AlternativeTitle
Creators: name: Hirschhäuser, Alexander
Publisher: name: Philipps-Universität Marburg
Year: 2023
Subjects: Medical sciences Medicine
Medizin

description: Until recently, Drosophila immune cells, named hemocytes, were only characterized and clustered into subpopulations based on morphology, function, and a limited number of marker genes. Thus, the cells were subdivided into plasmatocytes, crystal cells, and lamellocytes, and the population of Drosophila plasmatocytes has been thought to be a relatively homogenous sub-group. However, new single-cell RNA sequencing approaches revealed a complex heterogeneity and plasticity within this cell population. Particularly, the transcriptional profile of hemocytes changes in response to the significant environmental changes during the transition from the larval to the pupal stage of development. Additionally, the here identified complex heterogeneity of Drosophila immune cells includes cells derived from embryonic and lymph gland precursors with a highly migratory and immune responsive Posterior Signaling Center (PSC) niche-like blood cell type that persists into the adult fly. Those niche-like progenitor cells could be potential precursor cells for known hemocyte subpopulations like the lamellocytes. However, so far, lamellocytes have only been reported to differentiate from progenitor hemocytes in response to infestation by parasitoid wasps. Hemocytes rely on the ability to rapidly adapt to different immune challenges and migrate to locations where they are needed. This is only possible because of the highly regulated actin cytoskeleton. Dynamic remodeling of this dense network – especially inside the lamellipodium - is highly regulated and a crucial step for the necessary cell shape changes to allow locomotion and efficient immune defense. A key regulator, which builds lamellipodial protrusions and thereby drives cell migration, is the Arp2/3 complex, which in turn is activated by the hetero-pentameric WAVE regulatory complex. The role of phosphorylation in regulating WAVE, an indispensable part of the complex, has been addressed in various in vitro studies. However, the in vivo relevance of WAVE phosphorylation on actin dynamics is still poorly understood and further investigated in this study. CK1α is a constitutively active and ubiquitously expressed serine/threonine kinase, which is involved in regulating many cellular processes ranging from cell division, and signaling to circadian rhythm and has now emerged as an essential regulator of WAVE. MARCM induced ck1α missense mutant hemocytes phenocopy WAVE depletion resulting in the disruption of the actin network that causes reduced lamellipodia formation and impaired migratory behavior. Rescue experiments using a phosphorylation-deficient mutation in the CK1α target sequence within the VCA domain of WAVE outline the dependency on CK1α phosphorylation for WAVE stability. Remarkably, loss of phosphorylation leads to proteasomal degradation of WAVE. This suggests that WAVE has a basal level of phosphorylation by CK1α, which protects it from degradation and thus promotes its function in vivo.