A survey of oral biopsies in Brazilian pediatric patients.

This paper presents a review of 1018 oral biopsies in pediatric patients from the Oral Pathology Service, Minas Gerais Federal University, Brazil. The lesions were divided into ten main categories. The most common oral lesions in this study were follicular cyst in the maxillary anterior region, followed by inflammatory fibrous hyperplasia in the same region, and mucocele in the lower lip. Cysts of the jaws and oral soft tissues comprised 26.1 percent of total oral biopsies. The importance of these findings in oral diagnosis is discussed.

Cell cycle-associated proteins in melanotic neuroectodermal tumor of infancy.

OBJECTIVE: The purpose of the present study was to compare the immunohistochemical expression of cell cycle-associated proteins in neuroblastic and melanocytic cell populations of melanotic neuroectodermal tumor of infancy. STUDY DESIGN: Three cases of melanotic neuroectodermal tumor of infancy were selected. The immunohistochemical expression of MDM-2, p53, proliferating cell nuclear antigen, cyclin D1, and cyclin A was assessed through use of the streptavidin-biotin-peroxidase complex technique. RESULTS: Positive immunostaining for MDM-2, proliferating cell nuclear antigen, cyclin D1, and cyclin A was occasionally observed in the large melanin-containing epithelioid cells. CONCLUSIONS: These data suggest that MDM-2 expression may be important for the development of melanotic neuroectodermal tumor of infancy and that the melanocytic cell population, not the neuroblastic one, is the proliferative component of the tumor.

Macrophages enhance muscle satellite cell proliferation and delay their differentiation.

This study investigated the effect of macrophages on in vitro satellite cell myogenesis in the turkey and mouse. Macrophages are considered to act as scavengers of tissue debris during the muscle degeneration-regeneration process. The number of dividing cells and of myoblasts expressing the myogenic regulatory factor MyoD indicated that macrophages enhanced satellite cell proliferation in both species. This was confirmed by observations with cultures treated for bromodeoxyuridine (BrdU) incorporation. In mouse and turkey macrophage-satellite cell cocultures, the number of differentiated myoblasts, the frequency of myogenin-positive cells, and the expression of developmental myosin isoforms were reduced as compared with control cultures, indicating that macrophages delayed satellite cell differentiation. The possibility that macrophages facilitate muscle fiber reconstitution by enhancing satellite cell proliferation should be taken into consideration in designing future strategies of satellite cell transplantation as a treatment for muscular dystrophies.

Normal myoblast implantation in MDX mice prevents muscle damage by exercise.

One consequence of the lack of dystrophin is a higher vulnerability of myofibers to eccentric exercise. In this study, we compared the effect of downhill running on Biceps brachii of MDX mice with or without transplantation of normal myoblasts. Exercise induced damaged was detected by Evans blue staining. In control MDX mice, 26.3% of the fibers were permeated by this dye, myoblast transplantation prevented such necrosis. In the transplanted muscles, only dystrophin negative fibers were injured. Indeed, in muscles containing at least 40% dystrophin positive fibers, the damage was significantly reduced in the grafted muscle. Thus the transplantation of normal myoblasts increases the resistance of dystrophic muscles to exercise. Our results suggest that transplantation of normal myoblasts to DMD patients may have beneficial effects.

Transplantation of dermal fibroblasts expressing MyoD1 in mouse muscles.

Transplantation of normal myoblasts into dystrophic muscles is a potential treatment for Duchenne muscular dystrophy (DMD). However, the success of such grafts is limited by the immune system responses. To avoid rejection problems, autologous transplantation of the patient's corrected myoblasts has been proposed. Regretfully, the low proliferative capacity of DMD myoblasts in culture (due to their premature senescence) limits such procedure. On the other hand, modification of dermal fibroblasts leading to the myogenic pathway using a master regulatory gene for myogenesis is an interesting alternative approach. In this study, the retrovirally encoded MyoD1 cDNA was introduced in dermal fibroblasts of TnI LacZ mice to provoke their conversion into myoblast-like cells. In vitro and in vivo assays were done and the results were compared to those obtained with uninfected fibroblasts and myoblasts. Some MyoD1-expressing fibroblasts were able to fuse and to express beta-galactosidase (under the transcriptional control of the Troponin I promoter), dystrophin and desmin in vitro. Thirty days following implantation of these modified fibroblasts in muscles of mdx mice, an average of 7 beta-Gal+/Dys-muscle fibers were observed. No beta-Gal+ fibers were observed after the transplantation of uninfected fibroblasts. Our results indicate that the successful implantation of myoblasts obtained from genetically modified fibroblasts is indeed feasible. However, the in vitro conversion rate and the in vivo fusion of genetically modified fibroblasts must be largely increased to consider this approach as a potential therapy for DMD and other myopathies.

