[Pulmonary artery stenting in chronic thromboembolic pulmonary hypertension: a report of 2 cases].

Chronic thromboembolic pulmonary hypertension (CTEPH) is a pulmonary vascular disease characterized by an insidious onset, progressive deterioration, and poor prognosis. It is distinguished by the thrombotic organization within the pulmonary arteries, leading to vascular stenosis or occlusion. This results in a progressive increase in pulmonary vascular resistance and pulmonary arterial pressure, ultimately leading to right heart failure. In recent years, balloon pulmonary angioplasty (BPA) has emerged as an effective treatment option for patients ineligible for pulmonary endarterectomy (PEA). However, the use of stents in patients with suboptimal balloon dilation remains controversial. This article describes two cases of chronic thromboembolic pulmonary hypertension (CTEPH) in which balloon angioplasty yielded unsatisfactory results, subsequently leading to stent placement. Following stent implantation, there was improved blood flow, significant reduction in pulmonary arterial pressure, and notable alleviation of patient symptoms. One-year follow-up showed no recurrence of stenosis within the stent, suggesting potential guidance for the use of pulmonary artery stenting as a treatment modality for CTEPH. This report provided new insights into the therapeutic approach for CTEPH.

[Multicenter retrospective study of 38 cases with fumarate hydratase deficiency uterine leiomyoma].

Objective: To investigate the clinicopathological features of fumarate hydratase (FH) deficiency uterine leiomyoma. Methods: The data of 38 patients with FH deficiency uterine leiomyoma were screened and analyzed. The expressions of FH, S-(2-succino)-cysteine (2SC), desmin, p16, p53, CD10 and cell proliferation associated nuclear antigen (Ki-67) proteins were detected by immunohistochemistry, and their clinicopathological features were analyzed retrospectively. Results: (1) Clinical features: the median age of the patients was (42.5±7.4) years old. Twenty-one cases (55%) of them were myomas found in physical examination, and the median maximum diameter of the tumor was 6.0 cm (range: 5.0-7.5 cm); myomectomy was performed in 23 cases (61%), total hysterectomy with or without bilateral appendages in 15 cases (39%); laparoscopic surgery in 27 cases (71%), open surgery in 11 cases (29%); none of the patients had renal cell carcinoma. (2) Histological features: atypical nuclear cells were distributed locally or diffusely, eosinophilic nucleoli and intranuclear inclusion bodies could be seen, glass like globules could be seen in the cytoplasm, nuclear division was 0-4/10 high power field (HPF), and antler like blood vessels and pulmonary edema-like changes could be seen in the stroma. Among 38 patients with FH deficiency uterine leiomyoma, FH was negative in 37 cases (97%), and positive in 1 case (3%); 2SC, desmin, p16, p53, CD10 and Ki-67 showed focal positive expression in 38 cases (100%), including 35 cases (92%) with Ki-67 index<10% and 3 cases (8%) with Ki-67 index ≥10%. (3) Follow-up: 4 cases (11%) recurred, and there was no death. There were significant differences in age, family history, distribution of atypical nuclei and mitosis number between recurrent group and non-recurrent group (all P<0.05). Conclusions: FH deficiency uterine leiomyoma is a rare tumor, which needs pathological examination,immunohistochemical examination and clinical history. Patients younger than 43 years old, with family history, histologically atypical diffuse nuclear distribution and mitotic number ≥3/10 HPF should be alert to the risk of recurrence.

[Clinicopathological and genetic characteristics of bronchial sialadenoma papilliferum: report of four cases].

Objective: To investigate the clinicopathological, immunophenotypic, and molecular genetic features of bronchial sialadenoma papilliferum (BSP). Methods: Four cases of BSP collected at the Shanghai Pulmonary Hospital from May 2018 to June 2021 were retrieved and analyzed. These cases were evaluated for their clinical, histological, immunohistochemical (IHC) and genomic features. The patients were followed up and relevant literature was reviewed. Results: All four patients were male, aged from 55 to 75 years (mean 62 years), with tumor diameter of 6 to 21 mm (mean 13.5 mm), and lesions were located in the left lower lobe (n=2), right lower lobe (n=1), and trachea (n=1). They were characterized by a combination of surface exophytic endobronchial papillary proliferation and an endophytic two-cell layered ductal structure. IHC staining showed that CK7 and EMA were strongly positive in ductal epithelium; p63, p40, CK5/6 were positive in ductal and papillary basal cells; SOX10 was positive in ductal epithelium and basal cells; S-100 was positive in basal cells and ductal epithelium in two cases. Next generation sequencing showed that two cases harbored BRAF V600E mutation. Conclusions: BSP is an extremely rare primary lung tumor arising from the salivary gland under bronchial mucosa. The primary treatment choice of this tumor is complete surgical resection. The diagnosis and differential diagnosis of this tumor depend on classic histomorphologic and IHC features, and BRAF V600E gene mutation can be detected.

