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BACKGROUND AND AIM: The BRCA 1 and BRCA 2 genes are associated with an inherited susceptibility to breast cancer with a cumulative risk of 60% in BRCA 1 mutation carriers and of 30% in BRCA 2 mutation carriers. Several lifestyle factors could play a role in determining an individual's risk of breast cancer. Obesity, changes in body size or unhealthy lifestyle habits such as smoking, alcohol consumption and physical inactivity have been evaluated as possible determinants of breast cancer risk. The aim of this study was to explore the current understanding of the role of harmful lifestyle and obesity or weight change in the development of breast cancer in female carriers of BRCA 1/2 mutations. METHODS: Articles were identified from MEDLINE in October 2020 utilizing related keywords; they were then read and notes, study participants, measures, data analysis and results were used to write this review. RESULTS: Studies with very large case series have been carried out but only few of them have shown consistent results. Additional research would be beneficial to better determine the actual role and impact of such factors.
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Healing of open wounds is of great medical importance. Wound healing is a complex process that aims to restore the function and structure of damaged tissue. This study was conducted to compare secondary intention healing of wounds treated daily with a topical application of commercially available hyaluronic acid (HA), Manuka honey (MH), Acemannan gel (AG), or a placebo. Bilateral wounds were surgically created on the backs of six sheep. At two and six weeks post-wound creation, biopsies were obtained to perform histological, immunohistochemical, and molecular analyses of the wound site. Daily clinical evaluations were performed and weekly photographs were taken of the wounds. HA treatment promoted a physiological progression of the healing process in all wound healing phases, while stimulating an abundant cutaneous adnexa and promoting rapid healing, representing the most compelling treatment. MH-treated wounds were slightly dry. However, the main effect of MH was to promote cell proliferation and neovascularization, with an overall pro-inflammatory effect. Results suggest that MH treatment enhances the healing process. AG treatment dehydrated the wounds and stimulated late granulation tissue and cell proliferation. Moreover, AG-treated wounds produced a mild late pro-inflammatory and neovascularization effect. Our data indicate that AG treatment can have a positive influence on moist wounds with abundant granulation tissue and exudate.
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Miel , Ácido Hialurónico/farmacología , Mananos/farmacología , Enfermedades de las Ovejas/prevención & control , Enfermedades de la Piel/veterinaria , Cicatrización de Heridas/efectos de los fármacos , Animales , Geles , Ovinos , Piel/patología , Enfermedades de la Piel/prevención & control , Cicatrización de Heridas/fisiologíaRESUMEN
BACKGROUND: Delivering widespread BRCA testing to patients with ovarian cancer has been suggested by several scientists, recommended by professional societies and solicited by patients organizations. However, based on the lack of studies clearly demonstrating the cost-effectiveness of such approach compared to standard practice, we evaluated the possibility to better select subgroups of ovarian cancer (OC) patients with higher probability to be a BRCA mutation carrier'. METHODS: We analyzed the database of 2222 germline BRCA analyses from OC patients recently published by Song et al. (Song 2014) by applying multivariate and conditional inference regression tree-analyses. RESULTS: Overall, 178/2192 (8.1%) evaluable OC women showed pathogenic germline mutations in BRCA genes (84 BRCA1;94 BRCA2). BRCA mutations resulted significantly more frequent in Epithelial tumors (10.7%), less differentiated tumours (11.0%) and younger subjects (13.4%). Regression tree analysis permitted to individualize a subset of 66% OC patients with particularly low risk (3.5%) to carry a BRCA mutation vs a subgroup (24% of the series), with a probability higher than 17% to carry a pathogenic mutation. Younger age, OC and Breast Cancer family history were confirmed powerful factors in selecting subgroups of patients with significantly different BRCA mutation probability. CONCLUSIONS: Our regression tree-analysis can represent an innovative approach taking into consideration all main clinical pathological information to select OC patients to be candidated for BRCA test.
