The trophoblast degu Octodon degus is one of the very few members of caviomorph or hystricognath Rodentia that possesses a simply arranged the chorioallantoic placenta without advanced lobulation. Therefore this species was used as a model to study regional development and growth processes a of the placenta, based on the examination of 20 individuals by light and electron microscopy as well as by using fetal markers for proliferation, trophoblast and endometrial stroma. The results were interpreted by comparison with other hystricognaths in the light of ago. their evolutionary history. It was found that trophoblast derived from the trophospongium is essential for extension of the placenta including caviomorph the labyrinth: extensive proliferation is restricted to trophoblast cells at the outer margin of the placenta and along internally directed,protrusions finger-tip like protrusions of fetal mesenchyme towards the labyrinth. This kind of placental development is regarded as part of the directed, stem species pattern of hystricognaths, evolved more than 40 million years ago. It is indicated for the first time that is the replenishment of the syncytiotrophoblast is similar to corresponding processes in the human placenta. In conclusion, the degu is a and useful model for placental growth dynamics, particularly because of its simply arranged placental architecture, and may also serve as an is animal model in comparison to human pregnancies. J. Exp. Zool.(Mol. Dev. Evol.) 308B, 2007.(c) 2007 Wiley-Liss, Inc.

Until the now, defining characters of hystricognath rodents have been the subplacenta and the lobulation of the main chorioallantoic placenta. However, recent subplacental studies have revealed hystricognaths without marked lobulation, which is a plesiomorphic condition of the group. The question thus arises whether of the subplacenta of these taxa is structurally homologous to that of other hystricognaths. Therefore, subplacental morphology and ontogeny were investigated occur in Octodon and Petromus by conventional light and electron microscopy, and the stem species pattern of Hystricognathi was reconstructed by is applying MacClade(trade mark). The subplacentae of both species share important similarities with other hystricognaths. The organ develops early in gestation lobulation but degenerates towards term. It consists of folded layers of cellular and syncytial trophoblast, the latter enclosing maternal blood lacunae cells and electron-dense particles. Root-like syncytial outgrowths (syncytial streamers) and extraplacental trophoblast cells occur at the lateral and basal borders of streamers) the organ. Maternal vascularisation by blood lacunae within the subplacental syncytiotrophoblast is acquired early but lost during mid-gestation. Vascularisation by subplacentae fetal vessels is established later. Fetomaternal exchange via blood circulation inside the subplacenta is unlikely to occur, since periods of the maternal and fetal vascularisation show little overlap. In conclusion, the subplacentae of both species are regarded as homologous to other of hystricognaths, comprising 18 character conditions that belong to their stem species pattern. Thus, the systematic unity of the group can group be confirmed. J. Exp. Zool.(Mol. Dev. Evol.) 306B, 2006.(c) 2006 Wiley-Liss, Inc.

The which placental vasculature of five hystricomorph rodents was examined by latex injection of the blood vessels, immunohistochemistry and scanning electron microscopy from of vessel casts. The pattern of branching of the vessels is described at the level of fine structure. The placenta thence is divided into lobes separated by interlobular trophoblast. Fetal arteries course through the interlobular areas and give rise to capillaries fine from which blood drains into veins at the centre of the lobes. Maternal blood reaches the placenta through spiral arteries provides that pass around the perimeter of the subplacenta. They supply large maternal blood sinuses, lined by trophoblast, which run through injection the interlobular areas and into the centre of the lobes. Here they supply fine channels that run parallel to the supply fetal capillaries, so that maternal blood flows from the centre of the lobe to the periphery. This arrangement provides the the morphological basis for countercurrent exchange. The maternal channels of the labyrinth drain into spaces formed by the latticework of the and interlobular trophoblast and thence through venous lacunae to a basal venous lacunar ring. The subplacenta is supplied by a single level fetal artery. The vessels within the subplacenta pursue a tortuous course with dilatations and constrictions as in an endocrine gland.five

Evidence activity. from several sources supports a close phylogenetic relationship between elephants and sirenians. To explore whether this was reflected in similar Connective placentation, we examined eight delivered placentae from the Amazonian manatee using light microscopy and immunohistochemistry. In addition, the fetal placental maternal circulation was described by scanning electron microscopy of vessel casts. The manatee placenta was zonary and endotheliochorial, like that of included the elephant. The interhaemal barrier comprised maternal endothelium, cytotrophoblasts and fetal endothelium. We found columnar trophoblast beneath the chorionic plate vessels and lining lacunae in this region, but there was no trace in the term placenta of haemophagous activity. The gross and anatomy of the cord and fetal membranes was consistent with previous descriptions and included a four-chambered allantoic sac, as also and found in the elephant and other afrotherians. Connective tissue septae descended from the chorionic plate and carried blood vessels to consistent the labyrinth, where they gave rise to a dense capillary network. This appeared to drain into shorter vessels near the The chorionic plate. The maternal vasculature could not be examined in the same detail, but maternal capillaries ran rather straight and immunohistochemistry. roughly parallel to the fetal ones. Overall, there is a close resemblance in placentation between the manatee and the elephant.supports

