Mural cells are intrinsic to the endothelium and control vascular development, stability, and homeostasis (Sweeney et al., 2016; Trost et al., 2016). We identified 7 mural subclusters from 7 biological ICs (n=4,713 cells, Figure 2C and Data S4E). Mural cells have two subtypes: pericytes, which associate with capillaries, and smooth muscle alpha actin (SMA) cells, which associate with larger-bore vasculature and control blood flow (Hill et al., 2015; Hughes and Chan-Ling, 2004; Nehls and Drenckhahn, 1991). A single IC (IC 13) appeared to encode this distinction, with pericyte marker Vtn as the strongest loading gene (Figure 2C)(Vanlandewijck et al., 2018). Other enriched genes suggest specialized pericyte function. For example, expression of a potassium channel activated by diphosphate levels (encoded by Kcnj8 and Abcc9) and an ADP-ribosyltransferase (Art3) suggest signaling machinery that couples dinucleotide metabolites to membrane potential and post-translational modification. Among SMA cells, Acta2 expression correlates with a veinous versus arterial distribution (Vanlandewijck et al., 2018). IC 19 represented this difference in a graded rather than categorical way, as Rgs5/Acta2 expression and IC cell scores were continuously, rather than bimodally,
