Post-hatching development of the thymic epithelial cells in the rainbow trout Salmo gairdneri: an ultrastructural study.
This study reports the ultrastructure of subpopulations of epithelial cells of the thymic parenchyma during the post-hatching development of the rainbow trout, Salmo gairdner, kept at 14 degrees C. At hatching, the thymus contained a small number of medium and large thymocytes interspersed among three different types of epithelial cells: (1) epithelial cells adjacent to the connective tissue capsule; (2) ramified dark epithelial cells with electron-dense cytoplasm; and (3) pale electron-lucent epithelial cells displaying secretory-like features. All these cells types were anchored to one another by desmosomes and had apparently differentiated from the pharyngeal epithelium. At 4 days after hatching, the thymus enlarged, and numerous gaps occurred between the cell processes of contiguous epithelial cells adjacent to the capsular connective tissue. In 21-day-old trout, thymic trabeculae developed carrying blood vessels, and a subcapsular zone became evident containing lymphoblasts and large subcapsular epithelial cells. In 30-day-old trout, an outer thymic zone developed consisting of spindle-shaped epithelial cells which formed a dense network. At this stage, scattered cystic cells, which apparently differentiated from the pale epithelial cells, were present.
Castillo
A
A
Departamento de Biología Celular y Anatomía, Facultad de Biología, Universidad de León, Spain.
López-Fierro
P
P
Zapata
A
A
Villena
A
A
Razquin
B
B
D000818:Animals; D003593:Cytoplasm / Q000648:ultrastructure; D004848:Epithelium / Q000254:growth & development / Q000648:ultrastructure; D008854:Microscopy, Electron; D013950:Thymus Gland / Q000254:growth & development / Q000648:ultrastructure*; D014337:Trout / Q000033:anatomy & histology* / Q000254:growth & development