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Fig. S4 Lack of thymopoiesis in adult c-myb mutants. (A) The thymic epithelial anlage is present in c-myb mutants (age = 8 wk). Note that the epithelial cells are tightly clustered, because no hematopoietic cells are present in the tissue. No abnormality of the pharyngeal microenvironment was noted by alcian blue staining and foxn1-specific hybridization signals. The genotypes of fish are indicated. (B) Only long-lived macrophages are present in the mutant thymus (indicated by arrows in sections hybridized with spi1 and l-plastin); no other types of hematopoietic cells are present. Note that the wild-type thymus contains only very few cells positive for scl expression (arrow). RNA in situ hybridization of thymus sections with the indicated probes at 8 wk of age; similar results were obtained for 6 and 7 wk of age. The thymic rudiments are outlined by dashed lines. (Scale bar: 100 μm.)