[Analysis of genotypes, EEG and phenotypes of tuberous sclerosis complex patients].

Objective: Tuberous sclerosis complex (TSC) is a multi-system disease with TSC1 and TSC2 genes as the pathogenic genes. The purpose of our study was to analyze the gene mutation in patients with TSC with epilepsy as the main clinical manifestation. The relationship between genotype and phenotype, scalp EEG in patients was analyzed. Methods: The peripheral blood was extracted from 43 patients and their families. TSC gene was detected by second-generation sequencing. Long-term video EEG monitoring and MRI examination were performed to determine the onset area, seizure type and location of nodules. Results: 39 patients had TSC gene mutation, 4 patients did not detect the gene mutation.11 had TSC1 mutations and 28 had TSC2 mutations. 22 mutations were de novo. Patients with TSC2 mutations had earlier seizure and more nodules than patients with TSC1 mutations, but no significant difference in intelligence and spasm were observed. 28 patients had focal origin of scalp EEG, of which 85.7% of TSC2 mutations patients had focal origin. Conclusions: Patients of TSC2 mutations always has an early onset age. Although MRI shows multiple nodules, the onset of EEG is mainly focal origin.

[The application of stereo-electroencephalography guided radiofrequency thermocoagulation in refractory temporal epilepsy].

Objective: To investigate the clinical value of stereo-electroencephalography guided radiofrequency thermos-coagulation (RFTC) in drug resistant temporal epilepsy. Methods: The clinical data of 12 patients with refractory temporal epilepsy who underwent implantation of SEEG electrodes and radiofrequency thermos-coagulation from July 2016 to November 2017 were analysed retrospectively. Results: The mean follow-up time was 6.4±4.6 months after thermos-coagulation, and 10.2±3.5 months after resection. Engel Ⅰa was observed in 9 cases, with Ⅱa, Ⅲa and Ⅳa 1 cases respectively. Nine patients experienced a ≥50% decrease of seizure frequency after RFTC (R+ , 75%), of whom one had got a sustained seizure free for 15 months and the other with decrease of seizure frequency by over 90% for 14 months. There was a statistical significance in seizure frequency between pre- and post-thermo-coagulation (P=0.008). Ten cases underwent open surgery following SEEG-guided RFTC, of them 8 cases got seizure free. RFTC was effective in 6 of 8 cases. In our group, all patients have not suffered from any neurologic and cognitive deficiency, and even several patients have some improvements on memory quotient. Conclusions: Although it is less effective than resective surgery, SEEG-guided RFTC can be a relatively safe, effective treatment because of its precision and minimal invasion for patients with complex drug resistant temporal epilepsy, especially for impossible any cortical resection. In addition, its effect may be a predictor of outcome after conventional cortectomy.

A molecular epidemiological study of methicillin-resistant Staphylococci environmental contamination in railway stations and coach stations in Guangzhou of China.

Methicillin-resistant Staphylococcus aureus (MRSA) has caused a series of public health problems since it was first found in 1961. However, there are few research studies on the MRSA environmental contamination in railway stations and coach stations. Therefore, the aim of this study was to determine MRSA environmental contamination in public transport stations. Between December 2013 and January 2014, 380 surface samples from three railway stations (180) and four coach stations (200) in Guangzhou were collected to isolate and determine the prevalence and characteristics of Staphylococci strains. 39·21% of all samples were Staphylococci isolates, 1·58% of Staphylococci isolates were MRSA isolates, and 6·05% were methicillin-susceptible S. aureus. The proportion of multidrug resistant among 149 Staphylococci isolates was 75·84%. None of MRSA isolates was identified with the Panton-Valentine Leukocidin (PVL) genes, and one of them was identified with the qac gene. Four MRSA isolates were Staphylococcal Cassette Chromosome mec IVa, and the other two were nontypeable. Staphylococcus aureus isolates were classified into several sequence types (STs), and STs showed possible cross-transmissions of isolates from various sources. Methicillin-resistant Staphylococci contamination prevalence was high, and the environment of stations may be the vectors transmitting the Staphylococci to passengers. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to comprehensively report the prevalence, antibiotic resistance, and molecular characteristics of contamination of Staphylococci isolates in railway stations and coach stations of China. It will have great public health implications on infection control in community settings because of the serious hazard of Staphylococci, especially methicillin-resistant Staphylococci. Our findings have provided evidence for relevant departments to reduce the contamination of Staphylococci in environment of public transport stations.