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Genes BRCA1 , Genes BRCA2 , Pruebas Genéticas/estadística & datos numéricos , Mutación de Línea Germinal/genética , Neoplasias Ováricas/genética , Biomarcadores de Tumor/genética , Bases de Datos Factuales , Femenino , Humanos , Neoplasias Ováricas/patología , Selección de Paciente , Guías de Práctica Clínica como Asunto , Factores de RiesgoRESUMEN
The rapid involution that happens in some muscles of ungulate fetlock joints has never been investigated at an ultrastructural level. In this study, the proximal sesamoidean ligament (PSL) of sheep was chosen as a model to investigate, at the cellular level, the transition from muscle to connective structures that occurs during early development. In particular, we were interested in observing the presence of satellite cells and fibroblasts, detecting fluctuations in their numbers in the postnatal developing PSL, and evaluating putative apoptotic mechanisms. Interestingly, some features were shared by both PSL involution and muscle ageing; the most relevant being the significant and rapid decrease in the number of satellite cells together with a quick proliferation of fibroblasts in the muscle-connective transitional area (MCT-TA). Electron microscopy and immunohistochemical analyses revealed putative cellular mechanisms that led to a progressive involution of the muscle portion of the PSL during postnatal growth. Our findings showed a fast transition from muscle to connective tissue due to the depletion of satellite cells, apoptosis of some muscle fibres, and simultaneous proliferation of fibroblasts originating from mesenchymal progenitors or from differentiation of satellite cells typically located at the border between muscle and connective tissue of the PSL.
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Fibroblastos/fisiología , Ligamentos/crecimiento & desarrollo , Mioblastos/fisiología , Oveja Doméstica/crecimiento & desarrollo , Animales , Proliferación Celular , Ligamentos/ultraestructura , Microscopía Electrónica de Transmisión/veterinaria , Huesos SesamoideosRESUMEN
BACKGROUND: Skin wound healing includes a system of biological processes, collectively restoring the integrity of the skin after injury. Healing by second intention refers to repair of large and deep wounds where the tissue edges cannot be approximated and substantial scarring is often observed. The objective of this study was to evaluate the effects of mesenchymal stem cells (MSCs) in second intention healing using a surgical wound model in sheep. MSCs are known to contribute to the inflammatory, proliferative, and remodeling phases of the skin regeneration process in rodent models, but data are lacking for large animal models. This study used three different approaches (clinical, histopathological, and molecular analysis) to assess the putative action of allogeneic MSCs at 15 and 42 days after lesion creation. RESULTS: At 15 days post-lesion, the wounds treated with MSCs showed a higher degree of wound closure, a higher percentage of re-epithelialization, proliferation, neovascularization and increased contraction in comparison to a control group. At 42 days, the wounds treated with MSCs had more mature and denser cutaneous adnexa compared to the control group. The MSCs-treated group showed an absence of inflammation and expression of CD3+ and CD20+. Moreover, the mRNA expression of hair-keratine (hKER) was observed in the MSCs-treated group 15 days after wound creation and had increased significantly by 42 days post-wound creation. Collagen1 gene (Col1α1) expression was also greater in the MSCs-treated group compared to the control group at both days 15 and 42. CONCLUSION: Peripheral blood-derived MSCs may improve the quality of wound healing both for superficial injuries and deep lesions. MSCs did not induce an inflammatory response and accelerated the appearance of granulation tissue, neovascularization, structural proteins, and skin adnexa.
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Trasplante de Células Madre Mesenquimatosas/veterinaria , Piel/lesiones , Cicatrización de Heridas , Animales , Femenino , Reacción en Cadena en Tiempo Real de la Polimerasa/veterinaria , Ovinos , Piel/patologíaRESUMEN
The existence of progenitor cells that can readily differentiate into a specific cell type is a common cellular strategy for physiological tissue growth and repair mechanisms. In the mammalian cornea, many aspects regarding the nature and location of these cells are still unclear. In the human limbus (peripheral area of the cornea) progenitor cells have been found and characterized but in non-human mammals, the picture is not so clear. In this review, we examine current knowledge about the morphology of limbus and the localization of corneal epithelial stem cells in all species studied so far, comparing data with humans. We have also explored different research directions in the veterinary field in order to discuss the: i) currently used protocols and ii) best range of treatments for ocular pathologies in which corneal stem cells are involved.
