Degradation of an ubiquitin-conjugated protein is associated with myoblast differentiation in primary cell culture

At the early stages of myogenesis, myoblasts fuse to form multinucleated myotubes. This morphological differentiation is the result of dynamic changes in gene regulation and expression. The ubiquitin proteasome-dependent pathway has been reported to play an important role in many aspects of cellular functions such as regulation of growth and cell cycle progression. In this study, we showed that the amount of mRNA's corresponding to the iota subunit of the 20S proteasome, the level of the S4 subunit of the 19S complex and the 20S and 26S proteasomes peptidase activities increased during myoblast fusion. Cell permeable 20S proteasome inhibitor prevented fusion with concomitant accumulation of ubiquitin-conjugated protein. On the other hand, inhibition of ubiquitin ligase E3 enzymes prevented the formation of ubiquitin conjugate and decreased the fusion process. These results strongly support the involvement of the ubiquitin-proteasome proteolytic pathway in the events leading to myoblast fusion.     

Fibronectin promotes migration, alignment and fusion in an in vitro myoblast cell model

Myogenesis is a complex process in which committed myogenic cells differentiate and fuse into myotubes that mature into the muscle fibres of adult organisms. This process is initiated by a cascade of myogenic regulatory factors expressed upon entry of the cells into the myogenic differentiation programme. However, external signals such as those provided by the extracellular matrix (ECM) are also important in regulating muscle differentiation and morphogenesis. In the present work, we have addressed the role of various ECM substrata on C2C12 myoblast behaviour in vitro. Cells grown on fibronectin align and fuse earlier than cells on laminin or gelatine. Live imaging of C2C12 myoblasts on fibronectin versus gelatine has revealed that fibronectin promotes a directional collective migratory behaviour favouring cell-cell alignment and fusion. We further demonstrate that this effect of fibronectin is mediated by RGD-binding integrins expressed on myoblasts, that N-cadherin contributes to this behaviour, and that it does not involve enhanced myogenic differentiation. Therefore, we suggest that the collective migration and alignment of cells seen on fibronectin leads to a more predictable movement and a positioning that facilitates subsequent fusion of myoblasts. This study highlights the importance of addressing the role of fibronectin, an abundant component of the interstitial ECM during embryogenesis and tissue repair, in the context of myogenesis and muscle regeneration.     

Development of an optimized protocol for primary culture of smooth muscle cells from rat thoracic aortas

Primary culture of smooth muscle cells has been widely used as a valuable tool to study the molecular mechanisms underlying atherosclerosis and restenosis. Currently, tissue explants and enzymatic digestion methods are frequently applied to produce smooth muscle cells. Explants method is time consuming, usually taking several weeks. The enzymatic digestion method requires large amounts of proteolytic enzymes to generate enough cells for cardiovascular research. The present study reports an optimized method by combining both techniques to obtain high purity smooth muscle cells. The cultured cells exhibited the characteristic “hills and valleys” growth pattern as observed by phase contrast microscopy and showed α-SM-actin positive staining by indirect immunocytochemistry and immunofluorescence. Purity of the cells is guaranteed by the lack of von Willebrand Factor immunoreactivity. Finally, the cultured cells well proliferate on oxidized-LDL stimulation, suggesting the practical utility of this new method.     

Basal serum-free culture system which supports growth of fetal rat adrenal cells in primary monolayer cell culture

A serum-free culture system has been developed which allows primary cultures of fetal rat adrenal cells to divide in response to insulin 10 micrograms/l, yet retain their ability to respond to adrenocorticotropic hormone (ACTH) by increased corticosterone production. The essential components of this culture system are: (1) a high initial plating number of 125-130 x 10(3) cells/cm2; (2) a low oxygen concentration of 2.5% O2; (3) an initial plating period of 48 h in greater than or equal to 5% (v/v) fetal bovine serum. In contrast to reported requirements for the serum-free growth of adult adrenal cells, the fetal adrenal cells do not require the provision of any special matrix or a competence factor for serum-free growth or steroidogenic activity. This suggests that they are capable of rapidly generating their own matrix and competence factor in primary culture.     

