Specific arrest of cardiogenesis in cultured embryonic stem cells lacking Cripto-1

The molecular events of cardiac lineage specification and differentiation are largely unknown. Here we describe the involvement of a growth factor with an EGF-like domain, Cripto-1 (Cr-1), in cardiac differentiation. During embryonic development, Cr-1 is expressed in the mouse blastocyst, primitive streak, and later is restricted to the developing heart. To investigate the role of Cr-1, we have generated Cr-1-negative embryonic stem (ES) cell lines by homologous recombination. The resulting double "knockout" ES cells have selectively lost the ability to form beating cardiac myocytes, a process that can be rescued by reintroducing Cr-1 gene back into the Cr(-/-) cells. Furthermore, the lack of functional Cr-1 is correlated with absence of expression of cardiac-specific myosin light and heavy chain genes during differentiation. Differentiation into other cell types including skeletal muscle is not disrupted. These results suggest that Cr-1 is essential for contractile cardiomyocyte formation in vitro.

Specific localization of serine 19 phosphorylated myosin II during cell locomotion and mitosis of cultured cells

Phosphorylation of the regulatory light chain of myosin II (RMLC) at Serine 19 by a specific enzyme, MLC kinase, is believed to control the contractility of actomyosin in smooth muscle and vertebrate nonmuscle cells. To examine how such phosphorylation is regulated in space and time within cells during coordinated cell movements, including cell locomotion and cell division, we generated a phosphorylation-specific antibody. Motile fibroblasts with a polarized cell shape exhibit a bimodal distribution of phosphorylated myosin along the direction of cell movement. The level of myosin phosphorylation is high in an anterior region near membrane ruffles, as well as in a posterior region containing the nucleus, suggesting that the contractility of both ends is involved in cell locomotion. Phosphorylated myosin is also concentrated in cortical microfilament bundles, indicating that cortical filaments are under tension. The enrichment of phosphorylated myosin in the moving edge is shared with an epithelial cell sheet; peripheral microfilament bundles at the leading edge contain a higher level of phosphorylated myosin. On the other hand, the phosphorylation level of circumferential microfilament bundles in cell-cell contacts is low. These observations suggest that peripheral microfilaments at the edge are involved in force production to drive the cell margin forward while microfilaments in cell-cell contacts play a structural role. During cell division, both fibroblastic and epithelial cells exhibit an increased level of myosin phosphorylation upon cytokinesis, which is consistent with our previous biochemical study (Yamakita, Y., S. Yamashiro, and F. Matsumura. 1994. J. Cell Biol. 124:129-137). In the case of the NRK epithelial cells, phosphorylated myosin first appears in the midzones of the separating chromosomes during late anaphase, but apparently before the formation of cleavage furrows, suggesting that phosphorylation of RMLC is an initial signal for cytokinesis.

Cellular adaptations in the diaphragm in chronic obstructive pulmonary disease

BACKGROUND

In patients with severe chronic obstructive pulmonary disease, the diaphragm undergoes physiologic adaptations characterized by an increase in energy expenditure and relative resistance to fatigue. We hypothesized that these physiologic characteristics would be associated with structural adaptations consisting of an increased proportion of less-fatigable slow-twitch muscle fibers and slow isoforms of myofibrillar proteins.

METHODS

We obtained biopsy specimens of the diaphragm from 6 patients with severe chronic obstructive pulmonary disease (mean [+/-SE] forced expiratory volume in one second, 33+/-4 percent of the predicted value; residual volume, 259+/-25 percent of the predicted value) and 10 control subjects. The proportions of the various isoforms of myosin heavy chains, myosin light chains, troponin, and tropomyosin were determined by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. We also used immunocytochemical techniques to determine the proportions of the various types of muscle fibers.

