Metabolic-morphologic events in the integument of the Pacific hagfish (Eptatretus stoutii)

Summary Light- and electron-microscopic autoradiography were used to obtain a coordinated metabolic-morphologic view of some of the events of cellular differentiation that occur across the epidermis of the Pacific hagfish (Eptatretus stoutii) and which enable this animal to secrete copious amounts of mucus. As judged by epidermal incorporation of ³H]-thymidine in vivo, about 98 % of DNA replication is confined to the basal three layers of the total of 6–8 layers of cells. Small mucous cells (SMC), the most numerous of the three major cell types involved in mucigenesis, show in vitro and in vivo radioincorporation profiles of ³H]-L-lysine and ³H]-D-glucosamine which differ markedly from those of ³H]-L-fucose and ³H]-D-galactose. Time-course incorporation profiles (mean silver grains/cell and percentage of cells with at least one cluster of silver grains) of ³H]-L-lysine and ³H]-D-glucosamine not only reflected the metabolic activities of cell renewal and differentiation in basally-located cells but also the high mucigenic activity in cells near the epidermal surface. By contrast, ³H]-L-fucose and ³H]-D-galactose were mainly incorporated by the more mature SMC in juxtanuclear regions near Golgi complexes and newly formed secretory vesicles. The intensity of ³H]-fucose labeling appeared proportional to the intensity of histochemical staining of the apical cytoplasm. The prominent capsule, within SMC in basal and lateral regions, which arises from a tight intermingling of tonofilaments, appears to restrict secretory vesicles to apical regions while the cell progressively differentiates and migrates to the epidermal surface. The other mucigenic cell types, large mucous cells and thread cells, each show distinctive differentiation and radioincorporation patterns.This study was supported in part by General Research Support Grant, FR5366 of the NIH, Minnesota Medical Foundation Grants, and the Asthmatic Children's Aid of Chicago, Illinois. The authors wish to thank Karen Brintzenhofe and Doreen Fleetwood for their assistance