Aerobic Biodegradation of OCDD by P. Mendocina NSYSU: Effectiveness and Gene Inducement Studies.

The goals of this study were to assess the effectiveness of (1) enhancing octachlorinated dibenzo-p-dioxin (OCDD) biodegradation under aerobic conditions by Pseudomonas mendocina NSYSU (P. Mendocina NSYSU) with the addition of lecithin, and (2) inducing OCDD ring-cleavage genes by pentachlorophenol (PCP) and OCDD addition. P. Mendocina NSYSU could biodegrade OCDD via aerobic cometabolism and lecithin was used as a primary substrate. Approximately 74 and 67% of OCDD biodegradation was observed after 60 days of incubation with lecithin and glucose supplement, respectively. Lecithin was also used as the solubilization additive resulting in OCDD solubilization and enhanced bioavailability of OCDD to P. Mendocina NSYSU. Two intradiol and extradiol ring-cleavage dioxygenase genes (Pmen_0474 and Pmen_2526) were identified from gene analyses. Gene concentration was significantly enhanced after the inducement by PCP and OCDD. Higher gene inducement efficiency was obtained using PCP as the inducer, and Pmen_2526 played a more important role in OCDD biodegradation.

[Functional mapping of the insular and opercular cortex: A study using SEEG electrical stimulation in epileptic patients].

OBJECTIVE: Insular and opercular cortex is involved in complicated physiological function.Insular seizures involve extensive epileptic network, which results in the complex and diverse semiology.Electrical cortical stimulation(ECS) can explore the functional mapping and symptomatogenic zone. METHODS: The clinical presurgical evaluation and ECS data of 20 patients whose electrode contacts were located in the insular and opercular were analyzed retrospectively.CT scan/3D MRI data fusion was performed in order to accurately identify and locate each contact and check the electrode trajectory by the MRI images performed after the electrodes were removed.ECS was applied between two contiguous contacts.Stimulation usually lasted for 5 s at 50 Hz(pulse width=0.3 ms). Depending on the area of stimulated cortex, the stimulation intensities ranged from 0.2 to 3.0 mA.The classification of the insular were anterior short gyrus, middle short gyrus, precentral gyrus, postcentral gyrus, posterior long gyrus and insular pole.The classification of the opercular were orbital, frontal, precentral, central, parietal and temporal opercular. RESULTS: One hundred and six contacts were located in the insular and 51 responses were evoked (48.11%). Four hundred eighteen contacts were located in the insular and 132 responses were evoked (31.58%). We classified the principal responses as somatosensory, pain, auditory, oropharyngeal, speech disturbances and neurovegetative response.Somatosensory responses were mainly evoked in parietal opercular and postcentral gyrus, while pain response distributed sporadically.Auditory were only evoked in temporal opercular(transverse temporal gyri) and posterior long gyrus.Oropharyngeal symptoms were only evoked in central opercular.Speech disturbances were located in precentral and central opercular and neurovegetative responses were mainly evoked in insular pole and middle short gyrus. CONCLUSIONS: These findings may indicate a functional specificity for the insular gyrus and opercular, which contribute to the understanding of anatomo-functional organization and the role in insular and opercular epileptic network.Moreover, it could optimize the implantation strategy for exploring these structures.

Statin use reduces the risk of dementia in elderly patients: a nationwide data survey and propensity analysis.

