Histochemical differences in the responses of predominantly fast-twitch glycolytic muscle and slow-twitch oxidative muscle to veratrine

The aim of this study was to investigate if the Na(+)-channel activating alkaloid veratrine is able to change the oxidative and m-ATPase activities of a fast-twitch glycolytic muscle (EDL, extensor digitorum longus) and slow-twitch oxidative muscle (SOL, soleus) in mice. Oxidative fibers and glycolytic fibers were more sensitive to veratrine than oxidative-glycolytic fibers 15, 30 and 60 min after the i.m. injection of veratrine (10 ng/kg) with both showing an increase in their metabolic activity in both muscles. In EDL, the m-ATPase reaction revealed a significant (p < 0.001) decrease (50%) in the number of type IIB fibers after 30 min while the number of type I fibers increased by 550%. Type I fibers decreased from 34% in control SOL to 17% (50% decrease) in veratrinized muscles, with a 10% decrease in type IIA fibers within 15 min. A third type of fiber appeared in SOL veratrinized muscle, which accounted for 28% of the fibers. Our work gives evidence that the changes in the percentage of the fiber types induced by veratrine may be the result, at least partially, from a direct effect of veratrine on muscle fibers and else from an interaction with the muscle type influencing distinctively the response of a same fiber type. Based on the results obtained in the present study the alterations in EDL may be related to the higher number of Na(+) channels present in this muscle whereas those in SOL may involve an action of veratrine on mitochondria. Although it is unlikely that the shift of enzymes activities induced by veratrine involves genotypic expression changes an alternative explanation for the findings cannot be substantiated by the present experimental approach.

GLUT4 expression at the plasma membrane is related to fibre volume in human skeletal muscle fibres

In this study we examined the relationship between GLUT4 expression at the plasma membrane and muscle fibre size in fibre-typed human muscle fibres by immunocytochemistry and morphometry in order to gain further insight into the regulation of GLUT4 expression. At the site of the plasma membrane, GLUT4 was more abundantly expressed in slow as compared to fast fibres at the same fibre diameter (p < 0.01) and the GLUT4 expression increased with increasing fibre radius independently of fibre type (p < 0.01). The GLUT4 density at the surface of slow fibres of both diabetic and obese was reduced compared to control subjects at the same diameter (p < 0.001). Fast fibres in obese and type 2 diabetic subjects expressed a fibre-volume-dependent GLUT4 expression (p < 0.001), while this did not reach significance in slow fibres (obese p = 0.18 and diabetic p = 0.06). Our results show that increasing fibre volume is associated with increasing GLUT4 expression in both slow and fast fibres. Based on the possible dependency of GLUT4 expression on volume, we hypothesize that the reduced GLUT4 expression in obesity and type 2 diabetes may partly be compensated for by physical activity.

Functional properties of human muscle fibers after short-term resistance exercise training

The aim of this study was to assess the relationships between human muscle fiber hypertrophy, protein isoform content, and maximal Ca(2+)-activated contractile function following a short-term period of resistance exercise training. Six male subjects (age 27 +/- 2 yr) participated in a 12-wk progressive resistance exercise training program that increased voluntary lower limb extension strength by >60%. Single chemically skinned fibers were prepared from pre- and posttraining vastus lateralis muscle biopsies. Training increased the cross-sectional area (CSA) and peak Ca(2+)-activated force (P(o)) of fibers containing type I, IIa, or IIa/IIx myosin heavy chain by 30-40% without affecting fiber-specific force (P(o)/CSA) or unloaded shortening velocity (V(o)). Absolute fiber peak power rose as a result of the increase in P(o), whereas power normalized to fiber volume was unchanged. At the level of the cross bridge, the effects of short-term resistance training were quantitative (fiber hypertrophy and proportional increases in fiber P(o) and absolute power) rather than qualitative (no change in P(o)/CSA, V(o), or power/fiber volume).

Mass determination of native smooth muscle myosin filaments by scanning transmission electron microscopy

The thick filaments of vertebrate smooth muscle have a fundamentally different arrangement of myosin molecules from the bipolar, helical organization present in striated muscle filaments. This side-polar, non-helical structure is probably critical to the ability of smooth muscles to shorten by large amounts; however, details of myosin organization beyond this general description are unknown. The non-helical arrangement of myosin precludes the use of helical reconstruction methods for structural determination, and a tomographic approach is required. As a first step towards this goal we have determined the number of myosin molecules present at each 14.5 nm repeat in native smooth muscle myosin filaments by scanning transmission electron microscopy. The mass-per-length of myosin filaments was 159 kDa/nm, corresponding to 4.38(+/-0.11) (mean+/-s.e.m.) myosin molecules at each 14.5 nm level. The mass of thin filaments in the preparation (intrinsic control) was 21 kDa/nm, consistent with current models of smooth muscle thin filament structure, and the mass of tobacco mosaic virus (mass standard) was within 5% of the known value. We conclude that native smooth muscle myosin filaments contain four myosin molecules at each 14.5 nm level, two on each side of the side-polar structure.

