Chez les angiospermes, la reproduction passe par la double fécondation. Le tube pollinique délivre deux cellules spermatiques au sein du gamétophyte femelle. Une cellule féconde la cellule œuf pour produire un zygote; l’autre féconde la cellule centrale pour produire l’endosperme. Pour assurer un succès reproductif, le développement du gamétophyte femelle au sein de l’ovule doit établir un patron cellulaire qui favorise les interactions avec le tube pollinique et les cellules spermatiques. Pour ce faire, un dialogue doit s’établir entre les différentes cellules de l’ovule lors de son développement, de même que lors de la fécondation. D’ailleurs, plusieurs types de communications intercellulaires sont supposées suite à la caractérisation de plusieurs mutants développementaux. De même, ces communications semblent persister au sein du zygote et de l’endosperme pour permettre la formation d’un embryon viable au sein de la graine. Malgré les développements récents qui ont permis de trouver des molécules de signalisation supportant les modèles d’interactions cellulaires avancés par la communauté scientifique, les voies de signalisation sont de loin très incomplètes. Dans le but de caractériser des gènes encodant des protéines de signalisation potentiellement impliqués dans la reproduction chez Solanum chacoense, l’analyse d’expression des gènes de type RALF présents dans une banque d’ESTs (Expressed Sequence Tags) spécifiques à l’ovule après fécondation a été entreprise. RALF, Rapid Alcalinization Factor, est un peptide de 5 kDa qui fait partie de la superfamille des «protéines riches en cystéines (CRPs)», dont les rôles physiologiques au sein de la plante sont multiples. Cette analyse d’expression a conduit à une analyse approfondie de ScRALF3, dont l’expression au sein de la plante se limite essentiellement à l’ovule. L’analyse de plantes transgéniques d’interférence pour le gène ScRALF3 a révélé un rôle particulier lors de la mégagamétogénèse. Les plantes transgéniques présentent des divisions mitotiques anormales qui empêchent le développement complet du sac embryonnaire. Le positionnement des noyaux, de même que la synchronisation des divisions au sein du syncytium, semblent responsables de cette perte de progression lors de la mégagamétogénèse. L’isolement du promoteur de même que l’analyse plus précise d’expression au sein de l’ovule révèle une localisation sporophytique du transcrit. La voie de signalisation de l’auxine régule également la transcription de ScRALF3. De surcroît, ScRALF3 est un peptide empruntant la voie de sécrétion médiée par le réticulum endoplasmique et l’appareil de Golgi. En somme, ScRALF3 est un important facteur facilitant la communication entre le sporophyte et le gamétophyte pour amener à maturité le sac embryonnaire. L’identification d’un orthologue potentiel chez Arabidopsis thaliana a conduit à la caractérisation de AtRALF34. L’absence de phénotype lors du développement du sac embryonnaire suggère, cependant, de la redondance génétique au sein de la grande famille des gènes de type RALF. Néanmoins, les peptides RALFs apparaissent comme d’importants régulateurs lors de la reproduction chez Solanum chacoense et Arabidopsis thaliana. / In angiosperms, reproduction occurs through double fertilization. The pollen tube delivers two sperm cells into the female gametophyte. A first sperm cell fertilizes the egg cell to produce a zygote, while the other fertilizes the central cell to produce the endosperm. To ensure reproductive success, the development of the female gametophyte within the ovule must establish a cellular pattern allowing interaction with the pollen tube and sperm cells. To this end, a dialogue must be established amongst the various cells of the ovule during its development, as well as during fertilization. Several types of communication are suggested by the analysis of developmental mutants. These communications must persist in the zygote and endosperm to allow the formation of a viable embryo within the seed. Recent developments have helped to find signaling molecules that support cell interaction models developed by the scientific community, but the signaling pathways are far from complete. In order to characterise genes encoding signaling proteins which are potentially active during reproduction in Solanum chacoense, I undertook the expression analysis of the RALF-like genes present in a bank of ESTs (Expressed Sequence Tags) specific to the ovule after fertilization. RALF, Rapid Alcalinization Factor, is a 5 kDa peptide that is part of the superfamily of Cysteine Rich Proteins (CRPs), which play a wide variety physiological roles within the plant. This expression analysis led to a detailed analysis of ScRALF3, whose expression in the plant is largely restricted to the ovule. The analysis of ScRALF3 RNAi transgenic plants revealed a function during megagametogenesis. The transgenic plants exhibit abnormal mitotic divisions that prevent the maturity of the embryo sac. The positioning of the nuclei, as well as the timing of divisions in the syncytium, appear to be responsible for the arrest of development during megagametogenesis. Isolation of the promoter as well as more accurate analysis of transcript expression reveals localisation within the ovule sporophytic tissue. The auxin signaling pathway is also involved in the regulation of ScRALF3 expression. ScRALF3 is a secreted peptide passing via the endoplasmic reticulum and the Golgi apparatus. In summary, ScRALF3 may be an important factor facilitating communication between the gametophyte and the sporophyte to allow maturation of the embryo sac. The identification of a potential orthologue in Arabidopsis thaliana led to the characterisation of AtRALF34. The lack of a phenotype during embryo sac development, however, suggests that genetic redundancy within the family of RALF-like genes is very complex. Nevertheless, the RALF peptides appear to be important regulators during reproduction in Solanum chacoense and Arabidopsis thaliana.

