Mechanistic studies of Drosophila lymph gland hematopoiesis are limited by the availability of cell-type-specific markers.Using a combination of bulk RNA-Seq of FACS-sorted cells, single-cell RNA-Seq, and genetic dissection, we identify new blood cell subpopulations along a developmental trajectory with multiple paths to mature cell types.This provides functional insights into key developmental processes and signaling pathways.
We highlight metabolism as a driver of development, show that graded Pointed expression allows Voltage Tester distinct roles in successive developmental steps, and that mature crystal cells specifically express an alternate isoform of Hypoxia-inducible factor (Hif/Sima).Mechanistically, the Musashi-regulated protein trio passeggino Numb facilitates Sima-dependent non-canonical, and inhibits canonical, Notch signaling.Broadly, we find that prior to making a fate choice, a progenitor selects between alternative, biologically relevant, transitory states allowing smooth transitions reflective of combinatorial expressions rather than stepwise binary decisions.
Increasingly, this view is gaining support in mammalian hematopoiesis.