[Histological and ultrastructural characteristics of jaw-closing muscles. A review]

The aim of this work is giving, through a wide literature review, a detailed analysis of the histological and ultrastructural characteristics that distinguish masseter and temporal muscles from the other skeletal muscles. Furthermore we'll explain the functional meanings of these differences. We developed the following points: fibre type composition and relative frequency of the various fibre types, fibre size, myosin composition, capillarization and age-related changes. With standard staining method for the myofibrillar ATPase, besides the two main fibre types, I and II, in the masticatory muscles a moderate share of IM fibres with intermediate stainability, which usually don't appear in adult skeletal muscles, are shown. The relative frequency of the various fibre types is also peculiar, with a prevalence of type I fibres in almost every portion of the masseter and temporal muscles, which therefore are functionally slow muscles. Another unusual characteristic is also the mean diameter of type I fibres, that are commonly larger than type II fibres. This finding suggests that masticatory muscles are adapted to carry out specially prolonged and fatiguing tasks. The findings about contractile protein patterns and the changes in myosin heavy chain composition during ageing are also relevant. The deep differences between jaw-closing and limb and trunk muscles are reviewed on the basis of their special functional activities.

Low-grade mucoepidermoid carcinoma of salivary glands: characteristic immunohistochemical profile and evidence of striated duct differentiation

The purpose of the present study is to determine the presence and distribution of epithelial and myoepithelial cells in mucoepidermoid carcinoma (MEC) of salivary glands and to compare them with normal salivary gland tissue and other primary carcinomas. This is in order to establish novel diagnostic criteria and to better understand MEC histogenesis. Formalin-fixed paraffin-embedded tissues from ten well-differentiated MECs, three adenoid cystic carcinomas (ACC), four acinic cell carcinomas (AC), and three epithelial-myoepithelial carcinomas (EMCC) of salivary glands were studied with immunohistochemistry using antibodies that recognise antigens indicative of epithelial and myoepithelial cell differentiation. An anti-mitochondrial antibody was also employed. Normal salivary tissue was present for comparative study in non-tumorous areas of the same section from 12 cases. MEC contained numerous keratin-positive cells. Anti mitochondrial antibody was diffusely positive in all ten of these tumours. Smooth muscle actin, h-caldesmon, and smooth muscle heavy chain myosin, which are indicative of myoepithelial cell differentiation, were negative. Rare cells in only one case were stained by calponin. Cytokeratin 14 (CK14) and anti mitochondrial antibody stained cells located mainly at the periphery of neoplastic nests and cystic spaces, while CK7 was mainly present in cells bordering gland lumina (zoning pattern). The immunohistochemical cell profile was similar to that seen in striated normal ducts. All others tumours studied showed a different immunohistochemical pattern, mostly consisting of a lack of mitochondrion-rich cells and the presence of myoepithelial cells in ACC and EMCC. Immunoreactivity in MEC for CK7, CK14 and mitochondrial antibodies appears as a peculiar pattern of staining, different from that of other salivary gland tumors; this seems helpful for diagnostic purposes. In addition, a differentiation of the "striated duct phenotype" is suggested.

Adhesion molecule expression in experimental myositis

Experimental allergic myositis (EAM) in Lewis rats, induced with partially purified myosin, is regarded as a model of human polymyositis. To clarify the role of adhesion molecules in the pathogenesis of EAM in Lewis rats, we investigated intramysial expressions of the intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1, and the serum level of soluble ICAM-1 in EAM rats. All the EAM rat muscles had scattered inflammatory foci, as well as cell infiltration and necrosis, by week 4 after the initial immunization (i.e., day 0 after the last immunization). As compared with the control muscles, ICAM-1 and VCAM-1 were strongly expressed immunohistochemically in the endothelium of vessels in the endomysium and perimysium, and to lesser extents in the inflammatory infiltrates and on the sarcolemma of nonnecrotic muscle fibers adjacent to the inflammatory infiltrates or invaded muscle fibers. ICAM-1 in the muscle extracts and sera from EAM rats increased on each test day, as compared with extracts from the normal controls. The values peaked on day 0 after the last immunization, then gradually decreased with time. ICAM-1 elevations in the muscle extracts were correlated with the percent of sections that had inflammatory lesions (P = 0.032) and the histological scores (P = 0.005) on day 0, whereas there was no significance on days 3 and 7. These findings suggest that the adhesion molecules ICAM-1 and VCAM-1 increase in the early stage of EAM, and function in the initiation of the inflammatory process of myositis.

