Oxygen enhances fusion of cultured chick embryo myoblasts

Fusion of mononucleate myoblasts to form multinucleated myotubes increases when skeletal muscle cells are grown in progressively higher oxygen concentrations (5%, 20%, and 40% oxygen). At four days of growth fusion of myoblasts (as expressed by the percent of all muscle nuclei that are located in myotubes) is 57 ± 2% in 5% oxygen, 68 ± 1% in 20% oxygen, and 78 ± 2% in 40% oxygen (P<0.001). However, at a concentration of 40%, oxygen depresses the rate of cell division and thereby affects the number of myoblasts available for fusion. Thus, oxygen concentration significantly modifies growth of skeletal muscle in vitro. Its net effect on myotube formation results from the interaction of its separate effects to enhance cell fusion and to depress cell proliferation.     

Electron microscope study of the developing chick embryo heart

Summary Myofibrillar differentiation in heart myocells of the chick embryo was studied with aid of the electronmicroscope. At early stages (29 hrs.) thin myofibrillar bundles are seen already differentiated in the cytoplasm of the myoblast and a few hours later cross striation can be depicted as ill-defined densities regularly spaced along the myofilaments.At later stages it was seen that some myofibrillar bundles seem to arise from a Z-band belonging to a thicker bundle. This disposition was frequently seen but the number of bundles observed arising from a single Z-band is varied. Cases were found in which two or three bundles were interconnected by myofibrillar bridges. The disposition was nominated Z center and it is interpreted as favouring spreading of the contractil wave from bundle to bundle. Conduction of the contractil wave from cell to cell is insured through intercalated discs.Desmosomes and intercalated discs were observed during the course of this study, but no relationship between both components of the cell membranes nor between desmosomes and myofilaments were found.Fellow working under a local fellowship program supported by Grant No. 56030 of The Rockefeller Foundation.     

Outgrowth from chick embryo spinal cord in vitro,studied with the scanning electron microscope

Summary Cultures of chick spinal cord have been grown upon a plastic substrate, using the Maximov flying coverslip technique. After fixation, drying and coating in vacuo with carbon and gold, they have been examined with a Cambridge Instrument Company Stereoscan scanning electron microscope. A number of cell types — fibroblasts, oligodendrocytes and astrocytes — have been identified in the outgrowth, and in a single case possibly a neuron. The appearance of these cells as seen with scanning electron microscopy is described. What appear under light microscopic examination to be single processes often possess a multicomponent structure, and are axon bundles rather than single axons. Both bundles and cells are attached to the substrate by discreet finger-like processes. Some relations of glial cells to axon bundles are shown, and appearances suggestive of early myelination are recorded.     

3,4-Dihydroxyphenylalanine in cultured ventricular cells from chick embryo heart

Abstract— —A substance resembling catecholamine found in chick hearts during the early stages of embryologic development was identified as DOPA. Cell cultures and fluorescence microscopy indicated intracellular location of this substance in myocardial cells. The absence of nerve tissue in the cell cultures was demonstrated by electron microscopy.     

An electron microscope study on in vitro parthenogenesis in sunflower

Summary Electron microscope studies have been conducted on the parthenogenesis induced by in vitro culture of unfertilized ovules of sunflower (Helianthus annuus). In comparison with the state of the egg prior to inoculation, some eggs 5 days after culture show striking ultrastructural changes, which include, among others, nuclear migration, an increase in the number and activity of the organelles, a loss of polarity and wall formation at the chalazal end of the cell. Most of these changes are similar to those that occur normally in the zygote, indicating that parthenogenic development has been triggered in these eggs. Such eggs have been termed activated and are presumed to be capable of undergoing parthenogenesis. The parthenogenic proembryos which result share some features in common with zygotic proembryos. In addition, some parthenogenic proembryos exhibit unique properties not found in zygotic proembryos. These include embryos that consist of two parts differing markedly in density, an inversion of polarity, the frequent occurrence of autophagic vacuoles, the thickening of cell walls, a centripetal growth mode of wall formation, the appearance of an incomplete cell wall, free nuclear division, amitosis and degeneration. We believe that these ultrastructural peculiarities are the effects of in vitro culture.     

A scanning electron microscope study of normal and vitrified leaves from Datura insignis plantlets cultured in vitro

The surface anatomy of normal and vitreous leaves of plantlets obtained from Datura insignis Barb Rodr nodal segment cultures was compared using scanning electron microscopy. Normal and vitrified leaves are similar in several ways. They are both amphistomatic, and have similar distributions of glandular and non-glandular trichomes. Stomata have similar length, diameter and distribution in normal and vitreous plants. Immature stomata, which have closed pores, and plugged stomata, which contain an amorphous material between their guard cells, occur in both normal and vitrified leaves. Normal and vitreous leaves differ in the frequency of normal and abnormal stomata. Normal stomata have kidney-shaped guard cells and resemble closely those found in field-grown plants, whereas abnormal stomata have deformed guard cells. Normal stomata represent approximately 80% of the total number of stomata in normal leaves, but only 7% of the total number of stomata in vitreous leaves. Abnormal stomata represent 90% of the total number in vitreous leaves. The deformation of guard cells could possibly be a mechanical impediment to stomatal function.     

