Cross-species comparative analysis using single-cell RNA-sequencing data of Drosophila hemocytes, zebrafish, mouse and human immune cells

Drosophila hemocytes are the primary defense system required for the animals to thrive and overcome harmful threats and are often compared to the innate immune system of vertebrates. However, their homology has been described using only a limited number of genes and a systematic analysis using transcriptomic data would provide novel insights about the evolution of immune systems. In this study, we performed cross-species comparative analysis using single-cell RNA-sequencing data of Drosophila hemocytes, zebrafish, mouse, and human immune cells in both supervised and unsupervised manner. A small subset of prohemocytes with hematopoietic potential displayed a homology to progenitor populations in vertebrates. Drosophila hemocytes appeared to be largely homologous to the myeloid cells of vertebrates, especially plasmatocytes to monocytes/macrophages and lamellocytes to neutrophils. CG14767 (LAPTM4A) which encodes a lysosomal protein is well conserved in various phagocytic cells suggesting its common role in degradation of foreign uptake. Our results provide deeper understanding in molecular conservation of the Drosophila immune system. Overall design: Single-cell RNA-sequencing of circulating hemocytes from larvae of Drosophila melanogaster