Le muscle strié squelettique est un tissu richement vascularisé. Au delà de l'apport en oxygène et en nutriments, de nouvelles fonctions des vaisseaux ont été récemment identifiées, par le biais des interactions établies entre les cellules du vaisseau (cellules endothéliales) et les cellules du muscle, en particulier les cellules souches musculaires (cellules satellites). Celles-ci interagissent étroitement avec les cellules endothéliales pour leur expansion et leur différenciation, puis avec les cellules péri-endothéliales pour leur auto-renouvellement et leur retour à la quiescence. Les vaisseaux participent ainsi au contrôle de l’homéostasie du muscle squelettique. Grâce à ces interactions, les cellules vasculaires jouent donc un rôle central dans le remodelage tissulaire après un phénomène destructif, survenant par exemple au cours d’un trauma ou d’une myopathie. Pour étudier, les mécanismes de la plasticité vasculaire au cours du remodelage tissulaire, deux situations paradigmatiques de muscle en régénération chez l’enfant : la dermatomyosite juvénile (DMJ) et la dystrophie musculaire de Duchenne (DMD) ont été étudiées. Il existe, dans ces deux pathologies une souffrance musculaire associée à des cycles de nécrose/régénération. Elles se différencient par leur plasticité vasculaire et par leur évolution. En effet, la DMJ, la myopathie inflammatoire la plus fréquente de l’enfant est caractérisée par une vasculopathie avec perte en capillaires. L’évolution peut être favorable avec restitution ad integrum du muscle. La DMD est une myopathie génétique conduisant à une dégradation progressive de la force musculaire associée à une néovascularisation compensatrice. Le volet clinique/histologique incluant une analyse multiparamétrique des critères évolutifs cliniques et de réponse thérapeutique couplée à une réévaluation des données histologiques de la DMJ (analyse morphométrique des muscles DMJ) a permis de montrer qu’il existait des sous groupes phénotypiques homogènes de sévérité différente dans la DMJ. Le degré de sévérité clinique est relié à la gravité de la vasculopathie musculaire Par ailleurs, des marqueurs cliniques et histologiques simples permettant de repérer au diagnostic les patients nécessitant une escalade thérapeutique rapide (CMAS>34, atteinte gastrointestinale, fibrose endomysiale musculaire au diagnostic) ont été identifiés. Le volet cellulaire a permis l’identification in vitro des interactions cellulaires spécifiques et différentielles des myoblastes issues de patients DMD et DMJ sur les cellules endothéliales normales par l’analyse de leur rôle sur la prolifération, migration et différenciation des cellules vasculaires. Dans la DMD, les myoblastes entrainent une réponse angiogénique importante mais non efficace (néovascularisation anarchique). Dans la DMJ, les myoblastes participent efficacement à la reconstruction vasculaire notamment via la sécrétion de facteurs proangiogéniques. Ces résultats ont été renforcés par analyse transcriptomique effectuée à partir de cellules endothéliales et satellites isolées de muscles de patients confirmant le rôle central de la vasculopathie associée à un contexte inflammatoire spécifique lié à l’interféron dans la physiopathologie de la DMJ et montrant dans la DMD une dérégulation de l’homéostasie normale des interactions vaisseau-muscle avec mise en jeu d’un remodelage tissulaire non efficace. Ces données permettent d'identifier de nouvelles fonctions des cellules vasculaires dans le remodelage du muscle strié squelettique au cours des pathologies musculaires de l'enfant, et devraient ouvrir la voie à de nouvelles approches thérapeutiques. / Skeletal muscle is highly vascularised. Beyond oxygen and nutriment supply, new functions for vessels have been recently identified, through the interactions that vessel cells (endothelial cells) establish with muscle cells, particularly with muscle stem cells (satellite cells). These latter closely interact with endothelial cells for their expansion and their differentiation, then with periendothelial cells for their self-renewal and return to quiescence. During