Troponin in embryonic chick skeletal muscle cells in vitro. An immunoelectron microscope study

The fine structurel distribution of troponin on thin filaments in developing myofibrils was investigated by the use of immunoelectron microscopy. Embryonic chick skeletal muscle cells grown in vitro were treated with antibodies against each of the troponin components (troponin T, I, and C) from adult chicken muscles. Each antibody was distributed along the thin filaments with a period of 38 nm. It is concluded that these newly synthesized regulatory proteins are assembled at their characteristic position from the initial phases of myofibrillogenesis.     

Cicatrization of the skin of the 7-day-old chick embryo cultured in vitro

A morphological study of in vitro wound healing has been performed by light, transmission and scanning electron microscopy in dorsal thoraco-lumbar skin of 7-day chick embryos. A circular wound, 750 microns in diameter, was punched out of dorsal skin, removing epidermis and the underlying dense dermis. Wound closure was completed within 96 to 120 hours. Feather bud development was not observed at the wound site. The epidermis began to migrate some 24 h after the wounding; the migration of peridermal cells preceded that of basal epidermal cells by some 12 hours. Mechanisms of the epidermal migration were similar to those observed in situ during wound healing of the integument in 5-day chick embryos (THEVENET, 1981), Superficial epithelization of bare dermis occurred as soon as 12 h after the injury. Cytoplasm of dermal cells exhibited many microtubules and a dilated rough endoplasmic reticulum. During the first 48 h, the epidermal cells established direct contacts and zones of close parallel apposition with epithelized dermal cell processes. The basement membrane lamina densa was maintained at the edges of the wound without retraction or ruffling. It was reconstituted concomitantly with the epidermal migration within 72 h. Cytoplasm of migratory epidermal and epithelized dermal cells exhibited many cytoskeleton structures.     

Filament-directed intercellular contacts during differentiation of cultured chick myoblasts

Detergent-extracted, critical point dried chicken myoblasts at early stages of development in tissue culture were observed by electron microscopy. It was found that the organization of filaments within these cells changes significantly during development. A particular specialization of the cellular filament framework is the formation of microprocesses; long extensions of the cellular filament system. These microprocesses appear to be involved in cell-to-cell contact. The filaments of these processes appear to integrate with the filament system of a contacted cell, and possibly transmit tension from one cell to another. The role of these structures in effecting muscle differentiation by forming cytoplasmic connections and the implications for muscle gene expression are discussed.     

Synaptic junction development in the spinal cord of an amphibian embryo: An electron microscope study

Summary An electron microscopical study has been made of the cervical spinal cord of Xenopus laevis embryos, from the time that the neural tube closes until the larvae were hatched and could swim. Sections of the whole cord were searched for intercellular junctions during this period. Two nonsynaptic types were found, the first were widely distributed puncta adherentia, the second were rare and similar to gap junctions. Membrane specializations with synaptic vesicles were first found when the neural folds had fused; membrane-vesicle clusters which looked like the presynaptic half of a synaptic junction were present, together with synaptic junctions lacking any postsynaptic membrane thickening or cytoplasm density. About four hours later, mature synaptic junctions with full thickening of the postsynaptic membrane, dense cytoplasm and striated or dense material in the synaptic cleft were present. Presynaptic mitochondria, dense-cored and flattened vesicles, fibre to fibre and fibre to cell body synapses were present from the first, as were synapses onto very fine dendrites which might be filopodia from dendritic growth cones. Synaptogenesis may start with the accumulation of vesicles in dense cytoplasm near a thickened cell membrane; the postsynaptic element becomes associated with this membrane-vesicle cluster and matures by increasing cleft and cytoplasmic density, and by membrane thickening.     

The development of the tongue in the chick embryo: observation under a scanning electron microscope

The morphological features of the chick embryo tongue from the 8th day of incubation till hatching and during the early post incubation period have been investigated by means of Scanning Electron Microscope. At the SEM, it is possible to observe that already at the 8th day of incubation, the body and the root are separated by a low smooth-surfaced ridge. In the following days this ridge develops, giving rise to the so-called lingual spines, whose significance is still uncertain. As concerns the evolutive pattern of the superficial layer of the epithelium, in the first days of the considered incubation period the cells appear dome-shaped and have microvilli on their apical surface; afterwards they tend to become more flattened, and the microvilli are replaced by a thick net of microplicae. In the last days of incubation and after hatching desquamative phenomena become evident. The above described evolutive process can be regarded as a common feature of the whole dorsal lingual surface; only few regional differences are to be noted, such as the earlier development of the microplicae on the apex and borders of the tongue. In particular, the microplicae observed at the apex of the tongue show a typical aspect and arrangement; they run regularly parallel to each other. On the lingual dorsal surface taste bud-like structures have never been observed.     

An electron microscope study of myelin figures

In the electron microscope, thin sections of OsO(4)-fixed myelin figures from the phospholipide fraction of human brain show a pattern of parallel dark lines with a repeating period of about 40 A. It is shown that the dark lines probably represent the reaction product of OsO(4) with double bonds in the fatty acid chains, thereby marking the central portion of one bimolecular lamella. The addition of globin results in dense lines 25 to 50 A wide that cover the surface of the myelin figures. When such a figure consists of only two bimolecular leaflets of lipide covered with globin, the structure shows striking similarity to the image of cell membranes in fixed tissue sections. A hypothetical schema is given of the molecular structure of the figure, and the distribution of OsO(4) in it.