Submitted by Noeme Timbo (noeme.timbo@metodista.br) on 2016-09-12T17:54:01Z No. of bitstreams: 1 Deise Balek Lahoz.pdf: 3674427 bytes, checksum: 389bd48e76a52f247a79585185d9ae27 (MD5) / Made available in DSpace on 2016-09-12T17:54:01Z (GMT). No. of bitstreams: 1 Deise Balek Lahoz.pdf: 3674427 bytes, checksum: 389bd48e76a52f247a79585185d9ae27 (MD5) Previous issue date: 2016-04-25 / Study on the communication practices of post-sales area in social networks on-line, regarding the service of companies and channels available for interaction to the consumers. Among the steps, there was an analysis of consumer habits to conduct searches on social networks on-line; in order to draw the attention of companies on after-sales problems in these channels (complaints, technical questions, suggestions, etc.). The main objective was to develop chronologically and structured communication practices in after-sales through various channels of SAC; recovering the evolutionary phases of the SAC, consumer protection law, since the analog era (without internet access and spontaneous), until the arrival of social networking online. For this study were performed: bibliographic, exploratory and documental survey on the area of after-sales, relationship marketing and research results on the habits of consumers connected to the Internet; presentation of cases that exemplify the communication market practices; interview applied with eight market experts; and electronic form applied with managers of call centers. With all of these analyzes, it was possible to draw a diagnosis of the current situation of the customer service area of the selected companies in the online social networks, in addition to significantly reinforce the idea of consumer content producer (prosumer) and the change in the flow communicational consumer versus business. / Estudo sobre as práticas comunicacionais da área de pós-vendas nas redes sociais on-line, com relação ao atendimento das empresas e os canais por elas disponibilizados para interação com o consumidor. Dentre as etapas, realizou-se uma análise sobre os hábitos dos consumidores de realizar buscas nas redes socais on-line; com o intuito de chamar a atenção das empresas sobre problemas de pós-venda nestes canais (reclamações, dúvidas técnicas, sugestões etc.). O objetivo principal foi elaborar de forma cronológica e estruturada a práticas de comunicação no pós-venda por meio dos diversos canais do SAC; resgatando as fases evolutivas do SAC, a lei de proteção do consumidor, desde a era analógica (sem acesso à internet e espontânea), até a chegada das redes sociais on-line. Para tal estudo foram realizados: levantamento bibliográfico, exploratório e documental sobre a área de pós-venda, marketing de relacionamento e de resultados de pesquisas sobre os hábitos dos consumidores conectados à internet; apresentação de casos que exemplificam as práticas comunicacionais do mercado; entrevista aplicada com oito especialistas do mercado; e formulário eletrônico aplicado com gestores das centrais de atendimento. Com todas essas análises, foi possível traçar um diagnóstico sobre a realidade atual da área de atendimento ao cliente das empresas selecionadas, nas redes sociais on-line, além de reforçar sensivelmente a ideia do consumidor produtor de conteúdo (prosumer) e a mudança no fluxo comunicacional consumidor versus empresa.