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Epitelio Corneal/citología , Células Madre , Animales , Células Epiteliales , Humanos , Limbo de la CórneaRESUMEN
The cornea provides protection and transparency to the eye, allowing an optimal sharpness view. In some pathological conditions the cornea is able to regenerate thanks to the presence of a stem cells reservoir present at the level of the transition area between cornea and sclera (limbus). Corneal cell therapies in Veterinary Medicine are really limited due to the lacking of knowledge about the anatomy of the limbal area, the putative presence of stem cells and their identification in domestic species. The aim of this study was to provide an overview of the main distinctive structural features of the sclero-corneal junction and conjunctival-corneal junction areas in some species of veterinary importance, using optic microscope observations of histological sections. The resulting data were compared with cornea from humans adapting protocols already used to identify stem cells by means of a specific cellular marker. We tested the expression of ΔNp63α isoform in the cornea basal cells, trying to correlate the distribution profile with areas of highly proliferative turnover. The results obtained from this study represent a first step towards the identification of a corneal stem cells reservoir in different animals.
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Gatos/anatomía & histología , Bovinos/anatomía & histología , Perros/anatomía & histología , Endotelio Corneal/anatomía & histología , Caballos/anatomía & histología , Esclerótica/anatomía & histología , Ovinos/anatomía & histología , Células Madre/citología , Porcinos/anatomía & histología , Animales , Endotelio Corneal/citología , Células Epiteliales , Epitelio/anatomía & histología , Esclerótica/citologíaAsunto(s)
Enfermedades de los Gatos/diagnóstico , Bocio/veterinaria , Hipotiroidismo/veterinaria , Animales , Enfermedades de los Gatos/patología , Gatos , Bocio/diagnóstico , Bocio/patología , Hipotiroidismo/diagnóstico , Hipotiroidismo/patología , Masculino , Glándula Tiroides/diagnóstico por imagen , Glándula Tiroides/patología , Tomografía Computarizada por Rayos X/veterinariaRESUMEN
The use of Mesenchymal Stromal Cells (MSCs) in orthopedic practice has recently and rapidly acquired an important role. Therapies based on the use of MSCs for the treatment of acute injuries as well as chronic inflammatory disorders are gradually becoming clinical routine. These cells have demonstrated intriguing therapeutic potentialities (i.e.: inflammation control, tissue regeneration and pathological scar prevention), that have been taken into consideration for use in both human and veterinary medicine. In particular, horses represent high performance athletes considered models for human pathologies since musculo-skeletal disorders frequently occur in this species. In the past, repair of tendon injures were performed by different methods. In particular, clinical therapy was based on ice application, bandage, box rest and controlled exercise. An alternative approach consisted on the use of corticosteroid (inflammation reduction) and other drugs (sodium hyaluronate, polysulphated glycosaminoglycans, beta aminoproprionitrile fumarate). Furthermore, surgical treatments like accessory ligament desmotomy, local irritation by line firing or pin firing were commonly used. More recently ultrasound, laser therapy, electromagnetic field therapy have been considered. Unfortunately, they did not allow complete tissue healing and quite often animals did not regain competitiveness. In order to minimize this inconvenience, the use of MSCs has been introduced as an alternative to the traditional approach since it represents a potential tool to improve tissue regeneration. Aim of this study was to evaluate the capability of MSCs to improve the functional outcome of horses affected by tendonitis and desmitis. Thirty-three breed and activity-matched horses affected by tendonitis or desmitis, were included in clinical trial scored for lesions and subdivided into two groups. Group 1 animals were treated with autologous MSCs, associated with platelet rich plasma (group 1). Bone marrow samples were collected from the sternum of the treated horses and processed in order to isolate MSCs. Following cell therapy, they were subjected to a rehabilitation period and their ability to resume training was evaluated. In this study, implanted MSCs caused no adverse reactions and thirteen out of the eighteen inoculated horses returned to race competitions. On the contrary, no improvement was seen in the twelve animals of group 2 treated with pin firing, that were not able to resume sport activity. In conclusion the clinical trial proves the safety of equine bone-marrow derived MSCs and a successful outcome of the treated animals that returned to their previous level of sport activity.
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Enfermedades de los Caballos/cirugía , Trasplante de Células Madre Mesenquimatosas/veterinaria , Células Madre Mesenquimatosas/citología , Tendinopatía/veterinaria , Animales , Diferenciación Celular/fisiología , Enfermedades de los Caballos/patología , Caballos , Masculino , Trasplante de Células Madre Mesenquimatosas/métodos , Medicina Regenerativa/métodos , Tendinopatía/cirugíaRESUMEN
Cell-based therapies, such as the use of mesenchymal stromal cells (MSCs), are becoming popular in veterinary medicine. When MSCs are not cryopreserved, they are shipped in suspension, but no previous studies have analyzed MSC viability during delivery. Here, the impact of several experimental shipping conditions on the number of equine blood-derived (ePB-MSC) and canine adipose-derived (cA-MSC) MSCs were evaluated. Among the different parameters tested, only time and temperature influenced MSC number during the experimental shipping conditions. Cells were monitored over different time intervals for gene expression of typical MSC markers and to evaluate acquired resistance to apoptosis and beta-galactosidase activity. Overall, these results indicate that ePB-MSC and cA-MSC should be delivered in phosphate buffered saline at room temperature and within 9-12 h.