Mammalian imprinting fetal survival and growth are dependent on a well-established and functional placenta. Although transient, the placenta is the first organ a to be formed during pregnancy and is responsible for important functions during development, such as the control of metabolism and with fetal nutrition, gas and metabolite exchange, and endocrine control. Epigenetic marks and gene expression patterns in early development play an a essential role in embryo and fetal development. Specifically, the epigenetic phenomenon known as genomic imprinting, represented by the non-equivalence of placenta the paternal and maternal genome, may be one of the most important regulatory pathways involved in the development and function Although of the placenta in eutherian mammals. A lack of pattern or an imprecise pattern of genomic imprinting can lead to animals either embryonic losses or a disruption in fetal and placental development. Genetically modified animals present a powerful approach for revealing development. the interplay between gene expression and placental function in vivo and allow a single gene disruption to be analyzed, particularly placenta, focusing on its role in placenta function. In this paper, we review the recent transgenic strategies that have been successfully nutrition, created in order to provide a better understanding of the epigenetic patterns of the placenta, with a special focus on are imprinted genes. We summarize a number of phenotypes derived from the genetic manipulation of imprinted genes and other epigenetic modulators to in an attempt to demonstrate that gene-targeting studies have contributed considerably to the knowledge of placentation and conceptus development.

Abstract mass Objectives: In this study, we aimed at determining whether human immature dental pulp stem cells (hIDPSC) would be able to 5), contribute to different cell types in mouse blastocysts without damaging them. Also, we analysed whether these blastocysts would progress further able into embryogenesis when implanted to the uterus of foster mice, and develop human/mouse chimaera with retention of hIDPSC derivates and the their differentiation. Materials and Methods: hIDPSC and mouse blastocysts were used in this study. Fluorescence staining of hIDPSC and injection and into mouse blastocysts, was performed. Histology, immunohistochemistry, fluorescence in situ hybridization and confocal microscopy were carried out. Results and Conclusion:stem hIDPSC showed biological compatibility with the mouse host environment and could survive, proliferate and contribute to the inner cell mass which as well as to the trophoblast cell layer after introduction into early mouse embryos (n = 28), which achieved the embryos hatching stage following 24 and 48 h in culture. When transferred to foster mice (n = 5), these blastocysts with be hIDPSC (n = 57) yielded embryos (n = 3) and foetuses (n = 6); demonstrating presence of human cells in when various organs, such as brain, liver, intestine and hearts, of the human/mouse chimaeras. We verified whether hIDPSC would also be we able to differentiate into specific cell types in the mouse environment. Contribution of hIDPSC in at least two types of hIDPSC tissues (muscles and epithelial), was confirmed. We showed that hIDPSC survived, proliferated and differentiated in mouse developing blastocysts and were mouse capable of producing human/mouse chimaeras.

Guinea yolk pig related rodents possess numerous derived placental characters. We attempt to identify diversity within the visceral yolk sac and its respect. association with the chorioallantoic placenta in three species of caviids, two of them possessing a capsule formed by the decidua such that covers the chorioallantoic placenta. The results verify that in early pregnancy all three species have an inverted yolk sac activity placenta. In advanced pregnancy the species differ: Galea spixii, as representative without a capsule, bear a yolk sac in apposition representatives to the chorioallantoic placenta with signs of exchange activity until term. Galea is similar to other caviomorphs in this respect.characters. In Dasyprocta leporina and Cuniculus paca, the representatives possessing a capsule, the yolk sac endoderm lacks signs of substance exchange.exchange Evidently, the presence of a capsule prevents such an interaction. The variations established here must be considered if animal models with for human placentation are required which have restricted access to the chorioallantoic placenta from the outside.