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Compared with the terrestrial network (TN), which can only support limited covered areas, satellite communication (SC) can provide global coverage and high survivability in case of an emergency like an earthquake. Especially low-earth orbit (LEO) satellites, as a promising technology, which is integral to achieving the goal of global seamless coverage and reliable communication, catering to 6G’s communication requirements. Nevertheless, the swift movement of the LEO satellites poses a challenge: frequent handovers are inevitable, compromising the quality of service (QoS) of users and leading to discontinuous connectivity. Moreover, considering LEO satellite connectivity for different flying vehicles (FVs) when coexisting with ground terminals, an efficient satellite handover decision control and mobility management strategy is required to reduce the number of handovers and allocate resources that align with different user requirements. With the development of machine learning (ML) methods, which can greatly enhance system performance and automation, reinforcement learning (RL), as a sub-field in ML has been employed to optimize decision control. Due to the challenges of dimensionality explosion and the propensity for traditional Q-learning algorithms to get trapped in local minima, deep learning has been introduced with RL. In this thesis, the high-dimensionality user-satellite network is constructed including the LEO constellation from the ephemeris data, different types of flying vehicles such as aircraft and drones, and ground terminals. Two mathematical optimization models named the traditional low handover model and network utility model when considering the full criteria including the remaining visible time, downlink (DL) carrier-to-interference-plus-noise ratio (CINR) and the available idle channels are formulated. In this way, a novel satellite handover strategy based on Multi-Agent Reinforcement Learning (MARL) and game theory named Nash-SAC has been proposed to solve these problems. From the simulation results, compared with different benchmarks such as the traditional Q-learning algorithm, Maximum available channel (MAC)-based strategy, and Maximum instantaneous signal strength (MIS)-based strategy, Nash-SAC can effectively reduce the number of satellite handovers by over 16% close to the lower limit, and the blocking rate by over 18%. Moreover, Nash-SAC can greatly improve the network utility of the whole system by up to 48% and cater to different users’ requirements, providing reliable and robust connectivity for both FVs and ground terminals. / Jämfört med det markbundna nätet (TN), som endast kan stödja begränsade täckta områden, kan satellitkommunikation (SC) ge global täckning och hög överlevnad vid en nödsituation som en jordbävning. Speciellt lågjordiga satelliter (LEO), som en lovande teknik, som är integrerad för att uppnå målet om global sömlös täckning och tillförlitlig kommunikation, tillgodose 6G:s kommunikationskrav. Icke desto mindre utgör LEO-satelliternas snabba förflyttning en utmaning: täta överlämningar är oundvikliga, vilket äventyrar användarnas tjänstekvalitet och leder till kontinuerlig uppkoppling. Med tanke på LEO:s satellitanslutning för olika flygande fordon när de samexisterar med markterminaler krävs dessutom en effektiv strategi för kontroll av satellitöverlämning och mobilitetshantering för att minska antalet överlämningar och fördela resurser som överensstämmer med olika användarkrav. Med utvecklingen av maskininlärningsmetoder (ML), som avsevärt kan förbättra systemprestanda och automation, har förstärkningsinlärning (RL), som ett delområde i ML använts för att optimera beslutskontrollen. På grund av utmaningarna med dimensionsexplosion och benägenheten för traditionella Q-inlärningsalgoritmer att fastna i lokala minimi har djupinlärning introducerats med RL. I denna avhandling konstrueras det högdimensionella användarsatellitnätet inklusive LEO-konstellationen från ephemerisdata, olika typer av flygande fordon såsom flygplan och drönare samt markterminaler. Två matematiska optimeringsmodeller kallas den traditionella lågöverlämningsmodellen och nätverksbruksmodellen när man beaktar de fullständiga kriterierna inklusive återstående synliga tiden, nedlänk (DL) carrier-to-interferens-plus-noise ratio (CINR) och tillgängliga inaktiva kanaler formuleras. På detta sätt har en ny satellitöverlämningsstrategi baserad på Multi-Agent Reinforcement Learning (MARL) och spelteori vid namn Nash-SAC föreslagits för att lösa dessa problem. Från simuleringsresultaten, jämfört med olika riktmärken såsom den traditionella Q-learning algoritmen, Maximal available channel (MAC)-baserad strategi och Maximal instantaneous signalstyrka (MIS)-baserad strategi, kan Nash-SAC effektivt minska antalet satellitöverlämningar med över 16% nära den nedre gränsen och blockeringshastigheten med över 18%. Dessutom kan Nash-SAC avsevärt förbättra nätverksnyttan i hela systemet med upp till 48% och tillgodose olika användares krav, vilket ger tillförlitlig och robust anslutning för både flygande fordon och markterminaler.