skeletal muscle regeneration endothelial cells reciprocally interact with myogenic cells by direct contact or by releasing soluble factors to promote both myogenesis and angiogenesis processes. Skeletal muscle regeneration typically occurs as a result of a trauma or disease, such as congenital or myopathies. To better understand the role of vessel plasticity in tissue remodeling, we took advantage of two muscular disorders that could be considered as paradigmatic situations of regenerating skeletal muscle in the child: Juvenile Dermatomyositis (JDM), the most frequent inflammatory myopathy and Duchenne Muscular Dystrophy (DMD), the most common type of muscular dystrophy. Although these two muscular disorders share, at the tissue level, similar mechanisms of necrosis-inflammation, they differ regarding the vessel domain. In JDM patients, microvascular changes consist in a destruction of endothelial cells assessed by focal capillary loss. This capillary bed destruction is transient. The tissue remodeling is efficient and muscle may progressively recover its function. By contrast, in DMD, despite an increase of vessels density in an attempt to improve the muscle perfusion, the muscle function progressively alters with age. We identified clinical and pathological markers of severity and predictive factors for poor clinical outcome in JDM by computing a comprehensive initial and follow-up clinical data set with deltoid muscle biopsy alterations controlled by age-based analysis of the deltoid muscle capillarization. We demonstrated that JDM can be divided into two distinctive clinical subgroups. The severe clinical presentation and outcome are linked to vasculopathy. Furthermore, a set of simple predictors (CMAS<34, gastrointestinal involvement, muscle endomysial fibrosis at disease onset) allow early recognition of patients needing rapid therapeutic escalation with more potent drugs. We studied in vitro the specific cell interactions between myogenic cells issued from JDM and DMD patients and normal endothelial cells to explore whether myogenic cells participate to the vessel remodeling observed in the two pathologies. We demonstrated that MPCs possessed angiogenic properties depending on the pathological environment. In DMD, MPCs promoted the development of establishment of an anarchic, although strong, EC stimulation, leading to the formation of weakly functional vessels. In JDM, MPCs enhanced the vessel reconstruction via the secretion of proangiogenic factors. This functional analysis was supported by the transcriptomic analysis consistent with a central vasculopathy in JDM including a strong and specific response to an inflammatory environment. On the contrary, DMD cells presented an unbalanced homeostasis with deregulation of several processes including muscle and vessel development with attempts to recover neuromuscular system by MPCs. To summarize, our data should allow the definition of new functions of vessel cells in skeletal muscle remodelling during muscle pathologies of the child that will open the way to explore new therapeutic options and to gain further insights in the pathogenesis of these diseases.

L’atteinte de la fonction endothéliale représente une phase précoce de l’athérosclérose, un stade où les patients sont généralement asymptomatiques. Il existe donc un intérêt certain à détecter la dysfonction endothéliale. Nous avons développé une technique de mesure des variations de flot artériel au niveau des membres supérieurs, basée sur la spectroscopie proche infrarouge (NIRS). Cette approche permettrait d’étudier le niveau d’atteinte vasculaire et probablement de quantifier le degré de dysfonction endothéliale périphérique lors d’une hyperémie réactive. L'expérience a été exécutée sur deux cohortes de 13 et de 15 patients et a été comparée à la pléthysmographie par jauge de contrainte (SGP) qui est considérée comme une méthode de référence. Par la suite, nous avons caractérisé la réponse endothéliale par modélisation de la courbe hyperémique du flot artériel. Des études préliminaires avaient démontré que la réponse hyperémique adoptait