OBJECTIVES: The objective of this study was to examine the association between the use of statins and the risk of newly diagnosed dementia in an elderly population. DESIGN, SETTING AND PARTICIPANTS: Random samples of 1,000,000 individuals covered by the National Health Insurance in Taiwan were included in the analysis. All participants were 65 years or older without dementia and either did or did not start treatment with statins from 1 August 1997 to 31 December 2010. Patients with established dementia before the start of treatment were excluded. Baseline characteristics were matched (by propensity score) in those who did and did not receive statins. RESULTS: A total of 57,669 subjects were included in the analysis with approximately 12 years of follow-up. Propensity score matching identified 2003 patients who received statins and another 2003 patients who did not with comparable baseline characteristics. Adjusted hazard ratios (HRs) for dementia were significantly inversely associated with total or daily equivalent statin dosage (total accumulated dose: HRs 0.829, 0.720 and 0.385 from T1 to T3 vs. control, P < 0.001 for trend; mean daily dose: HRs 0.667, 0.798 and 0.503 from T1 to T3 vs. control, P < 0.001). The results remained robust after propensity adjustment. CONCLUSION: Independent of traditional risk factors, there was a decrease in newly diagnosed cases of dementia in elderly patients who had received a high total or daily dose of statins. The more potent statins (e.g. atorvastatin and rosuvastatin) seemed to be particularly effective in the prevention of dementia.

Immunologic assessment and KMT2D mutation detection in Kabuki syndrome.

Kabuki or Niikawa-Kuroki syndrome (KS) is a rare disorder with multiple malformations and recurrent infections, especially otitis media. This study aimed to investigate the genetic defects in Kabuki syndrome and determine if immune status is related to recurrent otitis media. Fourteen patients from 12 unrelated families were enrolled in the 9-year study period (2005-2013). All had Kabuki faces, cleft palate, developmental delay, mental retardation, and the short fifth finger. Recurrent otitis media (12/14) and hearing impairment (8/14) were also more common features. Immunologic analysis revealed lower memory CD19+ cells (11/13), lower memory CD4+ cells (8/13), undetectable anti-HBs antibodies (7/13), and antibody deficiency (7/13), including lower IgA (4), IgG (2), and IgG2 (1). Naïve emigrant lymphocytes, lymphocyte proliferation function, complement activity, and superoxide production in polymorphonuclear cells were all normal. All the patients had KMT2D mutations and 10 novel mutations of R1252X, R1757X,Y1998C, P2550R fs2604X, Q4013X, G5379X, E5425K, R5432X, R5432W, and R5500W. Resembling the phenotype of common variable immunodeficiency, KS patients with antibody deficiency, decreased memory cells, and poor vaccine response increased susceptibility to recurrent otitis media. Large-scale prospective studies are warranted to determine if regular immunoglobulin supplementation decreases the frequency of otitis media and severity of hearing impairment.

MicroRNA-19b targets Mfn1 to inhibit Mfn1-induced apoptosis in osteosarcoma cells.

Accumulative evidence has confirmed that, miR-17-92, a typical polycistronic mRNA cluster, was up-regulated in various solid tumors, and play an important role in the occurrence and development progress of tumors. In our study, we detected the six members of miR-17-92 cluster in osteosarcoma cell line, finding that the expression of miR-17 and miR-19b was up-regulated significantly. Further studies have found that Mfn1 was one of the target genes of miR-19b and the transcription and expression level of Mfn1 were down-regulated by miR-19b. MTS, flow cytometry, TUNEL-DAPI, Annexin V-FITC and transwell assay demonstrated that Mfn1 significantly blocked the cell cycle, promoted apoptosis and inhibited proliferation and invasion of osteosarcoma cells. Whereas, miR-19b targets 3'UTR sequences of Mfn1 genes inhibit the expression of Mfn1, thus inhibited Mfn1 triggered anti-cancer effect. Taken together, miR-19b functions by targeting Mfn1 reduce the protein expression level, thus provides a novel target to understand the molecular biology and genetics mechanisms of occurrence and development of osteosarcoma, contributing to the diagnosis and therapy of osteosarcoma.

Aliskiren attenuates proteinuria in mice with lupus nephritis by a blood pressure-independent mechanism.