Pour permettre à un robot autonome de faire des tâches complexes, il est important qu'il puisse cartographier son environnement pour s'y localiser. À long terme, pour corriger sa carte globale, il est nécessaire qu'il détecte les endroits déjà visités. C'est une des caractéristiques les plus importantes en localisation et cartographie simultanée (SLAM), mais aussi sa principale limitation. La charge de calcul augmente en fonction de la taille de l'environnement, et alors les algorithmes n'arrivent plus à s'exécuter en temps réel. Pour résoudre cette problématique, l'objectif est de développer un nouvel algorithme de détection en temps réel d'endroits déjà visités, et qui fonctionne peu importe la taille de l'environnement. La détection de fermetures de boucle, c'est-à-dire la reconnaissance des endroits déjà visités, est réalisée par un algorithme probabiliste robuste d'évaluation de la similitude entre les images acquises par une caméra à intervalles réguliers. Pour gérer efficacement la charge de calcul de cet algorithme, la mémoire du robot est divisée en mémoires à long terme (base de données), à court terme et de travail (mémoires vives). La mémoire de travail garde les images les plus caractéristiques de l'environnement afin de respecter la contrainte d'exécution temps réel. Lorsque la contrainte de temps réel est atteinte, les images des endroits vus les moins souvent depuis longtemps sont transférées de la mémoire de travail à la mémoire à long terme. Ces images transférées peuvent être récupérées de la mémoire à long terme à la mémoire de travail lorsqu'une image voisine dans la mémoire de travail reçoit une haute probabilité que le robot soit déjà passé par cet endroit, augmentant ainsi la capacité de détecter des endroits déjà visités avec les prochaines images acquises. Le système a été testé avec des données préalablement prises sur le campus de l'Université de Sherbrooke afin d'évaluer sa performance sur de longues distances, ainsi qu'avec quatre autres ensembles de données standards afin d'évaluer sa capacité d'adaptation avec différents environnements. Les résultats suggèrent que l'algorithme atteint les objectifs fixés et permet d'obtenir des performances supérieures que les approches existantes. Ce nouvel algorithme de détection de fermeture de boucle peut être utilisé directement comme une technique de SLAM topologique ou en parallèle avec une technique de SLAM existante afin de détecter les endroits déjà visités par un robot autonome. Lors d'une détection de boucle, la carte globale peut alors être corrigée en utilisant la nouvelle contrainte créée entre le nouveau et l'ancien endroit semblable.

The interaction between figs (Ficus spp.) and their pollinating wasps (fig wasps; Chalcidoidea, Hymenoptera) is a classic example of an ancient and apparently stable mutualism. A striking property of this mutualism is that fig wasps consistently oviposit in the inner flowers of the fig syconium (gall flowers, which develop into galls that house developing larvae), but typically do not use the outer ring of flowers (seed flowers, which are pollinated and develop into seeds). This dissertation explores the potential differences between gall and seed flowers that might influence oviposition choices, and the unknown mechanisms underlying gall formation. To identify the microbial community that could influence oviposition choice, I identified fungi in both flower types across six species of Ficus. I found that whereas fungal communities differed significantly as a function of developmental stages of syconia and lineages of fig trees, communities did not differ significantly between receptive gall and seed flowers. Because secretions from the poison sac that are deposited at oviposition are thought to be important in gall formation by both pollinating fig wasps and non-pollinating, parasitic wasps, I examined poison sac morphology in diverse galling wasps from several species of Ficus in lowland Panama. I found that the size of the poison sac was positively associated with egg number across pollinating and non-pollinating fig wasps. Finally to determine difference in defense and metabolism between gall and seed flowers, and to identify genes involved in galling, I compared gene expression profiles of fig flowers at the time of oviposition choice and early gall development. I found a prominence of flavonoids and defensive genes in both pollinated and receptive gall flowers of Ficus obtusifolia, and revealed detectable differences between gall flowers and seed flowers before oviposition. Several highly expressed genes were also identified that have implications for the mechanism of gall initiation. This dissertation explores previously unstudied aspects of the fig and fig wasp mutualism and provides important molecular tools for future study of this iconic and ecologically important association.