majoritairement une forme bi-modale. Nous avons tenté de séparer les composantes endothéliales-dépendantes et endothéliales-indépendantes de l’hyperémie. La quantification des deux composantes de la réaction hyperémique permet de calculer un indice de la ‘santé’ du système endothélial local. Cet indice est nommé le ηfactor. Les résultats montrent une forte corrélation des mesures de flots entre la technique développée et la méthode de référence (r=0.91). Nous avons conclu que NIRS est une approche précise pour la mesure non-invasive du flot artériel. Nous avons obtenu une bonne répétabilité (ICC = 0.9313) pour le ηfactor indiquant sa robustesse. Cependant des études supplémentaires sont nécessaires pour valider la valeur de diagnostic du facteur défini. Mots clés: hyperémie réactive, réponse myogénique, oxyde nitrique, athérosclérose, spectroscopie proche infrarouge / Atherosclerotic diseases are mainly caused by coronary and peripheral blood vessel disorders. Endothelial dysfunction represents an early phase in these diseases, when patients are generally asymptomatic. We developed a technique, based on near infrared spectroscopy (NIRS), for measurement of arterial blood flow variations in limbs during reactive hyperemia. The technique allows the study of the level of vascular impairment and probably quantifying the level of endothelial dysfunction at peripheral arteries. The experiment was performed on two cohorts of 13 and 15 patients and was compared to strain gauge plethysmography (SGP) which is considered as gold standard. Afterward, we characterized endothelial reaction during reactive hyperemia through blood flow variations by modeling the hyperemic curve. Preliminary studies have shown that the hyperemic response generally adopts a bimodal form. The first peak was attributed to myogenic reaction that is endothelial independent and the second one to local endothelial cells reaction. The quantification of the two hyperemic response components makes it possible to calculate an index of ‘health’ for local endothelial cells, named ηfactor. The results showed a strong correlation (r = 0.91) of blood flow measurements between the developed method and the gold standard. We concluded that NIRS is a precise technique for non-invasive measurement of blood flow. Moreover, we found a high repeatability (ICC = 0.9313) of the ηfactor in repeated measurements indicating its robustness. Nonetheless, more studies are required to validate the diagnosis value of the defined factor. Key words: reactive hyperemia, myogenic response, endothelial dependent vasodilatation, nitric oxide, atherosclerosis, near infrared spectroscopy (NIRS)

Malfunction of the system which regulates the bloodflow in the brain is a major cause of stroke and dementia, costing many lives and many billions of pounds each year in the UK alone. This regulatory system, known as cerebral autoregulation, has been the subject of much experimental and mathematical investigation yet our understanding of it is still quite limited. One area in which our understanding is particularly lacking is that of the role of nitric oxide, understood to be a potent vasodilator. The interactions of nitric oxide with the better understood myogenic response remain un-modelled and poorly understood. In this thesis we present a novel model of the arteriolar control mechanism, comprising a mixture of well-established and new models of individual processes, brought together for the first time. We show that this model is capable of reproducing experimentally observed behaviour very closely and go on to investigate its stability in the context of the vasculature of the whole brain. In conclusion we find that nitric oxide, although it plays a central role in determining equilibrium vessel radius, is unimportant to the dynamics of the system and its responses to variation in arterial blood pressure. We also find that the stability of the system is very sensitive to the dynamics of Ca²⁺ within the muscle cell, and that self-sustaining Ca2+ waves are not necessary to cause whole-vessel radius oscillations consistent with vasomotion.

