Autoradiographic evidence for epithelial origin of glucose-rich components of the basement membrane (basal lamina) and basement lamella in the skin of Fundulus heteroclitus

The fine structure of the developing pelvic fin dermal skeleton in the trout Salmo gairdneri

The morphogenetic and ultrastructural features of the dermal skeleton in the pelvic fin bud of a teleost, the rainbow trout Salmo gairdneri, have been examined by light and electron microscopy. The principal structural components observed are lepidotrichia and actinotrichia. Lepidotrichia consist of two parallel and symmetrical bony demirays that form jointed segments within the fin. The demirays calcify in a proximodistal direction within the extracellular collagen network of the basal lamella belonging to the epidermal-dermal interface of the fin. Needle- and plate-like particles of a solid mineral phase appear to be associated with the collagen fibrils and with a fine, granular, interfibrillar material central to the demirays. Cellular processes and membrane-bound vesicles are absent from the regions of calcification. During fin growth, the bony, acellular lepidotrichia are separated from the epidermal-dermal interface by infiltrating mesenchymal cells in proximal fin regions; in distal areas, the lepidotrichia remain within the basal lamella. The actinotrichia are extensive unmineralized rods of elastoidin that occupy the distal margin of the fin and precede the differentiation of lepidotrichia. Once the lepidotrichia form, actinotrichia lie preferentially between their demirays. In some instances, structural interactions are suggested between actinotrichia and lepidotrichia. Considerations of embryologic and structural features of fin components fail to support the hypothesis that individual segments of lepidotrichia are modified scales in all fish.

Localization of newly synthesized precursors of basal lamina in the regenerating planarian as revealed by autoradiography

Autoradiography has been carried out to investigate the site of synthesis of the basal lamina in the regenerating planarian, Dugesia japonica. Since the basic collagenous structures of the basal lamina rose from RR-positive amorphous precursor, [3H]proline, [3H]glucose and [35S]sodium sulphate were used as radioactive precursors of collagen, unsulphated and sulphated GAG respectively. Cytoplasm of the most regenerating epidermal cells was heavily labeled with [3H]proline during epithelization. A quantitative uptake analysis of [3H]proline indicates a progressive decline in the amount of labeled precursor in the epidermis with a corresponding increase in deposition of the labeled collagen at the presumptive basal lamina. Several myoblasts at the subepidermal region were highly labeled with both [3H]glucose and [35S]sodium sulphate. Silver grains of these labeled precursors were also present in the presumptive portion of basal lamina. These observations suggest that the regenerating epidermal cell is the only site of synthesis of the basal lamina collagen while the myoblast exclusively secretes extracellular GAG. Some of the GAG may be closely associated with the amorphous zone.

Basal lamina of embryonic salivary epithelia. Production by the epithelium and role in maintaining lobular morphology

The role of the basal lamina in maintaining the normal morphology of mouse embryo submandibular epithelia was assessed by examining its production as well as the cellular and organ culture changes associated with its removal and replacement. The lamina was removed from epithelia isolated free of mesenchyme by brief treatment with testicular hyaluronidase in the absence of calcium. The treatment causes rounding-up of the cells, loss of cellular cohesion, appearance of microvilli, and changes in the organization of cytoskeletal structures. The lamina is not removed and the cellular alterations do not occur in the absence of hyaluronidase in calcium-free medium or when both enzyme and calcium are present, possibly because digestion of chondroitin sulfate, a component of the lamina, is inhibited by calcium. Within 2 h after treatment, in the absence of mesenchyme or biological substrata, the epithelia deposits a new lamina, which is identical by several criteria to the preexisting lamina, and reverses the cellular alterations. Epithelia treated with hyaluronidase lose lobular morphology during culture with mesenchyme. Delaying culture with mesenchyme, to allow restoration of the lamina and of normal cellular architecture, prevents the loss of lobular morphology. The results indicate that the basal lamina imposes morphologic stability on the epithelium, while the mesenchyme apparently affects processes involved in changes in morphology, possibly by selective degradation of the basal lamina.