Hearts from mice lacking desmin have a myopathy with impaired active force generation and unaltered wall compliance

OBJECTIVE

Desmin intermediate filaments are key structures in the cytoskeleton of cardiac muscle. Since they are associated with Z-discs and intercalated discs, they may have a role in sarcomere alignment or force transmission. We have explored the mechanical function of the desmin filaments in the cardiac wall by comparing desmin-deficient (Des-/-) and wild-type (Des+/+) mice.

METHODS

The Langendorff technique was used to examine the contractility of the whole heart. Rate of force generation, Ca(2+)-sensitivity and force per cross-sectional area were measured in skinned ventricle muscle preparations.

RESULTS

Des-/- mice have a cardiomyopathy with increased heart weight. Diastolic pressure was increased at all filling volumes in the Des-/- group. Since passive wall stress (i.e. force per area) was unchanged, the alteration in diastolic pressure is a consequence of the thicker ventricle wall. Developed pressure, rate of pressure increase and developed wall stress were significantly reduced, suggesting that active force generation of the contractile apparatus is reduced in Des-/-. Concentrations of actin and myosin in the ventricle were unaltered. Measurements in skinned muscle preparations showed a lower active force development with unaltered Ca(2+)-sensitivity and rate of tension development.

CONCLUSION

It is suggested that the intermediate filaments have a role in active force generation of cardiac muscle, possibly by supporting sarcomere alignment or force transmission. The desmin filaments do not contribute the passive elasticity of the ventricle wall. Des-/- mice provide a model for genetic cardiomyopathy where the main factor contributing to altered cardiac performance is a decrease in active force generation, possibly in combination with a loss of functional contractile units.

Rhabdomyosarcoma of the uterus: report of two cases, including one of the spindle cell variant

Most uterine sarcomas fall into the category of leiomyosarcoma, endometrial stromal sarcoma, or undifferentiated sarcoma. Pure rhabdomyosarcomas are extremely rare, although a rhabdomyosarcomatous element may be present as a component of an adenosarcoma or carcinosarcoma (malignant mixed müllerian tumor). This report describes two uterine rhabdomyosarcomas in 28- and 67-year-old women. These were of spindle cell and pleomorphic types, respectively. At presentation the pleomorphic rhabdomyosaroma was stage IV, exhibiting massive pelvic and abdominal dissemination that mimicked an ovarian neoplasm. The spindle cell rhabdomyosarcoma was stage I, being confined to the uterus. Grossly, both uterine tumors had a polypoid appearance. Immunohistochemically, tumor cells were positive with the skeletal muscle markers sarcomeric actin, myoglobin, and myoD1. The patient with stage IV disease died within a short time of diagnosis and the other patient is alive and well at 2 years' follow-up. This report adds to the published literature on uterine rhabdomyosarcomas. This is the first reported uterine case of the spindle cell variant of embryonal rhabdomyosarcoma. Based on these cases and the published literature, rhabdomyosarcoma, especially the pleomorphic variant, appears to be a very aggressive neoplasm with an extremely poor prognosis. Immunohistochemical demonstration of skeletal muscle differentiation is necessary for a definitive diagnosis.