A insuficiência cardíaca (IC) é uma síndrome que cursa com sintomas como intolerância ao exercício e sinais como o edema periférico (EP). Prejuízo na constrição miogênica (CM) acarreta em aumento da pressão hidrostática capilar e EP. Sabendo dos efeitos benéficos do treinamento físico (TF) sobre o sistema cardiovascular na IC, hipotetizou-se que o TF aeróbio é eficaz em restaurar o prejuízo na CM em artérias tibiais caudais (ATC) e o EP induzido pela IC. A IC induziu aumento no volume da pata o qual foi revertido pelo TF. A CM em ATC foi atenuada nos ICs, e o TF restaurou a mesma por vias como ROCK e razão SERCA-2/Fosfolambano, aumentando à cinética e a sensibilidade ao Ca2+. O TF restaurou o aumento no diâmetro interno (Di) observado nas ATC dos IC. Conclui-se, que as ATCs de ratos com IC apresentam prejuízo da CM e remodelamento eutrófico para fora os quais foram restaurados pelo TF. Os ajustes na CM induzidos pelo TF estão associados a uma melhora na mobilização do Ca2+i e na sensibilização das proteínas contráteis. / Heart failure (HF) is a syndrome with symptoms as exercise intolerance and signs as peripheral edema (PE). Impairment of myogenic constriction (MC) leads to enhancement of capillary hydrostatic pressure and PE. Knowing about the beneficial effects of physical training (PT) on cardiovascular system of HF, we hypothesize that PT is efficient in restore the impaired MC of caudal tibial artery (CTA) and PE induced by HF. HF increases paw volume, which was reversed by PT. The MC of CTA was blunted in HF, and PT restored it by pathway such as ROCK and SERCA-2/Phospholamban ratio, that increases Ca2+ kinetics and sensitization. PT restores the enhanced internal diameter (Di) observed in CTA of HF. Taken together, the CTAs of HF rats present an impairment of MC and eutrophic outward remodelling which are restored by PT. The PT adjustments observed in MC are associated with an improvement in Ca2+ mobilization and contractile protein sensitization.

Le muscle strié squelettique est un tissu richement vascularisé. Au delà de l'apport en oxygène et en nutriments, de nouvelles fonctions des vaisseaux ont été récemment identifiées, par le biais des interactions établies entre les cellules du vaisseau (cellules endothéliales) et les cellules du muscle, en particulier les cellules souches musculaires (cellules satellites). Celles-ci interagissent étroitement avec les cellules endothéliales pour leur expansion et leur différenciation, puis avec les cellules péri-endothéliales pour leur auto-renouvellement et leur retour à la quiescence. Les vaisseaux participent ainsi au contrôle de l’homéostasie du muscle squelettique. Grâce à ces interactions, les cellules vasculaires jouent donc un rôle central dans le remodelage tissulaire après un phénomène destructif, survenant par exemple au cours d’un trauma ou d’une myopathie. Pour étudier, les mécanismes de la plasticité vasculaire au cours du remodelage tissulaire, deux situations paradigmatiques de muscle en régénération chez l’enfant : la dermatomyosite juvénile (DMJ) et la dystrophie musculaire de Duchenne (DMD) ont été étudiées. Il existe, dans ces deux pathologies une souffrance musculaire associée à des cycles de nécrose/régénération. Elles se différencient par leur plasticité vasculaire et par leur évolution. En effet, la DMJ, la myopathie inflammatoire la plus fréquente de l’enfant est caractérisée par une vasculopathie avec perte en capillaires. L’évolution peut être favorable avec restitution ad integrum du muscle. La DMD est une myopathie génétique conduisant à une dégradation progressive de la force musculaire associée à une néovascularisation compensatrice. Le volet clinique/histologique incluant une analyse multiparamétrique des critères évolutifs cliniques et de réponse thérapeutique couplée à une réévaluation des données histologiques de la DMJ (analyse morphométrique des muscles DMJ) a permis de montrer qu’il existait des sous groupes phénotypiques homogènes de sévérité différente dans la DMJ. Le degré de sévérité clinique est relié à la gravité de la vasculopathie musculaire Par ailleurs, des marqueurs cliniques et histologiques simples permettant de repérer au diagnostic les patients nécessitant une escalade thérapeutique rapide (CMAS>34, atteinte gastrointestinale, fibrose endomysiale musculaire au diagnostic) ont été identifiés. Le volet cellulaire a permis l’identification in vitro des interactions cellulaires spécifiques et différentielles des myoblastes issues de patients DMD et DMJ sur les cellules endothéliales normales par l’analyse de leur rôle sur la prolifération, migration et différenciation