RESULTS

The diaphragm-biopsy specimens from the patients had higher percentages of slow myosin heavy chain I (64+/-3 vs. 45+/-2 percent, P<0.001), and lower percentages of fast myosin heavy chains IIa (29+/-3 vs. 39+/-2 percent, P=0.01) and IIb (8+/-1 vs. 17+/-1 percent, P<0.001) than the diaphragms of the controls. Similar differences were noted when immunohistochemical techniques were used to compare the percentages of these fiber types in the two groups. In addition, the patients had higher percentages of the slow isoforms of myosin light chains, troponins, and tropomyosin, whereas the controls had higher percentages of the fast isoforms of these proteins.

CONCLUSIONS

Severe chronic obstructive pulmonary disease increases the slow-twitch characteristics of the muscle fibers in the diaphragm, an adaptation that increases resistance to fatigue.

Fibre types in skeletal muscles of chronic obstructive pulmonary disease patients related to respiratory function and exercise tolerance

This study aimed to investigate the relationship between skeletal muscle, fibre type composition, functional respiratory impairment and exercise tolerance in patients with moderate to severe chronic obstructive pulmonary disease (COPD). A group of 22 COPD patients and 10 healthy control subjects were studied. In COPD patients, vital capacity (VC) and forced expiratory volume in one second (FEV1) were reduced to 79% and 51%, respectively. Diffusion indices (transfer factor of the lung for carbon monoxide (TL,CO) and carbon monoxide transfer coefficient (KCO)) were also reduced. Arterial oxygen tension (Pa,O2) was normal or slightly altered. A maximal exercise test was performed and anaerobic threshold was calculated. Muscle samples from vastus lateralis were obtained by needle biopsy. Myosin heavy chain (MHC) and light chain (MLC) isoforms were separated by gel electrophoresis and quantified by densitometry. MHC isoforms were considered as molecular markers of fibre types. The proportion of the fast MHC-2B isoform was increased in COPD patients. TL,CO, KCO, VC and FEV1 were positively correlated with slow MHC isoform content. TL,CO and KCO were also negatively correlated with the content of the fast MHC-2B isoform. No correlation was found between exercise parameters and MHC isoform composition. The co-ordinated expression between MHC and MLC isoforms was altered in COPD patients. We conclude that reduced oxygen availability, probably in combination with muscle disuse, may determine muscle alterations in chronic obstructive pulmonary disease patients. The altered correlations between myosin heavy chain and light chain isoforms suggest that co-ordinated protein expression is lost in chronic obstructive pulmonary disease muscles.

Isoform distribution of parvalbumins and of some myofibrillar proteins in adult and developing Chrysichthys auratus (Geoffroy St. Hilaire, 1808) (Pisces, Claroteidae)

Polyacrylamide gel electrophoresis was used to analyse the distribution of parvalbumin, myosin light chain, and troponin I isoforms in white muscles of larval, juvenile, and adult Chrysichthys auratus (catfish, siluriforms) and to study the kinetics of their synthesis. Parvalbumin isoform PA II was first detected from day 5 post-hatching and was the main "larval" isoform in this species. PA III appeared at the beginning of the juvenile stage but always remained the minor isoform, even in adult fish. Young mature specimens (approximately 12 cm long) displayed the highest total parvalbumin content. Adult-type myosin light chains were detected from day 8. Densitometric analysis confirmed the light-chain distribution typical of fish muscles, with a relatively high amount of LC3 and a low amount of LC1. We evidenced a "larval" form of troponin-I and its progressive replacement by an "adult" form.

Firing rate of the lower motoneuron and contractile properties of its muscle fibers after upper motoneuron lesion in man

We studied motor unit (MU) firing rate and contractile properties and myosin isoform composition of single muscle fibers after upper motoneuron lesion. Single-MUs and surface electromyogram (EMG) were recorded during voluntary contractions and locomotion in the paretic (P) and nonparetic (NP) tibialis anterior (TA) of 15 hemiparetics. P TA low-threshold MUs fired within the lower end of their normal range. High-threshold MUs fired below their normal range or were not recruited. Surface EMG was abnormally low and high in the P TA and NP TA, respectively. On muscle cross sections stained with histochemical methods, type I fibers represented 99.4%, 74.3% and 66.6% of NP, P, and control TA, respectively. P TA fibers expressing type I myosin heavy chain (MyHC) were smaller, weaker, and slower. In conclusion, low MU firing rate and activity in the P TA was associated with slower type I MyHC fibers, while increased activity in NP TA resulted in homogenous expression of type I MyHC.

