I have scRNA-seq data with annotated cell subpopulations. I am using PAGA for trajectory inference. To do that, I need to know a "root" cell type or potential progenitor cells. Particularly, in the stromal cell compartment, I have stromal 1, 2, 3 subtypes, myofibroblasts, and pericytes. I searched the literature and couldn't find any univocal stromal cell differentiation paths. Whereas for example for T cells, differentiation/maturation is described more thoroughly and unambiguously. I would appreciate any advice/direction on where to look for stromal cell differentiation in cancer.