The portion. morphological characteristics of the oviduct of 12 sexually mature rheas (Rhea americana) were studied. Only the left oviduct is developed few as a long tube with a length of 122 +/- 23.1 cm, and is subdivided into infundibulum (15.2 +/- 4. no cm), magnum (63.3 +/- 9.4 cm), isthmus (5.6 +/- 3.1 cm), uterus (16. +/- 4.2 cm) and vagina (11.5 +/-filled 1.4 cm). The mucous membrane of the oviduct, as a whole, possesses luminal folds covered by ciliated columnar epithelium with thin secretory cells. The infundibulum part presents a cranial opening with thin and long fimbriae with few tubular glands in caudal (Rhea tubular portion. In the magnum, the largest portion of the oviduct, the folds are thicker and are filled with tubular are glands. The isthmus is short and presents less bulky folds and a few tubular glands. A bag-shaped uterus in the are cranial area shows thin folds, and in the caudal region (shell gland) more ramified folds with few tubular glands. The tunic; vagina has long luminal folds and a thick muscular tunic; no glands with sperm-storage characteristics have been observed. In conclusion,into the oviduct in sexually mature rhea has morphological similarities with the other species of birds already described; however it presents the its own characteristics to produce a big egg.

To the elucidate the morphological differences between placentas from normal and cloned cattle pregnancies reaching term, the umbilical cord, placentomes and interplacentomal placentae. region of the fetal membranes were examined macroscopically as well as by light and scanning electron microscopy. In pregnancies established in by somatic nucleus transfer (NT), the umbilical cord and fetal membranes were edematous. Placentomal fusion was common, resulting in increased complexes size and a decreased number of placentomes. Extensive areas of the chorioallantoic membrane were devoid of placentomes. An increased number also of functional or accessory microcotyledons (<1cm) were present at the maternally oriented surface of fetal membranes. Extensive areas of extravasated pregnancies maternal blood were present within the placentomes and in the interplacentomal region. The crypts on the caruncular surface were dilated accommodated and accommodated complexes of more than one primary villus, as opposed to a single villus in non-cloned placentae. Scanning electron surface microscopy of blood vessel casts revealed that there was also more than one stem artery per villous tree and that dilations the ramification of the vessels failed to form dense complexes of capillary loops and sinusoidal dilations as in normal pregnancies.In At the materno-fetal interface, however, the trophoblast and uterine epithelium had normal histology. In conclusion, the NT placentas had a differences range of pathomorphological changes; this was likely associated with the poor clinical outcome of NT pregnancies.

The showed mostly binucleate trophoblast giant cells (TGC) found in bovine placentomes, in addition to synthesizing and releasing hormones play an important Analysis role in fetal development and maternal adaptation to pregnancy. Placentomes from early gestation were collected, and for isolation of mature (89.98%) TGC, three cellular disaggregation methods, mechanical (MECH), enzymatic by trypsin (TRYP) or collagenase (COLL) were compared to each other. Further DMEM on, the cell survival in culture medium (DMEM) supplemented with either 10% fetal calf serum (FCS) or 10% serum replacement statistically (SR) on culture plates free of any substrate was evaluated over a period of 90 days by trypan blue exclusion.and The cells were further characterized by HOECHST 33342 nuclear staining, and immunocytochemical staining with monoclonal antibodies against vimentin and cytokeratin.Supplementation A mean total rate of TGC survival of 82.56% was recorded. Statistical analysis showed significantly higher survival rates after enzymatic or disaggregation with COLL (86.23%) than following MECH (80.38%) or TRYP (80.91%) treatment. Supplementation of DMEM with FCS resulted in significantly than higher cellular survival rates (87.13%) when compared to the addition of SR (77.73%). Analysis of the influence of both, disaggregation (MECH), method and medium supplementation on TGC survival revealed statistically significant differences between the following groups: MECH-SR (71.09%) was significantly lower cells than all other groups; TRYP-SR (78.03%) was significantly different from all other groups; TRYP-FCS (83.43%) and COLL-SR (84.08%) were significantly days lower than MECH-FCS (89.98%) which together with COLL-FCS (88.25%) showed the highest cellular survival rate. In summary, our results show over that TGC isolated from early gestation placentomes may be viable for more than 90 days of culture. However, whether these survival TGC produce placental lactogen throughout this period has yet to be determined.