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Medios de Cultivo/química , Células Madre Mesenquimatosas/fisiología , Manejo de Especímenes/veterinaria , Animales , Supervivencia Celular , Medios de Cultivo/farmacología , Perros , Regulación de la Expresión Génica , Caballos , Células Madre Mesenquimatosas/efectos de los fármacos , Reacción en Cadena en Tiempo Real de la Polimerasa , Manejo de Especímenes/métodos , Temperatura , Factores de TiempoRESUMEN
Histidine-rich calcium binding protein (HRC) is a high capacity, low affinity Ca(2+) binding protein, specifically expressed in striated muscles of mammals. In rabbit skeletal and cardiac muscles, HRC binds to sarcoplasmic reticulum (SR) membranes via triadin, a junctional SR protein. Recently, a potential role in heart failure and arrhythmogenesis has been assigned to HRC due to its activity as regulator of SR Ca(2+) uptake and Ca(2+) release. HRC might play a particularly relevant role in the equine heart, given its slower resting heart rate (20-35 beats/min) and longer action potential duration (APD) (0.6-1.0 s) than are found in other mammals. The results from this study showed for the first time direct evidence that HRC protein in equine cardiac muscle was expressed in association with the SR membranes and that HRC transcriptional activity was three times higher in the ventricles compared to the atria. The predominance of HRC mRNA up-regulation in ventricular myocardium was specific to the horse heart, since a more even distribution between atria and ventricles was found in animals of similar body size or species, such as cattle or domestic donkeys.
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Proteínas de Unión al Calcio/metabolismo , Caballos/fisiología , Miocardio/metabolismo , Proteínas/metabolismo , Potenciales de Acción , Animales , Calcio/metabolismo , Bovinos/fisiología , Equidae/fisiología , Atrios Cardíacos/metabolismo , Ventrículos Cardíacos/metabolismo , Contracción Miocárdica , ARN Mensajero/metabolismo , Reacción en Cadena en Tiempo Real de la Polimerasa , Retículo Sarcoplasmático/metabolismo , Alineación de Secuencia , Análisis de Secuencia de Proteína , Factores de TiempoRESUMEN
Adult stem cells are nowadays used for treating several pathologies. A putative stem cell population was found in the adipose tissue of mammals and canine adipose tissue-derived-mesenchymal stem cells (cA-MSC) have been shown to possess the capacity to differentiate into several lineages. The main goal of our research was to fully characterize cA-MSC and examine the effects of cryopreservation on their stemness features. Each sample of cA-MSC was analyzed immediately and then again after being frozen in liquid nitrogen for one year. After the cryopreservation period cells conserved their fibroblast-like morphology, alkaline phosphatase positivity and CD expression but showed a lower proliferation ratio and a lower telomerase activity in comparison with fresh cells. Finally, the cryopreservation protocol did not change the cA-MSC adipogenic, osteogenic and myogenic differentiative potential. Our data demonstrate that stored cA-MSC might represent a promising type of progenitor cell for autologous cellular-based therapies in veterinary medicine.
