Cutting Edge: Thymocyte-Independent and Thymocyte-Dependent Phases of Epithelial Patterning in the Fetal Thymus

TLDR

Thymic epithelial cells in adult mice are classified into distinct subsets based on keratin expression profiles. The study aimed to investigate how TEC subsets emerge during fetal development by analyzing keratin 8 and keratin 5 expression. Researchers examined keratin expression at multiple fetal stages in normal C57BL/6J mice and assessed epithelial development in RAG2/γc‑deficient and Ikaros‑null mice that block thymocyte differentiation. Initial TEC patterning defined by keratin expression occurs independently of hematopoietic signals, but thymocyte‑derived signals are necessary during late fetal stages for continued TEC development and maintenance into adulthood.

Abstract

Abstract Thymic epithelial cells (TECs) in adult mice have been classified into distinct subsets based on keratin expression profiles. To explore the emergence of TEC subsets during ontogeny, we analyzed keratin 8 and keratin 5 expression at several stages of fetal development in normal C57BL/6J mice. In addition, thymic epithelial development and compartmentalization were explored in recombination-activating gene 2/common cytokine receptor γ-chain-deficient and Ikaros-null mice that sustain early and profound blocks in thymocyte differentiation. The results demonstrate that initial patterning of the thymic epithelial compartment as defined by differential keratin expression does not depend on inductive signals from hematopoietic cells. However, thymocyte-derived signals are required during late fetal stages for continued development and maintenance of TEC subsets in the neonate and adult.