Transgenic remodeling of the regulatory myosin light chains in the mammalian heart

The regulatory myosin light chain (MLC) regulates contraction in smooth muscle. However, its function in striated muscle remains obscure, and the different functional activities of the various isoforms that are expressed in the mammalian heart (ventricle- and atrium-specific MLC2) remain undefined. To begin to explore these issues, we used transgenesis to determine the feasibility of effecting a complete or partial replacement of the cardiac regulatory light chains with the isoform that is normally expressed in fast skeletal muscle fibers (fast muscle-specific MLC2). Multiple lines of transgenic mice were generated that expressed the transgene at varying levels in the heart in a copy number-dependent fashion. There is a major discordance in the manner in which the different cardiac compartments respond to high levels of overexpression of the transgene. In atria, isoform replacement with the skeletal protein was quite efficient, even at low copy number. The ventricle is much more refractory to replacement, and despite high levels of transgenic transcript, protein replacement was incomplete. Replacement could be further increased by breeding the transgenic lines with one another. Despite very high levels of transgenic transcript in these mice, the overall level of the regulatory light chain in both compartments remained essentially constant; only the protein isoform ratios were altered. The partial replacement of the ventricular with the skeletal isoform reduced both left ventricular contractility and relaxation, although the unloaded shortening velocity of isolated ventricular cardiomyocytes was not significantly different.

Protein expression changes associated with radiation-induced neoplastic progression of human prostate epithelial cells

Carcinogenic progression in most epithelial systems is a multistep process and presents as numerous (un)stable intermediate stages prior to the development of a fully malignant phenotype. Recently, we reported the neoplastic transformation of an SV40 immortalized, neonatal human prostate epithelial cell line (267B1) by multiple exposures to X-rays [1, 2]. The parental 267B1 cells acquired anchorage-independence and exhibited morphological transformation following exposure to two consecutive doses of 2 Gy. Exposure of either the parental 267B1 cells or the anchorage-independent derivatives (F3-SAC) to a total dose of 30 Gy of X-rays yielded tumorigenic transformants (267B1-XR and 267B1-SXR, respectively). All of these radiation-treated derivatives (F3-SAC, 267B1-XR, and 267B1-SXR) were characterized by reduced cell size and poorly organized actin stress fibers [2, 3]. The present study examines the protein expression changes associated with cytoskeletal alterations during the different steps of neoplastic progression induced by X-rays in the in vitro human prostate cell system. This analysis was achieved by using the high resolving power of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) in the 267B1, F3-SAC, 267B1-XR, and 267B1-SXR cells. We report changes in the expression of gelsolin in the partially transformed, anchorage-independent, nontumorigenic (F3-SAC) cells and a progressive loss of expression of tropomyosin isoforms (TM-1 and TM-3), and myosin light chain-2 (MLC-2) in the tumorigenic (267B1-XR; 267B1-SXR) cells, respectively. In contrast, our results demonstrate that the levels of the small GTP-binding protein Rho-A, an active participant in the actin stress fiber organization, are not altered during neoplastic progression of these 267B1 cells. Thus the changes in synthesis of gelsolin, tropomyosins, and MLC-2 provide a rationale for the alterations in the actin stress fiber formation and reduction in cell size during the exposure of prostate epithelial cells to multiple doses of X-rays.

