Unique Junction Research Articles

Septate-like junctions in abnormal erythroblasts: cytochemical, ultrastructural and freeze-etch studies.

Ultrastructural studies of the bone marrow of a patient with refractory anemia revealed aberrant erythroblasts with unique cell junctions. Periodic structures linked adjacent processes on the same cell as well as surfaces of neighboring erythroblasts. Inclusions circumscribed by similar complexes were also present in the cytoplasm. The junction appeared in cross sections as two rigidly parallel unit membranes separated by 250-300 A interspace with two regular arrays of facing 70 A particles at intervals of 160-200 A. These intracellular specializations were present between erythroblasts at various stages of maturation and between, mono, bi or multinucleated erythroblasts. Junctions were permeable to lanthanum and many that appeared to be intracellular were demonstrated to be continuous with the extracellular space. The fact that others were not penetrated by lanthanum indicates that detachment of the interdigitating processes from cells of origin could have occurred. In freeze-etched replicas, distribution of membrane particles was random in areas of septate-like junctions, although parallel rows were sometimes observed both on A and B inner hydrophobic faces of the membrane leaflets. Junctional complexes in tissue culture appeared to have been disrupted and were not reestablished; however, inclusions resembling internalized junctions were observed associated with multivesicular bodies. Ineffective erythropoiesis and the resulting refractory anemia appear to be associated with the presence of the described anomalous junctional complexes.

Structural changes inducted by follicle-stimulating hormone or dibutyryl cyclic AMP on presumptive Sertoli cells in culture.

Cells isolated from testes of 20-day-old rats, maintained in primary culture in a defined medium, are shown to respond to follicle-stimulating hormone or 3:5-cyclic AMP with characteristic morphological changes. No response is observed in cells treated with luteinizing hormone or 5-?AMP. The cells form a mono-layer, and have been identified as presumptive Sertoli cells structurally by identification of unique tight junctions in electron micrographs of the preparations, along with other ultrastructural properties characteristic of Sertoli cells in situ. These cells do not undergo mitosis. The presumptive Sertoli cells are shown to be morphologically and functionally different from peritubular fibroblasts grown in parallel cultures. Fibroblasts have high rates of mitosis, do not respond to follicle-stimulating hormone, and frequently form multilayers. Other information on the biochemical responses of the cells is cited, which supports the conclusion that the cultured cell preparations consist primarily of Sertoli cells.