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Tejido Adiposo/citología , Criopreservación/veterinaria , Células Madre Mesenquimatosas/fisiología , Fosfatasa Alcalina/metabolismo , Animales , Antígenos de Superficie/metabolismo , Técnicas de Cultivo de Célula/veterinaria , Diferenciación Celular , Perros , Femenino , Citometría de Flujo/veterinaria , Células Madre Mesenquimatosas/citología , Células Madre Mesenquimatosas/metabolismo , Reacción en Cadena de la Polimerasa/veterinaria , Análisis de Secuencia de ARN/veterinaria , Telomerasa/metabolismoAsunto(s)
Calcio/metabolismo , Miocitos Cardíacos/metabolismo , Animales , Proteínas de Unión al Calcio/genética , Citoplasma/metabolismo , Ventrículos Cardíacos/citología , Ventrículos Cardíacos/metabolismo , Homeostasis , Caballos/metabolismo , Contracción Miocárdica/fisiología , Reacción en Cadena de la Polimerasa , Canal Liberador de Calcio Receptor de Rianodina/fisiología , Sarcolema/metabolismo , Retículo Sarcoplasmático/metabolismoRESUMEN
Skeletal muscles not only obey carefully all motor commands received via motor nerves from nervous system, but also are ready to modify their structure and function to be more suited to the tasks assigned by nervous system. Thus, nervous system appears as the major modulator of the muscle structure and function. Other factors, however, may interfere with the nerve-muscle partnership and among them, hypoxia plays a pivotal role because skeletal muscles exhibit a great variability of the oxygen fluxes and because hypoxia per se has a powerful influence on muscle fibers. The adaptation of skeletal muscles to nerve-induced activity is particularly evident with low frequency tonic patterns and examples are given by chronic low frequency stimulation and by endurance training. Adaptation includes fiber type transitions towards a slow-oxidative phenotype, increased mitochondrial density and increased capillary/fiber ratio. Hypoxia can trigger some of such changes and this has suggested that low oxygen tension at fiber level might be a mediator, possibly based on HIF and VEGF, of the muscle adaptation to increased contractile activity. Chronic hypoxia can, however, induce opposite modifications, such as a fiber type transition from slow-oxidative to fast-glycolytic and mitochondrial loss. In such conditions, the increased contractile activity can antagonize hypoxia effects. Thus, hypoxia can play a double role in the nerve-muscle relationship, either reinforcing the nerve influence or antagonizing it. This short review aims to re-examine the ambiguous relationships between nerve-induced contractile activity and hypoxic conditions and to suggest possible interpretations of the double role played by hypoxia.
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Hipoxia/patología , Músculo Esquelético/fisiopatología , Sistema Nervioso/fisiopatología , Adaptación Fisiológica , Animales , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Humanos , Oxígeno/administración & dosificación , Factor A de Crecimiento Endotelial Vascular/genética , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
The paired box domain gene Pax7 plays a pivotal role in satellite cell physiology and may represent one of the candidate genes influencing the dynamic stages of early post-natal growth observed in pig. Quiescent satellite cells express Pax7 and, when activated, they co-express the myogenic bHLH protein MyoD. The aims of this study were to investigate, by immunohistochemistry, the putative differential expression of Pax7 and to ascertain the amount of activated satellite cells (Pax7(+)/MyoD(+)) in myogenic cells isolated at different post-natal time points and in adults. Our results indicate that Pax7(+) cells represent between 10 and 15% of the whole myogenic cell population found at birth indicating that these cells provide a modest contribution to the development of new fibres. The number of activated satellite cells (Pax7(+)/MyoD(+)) was scarce after birth but it was higher respect to adults. An interesting result was that at 1 month after birth the number of Pax7(+) cells had increased within the pool of myogenic cells with respect to myogenic cells extracted at birth. We speculate that Pax7 might be one of the molecules involved in controlling the proliferation/differentiation ratio in the pool of satellite cells present in post-natal porcine skeletal muscles.
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Músculo Esquelético/metabolismo , Factor de Transcripción PAX7/metabolismo , Células Satélite del Músculo Esquelético/metabolismo , Sus scrofa/crecimiento & desarrollo , Animales , Diferenciación Celular , Proliferación Celular , Células Cultivadas , Inmunohistoquímica , Músculo Esquelético/crecimiento & desarrollo , Estructura Terciaria de Proteína , Células Satélite del Músculo Esquelético/citología , Sus scrofa/metabolismoRESUMEN
In mammals, glial cell line-derived neurotrophic factor (GDNF) is a growth factor of many neuronal populations in the central, peripheral and autonomous nervous system. GDNF may also function as a morphogen during kidney development and may regulate spermatogonial differentiation. GDNF has been characterised in zebrafish embryos and was demonstrated experimentally to be critical for the development of the enteric nervous system. However, in adult zebrafish, no data exist regarding GDNF expression and localisation in the brain and in different organs. Thus, the aim of the present study was to investigate the expression of GDNF in the brain of adult zebrafish (Danio rerio). Transcripts of GDNF mRNA were observed in brain extracts by a standard RT-PCR. The presence of the protein in the brain homogenates was confirmed by SDS-PAGE electrophoresis and Western blotting analysis. Immunohistochemistry and in situ hybridization experiments showed that GDNF protein and mRNA were localised in various nuclei of the telencephalon, diencephalon, mesencephalon, cerebellum and medulla oblongata of the zebrafish brain. In conclusion, this study showed that the expression of GDNF was not restricted to developmental periods but it seems that this factor might be involved in adult zebrafish brain physiology, as observed in mammals.