This study revealed that low-dose aliskiren treatment could attenuate proteinuria by interrupting the renin-angiotensin system in mice with lupus nephritis, and the beneficial effect was beyond blood pressure control. An in and ex vivo fluorescence imaging (using a non-invasion in vivo imaging system) showed intense labeling of renin in the kidneys of female MRL/lpr mice. In the study, Alzet mini-osmotic pumps were implanted into 6-week-old female MRL/lpr mice. Pumps were filled with either phosphate-buffered saline or a solution of aliskiren dissolved in phosphate-buffered saline (20 mg/kg/day) and replaced at 28-day intervals. Mice were sacrificed at four and eight weeks. To label cells for DNA synthesis, bromodeoxyuridine (BrdU) (50 mg/kg) was injected intraperitoneally an hour prior to sacrifice. The level of renin inhibition was adequate, as aliskiren-treated mice demonstrated higher renal renin mRNA expression than controls (p < 0.05). Although there were no significant differences in the systolic blood pressure (control versus aliskiren-treated: 127.20 ± 4.44 mmHg versus 103.80 ± 7.40 mmHg, p > 0.05) and heart rate (control versus aliskiren-treated: 680.50 ± 11.71 versus 647.80 ± 13.90, p > 0.05) of both groups after eight weeks, there was significant reduction of inflammatory cytokines (transforming growth factor-beta1, regulated on activation normal T cell expressed, monocyte chemoattractant protein-1 and osteopontin, p < 0.05), reduction of innate immunity (toll-like receptor 7, p < 0.05), as well as a reduction of glomerular proliferation and inflammation (BrdU-, CD45-, CD3- and F4/80-positive glomerular cells, p < 0.01) after aliskiren infusion, which might translate into an improvement in proteinuria (control versus aliskiren-treated: 493.7 versus 843.7 mg/g, p < 0.01) or weight gain (control versus aliskiren-treated: 5.65 ± 1.61 versus 8.67 ± 0.97%, p < 0.05).

A functional variant in the promoter region regulates the C-reactive protein gene and is a potential candidate for increased risk of atrial fibrillation.

OBJECTIVES: In a large population-based cohort, the level of C-reactive protein (CRP) in patients at baseline predicts an increased risk of future development of atrial fibrillation (AF). The mechanism of this increased risk is unknown. Furthermore, both the molecular effects of CRP on atrial myocytes and fibroblasts and whether genetic variants in the CRP gene predispose to AF are also unknown. METHODS: A genetic association study between CRP gene polymorphisms and AF was performed in two independent populations (I: 100 AF patients and 101 controls; II: 348 AF patients and 356 controls), with functional studies to elucidate the mechanism of association. RESULTS: Three polymorphisms (T-861C, A-821G and C-390A/C-390T) were found in the 1-kb promoter of CRP. A triallelic polymorphism (C-390A/C-390T) captured all haplotype information and determined the CRP gene promoter activity and the plasma CRP level, and was in nearly complete linkage disequilibrium with G1059C polymorphism in exon 2. The -390A variant was associated with a higher CRP gene promoter activity, a higher plasma CRP level and a higher risk of AF. Patients with AF also had a higher plasma CRP level than controls. CRP significantly increased the inward L-type calcium current in atrial myocytes with no changes in other ionic currents. CRP did not affect the expressions of type I alpha 1 (COL1A1), type III alpha 1 (COL3A1) and type 1 alpha 2 (COL1A2) procollagens in atrial fibroblasts. CONCLUSION: A CRP gene promoter triallelic polymorphism was associated with CRP gene promoter activity, determined the plasma level of CRP, and predicted the risk of AF. The mechanism of this may be via augmention of calcium influx by CRP in atrial myocytes, but not because of atrial fibrosis.

[A cohort study of association between sleep duration and cognitive impairment in the elderly aged 65 years and older in China].

Objective: To explore the effect of sleep duration on the risk of cognitive impairment in the elderly in China. Methods: Baseline data of 9 679 elderly individuals with intact cognition were collected from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) in 2005, and followed up was conducted until 2018. Cox proportional hazards model was used to analyze the association between different sleep durations and the risk for cognitive impairment in the elderly. Results: Compared with elderly with sleep duration of 6 hours per day, those with sleep duration less than 5 hours had increased risk for cognitive impairment by 30% (HR=1.30, 95%CI: 1.05-1.62), and those with sleep durations of 7 hours, 8 hours and more than 9 hours had increased risk for cognitive impairment by 34% (HR=1.34,95%CI: 1.09-1.64), 40% (HR=1.40,95%CI: 1.17-1.69) and 43% (HR=1.43,95%CI: 1.19-1.70), respectively. Trend test showed that the risk of cognitive impairment increased with the extension of sleep duration (>6 h), and there was a dose-response relationship (P<0.001). However, self-rated sleep quality was not associated with the risk for cognitive impairment in the elderly. Conclusions: The shorter and longer sleep duration were associated an increased risk of cognitive impairment in the elderly aged ≥65 years in China, suggesting that optimizing sleep duration might delay the occurrence of cognitive impairment.

[A cohort study on the influence of the chronic diseases on falls among middle-aged and older Chinese].

