Visualization of Lymphotoxin-β and Lymphotoxin-β Receptor Expression in Mouse Embryos

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Abstract
The heteromeric lymphotoxin αβ ligand (LT) binds to the LTβ receptor (LTβR) and provides an essential trigger for lymph node (LN) development. LTβR signaling is also critical for the emergence of pathological ectopic lymph node-like structures and the maintenance of an organized splenic white pulp. To better understand the role of LT in development, the expression patterns of LTβ and LTβR mRNA were examined by in situ hybridization in the developing mouse embryo. Images of LTβ ligand expression in developing peripheral LN in the E18.5 embryo revealed a relatively early phase structure and allowed for comparative staging with LN development in rat and humans. The LTβR is expressed from E16.5 onward in respiratory, salivary, bronchial, and gastric epithelium, which may be consistent with early communication events between lymphoid elements and epithelial specialization over emerging mucosal LN. Direct comparison of mouse fetal and adult tissues by FACS analysis confirmed the elevated expression of LTBR in some embryonic epithelial layers. Therefore, surface LTBR expression may be elevated during fetal development in some epithelial layers.