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Encéfalo/metabolismo , Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Pez Cebra/metabolismo , Animales , Diencéfalo/citología , Diencéfalo/metabolismo , Femenino , Masculino , Mesencéfalo/citología , Mesencéfalo/metabolismo , Modelos Animales , Regeneración Nerviosa/fisiología , Neuronas/citología , Neuronas/metabolismo , Rombencéfalo/citología , Rombencéfalo/metabolismo , Telencéfalo/citología , Telencéfalo/metabolismoRESUMEN
In aquaculture, fish are exposed to stressful conditions, which cause an increased synthesis of heat shock proteins (HSPs) at the cellular level. In this work we considered the expression of the constitutive and inducible forms of HSP70 as an indicator of stress caused by transport, during development of the sea bass (Dicentrarchus labrax), a teleost fish of high value for aquaculture. Qualitative RT-PCR analysis revealed expression of inducible HSP70 gene in larvae and fry (25, 40 and 80 days) as well as in adult tissues (liver, brain, muscle, gills, kidney, gonads, heart, spleen and skin) of both control and stressed animals. Expression of inducible HSP70 mRNA examined in different adult tissues by Real-Time PCR, was significantly higher in skin and skeletal muscle of stressed animals than in controls. Immunolocalization of inducible and constitutive forms of heat shock protein 70 (HSP70 and HSC70), reported here for the first time, demonstrated an ubiquitous distribution of HSC70 protein in several tissues of both stressed and control animals (at all stages), while inducible HSP70 protein was found only in skeletal muscle of stressed animals. In all stressed animals, regardless of their developmental stage, cortisol levels were higher than in control animals.
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Lubina/genética , Lubina/metabolismo , Proteínas HSP70 de Choque Térmico/genética , Proteínas HSP70 de Choque Térmico/metabolismo , Animales , Secuencia de Bases , Lubina/crecimiento & desarrollo , Cartilla de ADN/genética , Proteínas del Choque Térmico HSC70/metabolismo , Hidrocortisona/sangre , Inmunohistoquímica , Larva/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Estrés Fisiológico/genética , Estrés Fisiológico/metabolismo , Distribución TisularRESUMEN
This study aimed to analyse the expression of myosin heavy chain (MHC) isoforms in bovine muscles, with particular attention to the MHC-2B gene. Diaphragm, longissimus dorsi, masseter, several laryngeal muscles and two extraocular muscles (rectus lateralis and retractor bulbi) were sampled in adult male Bos taurus (age 18-24 months, mass 400-500 kg) and analysed by RT-PCR, gel electrophoresis and immunohistochemistry. Transcripts and proteins corresponding to eight MHC isoforms were identified: MHC-alpha and MHC-beta/slow (or MHC-1), two developmental isoforms (MHC-embryonic and MHC-neonatal), three adult fast isoforms (MHC-2A, MHC-2X and MHC-2B) and the extraocular isoform MHC-Eo. All eight MHC isoforms were found to be co-expressed in extrinsic eye muscles, retractor bulbi and rectus lateralis, four (beta/slow, 2A, 2X, neonatal) in laryngeal muscles, three (beta/slow, 2A and 2X) in trunk and limb muscles and two (beta/slow and alpha) in masseter. The expression of MHC-2B and MHC-Eo was restricted to extraocular muscles. Developmental MHC isoforms (neonatal and embryonic) were only found in specialized muscles in the larynx and in the eye. MHC-alpha was only found in extraocular and masseter muscle. Single fibres dissected from masseter, diaphragm and longissimus were classified into five groups (expressing, respectively, beta/slow, alpha, slow and 2A, 2A and 2X) on the basis of MHC isoform electrophoretical separation, and their contractile properties [maximum shortening velocity (v(0)) and isometric tension (P(0))] were determined. v(0) increased progressively from slow to fast 2A and fast 2X, whereas hybrid 1-2A fibres and fibres containing MHC-alpha were intermediate between slow and fast 2A.