Ce travail examine l’œuvre de l’artiste abstrait italien Alberto Burri (Città di Castello, 1915 - Nice, 1995) et ses nouvelles contributions à partir de 1945, notamment dans l’utilisation de la matière en peinture : Goudrons, Sacs, Bois, Fers, Plastiques, jusqu’aux Cretti et Cellotex. La métamorphose de sa recherche est contemplée en faisant état des différentes phases de sa création. C’est dans le Texas, durant sa captivité au cours de la Seconde Guerre mondiale qu’elle vit le jour et continua sans cesse de prendre forme, dans chaque lieu qu’il habita : Rome, où il entra en contact et influença nombre d’artistes, et aussi Los Angeles, Beaulieu-sur-Mer. Prenant également en compte la réception critique de ses créations en Italie et ailleurs, on étudie ses spéculations par rapport à celles des Avant-gardes et à d’autres artistes travaillant avec de la matière, en France, en Italie, dans d’autres pays européens, aux États-Unis et au Japon (entre autres, Gutaï, Néo-Dada, Nouveau Réalisme, Arte Povera…) Tableaux, sculptures, grands «Cycles», œuvre gravé, livres d’artiste, décors pour le théâtre, Sculptures-Théâtre : un voyage monumental, où Burri - entre révolution et classicisme - concevant des œuvres puissantes et raffinées, à l’ «équilibre déséquilibré», renouvela complètement le langage artistique de l’après-guerre. / This survey examines the work of the Italian abstract artist Alberto Burri (Città di Castello, 1915 - Nice, 1995) and his original contributions using a variety of materials in artistic creation since 1945: Tar, Burlap, Wood, Iron, Plastic, and finally Cretti and Cellotex. The metamorphosis of his research is evidenced through all the different phases of his activity, starting in Texas at the time of his internment during WWII and constantly continued in every place he lived: Rome, where he met and influenced many artists, Los Angeles, Beaulieu-sur-Mer. Also examining the critical reception of his work in Italy and elsewhere, his speculations have been studied in relation to those of the Avant-garde and other artists working with materials, in France, Italy, other European countries, United States and Japan (among others, Gutaï, New-Dada, Nouveau Réalisme, Arte Povera…) Paintings, sculptures, big "Cycles", graphic work, artists’ books, stage sets, Theatre-Sculptures: a monumental journey, during which Burri - between revolution and classicism - created powerful and refined works of "unbalanced balance", completely renewing the post-war artistic language.

O objetivo deste estudo foi caracterizar morfologicamente o desenvolvimento inicial da gestação bovina proveniente de monta natural, com idades compreendidas entre 15 a 70 dias, e de fecundação in vitro (FIV) com 35 dias, com ênfase no desenvolvimento placentário inicial, e diferenciação das estruturas extra embrionárias. Para tanto, foram utilizados 141 conceptos, provenientes de monta natural, e sete conceptos obtidos pela técnica de FIV. Após as coletas, os conceptos foram dissecados, mensurados macroscopicamente e fotodocumentados. As membranas extra-embrionárias foram cortadas em fragmentos de 5 cm2, e, em seguida fixadas em paraformoldeído 4%, para análise por microscopia de luz, e glutaraldeído 2,5%, para utilização em microscopia eletrônica de varredura e transmissão. As membranas extra-embrionárias e fetais apresentaram graus variáveis de desenvolvimento ao longo dos períodos analisados. O aparecimento macroscópico da vascularização do alantóide, sua tentativa de se fundir com o cório e o aparecimento efetivo dos primeiros cotilédones em desenvolvimento, foram eventos observados em embriões a partir de 1,9±0,27 cm de \"Crown-Rump\" (CR) (30 a 40 dias da gestação). O CR médio, o peso do embrião, o peso do saco gestacional e os comprimentos do cório e âmnio aumentaram gradativamente com o evoluir da gestação. O epitélio alantoidiano apresentou um dimorfismo celular a partir de 0,9 cm de CR (15 a 20 dias de gestação), porém, mostrou-se imaturo até o feto atingir o comprimento de 7,2 cm de CR (60 a 70 dias da gestação). O trofoblasto apresentou células mononucleadas e células gigantes binucleadas em diferentes níveis ao longo da gestação. O saco vitelino persistiu até 70 dias de gestação, e o seu epitélio apresentou indícios de atividade funcional até 50 dias de gestação. De todos os parâmetros mensurados na análise macroscópica, somente o comprimento o CR e o saco vitelino apresentaram diferença significativa entre os conceptos de monta natural e de FIV. Nos conceptos de monta natural, o comprimento do saco vitelino foi de 5,53 cm, em média, e nos conceptos de FIV, de apenas 1,07 cm. Todavia, faz-se necessário analisar um número maior de animais submetidos a FIV para corroborar a diferença encontrada nestas medidas. Os resultados sugerem ainda a existência de uma placenta vitelínica ativa, importante para a manutenção da gestação, que se estabelece temporariamente entre a placenta coriovitelínica e alantovitelínica transitória e a placenta cório-alantóide definitiva. / The main goal of this study was to describe morphology and the early gestational development of 15 to 70 day-old bovine embryos obtained by natural mating and 35 