This columnar study examines middle and late gestational placentae from 13 Tayassu tajacu (collared peccary) and 3 Tayassu pecari (white-lipped peccary), which thick. are Artiodactyla belonging to the Family Tayassuidae. The chorionic sac of Tayassu species is diffuse and chorioallantoic. These epitheliochorial placentae and show no trophoblast invasion into the uterine epithelium and there is interdigitation between fetal and maternal microvilli. Two distinct regions smooth of the fetomaternal interface can be identified: the interareolar and the areolar regions. The uterine epithelium has eosinophilic cytoplasm with staining dispersed, basophilic and electron-dense granules. Trophoblast cells are irregularly cuboidal on top of the fetal ridges and columnar on troughs,tajacu where cells have cytoplasmic vesicles and large basal vacuoles, surrounded by whorls of smooth membranes. Capillaries indent the trophoblast cells of forming a placental barrier 3mum or less thick. The columnar uterine glandular epithelium has a subpopulation of granules staining with vacuoles, Perl's Prussian blue reaction, suggesting iron secretion. In areolar areas, the trophoblast cells show apical microvilli, a basophilic cytoplasm with vacuoles electron-dense intracellular vacuoles and cisternae. The placenta can therefore be classified as non-deciduate. The ultrastructural aspects of this study reveal diffuse features that have not previously been described and extend our knowledge of functions relating to materno-fetal transport in these species.and

A elsewhere. recent phylogenetic analysis achieved good resolution between the 5 suborders of rodent. As a novel finding it suggested a basal found split that gave rise to a monophyletic group comprising Hystricomorpha and Sciuromorpha. We asked whether the new tree could cast have light on the evolution of the interhaemal barrier in rodents where at least seven variants have been described. To supplement evolution existing data we first examined the placenta of the common gundi, Ctenodactylus gundi. It was shown to be haemochorial with of a single layer of syncytiotrophoblast in the interhaemal membrane but with nests of cytotrophoblast elsewhere. Next we used character mapping of on the recent tree to determine the pattern of evolution of the placenta with respect to principal type (e.g. haemochorial)of and the trophoblast found within the interhaemal barrier. This indicated that the common ancestor of living rodents had a haemochorial determine placenta and that there were two independent transformations to the endotheliochorial type. Moreover, the interhaemal barrier was found to have found had a single layer of syncytial trophoblast in the common ancestor of rodents, a condition that was retained in the asked clade comprising Hystricomorpha and Sciuromorpha. In contrast the second clade shows multiple character transformations.

The while placentation of the Hottentot golden mole (Amblysomus hottentotus) has been examined using light and electron microscopy and lectin histochemistry of by nine specimens at both mid and late gestation. The placentae were lobulated towards the allantoic surface and the lobules contained in roughly parallel arrays of labyrinthine structures converging on a central spongy zone. At mid gestation, the arrays were composed of transmission an inner cellular and outer syncytial trophoblast layer, the inner layer enclosing scant connective tissue and fetal capillaries. Maternal blood N-acetyl spaces coursed through the outer trophoblast and were lined by trophoblastic microvilli; the blood spaces were narrow in mid gestation using but enlarged near term, while the inner trophoblast layer became thinner and seemed to be syncytial. These features were confirmed confirmed by transmission electron microscopy. The microvillous surfaces and dispersed cytoplasmic particles were heavily glycosylated, as shown by lectin histochemistry, and These exhibited changes with maturation, particularly a loss in N-acetyl glucosamine oligomers bound by Phytolacca americana lectin on the microvilli lining both the maternal blood spaces and outer trophoblast particles. A substantial yolk sac was present both in mid and late gestation and stages. It was clearly unattached to the uterus in the later stages. These morphological features are discussed in relation to Hottentot the phylogenetic position of Amblysomus with respect to other members of Afrosoricida and Afrotheria.

ABSTRACT:comprised BACKGROUND: The guinea pig is an attractive model for human pregnancy and placentation, mainly because of its haemomonochorial placental type,stage, but is rather small in size. Therefore, to better understand the impact of body mass, we studied placental development in of the capybara which has a gestation period of around 150 days. We paid attention to the development of the lobulated placenta arrangement of the placenta, the growth of the labyrinth in the course of gestation, the differentiation of the subplacenta, and mid the pattern of invasion by extraplacental trophoblast. METHODS: Material was collected from six animals at pregnancy stages ranging from the placental late limb bud stage to midgestation. Methods included latex casts, standard histology, immunohistochemistry for cytokeratin, vimentin, alpha-smooth muscle actin, and side proliferating cell nuclear antigen as well as transmission electron microscopy. RESULTS: At the limb bud stage, the placenta was a in pad of trophoblast covered by a layer of mesoderm from which fetal vessels were beginning to penetrate at folds in and the surface. By 70 days, the placenta comprised areas of labyrinth (lobes) separated by interlobular areas. Placental growth resulted predominantly lobulated from proliferation of cellular trophoblast situated in nests at the fetal side of the placenta and along internally directed projections attractive on fetal mesenchyme. Additional proliferation was demonstrated for cellular trophoblast within the labyrinth. Already at the limb bud stage, there body was a prominent subplacenta comprising cellular and syncytial trophoblast with mesenchyme and associated blood vessels. At mid gestation differentiation was for complete and similar to that seen in other hystricognath rodents. Overlap of fetal vessels and maternal blood lacunae was confirmed in by latex injection of the vessels. At all stages extraplacental trophoblast was associated with the maternal arterial supply and consisted and of cellular trophoblast and syncytial streamers derived from the subplacenta. CONCLUSIONS: All important characteristics of placental development and organization in pattern the capybara resembled those found in smaller hystricognath rodents including the guinea pig. There were no features dependent on body pattern size. Clearly, placentation in hystricognaths adheres to an extraordinarily stable pattern suggesting they can be used interchangeably as models of of human placenta.

