Thymus development in amphibians: colonization by thymic endodermal rudiments by lymphoid stem-cells of mesenchymal origin in the urodele Pleurodeles waltlii Michah.
Pleurodeles waltlii thymus morphogenesis was studied by serial semi-thin sections and by electron microscopy. Thymus endodermal buds were first seen 9 days after fertilization. From 12 to 16 days, these rudiments are invaded by a small number of cells moving from the cephalic mesenchyme environment. These cells have the ultrastructural morphology of lymphoid stem-cells. Cytologic transitional forms from endodermal to lymphoid-like cells are never observed. These results clearly indicate that in amphibians the thymus lymphocytes are not derived from the initial endodermal rudiments.
D000818:Animals; D002454:Cell Differentiation; D004707:Endoderm; D006412:Hematopoietic Stem Cells; D007814:Larva; D008214:Lymphocytes / Q000166:cytology*; D013950:Thymus Gland / Q000166:cytology / Q000254:growth & development* / Q000648:ultrastructure; D013997:Time Factors; D014562:Caudata