Cellular distribution of myosin-V in the guinea pig cochlea

The importance of unconventional myosins to hearing has recently been revealed by the identification of myosins-VI and -VII as the defective genes in mouse mutations and in a human syndrome which lead to profound hearing loss. Another class of novel myosins (V) has been implicated in the trafficking of intracellular vesicles in neurons and other secretory cells. We used affinity-purified antibodies to determine the localization of myosin-V in the guinea pig inner ear. In the sensory epithelium of the cochlea, myosin-V epitopes were recognized in neuronal and supporting cells. Neuronal labelling was most intense in the afferent innervation of inner and outer hair cells. Supporting cells labelled were cells of Hensen and Deiters, and inner border, inner phalangeal, inner sulcus and interdental cells. In the vascular tissue of the cochlea, we observed staining of intermediate cells of the stria vascularis and of border cells between the stria and the spiral prominence. Staining of afferent chalice nerve endings was observed on type I vestibular hair cells. The results suggest that, like myosins VI and VII, myosin-V is localized in positions that may be critical to auditory function.

Myosin light-chain phosphorylation in diabetic cardiomyopathy in rats

The regulatory myosin light chain (MLC) is phosphorylated in cardiac muscle by Ca2+/calmodulin-dependent MLC kinase (MLCK) and is considered to play a modulatory role in the activation of myofibrillar adenosine triphosphatase (ATPase) and the process of force generation. Since the depression in cardiac contractile function in chronic diabetes is associated with a decrease in myofibrillar ATPase activity, we investigated changes in MLC phosphorylation in diabetic heart. Rats were made diabetic by injecting streptozotocin (65 mg/kg intravenously), and the hearts were removed 8 weeks later; some 6-week diabetic animals were injected with insulin (3 U/d) for 2 weeks. Changes in the relative MLC and MLCK protein contents were measured by electrophoresis and immunoblot assay, whereas phosphorylated and unphosphorylated MLCs were separated on 10% acrylamide/urea gel and identified by Western blot. MLC and MLCK contents were decreased markedly (40% to 45%) and MLC phosphorylation was decreased significantly (30% to 45%) in the diabetic rat heart homogenate in comparison to control values. The changes in MLC and MLCK content in diabetic heart were partially reversible, whereas changes in MLC phosphorylation were normalized upon treatment with insulin. These results suggest that decreased protein contents of MLC and MLCK and phosphorylation of MLC may contribute to the depression of cardiac myofibriliar ATPase activity and heart dysfunction in diabetic cardiomyopathy.

Isoforms of myosin in growing muscles of ky (kyphoscoliotic) mice

Kyphoscoliotic (ky) mice are spontaneous mutants of the BDL strain whose postural muscles atrophy during post-natal growth, resulting in extensive kyphoscoliosis in adult animals. At 21 days of age, the seven muscles examined were already well differentiated into fast, slow and mixed type on the basis of the proportions of their native myosin isoforms or their subunits. During post-natal growth, from 21 to 120 days of age, the normal pattern of myosin maturation was essentially respected by the ky mutation: fast muscles became faster, slow muscles became slower and mixed muscles specialized in both directions. However, the post-natal increases of myosin heavy chain 2B and fast myosin light chain LC3f were depressed in ky muscles, whilst there was novel expression of slow myosin light chains, LC1s and LC2s in muscles which normally did not express them. Intermediate native myosin IM was absent in adult ky soleus, but it increased in adult ky tibialis anterior. We conclude that the ky mutation depresses the normal post-natal transition towards faster muscles and results in adult muscles whose myosin isoforms are generally shifted in a fast-to-slow direction.

Nonmuscle and smooth muscle myosin heavy chain expression in rejected cardiac allografts. A study in rat and monkey models

BACKGROUND

Diagnosis of acute rejection and graft arteriosclerosis (chronic rejection) is critical to the success of cardiac transplantation, but accurate diagnosis is often difficult. We have reported that there are three types of vascular myosin heavy chain (MHC) isoforms: SM1, SM2, and SMemb. SM2 is specifically expressed in differentiated smooth muscle cells (SMCs). SMemb is a nonmuscle-type MHC abundantly expressed in SMCs of fetal aorta.