An improved protocol for primary culture of cardiomyocyte from neonatal mice

The primary culture of neonatal mice cardiomyocyte model enables researchers to study and understand the morphological, biochemical, and electrophysiological characteristics of the heart, besides being a valuable tool for pharmacological and toxicological studies. Because cardiomyocytes do not proliferate after birth, primary myocardial culture is recalcitrant. The present study describes an improved method for rapid isolation of cardiomyocytes from neonatal mice, as well as the maintenance and propagation of such cultures for the long term. Immunocytochemical and gene expression data also confirmed the presence of several cardiac markers in the beating cells during the long-term culture condition used in this protocol. The whole culture process can be effectively shortened by reducing the enzyme digestion period and the cardiomyocyte enrichment step. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of cesium on in vitro myoblast differentiation: An electron microscopic study

Summary This paper describes the microscopic evidence supporting a cesium-induced delay in the fusion of chick embryo myoblast membranes during in vitro myogenic differentiation. We have recently demonstrated that the sharp decrease in the conductivity and permittivity of the membranes of these myogenic cells at the time of fusion is delayed 30 h by the addition of cesium to the culture medium (Santini et al., Biochim. Biophys. Acta 945:56–64; 1988). We report here that this delay in fusion is substantiated by direct microscopic observation and that cesium also induces ultrastructural changes in the myoblast cells themselves. Possible mechanisms by which cesium may cause both the delay in fusion as well as the ultrastructural changes observed are discussed. This investigation was partially supported by an Italian Consiglio Nazionale delle Ricerche grant 85.00.304.02 (to P. L. I.).     

Improving the methods for isolation of monocyte and establishing macrophage cell culture in caprine model

Monocytes are widely used for immunological research, especially in the study of innate immune system. Although methods for isolation of human monocytes have been established, the procedure for non-human monocyte has not been well developed. This paper describes an improved method for isolation of monocyte and the subsequent macrophage cultivation from caprine blood. Monocytes were isolated from 16 ml of heparinized caprine blood using double density methods; the Ficoll and Percoll. The number of monocytes obtained was 5.12 ± 0.89 × 10⁷ cells/ml at 70 % purity. The isolated monocytes were maintained in 10 % fetal bovine serum-enriched Dulbecco’s Modified Eagle Medium for maturation to form macrophage cell culture. At the end of the experiment, the harvested macrophage was 2.48 ± 0.33 × 10⁶ cells/ml.     

Mammary transmission of caprine arthritis encephalitis virus: a 3D model for in vitro study

Transmission of Caprine Arthritis Encephalitis virus (CAEV) from the mother to offspring is principally mediated by infected cells from colostrum and milk. The infection of the dam is often sub-clinical, and results in increased cellularity of milk, sometimes exacerbated by bacterial co-infections. Although monocytes are the major viral host cells, several other cell types, including epithelial mammary cells, fibroblasts and endothelial cells show low levels of in vivo infection. In vitro, however, all phenotypes of mammary gland cells are individually highly sensitive to CAEV infection. This suggests that local mechanisms act to control viral expression. Our goal is to analyse the mechanisms regulating local virus infection, including the physiological status of the mammary gland and bacterial co-infections. In this work, we present the development of a model for the in vitro reconstitution of mammary gland tissue using 3D cultures in Matrigel. Mononuclear cells from the blood are added to the 3D cultures in vitro. In these experimental conditions, the mammary cells spontaneously organize into mammospheres. Blood leucocytes migrate into the culture gel, and localize particularly at the periphery of the mammospheres. Mammospheres were susceptible to infection in vitro by CAEV, as shown by a cytopathic effect and expression of late CAEV antigen p30. This model will allow the in vitro study of virus expression, transfer of infection to mammary gland cells and interactions between the mammary gland cells, infected monocytes and immunocompetent cells. It will allow the study of mechanisms participating in the control of passage of pathogens into milk, according to the physiological and CAEV-infection status of the animal, microenvironment and the presence of bacterial co-infections.     

