A single-cell survey of Drosophila blood

Abstract

Drosophila blood cells, called hemocytes, are classified into plasmatocytes, crystal cells, and lamellocytes based on the expression of a few marker genes and cell morphologies, which are inadequate to classify the complete hemocyte repertoire. Here, we used single-cell RNA sequencing (scRNA-seq) to map hemocytes across different inflammatory conditions in larvae. We resolved plasmatocytes into different states based on the expression of genes involved in cell cycle, antimicrobial response, and metabolism together with the identification of intermediate states. Further, we discovered rare subsets within crystal cells and lamellocytes that express fibroblast growth factor (FGF) ligand branchless and receptor breathless, respectively. We demonstrate that these FGF components are required for mediating effective immune responses against parasitoid wasp eggs, highlighting a novel role for FGF signaling in inter-hemocyte crosstalk. Our scRNA-seq analysis reveals the diversity of hemocytes and provides a rich resource of gene expression profiles for a systems-level understanding of their functions.

Single-cell analysis of mosquito hemocytes identifies signatures of immune cell subtypes and cell differentiation

“…gambiae based on gene expression, previous proteomics studies (Smith et al, 2016), and phagocytic properties. This expansion of the general "granulocyte" classification is supported by previous morphological observations of granulocytes in mosquitoes (Kwon & Smith, 2019;Pondeville et al, 2020), and more recently by parallel scRNA-seq experiments in Drosophila (Tattikota et al, 2020;Cattenoz et al, 2020) and An. gambiae (Raddi et al, 2020).…”

“…To better define these sub-types, we more closely investigated the putative functional roles of each of these cell populations. Cells of Cluster 2 display high levels of immune gene expression of anti-microbial peptides (AMPs), components of the Toll pathway, TEP1, MMP1, and Figure S13) that may represent a class of specialized immune cells similar to other recent studies (Raddi et al, 2020;Tattikota et al, 2020;Cattenoz et al, 2020). Cluster 6 display reduced expression of several phagocytic markers ( Figure S13), suggesting that cells of this sub-type lack the specialized phagocytic function of fully differentiated granulocytes.…”

“…Similar to previous characterizations (Castillo et al, 2006), we identify prohemocyte, oenocytoid, and granulocyte populations in our RNA-seq analysis. However, in both the oenocytoid and granulocyte classifications, we identify multiple, distinct immune cell populations defined by developmental progression, activation state, or specialized immune function similar to those recently described in Drosophila (Tattikota et al, 2020;Cattenoz et al, 2020). Moreover, we provide an initial set of markers to accurately distinguish between mosquito immune cell populations using RNA-FISH, and validate these identifications through co-localization experiments, phagocytosis experiments, and phagocyte depletion assays.…”

“…PPO1 indicative of Drosophila crystal cells (Tattikota et al, 2020;Evans et al, 2014;Cattenoz et al, 2020;Dudzic et al, 2015;Fossett et al, 2003) were most prevalent in Clusters 7 and 8 ( Figure 2C), suggesting that these cell clusters are representative of oenocytoids cell populations (equivalent to Drosophila crystal cells). However, little resolution into the roles of Clusters 5 and 6 was provided through these comparisons to known Drosophila markers ( Figure 2C).…”

“…Recently, the advent of single-cell sequencing (scRNA-seq) has continued to delineate and provide further resolution into new cell types and immune cell functions in mammals (Amara Korba et al, 2016;Szabo et al, 2019). In lesser studied invertebrates lacking adaptive immunity, single-cell technologies have enhanced descriptions of previously described cell types and have redefined cell complexity (Severo et al, 2018;Cattenoz et al, 2020;Cho et al, 2020;Raddi et al, 2020;Tattikota et al, 2020).…”