METHODS AND RESULTS

To evaluate the usefulness of MHC expression for diagnosis and analysis of acute and chronic rejection, heterotopic cardiac transplantation was performed in rats and monkeys. Immunohistochemistry, electron microscopy, and Northern blot assay were performed to evaluate MHC expression. SMemb was expressed in spindle-shaped cells located in acutely rejected myocardium in the rats and monkeys. These cells were also observed in areas lacking cellular infiltration. These SMemb-positive cells were activated fibroblasts or myofibroblasts. SMemb mRNA was enhanced parallel to the progression of acute rejection. In the coronary arteries of chronically rejected allografts, enhanced SMemb and reduced SM2 expression was observed in both thickened intima and media. The reduced medial SM2 expression was observed before the intimal thickening occurred. These cells were phenotypically modulated SMCs.

CONCLUSIONS

Altered expression of MHC isoforms is a sensitive indicator in the diagnosis of acute and chronic cardiac rejection. The pathophysiology of this alteration in MHC isoform expression should be studied further to elucidate the pathogenesis of cardiac rejection.

Myosin light chains in regenerating graft in chick gastrocnemii

Myosin light chains in normal and minced autografted chick gastrocnemii have been studied by disc gel electrophoresis during 70 days postgrafting period. As a result of induced mechanical trauma, the quantitative relationships between myosin light chain fractions are disturbed affecting the muscle functions.

Effects of clenbuterol on contractile and biochemical properties of skeletal muscle

We investigated the effects of clenbuterol on the muscle mass, contractile properties, myosin phenotype, and bioenergetic enzyme activity in the gastrocnemius (GS)-plantaris (PL)-soleus (SO) muscle complex. Rats were sham-injected or treated with clenbuterol (2 mg.kg-1, subcutaneously) for 14 d. Clenbuterol increased (P < 0.05) body weight and muscle complex weight. Also, clenbuterol treatment resulted in an increase in total muscle force production and maximal shortening velocity (P < 0.05). No difference (P > 0.05) in relative force production (force.g-1 muscle) existed between experimental groups. However, muscle fatigue increased with clenbuterol treatment. Myosin heavy chain (MHC) composition was not altered in the GS or PL muscles, but shifted toward the fast Type II MHC in the SO. Myosin light chain (MLC) composition was not altered in any of the muscles. Clenbuterol caused a decrease in oxidative and glycolytic enzyme activity in the GS and PL, but not the SO. These data suggest that the clenbuterol-induced increase in muscle mass and maximal force generation is due to hypertrophy of both fast and slow fibers. Furthermore, these findings support the notion that beta-agonists may be beneficial in combating conditions that result in muscle wasting and dysfunction.

Reduced positive feedback regulation between myosin crossbridge and cardiac troponin C in fast skeletal myofibrils

Several studies have shown that substitution of cardiac troponin C into fast skeletal muscle causes a marked reduction in cooperativity of Ca(2+)-activation of both myofibrillar ATPase and tension development. To clarify the underlying mechanisms, in the present study, Ca2+ binding to cardiac troponin C inserted into fast skeletal myofibrils was measured. Two classes of binding sites with different affinities (classes 1 and 2) were clearly identified, which were equivalent stoichiometrically to the two high-affinity sites (sites III and IV) and a single low-affinity site (site II) of troponin C, respectively. Ca2+ binding to class-2 sites and Ca(2+)-activation of myofibrillar ATPase occurred in roughly the same Ca2+ concentration range, indicating that site II is responsible for Ca2+ -regulation. Myosin crossbridge interactions with actin, both in the presence and absence of ATP, enhanced the Ca2+ binding affinity of only class-2 sites. These effects of myosin crossbridges, however, were much smaller than the effects on the Ca2+ binding to the low-affinity sites of fast skeletal troponin C, which are responsible for regulating fast skeletal myofibrillar ATPase. These findings provide strong evidence that the reduction in the cooperative response to Ca2+ upon substituting cardiac troponin C into fast skeletal myofibrils is due to a decrease in the positive feedback interaction between myosin crossbridge attachment and Ca2+ binding to the regulatory site of troponin C.