Initiation of the actinotrichial development in the early fin bud of the fish, Salmo

Ultrastructural analysis of initial development of actinotrichia, the skeleton anlage of the pelvic fin buds, was performed on the rainbow trout, Salmo gairdneri. It shows that the first actinotrichial rudiments appear in the subepidermal space of the pseudoapical cap. No mesenchymal cell bodies or their filopods are present. Hyaloplasmic protrusions of the basal epidermal cells are seen in the subepidermal space, limited by a dermoepidermal boundary reduced to a discontinuous thin adepidermal lamina without a collagenous layer. These morphological data suggest that the epidermal pseudoapical cap probably initiates the development of actinotrichia. Later, mesenchymal cells invade the subepidermal space and are probably involved in the further growth of actinotrichia.

Synthesis of the glomerular basement membrane in the rat kidney. Autoradiographic studies with the light and electron microscope

To study the origin and the formation of the glomerular basement membrane, autoradiographic investigations with 3H-proline and 3H-leucine have been performed in ultrathin with semithin sections of the glomeruli of 42 male rats. The results of this study indicate that, of the three cell types of the glomerulus, the epithelial cells (=podocytes) synthesize the proline-rich scleroproteins of the glomerular basement membrane. Our autoradiographic studies have yielded no evidence for participation of the endothelial or mesangial cells in the formation of the basement membrane. The mesangial cells appear to be responsible for the synthesis of the mesangial matrix only.

Secretion of collagen by corneal epithelium. I. Morphology of the collagenous products produced by isolated epithelia grown on frozen-killed lens

Corneal epithelium from 5-7-day old chick embryos was isolated with EDTA and grown in culture on frozen-killed lens as a substratum. Autoradiographs showed that in the presence of [(3)H]proline, the corneal epithelium synthesized and secreted onto the lens substratum, radioactive materials resistant to extraction by sodium hydroxide. The radioactive label was associated with newly formed striated collagen fibrils, large "sheets" of collagen, and basal lamina. The repeat period and interband pattern of the abundant new collagen sheets and fibrils was typical of "native" or so-called "mesenchymal" collagen. Collagen-like materials were observed in secretory (Golgi) vacuoles within the corneal cells and collagen fibrils within the intercellular canals (lateral interfaces) of the epithelium, as well as at the base of the cells. Both the granular endoplasmic reticulum and Golgi complexes were highly developed in the corneal epithelium. In the discussion, the role of cytoplasmic organelles in collagen secretion, the origin and structure of the basal lamina, and variations in collagen polymerization patterns in vitro are reviewed and evaluated. The morphogenetic significance of the synthesis and secretion of collagen by embryonic epithelium is appraised and the production of true native-striated collagen by epithelium is stressed.

Studies on regeneration blastemas of the planarianDugesia tigrina with special reference to differentiation of the muscle-connective tissue filament system

Head blastemas in regeneratingDugesia tigrina (Planaria) have been studied light microscopically and electron microscopically. Acid phosphatase activity has been followed in early blastemas using a light microscopical cytochemical method. The possibilities of a collagen synthesis inhibiting substance α-α'-dipyridyl in analyzing fibrillogenesis in planarians have been explored.Following a brief discussion of the neoblast concept the general organization and characteristics of the blastema are described. Regeneration of the muscle-connective tissue filament system including the subepidermal membrane is analyzed in detail. It is stressed that the muscle cells, the filamentous sheaths and the subepidermal membrane in planarians should be visualized as a mutually dependent, integrated system. The hypothesis is proposed that neoblasts differentiate into myoblasts which both synthesize myofilaments and collagen. Collagen forms the filaments of the subepidermal membrane-muscle sheath system. No certain interference with collagen synthesis and secretion could be demonstrated in the experiments involving α-α'-dipyridyl.There was no evidence for significant changes in the activity and pattern of acid phosphatase during early stages of regeneration.The problems concerning the existence of neoblasts, their participation in regeneration and their origin (stock cell or result of a dedifferentiation process) are discussed.