Expression dynamics of a heptad of HS-related genes enriched in erythroid populations and binding characteristics of the HS3A 8 scFv. (A) Heatmap of the expression of HS-related genes within clustered cell populations. Asterisks indicate genes uniquely enriched in the erythroid arm of hematopoiesis. Different cell populations are color coded. CEP, committed erythroid progenitor; Mk, megakaryocyte progenitor; Baso/Mast, basophil/mast cell progenitor; Mono, monocyte progenitor; Gran, granulocyte progenitor; Ly-T/NK, lymphocyte–T/natural killer cell progenitor; CLP, common lymphoid progenitor). (B) PHATE visualization of Gpc4, Tgfbr3, Agrn, Ext1, Extl3, Ndst2, and Hs6st1 expression within the MPP to EEP trajectory. (C) Expression of the identified HS-related gene heptad across pseudotime within the MPP to EEP trajectory. (D) Differentially expressed HS-related genes within CMP (CD27⁺), GMP, and MEP populations by microarray (GSE33937). Red asterisks indicate probes of the seven HS-related genes previously identified from scRNA-seq data. Yellow signifies up-regulation and blue down-regulation. (E) A quintuplet code that defines possible modifications on an HS disaccharide allows continuous coding of HS sequences (Townley and Bülow, 2018). The five positions that can be modified in a HS disaccharide are shown. 11 digits can describe a HS disaccharide in a quintuplet code. IdoA: iduronic acid, GluA: glucuronic acid. (F) Position weight matrix describing the presumptive HS epitopes bound by the HS3A8 scFv, calculated from published competitive ELISA data (Dennissen et al., 2002) using the quintuplet code. For details on calculations, see Materials and methods and Fig. S3, J and K.