des cellules vasculaires. Dans la DMD, les myoblastes entrainent une réponse angiogénique importante mais non efficace (néovascularisation anarchique). Dans la DMJ, les myoblastes participent efficacement à la reconstruction vasculaire notamment via la sécrétion de facteurs proangiogéniques. Ces résultats ont été renforcés par analyse transcriptomique effectuée à partir de cellules endothéliales et satellites isolées de muscles de patients confirmant le rôle central de la vasculopathie associée à un contexte inflammatoire spécifique lié à l’interféron dans la physiopathologie de la DMJ et montrant dans la DMD une dérégulation de l’homéostasie normale des interactions vaisseau-muscle avec mise en jeu d’un remodelage tissulaire non efficace. Ces données permettent d'identifier de nouvelles fonctions des cellules vasculaires dans le remodelage du muscle strié squelettique au cours des pathologies musculaires de l'enfant, et devraient ouvrir la voie à de nouvelles approches thérapeutiques. / Skeletal muscle is highly vascularised. Beyond oxygen and nutriment supply, new functions for vessels have been recently identified, through the interactions that vessel cells (endothelial cells) establish with muscle cells, particularly with muscle stem cells (satellite cells). These latter closely interact with endothelial cells for their expansion and their differentiation, then with periendothelial cells for their self-renewal and return to quiescence. During skeletal muscle regeneration endothelial cells reciprocally interact with myogenic cells by direct contact or by releasing soluble factors to promote both myogenesis and angiogenesis processes. Skeletal muscle regeneration typically occurs as a result of a trauma or disease, such as congenital or myopathies. To better understand the role of vessel plasticity in tissue remodeling, we took advantage of two muscular disorders that could be considered as paradigmatic situations of regenerating skeletal muscle in the child: Juvenile Dermatomyositis (JDM), the most frequent inflammatory myopathy and Duchenne Muscular Dystrophy (DMD), the most common type of muscular dystrophy. Although these two muscular disorders share, at the tissue level, similar mechanisms of necrosis-inflammation, they differ regarding the vessel domain. In JDM patients, microvascular changes consist in a destruction of endothelial cells assessed by focal capillary loss. This capillary bed destruction is transient. The tissue remodeling is efficient and muscle may progressively recover its function. By contrast, in DMD, despite an increase of vessels density in an attempt to improve the muscle perfusion, the muscle function progressively alters with age. We identified clinical and pathological markers of severity and predictive factors for poor clinical outcome in JDM by computing a comprehensive initial and follow-up clinical data set with deltoid muscle biopsy alterations controlled by age-based analysis of the deltoid muscle capillarization. We demonstrated that JDM can be divided into two distinctive clinical subgroups. The severe clinical presentation and outcome are linked to vasculopathy. Furthermore, a set of simple predictors (CMAS<34, gastrointestinal involvement, muscle endomysial fibrosis at disease onset) allow early recognition of patients needing rapid therapeutic escalation with more potent drugs. We studied in vitro the specific cell interactions between myogenic cells issued from JDM and DMD patients and normal endothelial cells to explore whether myogenic cells participate to the vessel remodeling observed in the two pathologies. We demonstrated that MPCs possessed angiogenic properties depending on the pathological environment. In DMD, MPCs promoted the development of establishment of an anarchic, although strong, EC stimulation, leading to the formation of weakly functional vessels. In JDM, MPCs enhanced the vessel reconstruction via the secretion of proangiogenic factors. This functional analysis was supported by the transcriptomic analysis consistent with a central vasculopathy in JDM including a strong and specific response to an inflammatory environment. On the contrary, DMD cells presented an unbalanced homeostasis with deregulation of several processes including muscle and vessel development with attempts to recover neuromuscular system by MPCs. To summarize, our data should allow the definition of new functions of vessel cells in skeletal muscle remodelling during muscle pathologies of the child that will open the way to explore new therapeutic options and to gain further insights in the pathogenesis of these diseases.

