RESUMO
BACKGROUND: Miguel Fernández was an Argentinian zoologist who published the first account of obligate polyembryony in armadillos. His contribution is here discussed in relation to his contemporaries, Newman and Patterson, and more recent work. FINDINGS: Fernandez worked on the mulita (Dasypus hybridus). He was able to get early stages before twinning occurred and show it was preceded by inversion of the germ layers. By the primitive streak stage there were separate embryonic shields and partition of the amnion. There was, however, a single exocoelom and all embryos were enclosed in a common set of membranes comprising chorion towards the attachment site in the uterine fundus and inverted yolk sac on the opposite face. He showed that monozygotic twinning did not occur in another armadillo, the peludo (Chaetophractus villosus). CONCLUSIONS: Fernández's work represented a major breakthrough in understanding how twinning occurred in armadillos. His work and that of others is of intrinsic interest to zoologists and has a direct bearing on the origin of monozygotic twins and birth defects in humans.
Assuntos
Anatomia Comparada/história , Tatus/embriologia , Embriologia/história , Desenvolvimento Embrionário , Camadas Germinativas/embriologia , Gemelaridade Monozigótica , Zoologia/história , Animais , Argentina , Tatus/crescimento & desenvolvimento , Tatus/fisiologia , Membranas Extraembrionárias/citologia , Membranas Extraembrionárias/embriologia , Membranas Extraembrionárias/fisiologia , Feminino , Pesquisa em Genética/história , Camadas Germinativas/citologia , Camadas Germinativas/fisiologia , História do Século XX , Masculino , Placentação , Gravidez , Especificidade da Espécie , Saco Vitelino/citologia , Saco Vitelino/embriologia , Saco Vitelino/fisiologiaRESUMO
We studied the development of the inverted yolk sac in a New World rodent, Necromys lasiurus during early placentation. Ten implantation sites were investigated by means of histology, immunohistochemistry and electron microscopy. The yolk sac was villous near its attachment to the placenta. Elsewhere it was non-villous and closely attached to the uterus. The uterine glands were shallow and wide mouthed. They were associated with vessels and filled with secretion, suggesting the release of histotroph. This feature was absent at later stages. The intimate association of the yolk sac with specialized glandular regions of the uterus may represent a derived character condition of Necromys and/or sigmodont rodents.
Assuntos
Placentação/fisiologia , Sigmodontinae/fisiologia , Saco Vitelino/fisiologia , Animais , Implantação do Embrião/fisiologia , Feminino , Microscopia Eletrônica de Transmissão , Gravidez , Sigmodontinae/anatomia & histologia , Útero/ultraestrutura , Saco Vitelino/irrigação sanguínea , Saco Vitelino/ultraestruturaRESUMO
To elucidate the morphological differences between placentas from normal and cloned cattle pregnancies reaching term, the umbilical cord, placentomes and interplacentomal region of the fetal membranes were examined macroscopically as well as by light and scanning electron microscopy. In pregnancies established by somatic nucleus transfer (NT), the umbilical cord and fetal membranes were edematous. Placentomal fusion was common, resulting in increased size and a decreased number of placentomes. Extensive areas of the chorioallantoic membrane were devoid of placentomes. An increased number of functional or accessory microcotyledons (<1 cm) were present at the maternally oriented surface of fetal membranes. Extensive areas of extravasated maternal blood were present within the placentomes and in the interplacentomal region. The crypts on the caruncular surface were dilated and accommodated complexes of more than one primary villus, as opposed to a single villus in non-cloned placentae. Scanning electron microscopy of blood vessel casts revealed that there was also more than one stem artery per villous tree and that the ramification of the vessels failed to form dense complexes of capillary loops and sinusoidal dilations as in normal pregnancies. At the materno-fetal interface, however, the trophoblast and uterine epithelium had normal histology. In conclusion, the NT placentas had a range of pathomorphological changes; this was likely associated with the poor clinical outcome of NT pregnancies.