Myogenic differentiation by human processed lipoaspirate cells

The use of undifferentiated cells for cell-based tissue engineering and regeneration strategies represents a promising approach for skeletal muscle repair. For such strategies to succeed, a readily available source of myogenic precursor cells must be identified. We have previously shown that cells isolated from raw human lipoaspirates, called processed lipoaspirate cells, display multilineage mesodermal potential in vitro. Because human liposuctioned fat is available in large quantities and can be harvested with low morbidity, it may be an ideal source of stem cells for tissue-engineering applications. In this study, processed lipoaspirate cells were isolated from raw lipoaspirates harvested from eight patients who underwent cosmetic surgery. Processed lipoaspirate cells were placed in promyogenic conditions for up to 6 weeks, and the expression of the myogenic markers MyoD1 and myosin heavy chain was confirmed by using structure, histology, and reverse transcriptase-polymerase chain reaction. Histologic results were quantitated as an indicator or myogenic differentiation levels. We found that induced human processed lipoaspirate cells form multinucleated cells after 3 weeks of induction, indicative of the formation of myotubes. In addition, MyoD1 and skeletal muscle myosin heavy chain are expressed at distinct time points during differentiation with MyoD1 expression preceding expression of myosin. Finally, approximately 15 percent of human processed lipoaspirate cells can be induced toward myogenic differentiation 6 weeks after induction. In summary, our findings suggest that human processed lipoaspirate cells differentiate into myogenic cells. Furthermore, these cells may be a useful source for skeletal muscle engineering and repair.

Analyses of muscular activity, energy metabolism, and muscle fiber type composition in a patient with bilateral masseteric hypertrophy

Hyperwork of the masseter muscles due to habitual parafunction is thought to induce masseteric hypertrophy (so called work hypertrophy). However, the causes underlying this disease are not yet fully understood. Recently, we had a patient with bilateral masseteric hypertrophy, and we performed a partial excision of the masseter muscles. In this patient's case, we examined muscular activity, energy metabolism, and fiber type composition of the masseter muscles using electromyograms (EMG), 31P-magnetic resonance spectroscopy (MRS), and enzyme-histochemistry. The EMG showed no hyperactivity, and the 31P-MRS showed normal energy spectral patterns and PCr contents of the masseter muscles. The fiber type composition, however, in the muscles in this case was very different from that in muscles with "work hypertrophy" and also that in normal masseter muscles: 1. Loss of type IIB fibers; 2. Increases in type IIA and in type IM & IIC fibers; and 3. Decrease in type I fibers. The findings suggest that this is not a case of work hypertrophy but a case of compensatory hypertrophy possibly due to a lack of high-tetanus-tension type IIB fibers.

Functional heterogeneity of mammalian single muscle fibres: do myosin isoforms tell the whole story?

The large amount of data published in the last 10-15 years indicate that myosin isoforms are the major determinant of the large functional heterogeneity of the key contractile and biochemical properties of skeletal muscle fibres, including velocity of shortening, ATP consumption and power. Recent evidences are difficult to reconcile with such an idea and suggest that the properties of muscle fibres that are likely to depend on myosin, such as velocity of shortening, can change without a change in myosin isoform. That a given myosin isoform can modify its properties without shifting to another isoform is confirmed by some analyses of isolated myosin in vitro. The present review is mainly focused on findings that challenge the role of myosin isoforms in determining the functional heterogeneity of skeletal muscle. The work also reports on potential mechanisms behind such changes in myosin function independent of a shift in myosin isoform: the coexistence of different myosin heavy chain (MHC) isoforms in the same fibre, the existence of as yet undetected MHC isoforms, myosin light chain isoforms, post-translational modifications of myosin, the role of other myofibrillar proteins, geometry of the sarcomere and the myosin concentration in single fibres.

Ischemia disrupts myosin I beta in renal tubules

In these studies we have examined rat kidneys biochemically and microscopically to determine where myosin I beta is located before, during, and after an acute ischemic injury. Myosin I beta is present in multiple tubule segments including the brush border (BB) of the proximal tubule cell (PTC). Its distribution is severely altered by a 15-min renal artery clamp. Myosin I beta is present in the urine during reflow and is found in the numerous cellular blebs arising from the damaged PTC and other tubules. Two hours of reflow result in a decrease in BB myosin I beta staining and an increase in its cytoplasmic staining. Interestingly, the return of the F-actin in the BB precedes the return of the myosin I beta, suggesting that this myosin I isoform may not play a role in rebuilding the microvilli after an ischemic injury. A nonstructural role for this myosin, such as transport or channel regulation, is supported by its presence in many tubule segments, all of which have transport and channel requirements but do not all contain microvilli.

Fat content in individual muscle fibers of lean and obese subjects

OBJECTIVE

To examine skeletal muscle intracellular triglyceride concentration in different fiber types in relation to obesity.

DESIGN

Skeletal muscle fiber type distribution and intracellular lipid content were measured in vastus lateralis samples obtained by needle biopsy from lean and obese individuals.

SUBJECTS

Seven lean controls (body mass index (BMI) 23.0+/-3.3 kg/m(2); mean+/-s.d.) and 14 obese (BMI 33.7+/-2.7 kg/m(2)) individuals; both groups included comparable proportions of men and women.

