E-selectin expression and stimulation by inflammatory mediators are developmentally regulated during embryogenesis

Leukocyte recruitment during inflammation is specified, in part, by the spa tial distribution and temporal regulation of endothelial adhesion molecules . In this study we investigated the developmental onset of E-selectin and i ntercellular adhesion molecule-1 (ICAM-1) basal expression and inducibility by inflammatory mediators as indices of lineage-restricted endothelial adh esion molecule expression. We studied both murine embryos and embryoid bodi es (EB), derived from differentiated embryonic stem cells, to examine a bro ad range of endothelial ontogeny. Our results reveal that E-selectin and IC AM-1 are differentially regulated during development and that three stages define the ontogeny of the E-selectin-inducible response. The earliest endo thelial lineage cells in Day 4 and Day 5 EB did not express E-selectin in t he basal state or after stimulation. A second stage, observed between embry onic Day 9.5 (E9.5) and E11.5 to E12.5 in cultured embryo cells and transie ntly at Day 6 of EB differentiation, was characterized by basal expression that was not stimulated by inflammatory mediators. A third stage was charac terized by both basal and inducible expression of E-selectin and was observ ed beginning at E12.5 to E13.5 in cultured embryo cells and at Day 7 in EB. In contrast ICAM-1 was stimulated at all of the embryonic stages examined and before the onset of E-selectin inducibility in both embryos and EB. E-s electin expression in embryos was also stimulated by introducing endotoxin into the embryonic, but not the maternal, peritoneum. This suggests that em bryos are protected from inflammatory insults present in the maternal circu lation. The developmentally regulated acquisition of E-selectin inducibilit y during embryogenesis likely involves changes in signal transduction casca des, transcription factors, and/or chromatin accessibility that specify ind ucible expression within the endothelial lineage and further restrict induc ibility to particular endothelial subpopulations.