Nuclear hormone receptors (NHR) constitute a superfamily of ligand inducible transcriptional activators that enable an organism to regulate development and homeostasis through switching on or off target genes in response to stimuli reflecting changes in environment as well as endocrine. NHRs include classical steroid hormone receptors (GR, AR, ER and MR) and retinoid, thyroid hormone receptors. One long-term goal of our lab is to understand the molecular mechanisms through which the transcriptional activity of NHRs is regulated. Extensive studies in the past few years have revealed that in addition to the dependence on ligand availability, the transcriptional activity of NHRs is also regulated by two types of proteins: co activators and corepressors. In the absence of ligand, many NHRs, including TR and RAR can actively repress target gene transcription with the help of corepressors, proteins that physically interact with both NHRs and histone deacetylases (HDACs). Functional interactions between NHRs and corepressors therefore lead to tightly compact and transcriptionally non-permissive chromatin structures after the removal of obstructive acetyl groups from histone tails by HDACs. On the other hand, ligand binding stabilizes NHRs in a conformation that favors interaction with proteins other than corepressors; many of these proteins are able to potentiate the transcriptional activity of NHRs through various mechanisms, such as histone acetylation, chromatin remodeling and recruitment of basal transcription machinery and are collectively termed coactivators. Two highly related corepressors, SMRT (silencing mediator of retinoid and thyroid hormone receptors) and N-CoR (nuclear receptor corepressor), have been cloned. This research in corepressor SMRT started by a systematic study of its subcellular localization. We found that SMRT predominantly forms a specific nuclear punctuate structure that does not appear to overlap with any other well-known subnuclear domains/speckles. Although our searching for specific sequence signals that may determine the specific speckle localization of SMRT did not yield conclusive results, we discovered the colocalization of unliganded RAR and certain HDACs, including HDAC1, 3,4 and 5, in the SMRT nuclear speckles. Moreover, SMRT is likely to be the organizer of such speckles since it appears to be able to recruit other proteins into these speckles. The presence of HDAC1 in the SMRT speckles suggests a direct association between these two proteins, which has not been detected by previous biochemical analyses. Interestingly, HDAC1 point mutants that are completely defective in deacetylase activity failed to locate to SMRT nuclear speckles, while another partially active mutant maintained the colocalization. These discoveries may indicate SMRT nuclear speckles as novel nuclear domains involved in transcriptional repression. More physiologically relevant support for this hypothesis arises from study of HDAC4 and 5. HDAC4 and 5 are potent inhibitors of transcriptional activator MEF2C. Nuclear presence of HDAC4/5 can block the activation of MEF2C, which is required during muscle differentiation. Normally, HDAC4 is predominantly located in cytoplasm. However, we found that in the presence of SMRT overexpression, HDAC4 was found mostly in SMRT nuclear speckles. This accumulation enhanced HDAC4 mediated inhibition on MEF2C transcriptional activity in a transient transfection assay. SMRT overexpression also resulted in accumulation of HDAC5 in the SMRT nuclear speckles compared to the nuclear diffuse distribution in the absence of SMRT. Again, this accumulation of HDAC5 in nuclear speckles correlated with enhanced inhibition of MEF2C. Taken together, our study suggested that instead of being merely a corepressor for NHRs, SMRT might function as an organizer of a nuclear repression domain, which may be involved in a broad array of cellular processes. In contrast to the limited number of corepressors, numerous co activators have been identified; the SRC (or p160) family is relatively well studied. This family includes three highly related members, SRC-1, TIF2/GRIP1, RAC3/AIB1/ACTR/p/CIP. Similar domain structures are shared among these factors, with the most highly conserved region, the bHLH-PAS domain found within the N terminal ~400 amino acid residues. This study of RAC3 aims to identify the function of the highly conserved N terminal bHLH-PAS domain by isolating interacting proteins through yeast two-hybrid screening. One candidate gene isolated encodes the C terminal fragment of the human homologue of the yeast protein MMS19. Functional studies of this small fragment revealed that it specifically interacted with human estrogen receptors (ERs) and inhibited ligand induced transcriptional activity of ERs in the transient transfection assay. Then we cloned the full-length human MMS19 cDNA and characterized the hMMS19 as a weak coactivator for estrogen receptors in the transient transfection assay. Furthermore, when tested on separate AF-1 or AF-2 of ERs, hMMS19 specifically enhanced AF-1 but had no effect on AF-2. These results identified hMMS19 as a specific coactivator for ER AF-1.