MEASUREMENTS

Samples were histochemically stained for the identification of muscle fiber types (myosin ATPase) and intracellular lipid aggregates (oil red O dye). The number and size of fat aggregates as well as their concentration within type I, IIA and IIB muscle fiber types were measured. The cellular distribution of the lipid aggregates was also examined.

RESULTS

The size of fat aggregates was not affected by obesity but the number of lipid droplets within muscle fibers was twice as abundant in obese compared to lean individuals. This was seen in type I (298+/-135 vs 129+/-75; obese vs lean, P<0.05), IIA (132+/-67 vs 79+/-29; P<0.05), and IIB (103+/-63 vs 51+/-13; P<0.05) muscle fibers. A more central distribution of lipid droplets was observed in muscle fibers of obese compared to lean subjects (27.2+/-5.7 vs 19.7+/-6.4%; P<0.05).

CONCLUSION

The higher number of lipid aggregates and the disposition to a greater central distribution in all fiber types in obesity indicate important changes in lipid metabolism and/or storage that are fiber type-independent.

Pleomorphic rhabdomyosarcoma in children: four cases in the pediatric age group

Pleomorphic rhabdomyosarcoma is considered rare and controversial, especially in children. Although pleomorphic rhabdomyosarcoma has been observed in children, its sparcity has taken it out of current childhood rhabdomyosarcoma classifications. We report four pediatric cases of pleomorphic rhabdomyosarcoma, review morphologic, immunohistochemical, and ultrastructural features, and discuss the rare need to include this category in children. The Soft Tissue Registry of the Armed Forces Institute of Pathology was searched for cases coded as "pleomorphic rhabdomyosarcoma" from 1970 to the present. Only cases in patients less than 21 years old were included. Clinical data, morphology, and immunohistochemical stains were reviewed and follow-up was obtained. Electron microscopy was performed on two cases. Molecular analysis by polymerase chain reaction was performed on one case with available material. Of four patients included, there were three boys and one girl. Patient ages ranged from 9 months to 10 years (median, 4.5 years). Tumors were located on the chest wall (n = 2) and one each on the upper and lower extremities. Tumor size ranged from 4.0 to 10.0 cm (median, 7 cm). Grossly, the tumors were lobulated and circumscribed. Microscopically, architectural patterns varied from solid to fascicular or storiform. All tumors had large, often multinucleated, polygonal, spindled or strap-like rhabdomyoblasts with abundant eosinophilic cytoplasm. Nuclear characteristics ranged from hyperchromatic to vesicular. Most tumor cells had large prominent nucleoli. Background rhabdomyoblasts varied from spindled to polygonal. No tumors displayed areas typical of embryonal or alveolar rhabdomyosarcoma. All tumors exhibited atypical mitotic figures. Immunohistochemistry revealed that the tumors were positive for the following markers: desmin (3/4), myoglobin (4/4), myoD1 (3/3), myf4 (3/3), and MSA (4/4). The two cases studied by electron microscopy both showed evidence for skeletal muscle differentiation. One case showed no evidence for a t(2;13) or t(1;13) translocation. Two patients were alive with no evidence of disease at 12 and 25 years. One patient was dead of disease at 9 years. Pleomorphic rhabdomyosarcoma is rare but exists in children. The diagnosis should be considered in pleomorphic sarcomas exhibiting skeletal muscle differentiation, which are otherwise devoid of typical areas or chromosomal changes of embryonal or alveolar rhabdomyosarcoma.

The perifollicular and marginal zones of the human splenic white pulp : do fibroblasts guide lymphocyte immigration?

We investigate the white pulp compartments of 73 human spleens and demonstrate that there are several microanatomical peculiarities in man that do not occur in rats or mice. Humans lack a marginal sinus separating the marginal zone (MZ) from the follicles or the follicular mantle zone. The MZ is divided into an inner and an outer compartment by a special type of fibroblasts. An additional compartment, termed the perifollicular zone, is present between the follicular MZ and the red pulp. The perifollicular zone contains sheathed capillaries and blood-filled spaces without endothelial lining. In the perifollicular zone, in the outer MZ, and in the T cell zone fibroblasts of an unusual phenotype occur. These cells stain for the adhesion molecules MAdCAM-1, VCAM-1 (CD106), and VAP-1; the Thy-1 (CD90) molecule; smooth muscle alpha-actin and smooth muscle myosin; cytokeratin 18; and thrombomodulin (CD141). They are, however, negative for the peripheral node addressin, the cutaneous lymphocyte antigen, CD34, PECAM-1 (CD31), and P- and E-selectin (CD62P and CD62E). In the MZ the fibroblasts are often tightly associated with CD4-positive T lymphocytes, whereas CD8-positive cells are almost absent. Our findings lead to the hypothesis, that recirculating CD4-positive T lymphocytes enter the human splenic white pulp from the open circulation of the perifollicular zone without crossing an endothelium. Specialized fibroblasts may attract these T cells and guide them into the periarteriolar T cell area.