Identification of human myocardial proteins separated by two-dimensional electrophoresis with matrix-assisted laser desorption/ionization mass spectrometry

Disease-associated proteins separated by two-dimensional electrophoresis (2-DE) are often in the femtomole range. Identification of 2-DE separated proteins by sequencing and amino acid analysis is limited to the lower picomole range. Identification down to the femtomole range can be achieved by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). We optimized the measurement by MALDI-MS for the analysis of proteolytic digests of 2-DE-separated proteins. The direct analysis of peptide mixtures can be used for rapid and sensitive protein identification. In some cases, more information about the protein can be obtained by separating the peptides by micro high-performance liquid chromatography (HPLC) before employing MALDI-MS analysis. More peptides are found than in the mixtures, and comparison of HPLC patterns can reveal some differences to be post-translational modifications of proteins, even in the case of identical peptide mass fingerprints. Furthermore, carboxy-terminal sequencing by on-target carboxypeptidase P digestion can be used to confirm the obtained result without the need for more material. The search program FRAGFIT was modified and renamed FRAGMOD to include the modifications of methionine and tryptophan oxidation and alkylation of cysteine by acrylamide into the mass search. By applying this procedure, 15 proteins were identified, among them two different putative phosphorylated forms of two proteins, a putative N-terminal blocking group and four dilated cardiomyopathy-associated proteins. The resulting approach for the identification may be used for large-scale investigations of 2-DE-separated proteins.

Green fluorescent protein marks skeletal muscle in murine cell lines and zebrafish

The green fluorescent protein (GFP) acts as a vital dye upon the absorption of blue light. When the gfp gene is expressed in bacteria, flies or nematodes, green fluorescence can be directly observed in the living organism. We inserted the cDNA encoding this 238-amino-acid (aa) jellyfish protein into an expression vector containing the rat myosin light-chain enhancer (MLC-GFP) to evaluate its ability to serve as a muscle-specific marker. Transiently, as well as stably, transfected C2C12 cell lines produced high levels of GFP distributed homogeneously throughout the cytoplasm and was not toxic through several cell passages. Expression of MLC-GFP was strictly muscle-specific, since Cos 7 fibroblasts transfected with MLC-GFP did not fluoresce. When GFP and beta Gal markers were compared, the GFP signal was visible in the cytoplasm of the living cell, whereas visualization of beta Gal required fixation and resulted in deformation of the cells. When the MLC-GFP construct was injected into zebrafish embryos, muscle-specific gfp expression was apparent within 24 h of development. gfp expression was never observed in non-muscle tissues using the MLC-GFP construct. Transgenic fish continued to express high levels of gfp in skeletal muscle at 1.5 months, demonstrating that GFP is an effective marker of muscle cells in vivo.

Isolation of unstable myosins and the analysis of light chains by capillary electrophoresis

A rapid method for the isolation of unstable fish myosins by Sepharose Q ion-exchange chromatography is described which yields a pure protein essentially free of contamination or breakdown products in less than 6 h. A protocol was developed for determining the molar ratios of myosin light chains (LC) by capillary electrophoresis. The method is quantitative, rapid (<20 min), highly reproducible (<2.1% variation in relative peak migration time), and only uses Femtomole quantities of protein. It was able to separate myosin light chains which could previously only be resolved by 2-D sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Capillary electrophoresis in the presence of SDS gave similar apparent relative molecular masses (M(r)) for most proteins, but an anomalously high M(r) for myosin light chain 3(LC3), as has been reported previously for SDS-PAGE methods.