A produção de aves no Brasil vem crescendo na ordem de 10% a cada ano, o que se explica pela atualização constante da tecnologia do setor (http://www.abef.com.br). Sendo a carne de frango a fonte de proteína animal mais barata e acessível ao consumidor, há necessidade de se produzir cada vez mais animais com maior acúmulo de massa muscular. Para isso, o entendimento dos mecanismos celulares e moleculares envolvidos na formação da musculatura esquelética é de extrema relevância. Os fatores miogênicos, genes responsáveis pela determinação e diferenciação de células musculares, foram clonados e progressos significativos foram desenvolvidos quanto ao controle da expressão dos mesmos. A utilização da técnica de seqüenciamento de DNA possibilita a identificação e caracterização de novos genes envolvidos na complexa rede de fatores que regulam a formação da musculatura esquelética em aves. Neste estudo, foram construídas duas bibliotecas de cDNA (fase embrionária e pós-eclosão) de músculo peitoral de uma linhagem de corte (TT) e uma biblioteca da fase embrionária de uma linhagem de postura (CC). A análise das seqüências EST (Expressed Sequence Tags) foi utilizada para identificar possíveis novos genes envolvidos no processo de formação da musculatura esquelética. As seqüências EST identificadas possibilitaram a construção de um banco com 6247 ESTs da musculatura peitoral das linhagens de corte e postura nas duas fases de desenvolvimento. Com o intuito de estabelecer uma relação entre o perfil de expressão dos fatores miogênicos: MyoD, MRF4 e miogenina; e dos genes Pax-3 e miostatina e a formação e maturação das fibras musculares, foi utilizada a técnica de PCR em tempo real. Em geral, a expressão dos fatores miogênicos foi maior na linhagem de corte em relação à de postura nas idades estudadas. Este estudo deverá contribuir para as áreas celular e molecular de desenvolvimento, além de fornecer recursos úteis aos programas de melhoramento genético de aves que visam obter animais com maior acúmulo de massa muscular. / Brazilian’s chicken production is increasing annually around 10%, which can be explained by the current technology applied to this sector (http://www.abef.com.br). Being chicken’s meat the cheapest animal protein source for consumers, there is a need to produce even more animals with increased muscular mass. For this purpose, understanding the molecular and cellular mechanisms involved with the skeletal muscle development is of great relevance. The myogenic factors, genes responsible for the determination and differentiation of muscle cells, were cloned and significant progress was made on the control of their expression. The use of DNA sequencing technique allows the identification and characterization of new genes involved in the complex chain of factors signalling systems that regulates the expression of avian skeletal muscles. In this study, two cDNA libraries (embryonic and post-hatching phases) were constructed from the breast muscle of a chicken broiler line (TT) and one library, from the embryonic phase, from a chicken layer line (CC). The EST (Expressed Sequencing Tags) analysis was used to identify probable new genes involved in the skeletal muscle development. The identified ESTs were used to generate a database containing 6247 breast muscle ESTs from two chicken lines in two development phases. Real time PCR was employed with the aim of establishing a relationship among the expression profile of myogenic factors (MyoD, MFR4, and myogenin), Pax-3 and myostatin genes with the formation and maturation of muscle fibers. In general, the expression of myogenic factors was greater in the broiler than in the layer chicken line in the phases under study. These results should contribute to other cellular and molecular development studies besides providing useful resources for chicken breeding programs whose objective is the deposition of skeletal muscle mass.

No description available.

No description available.

No description available.