Muscle differentiation after sciatic nerve transection and reinnervation in adult rats

Reinnervation after peripheral nerve transections generally leads to poor functional recovery. In order to study whether changes in muscles might be a contributing factor in this phenomenon we studied muscle morphology and fibre type distributions after sciatic nerve transection in the rat hind limb. Proximally, before the bifurcation in the tibial and common peroneal nerve, a 12 mm segment of the sciatic nerve was resected, reversed and re-implanted as an autologous nerve graft. After survival periods of 7, 15 and 21 weeks the lateral gastrocnemius, tibialis anterior and soleus muscles were dissected, stained with mATP-ase, and fibre type distributions were studied. In addition, numbers of muscle fibres were counted, and cross sectional areas were calculated. After 7 weeks, cross sectional areas were decreased in all muscles. In the gastrocnemius and tibialis anterior muscles the fibre number remained unaltered but the hypotrophy had been reversed at later ages. The number of muscle fibres in the soleus muscle remained decreased over the entire period of observation. The percentages of type II fibres in the gastrocnemius and tibialis anterior muscles were decreased at 7 and 15 weeks but these again approached normal values at 21 weeks. The type I fibres, however, remained arranged in groups. In the soleus muscle a large increase in the percentage of type II muscle fibres was observed and this remained until 21 weeks. We conclude that a non-selective reinnervation and later readjustments by regression of polyneural innervation may in part explain the changes in distributions of various fibre types.

A highly sensitive method for measurement of myosin ATPase activity by reversed-phase high-performance liquid chromatography

A new method for measurement of myosin ATPase activity has been developed utilizing reversed-phase high-performance liquid chromatography (HPLC), which detects as low as 0.05 nmol of ADP hydrolyzed from ATP. After termination of the ATPase reaction by addition of perchloric acid, the hydrolysate ADP and substrate ATP were separated by reversed-phase HPLC. The absorbance of ADP was monitored at 259 nm, and the amount of ADP was quantified from its peak area on the chromatogram by use of the NIH Image computer software. Our method showed linearity over a wide range from 0.05 to 10 nmol of ADP per 20 microl with a coefficient of determination (r(2)) of 0.99. Myosin ATPase activities determined by the HPLC method were almost identical to those determined by the malachite green method, a widely used spectrophotometric method with range of detection from 1 to 8 nmol of phosphate. Because our method requires only a small volume of reaction solution, it will be a powerful tool for measuring ATPase activity of motor proteins, which are difficult to obtain in large amount.

Pleomorphic rhabdomyosarcoma in adults: a clinicopathologic study of 38 cases with emphasis on morphologic variants and recent skeletal muscle-specific markers