day-old bovine embryos obtained by in vitro fertilization (IFV) technique. One hundred and forty-one concepts originated by natural mating and seven by IVF technique were used. All concepts were dissected, macroscopically measured and photographed. Extraembryonic membranes were cut in 5 cm2 fragments and fixed in 4% paraformoldehyde for light and Scanning Electron Microscopy (SEM) and in 2.5% glutaraldehyde for Transmition Electron Microscopy (TEM). Ali membranes showed different stages of development during analyzed periods. The beginning of allantois macroscopic vascularization, the attempt of fusion between allantois and chorium membranes and the effective development of the first cotyledons were observed in 30-to-40 day-old embryos with 1.9± 0.24 cm of Crown-Rump (CR) length. The average CR, the embryos and gestational sac weight, the chorion and amnion length increased during gestation. The allantoic epithelia showed a cellular dimorphism with 0.9 em CR, however, the maturation has not happened until the foetal length of 7.2 em CR. The trophoblast showed different levels of mononucleate cells and binucleate giant cells. The yolk sac persisted until 70 days of gestation and the epithelium seemed functionally activated until 50 days of gestation. The CR and yolk sac size were the only measured macroscopic parameter showingdifference between natural mating and FIV concepts. Yolk sac size presented average values of 5.53 cm and 1.07 cm for natural mating and FIV concepts, respectively. Therefore, it is necessary to analyze a higher number of FIV embryos to corroborate that observed yolk sac size difference. All results obtained in this study suggest the existent of an active vitelline placenta, important to the gestational maintenance and temporarily establish between the transitory choriovitelline placenta and the permanent chorioallantoic placenta.

A placenta é encontrada apenas em mamíferos, e é resultado do sucesso da implantação do blastocisto no útero, representando um órgão funcional de trocas materno-fetais, sendo também um importante órgão endócrino. Na família Cricetidae e Subfamília Sigmodontinae englobam os ratos e camundongos da América do Sul. Devido à semelhança entre a morfologia da placenta e o processo de placentação dos roedores com a placenta humana, estes animais representam um interessante modelo para estudos relacionados à placentação. O objetivo deste estudo foi descrever a morfologia da placenta e a placentação em 5 espécies de sigmodontes (Necromys lasiurus, Oryzomys subflavus, Oryzomys sp., Oryzomys megacephalus e Oligoryzomys sp.). Nas análises macroscópicas constatou-se que a placenta desse grupo apresenta um formato discóide, sendo classificada como zonária discoidal. Na microscopia observou-se que a placenta é do tipo corioalantóidea, labiríntica, hemocorial, com zonas de espongiotrofoblasto e uma região de decídua materna. A placenta vitelina é vilosa, completamente invertida e persistia até o final da gestação. Somente em Oryzomys subflavus foi observada na placenta vitelina uma intensa atividade hemofágica, evidenciada pela técnica de Tricrômo de Masson. A barreira placentária nas espécies Necromys lasiurus e Oryzomys sp. é do tipo hemotricorial, existindo três camadas trofoblásticas adjuntas ao endotélio do capilar fetal separando os sistemas sanguíneos materno e fetal. As células trofoblásticas gigantes foram observadas em diferentes regiões da placenta. Em todas as espécies as células deciduais foram positivas para reação histoquímica de ácido periódico de Schiff (P.A.S.). / Placenta is found only in mammals and it is result of the success of blastocyst implantation in the uterus, representing a functional organ to maternal-fetal exchanges and it is also an important endocrine organ. The Family Cricetidae and Subfamily Sigmodontinae include the rats and mice from South America. Due to the similarity of both the placenta morphology and the placentation between rodents and human, these animals represent an interesting model for studies related to the placenta and placentation. The aim of this research was to describe the placenta morphology and placentation in 5 species of sigmodonts (Necromys lasiurus, Oryzomys subflavus, Oryzomys sp., Oryzomys megacephalus Oryzomys sp. and Oligoryzomys sp.). In the macroscopic analysis the placenta shows a discoid shape, it is classified as discoid type. The microscopy results showed the placenta is chorioallantoic, labyrinth, hemochorial, with areas of spongio zone and a region of maternal decidua. The yolk sac placenta is villous, completely inverted and persisted until the end of pregnancy. Only in Oryzomys subflavus was observed in the yolk sac placenta an intense hemophagous activity, evidenced by the Masson\'s trichrome stain. The placental barrier in Necromys lasiurus and Oryzomys sp. is of the hemotrichorial type, composed by three trophoblast layers more the fetal capillary endothelium to separate the maternal and fetal blood systems. The trophoblast giant cells were observed in different regions of the placenta. In all species the decidual cells were positive to histochemical reaction using periodic acid-Schiff (PAS).