Comparative analysis of satellite cell properties in heavy- and lightweight strains of turkey.

The growth of muscle during postnatal development results partly from the proliferation of satellite cells and their fusion with muscle fibres. We analysed the properties of satellite cells in a heavyweight (HW) turkey strain characterized by high body weight and a fast growth rate, and in a lightweight farm strain (LW) characterized by low body weight and a slow growth rate. Satellite cell activation was then examined in stretched-overloaded anterior latissimus dorsi (ALD) muscle by weighting one wing in young turkeys from both strains. As early as day 1 of stretching for HW and day 2 for LW, small embryonic-like fibres expressing ventricular cardiac myosin heavy chain (MHC) isoform were observed. Following four days of stretching, the number of nascent fibres had increased in both strains but was significantly greater in HW than LW ALD muscle. The proliferation and differentiation capacities of satellite cells from HW and LW strains were investigated in culture. As judged by in vitro measurements of 3H-thymidine incorporation and DNA content, satellite cells of HW turkey exhibited a greater proliferative capability than those of LW turkey. No differences in the temporal appearance of muscle markers (desmin, MHC isoforms) were noted in vitro between the two strains. These data confirm our in vivo observations indicating that selection based on growth rate does not modify muscle fibre maturation. Our in vivo and in vitro observations suggest that variations in the postnatal muscle growth pattern between HW and LW strains may be related to a difference in the capacity of their satellite cells to proliferate.

Anti-inflammatory effect of transforming growth factor-beta1 in myoblast transplantation.

BACKGROUND: The inflammatory reaction that occurs during the 5 days after transplantation led at 3 days to the death of 70% of injected myoblasts. Use of anti-inflammatory agents appeared to be a possible way to increase myoblast survival. The application of gene transfer techniques to cell transplantation offers the potential for the prevention of inflammatory reaction. METHODS: In this study, transforming growth factor-beta1 (TGF-beta1) gene was introduced in myoblasts with a retroviral vector to permit the secretion of this anti-inflammatory cytokine. Survival of (1) infected myoblasts expressing TGF-beta1 or (2) normal myoblasts transplanted with genetically modified cloned myoblasts was compared with survival of normal myoblasts. RESULTS: Expression of TGF-beta1 by myoblasts or by cotransplanted cells decreased myoblast mortality after 3 days by roughly 20% (66.0+/-3.0% in control vs. 46.3+/-4.2% and 46.2+/-5.9%). The increase of myoblast survival by TGF-beta1 expression was correlated with a lower polymorphonuclear cell and macrophage infiltration in muscles compared with control. In addition, cytotoxicity of neutrophils against myoblasts was assayed in vitro. The oxidation of myoblasts by activated neutrophils was decreased after infection of the myoblasts with the TGF-beta1 retroviral vector. CONCLUSIONS: These data demonstrate that the insertion of TGF-beta1 decreases inflammatory reaction observed after myoblast transplantation and thus prolongs their survival.

Neural tube can induce fast myosin heavy chain isoform expression during embryonic development.

We investigated the role of the neural tube in muscle cell differentiation in developing somitic myotome of chick embryo, particularly through fast myosin heavy chain (MHC) isoform expression. An embryonic fast MHC labeled with EB165 mAb was expressed in somitic cells from stage 15 of Hamburger and Hamilton (H.H.) (24 somites). Moreover, a distinct early embryonic fast MHC was expressed only from stage 15 of H.H. to stage 36 (E10). Like neonatal MHC, this isoform was labeled with 2E9 mAb but differed in its immunopeptide mapping. Expression of EB165-labeled embryonic fast MHC occurred in somitic myotomes deprived of neural tube influence by in ovo ablation as well as in somite explants cultured alone in vitro. Conversely, ablation of the neural tube prevented somitic expression of MHC labeled with 2E9 mAb. The neural tube induced in vitro expression of this MHC in explants of somites which failed to express it when cultured alone. These results indicate that signals emanating from the neural tube are required for the expression of early embryonic fast MHC isoform in developing somitic myotome.

Comparison of postnatal development of anterior latissimus dorsi (ALD) muscle in heavy- and light-weight strains of turkey (Meleagris gallopavo).

ALD muscle development was studied from day 2 to week 15 in males of two turkey strains. At 15 weeks, the heavy-weight (HW) strain weighted 2.2 times as much as the light-weight strain (LW). Morphometric and immunocytochemical analysis showed the presence of small fibers in HW ALD muscle which simultaneously accumulated ventricular and embryonic fast myosin heavy chain isoforms. The appearance of these nascent myofibers suggests that hyperplasia contributes to the growth of HW ALD muscle.