Assuntos
Bovinos/fisiologia , Clonagem de Organismos/veterinária , Técnicas de Transferência Nuclear/veterinária , Placenta/irrigação sanguínea , Placenta/ultraestrutura , Placentação/fisiologia , Animais , Clonagem de Organismos/métodos , Membranas Extraembrionárias/ultraestrutura , Feminino , Masculino , Microscopia Eletrônica de Varredura/veterinária , Gravidez , Cordão Umbilical/anatomia & histologia , Cordão Umbilical/ultraestruturaRESUMO
Rock cavies are rodents found in the semi-arid caatinga of Brazil. We studied the structure of the rock cavy placenta by light and transmission electron microscopy. The exchange area of the labyrinth was organized in lobes separated by interlobular areas. The interhaemal barrier was syncytial haemomonochorial. The syncytiotrophoblast had recesses in the basal membrane and some invaginations of the apical membrane, but transtrophoblastic channels could not be found. The interlobular regions comprised syncytiotrophoblast, enclosing maternal venous blood channels, and cytotrophoblast. There was a prominent subplacenta composed of cytotrophoblast and syncytiotrophoblast. Microvilli projected into spaces between the cytotrophoblasts and into lacunae within the syncytiotrophoblast. The yolk sac epithelium exhibited coated pits, endocytotic vesicles and larger vacuoles, consistent with a role in protein uptake from the uterine lumen. Tight junctions between these cells provided a barrier to diffusion by the intercellular route. The reproductive biology of the rock cavy differs from other members of the family, including the guinea pig, but the architecture of the placenta remains remarkably constant.
Assuntos
Placenta/citologia , Placenta/ultraestrutura , Placentação/fisiologia , Roedores/fisiologia , Âmnio/citologia , Animais , Brasil , Decídua/citologia , Feminino , Masculino , Microscopia Eletrônica de Transmissão , Placenta/anatomia & histologia , Gravidez , Fatores de Tempo , Trofoblastos/citologia , Saco Vitelino/citologiaRESUMO
The placental vasculature of five hystricomorph rodents was examined by latex injection of the blood vessels, immunohistochemistry and scanning electron microscopy of vessel casts. The pattern of branching of the vessels is described at the level of fine structure. The placenta is divided into lobes separated by interlobular trophoblast. Fetal arteries course through the interlobular areas and give rise to capillaries from which blood drains into veins at the centre of the lobes. Maternal blood reaches the placenta through spiral arteries that pass around the perimeter of the subplacenta. They supply large maternal blood sinuses, lined by trophoblast, which run through the interlobular areas and into the centre of the lobes. Here they supply fine channels that run parallel to the fetal capillaries, so that maternal blood flows from the centre of the lobe to the periphery. This arrangement provides the morphological basis for countercurrent exchange. The maternal channels of the labyrinth drain into spaces formed by the latticework of the interlobular trophoblast and thence through venous lacunae to a basal venous lacunar ring. The subplacenta is supplied by a single fetal artery. The vessels within the subplacenta pursue a tortuous course with dilatations and constrictions as in an endocrine gland.
Assuntos
Vasos Sanguíneos/ultraestrutura , Placenta/irrigação sanguínea , Roedores/anatomia & histologia , Animais , Artérias/anatomia & histologia , Artérias/química , Artérias/ultraestrutura , Arteríolas/ultraestrutura , Vasos Sanguíneos/anatomia & histologia , Vasos Sanguíneos/química , Capilares/ultraestrutura , Feminino , Cobaias , Imuno-Histoquímica , Injeções Intra-Arteriais , Injeções Intravenosas , Queratinas/análise , Microscopia Eletrônica de Varredura , Modelos Anatômicos , Neopreno/química , Placenta/anatomia & histologia , Placenta/ultraestrutura , Poliésteres/química , Gravidez , Hidróxido de Sódio/química , Trofoblastos/citologia , Veias/anatomia & histologia , Veias/química , Veias/ultraestrutura , Vênulas/ultraestrutura , Vimentina/análiseRESUMO
Placentae of three hystricimorph rodents--capybara, agouti and paca--were examined by conventional histology, immunohistochemistry for cytokeratin and vimentin, and TUNEL staining. The placentae were divided into lobules of labyrinthine syncytium separated by interlobular and marginal trophoblast. The subplacenta comprised cytotrophoblasts, supported on lamellae of allantoic mesoderm, and syncytiotrophoblast. The central excavation was still apparent in the definitive placenta of capybara. In agouti and paca, the decidua of the junctional zone formed a mesoplacenta comprising a capsule and a pedicle. Towards term the pedicle formed a tenuous attachment between placenta and uterine wall comprising a few maternal vessels surrounded by degraded tissue. In paca placenta, it was shown by TUNEL staining that breakdown of this tissue occurred by apoptosis. The visceral yolk sac was highly villous and, in agouti, the yolk sac villi were extremely long. Lateral to its attachment to the placenta, the fetal surface was covered with non-vascular yolk sac endoderm. A layer of spongiotrophoblast cells was interposed between the endoderm and the marginal trophoblast.