Molecular traces of Drosophila hemocytes reveal transcriptomic conservation with vertebrate myeloid cells

Abstract

Drosophila hemocytes serve as the primary defense system against harmful threats, allowing the animals to thrive. Hemocytes are often compared to vertebrate innate immune system cells due to the observed functional similarities between the two. However, the similarities have primarily been established based on a limited number of genes and their functional homologies. Thus, a systematic analysis using transcriptomic data could offer novel insights into Drosophila hemocyte function and provide new perspectives on the evolution of the immune system. Here, we performed cross-species comparative analyses using single-cell RNA-sequencing data from Drosophila and vertebrate immune cells. We found several conserved markers for the cluster of differentiation (CD) genes in Drosophila hemocytes and validated the role of CG8501 (CD59) in phagocytosis by plasmatocytes, which function much like macrophages in vertebrates. By comparing whole transcriptome profiles in both supervised and unsupervised analyses, we showed that Drosophila hemocytes are largely homologous to vertebrate myeloid cells, especially plasmatocytes to monocytes/macrophages and prohemocyte 1 (PH1) to hematopoietic stem cells. Furthermore, a small subset of prohemocytes with hematopoietic potential displayed homology with hematopoietic progenitor populations in vertebrates. Overall, our results provide a deeper understanding of molecular conservation in the Drosophila immune system. immune cells from zebrafish, mice, and humans, revealing that a phagocytic cell type in Drosophila, plasmatocytes, is conserved as a myeloid cell in other organisms. We also report that a novel plasmatocyte marker gene, CG8501, which is conserved as in human as CD59, functions in the formation of normal NimC1+ plasmatocytes for bacterial uptake. Our work provides the first transcriptome-wide analysis between Drosophila and vertebrate species and documents the conservation of orthologous genes and cell types in Drosophila hemocytes.