Pleomorphic rhabdomyosarcoma (PRMS) is a rare and controversial tumor of skeletal muscle phenotype. Diagnostic criteria for PRMS by combined histology and currently available immunohistochemistry have not been clearly defined. We report 38 pleomorphic rhabdomyosarcomas in adults, explore morphologic variants, and discuss our experience with both specific and nonspecific skeletal muscle markers in these tumors. Clinical data, morphology, and immunohistochemistry were reviewed. Electron microscopy was performed. Of 38 cases, there were 28 males and 10 females. Patient ages ranged from 21 to 81 years (median = 54 y; mean = 51 y). Tumors were located in the lower extremity (n = 18), abdomen/retroperitoneum (n = 6), chest/abdominal wall (n = 5), spermatic cord/testes (n = 4), upper extremity (n = 3), and one each in the mouth and orbit. Tumor sizes ranged from 1.5 to 15.0 cm (mean = 7.3 cm; median = 6.8 cm). The cases were divided into three variants, each with large, atypical, pleomorphic polygonal rhabdomyoblasts (PRMB) with abundant eosinophilic cytoplasm in varying numbers and different morphologic backgrounds of round or spindled rhabdomyoblasts (RMB). 1. Classic PRMS: Predominantly atypical PRMB in sheets (n = 8). 2. Round cell PRMS: Clusters of PRMB throughout the tumor with a background of slightly atypical, medium-sized, round, blue RMB (n = 13). 3. Spindle cell PRMS: Scattered PRMB in a predominance of atypical spindled RMB arranged in a storiform growth pattern (n = 17). Immunohistochemistry revealed the following: myoglobin (37/38), MyoD1 (19/36), skeletal muscle myogenin (myf4; 19/34), fast skeletal muscle myosin (4/5), desmin (36/38), muscle-specific actin (MSA; 25/35), smooth muscle actin (SMA; 15/33), and muscle specific myogenin (myf3; 25/35). Immunohistochemistry was supportive of skeletal muscle differentiation with at least one positive skeletal muscle-specific marker (myoglobin, MyoD1, fast skeletal muscle myosin, or myf4). In addition, all cases had some positivity for nonspecific muscle markers (desmin, MSA, SMA, myf3). Electron microscopy (EM), performed on eight selected cases from all three morphologic groups, demonstrated definitive skeletal muscle differentiation in all cases. Follow-up, available on 30 (79%) cases, revealed that 70% of patients died of disease (mean 20 months, range 1 month-108 months), 3% were alive with disease at 12 months (n = 1); and 27% had no evidence of disease (mean, 83 mo; range, 18 to 108 mo). PRMS, a tumor of predominantly middle-aged adult males in the lower extremity, can be diagnosed by the morphologic presence of scattered PRMB with immunohistochemical evidence of at least one skeletal muscle-specific marker. There are three morphologic variants of PRMS. The appropriate diagnosis of PRMS is significant as it is a high-grade sarcoma, with an aggressive clinical course.

Quantitative electrophoretic analysis of myosin heavy chains in single muscle fibers

To better understand the molecular basis of the large variation in mechanical properties of different fiber types, there has been an intense effort to relate the mechanical and energetic properties measured in skinned single fibers to those of their constituent cross bridges. There is a significant technical obstacle, however, in estimating the number of cross bridges in a single fiber. In this study, we have developed a procedure for extraction and quantification of myosin heavy chains (MHCs) that permits the routine and direct measurement of the myosin content in single muscle fibers. To validate this method, we also compared MHC concentration measured in single fibers with the MHC concentration in whole fast-twitch (psoas and gracilis) and slow-twitch (soleus) muscles of rabbit. We found that the MHC concentration in intact psoas (184 microM) was larger than that in soleus (144 microM), as would be expected from their differing mitochondrial content and volume of myofibrils. We obtained excellent agreement between MHC concentration measured at the single fiber level with that measured at the whole muscle level. This not only verifies the efficacy of our procedure but also shows that the difference in concentration at the whole muscle level simply reflects the concentration differences in the constituent fiber types. This new procedure should be of considerable help in future attempts to determine kinetic differences in cross bridges from different fiber types.

Calyculin-A, an inhibitor for protein phosphatases, induces cortical contraction in unfertilized sea urchin eggs

When an unfertilized sea urchin egg was exposed to calyculin-A (CL-A), an inhibitor of protein phosphatases, for a short period and then lysed, the cortex contracted to exclude cytoplasm and became a cup-shaped mass. We call the contracted cortex "actin cup" since actin filaments were major structural components. Electron microscopic observation revealed that the cup consisted of inner electron-dense layer, middle microfilamentous layer, and outermost granular region. Microfilaments were heavily accumulated in the inner electron-dense layer. The middle layer also contained numerous microfilaments, which were determined to be actin filaments by myosin S1 decoration, and they were aligned so that their barbed ends directed toward the outermost region. Myosin II, Arp2, Arp3, and spectrin were concentrated in the actin cup. Immuno-electron microscopy revealed that myosin II was localized to the electron-dense layer. We further found that the cortical tension of the egg increased just after application of CL-A and reached maximum within 10 min. Cytochalasin B or butanedione monoxime blocked the contraction, which suggested that both actin filaments and myosin ATPase activity were required for the contraction. Myosin regulatory light chain (MRLC) in the actin cup was shown to be phosphorylated at the activation sites Ser-19 and Thr-18, by immunoblotting with anti-phosphoepitope antibodies. The phosphorylation of MRLC was also confirmed by a (32)P in vivo labeling experiment. The CL-A-induced cortical contraction may be a good model system for studying the mechanism of cytokinesis.