O saco vitelino é a principal fonte de nutrição do embrião durante o período em que a placenta verdadeira ainda não está completamente formada. É responsável pela hematopoiese, pois dele se desenvolvem os primórdios das células sanguíneas, bem como parte do sistema circulatório primitivo do embrião. Tivemos como objetivo caracterizar a área transicional do saco vitelino para o intestino primitivo através de análise macroscópica, microscopia de luz, microscopia eletrônica de transmissão e reação imunohistoquímica para detecção de células germinativas (Oct-4). Foram realizados cortes seqüenciais de todos os embriões para permitir a visualização da estrutura como um todo. Nas amostras obtidas, pudemos observar a presença do saco vitelino com a área de conexão com intestino primitivo composto por inúmeras ilhotas vasculares que correspondem aos vasos envolvidos pelas células vitelínicas e células mesenquimais. No interior dos vasos identificamos hemangioblastos em grande quantidade. A camada correspondente ao mesênquima é delgada e com células alongadas e endoderma da membrana vitelínica é composto por células endodérmicas, grandes, uni ou binucleadas. Tal arranjo celular se assemelha a uma glândula devido a sua arquitetura em ilhas vasculares somado às camadas teciduais. O epitélio do intestino primitivo inicia sua diferenciação com células colunares estratificadas e bordadura em escova seguido de células mesenquimais indiferenciadas. A área transicional entre o saco vitelínico e o intestino primitivo é estreita em relação à luz destas duas estruturas com células de formato irregular, constituindo um delicado revestimento no lúmen contendo hemangioblastos. No mesênquima da área transicional inúmeros e pequenos capilares foram observados com hemangioblastos em seu interior. Em embriões e fetos submetidos à imunohistoquímica, verificamos células reativas como o metanefro, gônadas, parênquima hepático e saco vitelino. / The yolk sac is the main source of embryo nutrition during the period that true placenta are not still formed and responsible by hematopoieses because from it were developed the blood cells, as a part of embryo primitive circulatory system. We aimed to characterize the transitional area between the yolk sac and the primitive intestine by light microscopy, transmission electron microscopy and detection of germ cell lines by Oct-4 immunohistochemistry. Were done in all embryos serial sections to permit the identification for all structures. Were possible identify the yolk sac connection with primitive intestine composed by many blood islet corresponding to relation with yolk and mesenchymals cells. Inside the vessels were identified hemangioblasts. The layer corresponding to mesenchyme is thin and with elongated cells and the vitellinic membrane endoderm is composed by large, uni or binucleate endodermic cells. This shape is similar to a gland related to their architecture, vessels islets and tissue layers. Primitive intestine epithelium begins their differentiation with stratified columnar cells and undifferentiated mesenchymals cells. This transitional area is thin related to their lumen with irregular shape and constituted by delicate lumen basement and hemangioblast. Inside the mesenchyme there are many smaller capillaries observed with hemangioblast in it. Embryos and fetus submitted to immunohistochemistry and were verified positive cells like metanefrons, gonads, hepatic parenchyma and yolk sac.