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0–0.3 g/l) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0–0.004 ng/l), thiamine (0–0.3 g/l), or pyruvate (0–0.46 g/l). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03/2-0.30 g moniliformin/l medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0–0.3 g/l or 0.0–0.15 g moniliformin/l, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0–0.15 g moniliformin/l and 7.5–50.0 M A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.     

BG-1 ovarian cell line: An alternative model for examining estrogen-dependent growth in vitro

Summary Examination of estrogen-responsive processes in cell culture is used to investigate hormonal influence on cancer cell growth and gene expression. Most experimental studies have used breast cancer cell lines, in particular MCF7 cells, to investigate estrogen responsiveness. In this study we examined an ovarian cancer cell line, BG-1, which is highly estrogen-responsive in vitro. This observation, plus the fact that the cells are of ovarian rather than mammary gland origin, makes it an attractive alternative model. 17β-Estradiol, epidermal growth factor, and insulin-like growth factor induced proliferation of BG-1 and MCF7 cells. Viability was dependent on these growth factors in BG-1 cells, but not in MCF7 cells. Therefore, we examined the differences between these two cell lines with respect to estrogen and growth factor receptors. BG-1 cells have twice as many estrogen receptors as MCF7 cells, and BG-1 cells have higher insulin-like growth factor-1 and epidermal growth factor receptor levels than MCF7 cells. This may also explain why BG-1 cells proliferate 56% more robustly in serum and show more serum dependence in culture. In both BG-1 and MCF7 cells, epidermal growth factor receptor number is low (<20 000/cell), while insulin-like growth factor-1 receptor level was highest in estrogen receptor positive cell lines. For example, insulin-like growth factor-1 receptor was higher in BG-1 and MCF7 cells than in estrogen receptor negative cells (HeLa>MDA-MB-435>HBL100). In conclusion, BG-1 cells are an excellent model for understanding hormone responsiveness in ovarian tissue and an alternative for examining estrogen receptor-mediated and insulin-like growth factor-1/epidermal growth factor/estrogen cross-talk processes because of their sensitivity to these factors.     

Uterine epithelial cells in primary culture: a model system to study cell proliferation

Guinea-pig uterine glandular epithelial cells were grown in primary culture. During the 4-day initial culture period, a 6.7 fold increase in DNA synthesis and a doubling time of approximately 30 hours were observed. Then the cells were submitted to serum depletion (60 hours) and the quiescent cells were stimulated with 15% fetal calf serum (FCS). The control cells were submitted to 1% heated and dextran-coated charcoal stripped FCS. In stimulated cells, the DNA synthesis increased and peaked between the 12th and 24th hour. In these cells, c-fos mRNAs increased rapidly, within 30 min., peaked at 75 min. (ratio to the control = 2.5), and returned to basal level within 90 min. These results prove that uterine epithelial cells in primary culture are able to respond to unspecific mitogen by both rapid expression of c-fos gene and DNA synthesis, suggesting that this cell culture system will be useful in studying the growth regulation in endometrium.     

An alternate method for estimation of cell growth kinetics from batch cultures

An alternative to estimation of cell growth kinetics via continuous culture experiments is proposed in this article. The method employed is based on batch culture experiments with very small inocula (initial cell concentrations being typically less than 5000 cells/mL). Such low initial cell concentrations result in extended exponential cell growth phase during which culture conditions remain unchanged, thereby permitting precise estimation of specific cell growth rates from batch experiments especially for fast-growing microorganisms such as Bacillus species. The effectiveness and utility of this approach are demonstrated via several experiments conducted with a wild-type strain (Bacillus subtilis TN106) and a recombinant strain (B. subtilis TN106[pAT5]). True establishment of exponential growth phase requires insignificant variance of most of the culture conditions during the initial growth phase. Satisfaction of this requirement is demonstrated for microbial systems investigated here. This approach is especially well suited for recombinant microorganisms containing segregationally unstable plasmids, since estimation of growth kinetics of these from continuous cultures is very difficult and highly unreliable due to continual reversion of recombinant ceils to plasmid-free host cells unless some selection pressure is applied at levels sufficient to keep the presence of plasmid-free cells minimal.     

