Proliferation and differentiation of isolated cells and symplasts of the skeletal muscle tissue of chick embryos

By means of the radioautography, morphometry and alkaline dissociation methods musculus tibialis anterior has been studied in 30 chick embryos and chickens. The muscle fibers are variable in their diameter and length, number of nuclei 3H-thymidine-labelled including. The greatest variability of the structures is noted in 11-14-day-old embryos. Three classes of myotubes (MT) and symplasts are described. The primary MT are evidently the source of cellular elements, that form new cellular-symplastic structures (muscular-proliferative units) that develop, for some time, in a close connection with the primary MT. Between the extreme morphological variants of structure of the muscular elements, there is a transitional form. All the forms of the myosymplasts and MT reflect various stages of differentiation of the myogenic elements; this results in formation of the cellular-symplastic system--muscle fiber.     

Quantitative analysis of the ultrastructural changes in the organoids of the visual cells of chick embryos exposed to actinomycin D

A quantitative analysis of ultrastructural changes in organelles of retina differentiating photoreceptors in 10, 11, 12, and 13 day old chick embryos in the presence of Actinomycin was done. Within 10-13th days of development, with the formation of ellipsoid and paraboloid photoreceptors, there is an increase in the areas of mitochondria and endoplasmic reticulum, and in the number of polyribosomes. Actinomycin injection to embryos sharply reduces some cell parameters: single mitochondrial area, areas of endoplasmic reticulum elements, their length and diameters. In addition to disintegration of polyribosomal complexes was noticed in the cell cytoplasm beginning from 1 hour to 24 hours of inhibitor action. A delay in formation of ellipsoid and paraboloid occurred, especially in membrane discs of the external segment of photoreceptor.     

ATPase activity and the contractile capacity of the muscle tissue in chick embryos during development

The value of ATPase activity of the myofibril preparations and the value and duration of actomyosin superprecipitation were estimated for different muscles during the chick embryonic development. The ATPase level increases during embryogenesis 4.5-fold, in the leg muscle this change takes place distinctly earlier than in the leg muscle. The value and rate of actomyosin superprecipitation also markedly increase, to a lesser extent for m. soleus than for m. pectoralis. It is suggested that these changes and differences are mainly due to the delay in synthesis of certain types of the embryonic myosin light chains.     

Handling of actinomycin D by preimplantation mouse embryos

A protein isolated from serum is required in the cell suspension for the chemotactic response of normal mouse peritoneal macrophages to complement-derived C5a. Macrophage stimulating protein (MSP) has a molecular weight of 100000 and an isoelectric point of 7.0. It is resistant to changes in pH over a range of 1.3–11, is heat labile especially after partial purification and does not survive proteolytic enzyme attack. Binding to ConA Sepharose suggests that it contains a carbohydrate moiety. Its concentration in normal serum is very low and it is detectable only by virtue of a sensitive bioassay. An upper limit has been estimated at 75 ng/ml; the actual concentration may be considerably lower.     

脊椎动物胚胎骨骼肌的生成

肌肉发生的起始和生肌节的形成是胚胎肌肉发育中的两个关键事件。研究表明,肌肉发生的起始有赖于体节周围组织所产生的分泌因子的影响。这些组织包括体轴结构,侧板中胚层及体节正上方的外胚层,代表性的分子有Ｗｎｔｓ家族的一些成员以及Ｓｈｈ和ＢＭＰ－４;而生肌节的形成则首先依赖与分节化相关的基因,如ｄｅｌｔａ,ｈｅｒ１等的正常功能,分节之后也同样需在周围环境的作用之下形成生肌节。两栖类非洲爪蟾的肌肉发生有其特殊性。本文对这一领域中最近的研究进展作一综合介绍。     

Physiological and structural properties of colchicine-treated chick skeletal muscle cells grown in tissue culture.

Chick muscle cells grown in tissue-culture medium containing colchicine developed into rounded cells called “myosacs.” Electron micrographs of myosacs were similar to untreated myofibers except that microtubules were absent and the contractile material was disorganized. Most of the electrophysiological characteristics of myosacs were similar to those of untreated myofibers. Thus, both cellular types had similar resting potentials, nonlinear current voltage curves, three types of action potentials (Na⁺, Ca²⁺, and Cl^? spikes), and acetylcholine sensitivity with “hot spots.” Both demonstrated contraction with electrical or chemical (acetylcholine, caffeine) stimuli. The one significant difference was that myosacs, unlike myofibers, were always isopotential throughout their intracellular space.     

Glycogen metabolic enzymes in the skeletal muscles of the developing chick embryo

In the skeletal muscles of the chick embryo from the 10th till the 15th day of embryogenesis, phosphorylase (EC. 2.4.1.1) is represented by two isozymes one of which corresponds, by electrophoretic mobility, to the liver phosphorylase and another to phosphorylase of the skeletal muscles of the adult rat. From the 17th day of embryogenesis on only one isozyme of phosphorylase is found in the skeletal muscles which is identical with that of the skeletal muscles of the adult bird. The isozyme spectrum of phosphorylase of the whole 4 days old embryo contains, besides phosphorylase L, a special "embryonic" isozyme which differs from that of the skeletal muscles by immunochemical characteristics and electrophoretic mobility. From the 10th day of embryogenesis till hatching, the activity of phosphorylase of the skeletal muscles increases more than 50 times and that of glycogen synthetase (EC. 2.4.1.11) only 4 times.     

Muscle tissue histogenesis of the lymph hearts of chick embryos

By means of electron microscope autoradiography, the ultrastructure of muscle fibers, and the capacity if muscle of cell nuclei of 3H-thymidine (3H-T) incorporating of were studed in developing lymph hearts of 0-13 day old chick embryos, rather active sarcomerogenesis developing lymph hearts of 9-13 day old chick embryos, a rather active sarcomerogenesis being observed. Filament of intermediate size microtubules, Golgi complexes, centrioles, and numbers free ribosomes and polysomes were observed in the sarcoplasm. The sarcoplasmic reticulum channels were not numerous, their terminal cisterns often formed "subsarcolemmal cisternae". Between muscle fibers, cell junctions of fasciae adherentes type were observed. Two hours after 3H-T administrations, only mononuclear cells without myofilaments were labeled. If fixation was made 70 hours after 3H-T administration, then the label was found in addition on muscle fiber nuclei. These data evidence that the lymph heart muscle tissue histogenesis undergoes the same patterns of development as does the somatic muscle tissue.