Ontogeny of CTX expression in xenopus

In Xenopus, the type I transmembrane protein, CTX (cortical thymocyte-specific antigen of Xenopus), is hypothesized to play a role in thymocyte differentiation and/or thymic selection. The present studies were undertaken to gather additional evidence in support of a postulated association of CTX with a differentiation step of a cell population that corresponds to the murine immature double positive (CD4+CD8+TCR+) thymocyte subset. During ontogeny, cell surface expression of CTX on thymocytes can first be detected by immunocytochemistry and flow cytometry at 8 days post-fertilization, about 1 day after CD8+ cells first appear. By 12 days post-fertilization, T-cells in the entire cortex except for the outer most layer of cells, are intensely CTX positive, whereas those in the medulla are negative. This pattern persists throughout larval and postmetamorphic life.