An organ culture system for study of fetal lung development

Fetal rat lungs placed in $\text{in}$$\text{vitro}$ organ culture at 15.5 days gestation grow significantly based on accumulation of DNA and protein. In the experimental system described, DNA accumulated rapidly during the first three days in culture and increased from 4.8 to 15.6 micrograms per lung culture. Protein content increased more slowly and reached a value more than double the initial value after six days in the culture system. Glycogen accumulated in the tissue during the first six days in culture and was depleted during the subsequent culture period, a pattern strikingly similar to that observed during lung development $\text{in}$$\text{vivo}$. Phospholipid accumulation was biphasic with respect to time with an inflection point at about the sixth day of culture. The phosphatidylcholine species synthesized in the culture system $\text{in}$$\text{vitro}$ were similar to those produced $\text{in}$$\text{vivo}$ in fetal lung at 21 days gestation.     

Evaluation of an in vitro muscle contraction model in mouse primary cultured myotubes

To construct an in vitro contraction model with the primary cultured myotubes, we isolated satellite cells from the mouse extensor digitorum longus. Differentiated myotubes possessed a greater number of sarcomere assemblies and higher expression levels of myosin heavy chain, cytochrome c oxidase IV, and myoglobin than in C2C12 myotubes. In agreement with these results regarding the sarcomere assemblies and protein expressions, the primary myotubes showed higher contractile activity stimulated by the electric pulses than that in the C2C12 myotubes. These data suggest that mouse primary myotubes will be a valuable research tool as an in vitro muscle contraction model.     

猪胎儿肾脏成纤维细胞体外培养体系的建立

本研究旨在建立猪胎儿肾脏成纤维细胞体外培养体系,并探讨其作为猪体细胞克隆供体的可能性。使用组织块培养法从体长为10cm以上的猪胎儿分离得到猪胎儿肾脏成纤维细胞,绘制了生长曲线,鉴定了细胞类型并且进行了细胞周期同期化效果的研究。结果表明:该培养体系可以支持猪胎儿肾脏成纤维细胞的体外生长,单个细胞均为梭形细胞,抗波形蛋白免疫荧光染色显示为阳性,而抗角形蛋白免疫荧光染色为阴性,分离到的细胞为胎儿肾脏成纤维细胞。使用血清饥饿法和接触抑制法诱导细胞进入G0/G1期,并且分别比较两者同期化效率,结果显示:血清饥饿2d和4d的同期化效率差异不显著,但都比8d组的高(88.97%和87.69%比82.45%,P<0.05);接触抑制4d、6d组间同期化效率差异不显著,但都比0d组的高(85.56%和85.89%比81.82%,P<0.05)。本研究在国内首次分离得到猪胎儿肾脏成纤维细胞,已经在体外传代培养到32代,其同期化效果好,可以作为体细胞克隆供体。     

Use of microgravity bioreactors for development of an in vitro rat salivary gland cell culture model

During development, salivary gland (SG) cells both secrete factors which modulate cellular behavior and express specific hormone receptors. Whether SG cell growth is modulated by an autocrine epidermal growth factor (EGF) receptor-mediated signal transduction pathway is not clearly understood. SG tissue is the synthesis site for functionally distinct products including growth factors, digestive enzymes, and homeostasis maintaining factors. Historically, SG cells have proven difficult to grow and may be only maintained as limited three-dimensional ductal-type structures in collagen gels or on reconstituted basement membrane gels. A novel approach to establishing primary rat SG cultures is use of microgravity bioreactors originally designed by NASA as low-shear culture systems for predicting cell growth and differentiation in the microgravity environment of space. These completely fluid-filled bioreactors, which are oriented horizontally and rotate, have proven advantageous for Earth-based culture of three-dimensional cell assemblies, tissue-like aggregates, and glandular structures. Use of microgravity bioreactors for establishing in vitro models to investigate steroid-mediated secretion of EGF by normal SG cells may also prove useful for the investigation of cancer and other salivary gland disorders. These microgravity bioreactors promise challenging opportunities for future applications in basic and applied cell research. © 1993 Wiley-Liss, Inc.