Objective: To analyze the influence of chronic diseases on falls among middle-aged and older Chinese. Methods: Baseline data of 13 670 middle-aged and older adults recruited from China Health and Retirement Longitudinal Study (CHARLS) in 2011 were used and followed up to 2018, among those were 7 443 (54.45%) middle-aged people aged 45-59 and 6 227 (45.55%) older adults aged 60 and above. The Cox proportional hazards model was used to analyze the effects of different types, the number of chronic diseases and the interaction between chronic illness and other factors on the fall risk of middle-aged and older people. Results: After adjusting for confounding factors, respiratory diseases increased the risk of falls by 21% (HR=1.21, 95%CI:1.02-1.45), and arthritis increased the risk of falls by 27% (HR=1.27,95%CI: 1.12-1.43) in the group aged 45-59, kidney disease increased the risk of falls by 26% (HR=1.26, 95%CI: 1.03-1.53) in the group aged 60 and above. A linear dose-response relationship between the number of chronic diseases and fall risk (χ2=133.61, P<0.001) was found in all the age groups. The interaction between having chronic diseases and the factors of females (HR=1.64, 95%CI: 1.43-1.89), impaired activities of daily living (ADL) (HR=1.66, 95%CI: 1.39-1.99), and having a fall history (HR=2.58, 95%CI: 2.24-2.97) increased the risk of falls. Conclusions: There is a positive linear relationship between the number of chronic diseases and the fall risk among Chinese aged 45 and above. The female middle-aged and elderly patients with chronic diseases and the middle-aged and elderly patients with impaired ADL or a history of falls are the high-risk groups for falls that need to be focused on intervention. The window of fall injury prevention should be moved forward to the middle-aged stage in time.

[Association between sleep duration and cognitive impairment in Chinese people aged 65 years and older].

Objective: To explore the association between sleep duration and cognitive impairment in older adults in China. Methods: The data was from 2018 Chinese Longitudinal Healthy Longevity Survey (CLHLS). According to the Chinese version of Mini-mental State Examination (CMMSE), 7 111 subjects aged 65 and above were divided into cognitive impaired group and cognitive intact group. Multiple logistic regression analysis was conducted to investigate the association between sleep duration and the risk of cognitive impairment after adjusting the potential confounding factors. Result: The score of cognitive function showed an inverted U-shape distribution with sleep duration. After adjusting for demographic, socioeconomic factors, lifestyle and health status, the OR were 1.21(95%CI: 0.90-1.64) and 1.41(95%CI: 1.06-1.86) in groups that sleep 8 h and ≥9 h per day respectively, compared with sleep 7 h group. Trend test showed that the risk of cognitive impairment in the elderly increased with the extension of sleep duration, and there was a dose-response relationship (trend P=0.017), while no association was observed between short sleep duration (<7 h) and cognitive function. Conclusion: Longer sleep duration was found to be associated with higher risk of cognitive impairment in the Chinese aged 65 years and older.

Assembly of different isoforms of actin and tropomyosin into the skeletal tropomyosin-enriched microfilaments during differentiation of muscle cells in vitro.

We have used a monoclonal antibody (CL2) directed against striated muscle isoforms of tropomyosin to selectively isolate a class of microfilaments (skeletal tropomyosin-enriched microfilaments) from differentiating muscle cells. This class of microfilaments differed from the one (tropomyosin-enriched microfilaments) isolated from the same cells by a monoclonal antibody (LCK16) recognizing all isoforms of muscle and nonmuscle tropomyosin. In myoblasts, the skeletal tropomyosin-enriched microfilaments had a higher content of alpha-actin and phosphorylated isoforms of tropomyosin as compared with the tropomyosin-enriched microfilaments. Moreover, besides muscle isoforms of actin and tropomyosin, significant amounts of nonmuscle isoforms of actin and tropomyosin were found in the skeletal tropomyosin-enriched microfilaments of myoblasts and myotubes. These results suggest that different isoforms of actin and tropomyosin can assemble into the same set of microfilaments, presumably pre-existing microfilaments, to form the skeletal tropomyosin-enriched microfilaments, which will eventually become the thin filaments of myofibrils. Therefore, the skeletal tropomyosin-enriched microfilaments detected here may represent an intermediate class of microfilaments formed during thin filament maturation. Electron microscopic studies of the isolated microfilaments from myoblasts and myotubes showed periodic localization of tropomyosin molecules along the microfilaments. The tropomyosin periodicity in the microfilaments of myoblasts and myotubes was 35 and 37 nm, respectively, whereas the nonmuscle tropomyosin along chicken embryo fibroblast microfilaments had a 34-nm repeat.