Development of regenerative cardiomyocytes from mesenchymal stem cells for cardiovascular tissue engineering

We have isolated a cardiomyogenic (CMG) cell line from murine bone marrow stroma. Stromal cells were immortalized, treated with 5-azacytidine, and spontaneous beating cells were repeatedly screened for. The cells showed a fibroblast-like morphology. However, this morphology changed after 5-azacytidine treatment in about 30% of the cells, which connected with adjoining cells after 1 week, formed myotube-like structures and began spontaneous beating after 2 weeks, and beat synchronously after 3 weeks. These cells expressed atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Electron microscopy revealed a cardiomyocyte-like ultrastructure including typical sarcomeres and atrial granules. They had sinus node-like or ventricular cell-like action potentials. Analysis of the isoform of contractile protein genes, such as myosin and alpha-actin, indicated that their phenotype was similar to fetal ventricular cardiomyocytes. These cells expressed Nkx2.5, GATA4, TEF-1, and MEF2-C mRNA before 5-azacytidine treatment, and expressed MEF2-A and MEF2-D after treatment. This new cell line provides a powerful model for the study of cardiomyocyte transplantation.

Maize myosins: diversity, localization, and function

This first analysis of monocotyledon myosin genes showed that at least five genes, one of which was probably spliced to yield two isoforms, were expressed in maize (Zea mays L.). The complete coding sequence of ZMM1 was determined, as were most of the sequences of two other myosin cDNAs (ZMM2 and ZMM3). ZMM1 and ZMM2 belonged to myosin class XI while ZMM3 was in class VIII. ZMM1 was abundantly expressed in leaves, roots, coleoptiles, and stems. ZMM3 showed a similar distribution but was expressed poorly in pollen. ZMM2 was predominantly expressed in seeds and may be part of a suite of cytoskeletal proteins in reproductive tissues. Phylogenetic analysis suggested that the origin of myosin classes VIII and XI predated that of angiosperms. Immunofluorescence studies using M11L1, a myosin XI antibody specific for the exposed loop 1 head region of myosin, indicated that myosin XI occurred in the cytoplasm of all root tip cells. The highest concentration of myosin XI was in the differentiating epidermal cells. In dividing cells, myosin XI was present near the cytokinetic apparatus at approximately the same concentration seen in other portions of the cytoplasm. Western blot analysis of subcellular fractions indicated that myosin XI was concentrated in mitochondria and low-density membranes.

[Alveolar rhabdomyosarcoma: apropos of a rare location]

Rhabdomyosarcoma is a soft tissue tumor of striated muscle origin. It is observed mainly in children and adolescents. Rhabdomyosarcoma predominantly occurs in three regions: head and neck, genito-urinary tract and retroperitoneum, and upper and lower extremities. We report a case of primary alveolar rhabdomyosarcoma of the mesentery occurring in a 68-year-old man. Rhabdomyosarcomas can be diagnosed on microscopic findings and immunohistochemical features. Cytogenetic findings can be helpful in the diagnosis.

Intraarterial injection of muscle-derived CD34(+)Sca-1(+) stem cells restores dystrophin in mdx mice

Duchenne muscular dystrophy is a lethal recessive disease characterized by widespread muscle damage throughout the body. This increases the difficulty of cell or gene therapy based on direct injections into muscles. One way to circumvent this obstacle would be to use circulating cells capable of homing to the sites of lesions. Here, we showed that stem cell antigen 1 (Sca-1), CD34 double-positive cells purified from the muscle tissues of newborn mice are multipotent in vitro and can undergo both myogenic and multimyeloid differentiation. These muscle-derived stem cells were isolated from newborn mice expressing the LacZ gene under the control of the muscle-specific desmin or troponin I promoter and injected into arterial circulation of the hindlimb of mdx mice. The ability of these cells to interact and firmly adhere to endothelium in mdx muscles microcirculation was demonstrated by intravital microscopy after an intraarterial injection. Donor Sca-1, CD34 muscle-derived stem cells were able to migrate from the circulation into host muscle tissues. Histochemical analysis showed colocalization of LacZ and dystrophin expression in all muscles of the injected hindlimb in all of five out of five 8-wk-old treated mdx mice. Their participation in the formation of muscle fibers was significantly increased by muscle damage done 48 h after their intraarterial injection, as indicated by the presence of 12% beta-galactosidase-positive fibers in muscle cross sections. Normal dystrophin transcripts detected enzymes in the muscles of the hind limb injected intraarterially by the mdx reverse transcription polymerase chain reaction method, which differentiates between normal and mdx message. Our results showed that the muscle-derived stem cells first attach to the capillaries of the muscles and then participate in regeneration after muscle damage.