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Bovine respiratory disease complex (BRDC) can be caused by several Gram negative bacteria. Lung endo-thelial cells may be damaged by the release of lipopolysaccharide (LPS) from these organisms. Toll-like receptor (TLR-4) signaling pathways include the myeloid differentiation primary response gene 88 (MyD88) and the Toll/interleukin (IL)-l receptor (TIR) domain-containing adapter-inducing interferon-ß (TRIF) pathways. The aim of this study was to determine which of these pathways is responsible for permeability changes, apoptosis and cytokine production in bovine lung microvascular cells exposed to LPS. Bovine lung endothelial cells were treated with a peptide to inhibit MyD88 signaling or small interfer-ing RNA (siRNA) to inhibit TRIF signaling. Effects were measured using trans-well endothelial electrical resistance to determine cell monolayer permeability, annexin staining to estimate apoptosis and real-time PCR to measure levels of expression of IL-lβ and tumor necrosis factor (TNF)-a mRNA. Inhibition of TRIF signaling reduced permeability changes and apoptosis in endothelial cells exposed to LPS. In con-trast, MyD88 inhibition reduced expression of IL-lβ and TNF-α mRNA in LPS treated cells, but had no effect on permeability. It was concluded that TRIF signaling in LPS-stimulated lung endothelial cells results in permeability changes and apoptosis. [ABSTRACT FROM AUTHOR]

Summary Cell fate transitions are essential for specification of stem cells and their niches, but the precise timing and sequence of molecular events during embryonic development are largely unknown. Here, we identify, with 3D and 4D microscopy, unclustered precursors of dermal condensates (DC), signaling niches for epithelial progenitors in hair placodes. With population-based and single-cell transcriptomics, we define a molecular time-lapse from pre-DC fate specification through DC niche formation and establish the developmental trajectory as the DC lineage emerges from fibroblasts. Co-expression of downregulated fibroblast and upregulated DC genes in niche precursors reveals a transitory molecular state following a proliferation shutdown. Waves of transcription factor and signaling molecule expression then coincide with DC formation. Finally, ablation of epidermal Wnt signaling and placode-derived FGF20 demonstrates their requirement for pre-DC specification. These findings uncover a progenitor-dependent niche precursor fate and the transitory molecular events controlling niche formation and function. Graphical Abstract Highlights • Precursors of the hair follicle niche are specified before niche cluster formation • Bulk and single-cell transcriptomics defines niche fate at molecular transitional state • Successive transcription factor and signaling waves mark niche fate acquisition • Niche fate acquisition is not "pre-programmed" and requires FGF20 from progenitors Mok et al. identify niche precursors during progenitor and niche formation in mouse embryonic hair follicles. Population-based and single-cell transcriptomics show that unclustered dermal condensate precursors are at a transitional fibroblast-to-DC state marked by successive waves of transcription factor and signaling molecule expression. Niche fate acquisition is not "pre-programmed" and requires placode progenitor-derived FGF20. [ABSTRACT FROM AUTHOR]