[Initial stages of the myocardial differentiation of the lymph hearts of frog tadpoles. A study by the methods of electron microscopy and electron microscopic autoradiography]. / Nachal'nye étapii differentsirovki "miokarda" limfaticheskikh serdets u golovastikov travianoi liagushki. Issledovanie metodami élektronnoi mikroskopii i élektronno-mikroskopicheskoi avtoradiografii.

Using electron microscope autoradiography, a study was made of the ultrastructure of early stages of muscle differentiation and 3H-thymidine (3H-T) labelled cells in the wall of the developing lymph heart of larvae of Rana temporaria L. The mononucleated postmitotic myoblasts with small bundles of thin and thick myofilaments deprived of Z-bodies were found in the lymph heart wall. No thin or intermediate-sized subsarcolemmal filaments were detected in the cytoplasm of these myoblasts. Myosatellites occurred under the basal lamina of muscle cells at stages 41-42. The primitive muscle-nerve junction was found at stages 44-45. Four hours after a single 3H-T administration only mononuclear cells without myofilaments were labelled. If the fixation was made 72 hours after a single 3H-T administration, the label was found, in addition, on the muscle cell nuclei. These data evidence that at the early stages of muscle differentiation in the developing lymph heart wall DNA synthesis and muscle specific protein synthesis are incompatible.

[Muscle tissue regeneration of the lymph hearts in adult Rana temporaria frogs. A study by light and electron microscopy autoradiography methods]. / Regeneratsiia myshechnoi tkani limfaticheskikh serdets vzroslykh liagushek Rana temporaria. Issledovanie metodami sveto- i élektronno-mikroskopicheskoi avtoradiografii.

The regeneration response of adult frog lymph heart muscle tissue was studied from 2 to 3 weeks after mechanical injury. High resolution autoradiographic studies showed that regenerative necrotic zones have many actively proliferating mononuclear cells deprived of cytoplasmic myofilaments. Some of them have numerous free ribosomes, so they might be identified as myoblasts. On the 13th day after injury newly-formed myotubes with chains of myonuclei and pictures of active sarcomerogenesis were observed. On the other hand, the surviving muscle fibers of the perinecrotic zone were rich in myonuclei at their growing ends. In the vicinity of nuclei, accumulation of a mass of non-differentiated cytoplasm rich in free ribosomes and polysomes, rough endoplasmic reticulum, Golgi apparatus, and centrioles are seen. Tritiated thymidine pulse-labeling showed that only rare myonuclei of the perinecrotic zone muscle fibers were labeled, whereas numerous non-differentiated cells of granulation tissue and myosatellites incorporated thymidine. The number of labeled myonuclei markedly increased 96 hours after 3HTdr administration. These data evidence that the myoblastic mechanism is predominant in the regeneration of adult frog lymph heart muscle tissue. It is necessary to emphasize that during the lymph heart muscle tissue reparative myogenesis some of the perinecrotic myonuclei are able to synthesize DNA and to divide mitotically, which distinguishes this type of muscle from skeletal muscle tissue of vertebrates.

[Electron microscopic study of the differentiation of decidual cells. I. The ultrastructure of large decidual cells in the antimesometrial portion of the rat decidua]. / Elektronno-mikroskopicheskoe izuchenie differentsirovki detsidual'nykh kletok. I. Ul'trastruktura bol'shikh detsidual'nykh kletok antimezometral'noi chasti detsidua krys.

The large decidual cells (LDC) of the antimesometrial part of decidua in rats of 7-9 days of gestation were studied by electron microscope. The decidual tissue has an epithelium-like pattern of organization. The apical surface of LDC is facing the pericapillar space making numerous villi. Lateral surfaces of these cells maintain close contact with each other by means of zona adhaerens, gap junctions, spot desmosomes and simple junctions. Accumulation of electron dense granules measuring from 0.05 to 0.3 mkm is seen in the apical parts of LDC. The Golgi complex and rough endoplasmic reticulum are much developed. The material of rough endoplasmic reticulum is denser than the cell matrix. Disperse chromatin is seen in the nucleus, whereas the granular component is dominanting in the nucleolus. It is concluded that the LDC may have a high metabolic activity, and that the secretion is a mode of fulfilling specific functions of LDC.

Ultrastructure of muscle fibers and cells synthesizing DNA in lymph hearts of developing frogs and chick embryos.

The ultrastructure of striated muscle fibers and 3H-thymidine (3HTdr)-labeled cells adjacent to them in the lymph hearts of larvae of Rana temporaria, yearling frogs, and 9- to 13-day-old chick embryos was studied by use of electron-microscopic autoradiography. A comparatively high level of differentiation of lymph-heart muscle fibers was observed not only in yearling frogs but also in larvae. Myosatellites occurred in all stages of development. No mitoses were found in muscle fibers. In 9- to 13-day-old chick embryos the myofibers of lymph hearts were somewhat less differentiated than those of the larvae and yearling frogs. Differentiating sarcomeres were often seen in the sarcoplasm of myofibers of chick embryos. The analysis of the ultrastructure of 3HTdr-incorporating cells shows that 2-4 h after the single 3HTdr administration only mononucleated cells devoid of myofilaments are commonly labeled both in tadpoles and chick embryos. When fixation is postponed by 48-70 h, myonuclei frequently become labeled. Thus, the data obtained support the evidence that proliferation and differentiation processes in the developing muscle tissue of the lymph heart of both species studied are mutually exclusive, similar to the situation in differentiating vertebrate skeletal muscle.

[Histogenesis of muscle tissue in the developing lymph hearts of Rana temporaria larvae and younglings. A study by electron microscopic and electron microscopic autoradiographic methods]. / Gistogenez myshechnoi tkani razvivaiushchikhsia limfaticheskikh serdets lichinok i segoletok travianoi liagushki. Issledovanie metodami élektronnoi mikroskopii i élektronno-mikroskopicheskoi avtoradiografii.

Using 3HT electron microscope autoradiography, the ultrastructure of muscle fibers and the capacity of 3HT-incorporation into the nuclei of these fibers and the adjacent cells were studied in the developing lymph hearts of larvae and yearlings of R. temporaria. The presence of myofilaments arranged in sarcomeres of prominent disks Z, I, A, H and M line, and of the well developed sarcoplasmic reticulum may serve a good evidence of a high level of myofibrillar differentiation both in larvae and in yearlings. Myosatellite cells were found in the close contact with muscle fibers at all the investigated stages of the lymph heart development. 4 hours after 3HT administration to larvae, only mononuclear cells deprived of myofibers were seen labeled. The labeled myonuclei were observed in the experiments with double 3HT injections to larvae and with the fixation following 24 hours after the last 3HT administration. These data evidence that, according to the ratio of differentiation and reproduction, the histogenesis of the lymph heart muscle tissues of larvae and yearlings of R. temporaria corresponds to the myogenesis of cross striated skeletal muscles of vertebrates.