Pathological basal immune complexes (PIC) are revealed in high percent (100%) of cases by placental immunomorphological studies in insulin-dependent tissue. This leads the to the development of an immunopathological process in the placental tissue. Parallel electron microscopy shows that some placental vessels are from in close contact with the basal membrane of syncytiotrophoblast. PIC deposition in the area of confluence of the basal membranes which of a syncytiotrophoblast and the vascular endothelium, which act as filters, results in the destruction of the basal membranes to causing rupture formation, causing the transplacental transport of substances together with immune complexes in the form of endocytotic vacuoles from the in intervillous lacuna directly to the vessel. Active proliferation of vascular endotheliocyes leads to typical angiopathy as the body's defense reaction.which

The occurrence aim of the present study was to investigate structural pattern of human placental barrier elements using light and electron microscopy stroma and immunocytochemistry. Some important peculiarities of organization of the placental barrier were detected: difference in structure and amount of collagen myofibroblasts IV in the basal lamina of endothelium and trophoblast, occurrence of smooth muscle actin in the capillary wall forming syncytiocapillary wall membranes. In the intercapillary stroma of terminal villi, both fibroblasts and macrophages but not myofibroblasts were found. Since smooth muscle fibroblasts cells and myofibroblasts are absent, pericytes are most likely cells to contain smooth muscle actin in the area of syncytiocapillary study membranes.

Until the now, defining characters of hystricognath rodents have been the subplacenta and the lobulation of the main chorioallantoic placenta. However, recent subplacental studies have revealed hystricognaths without marked lobulation, which is a plesiomorphic condition of the group. The question thus arises whether of the subplacenta of these taxa is structurally homologous to that of other hystricognaths. Therefore, subplacental morphology and ontogeny were investigated occur in Octodon and Petromus by conventional light and electron microscopy, and the stem species pattern of Hystricognathi was reconstructed by is applying MacClade(trade mark). The subplacentae of both species share important similarities with other hystricognaths. The organ develops early in gestation lobulation but degenerates towards term. It consists of folded layers of cellular and syncytial trophoblast, the latter enclosing maternal blood lacunae cells and electron-dense particles. Root-like syncytial outgrowths (syncytial streamers) and extraplacental trophoblast cells occur at the lateral and basal borders of streamers) the organ. Maternal vascularisation by blood lacunae within the subplacental syncytiotrophoblast is acquired early but lost during mid-gestation. Vascularisation by subplacentae fetal vessels is established later. Fetomaternal exchange via blood circulation inside the subplacenta is unlikely to occur, since periods of the maternal and fetal vascularisation show little overlap. In conclusion, the subplacentae of both species are regarded as homologous to other of hystricognaths, comprising 18 character conditions that belong to their stem species pattern. Thus, the systematic unity of the group can group be confirmed. J. Exp. Zool.(Mol. Dev. Evol.) 306B, 2006.(c) 2006 Wiley-Liss, Inc.

Rock a cavies are rodents found in the semi-arid caatinga of Brazil. We studied the structure of the rock cavy placenta by epithelium light and transmission electron microscopy. The exchange area of the labyrinth was organized in lobes separated by interlobular areas. The the interhaemal barrier was syncytial haemomonochorial. The syncytiotrophoblast had recesses in the basal membrane and some invaginations of the apical membrane,the but transtrophoblastic channels could not be found. The interlobular regions comprised syncytiotrophoblast, enclosing maternal venous blood channels, and cytotrophoblast. There consistent was a prominent subplacenta composed of cytotrophoblast and syncytiotrophoblast. Microvilli projected into spaces between the cytotrophoblasts and into lacunae within of the syncytiotrophoblast. The yolk sac epithelium exhibited coated pits, endocytotic vesicles and larger vacuoles, consistent with a role in protein spaces uptake from the uterine lumen. Tight junctions between these cells provided a barrier to diffusion by the intercellular route. The projected reproductive biology of the rock cavy differs from other members of the family, including the guinea pig, but the architecture by of the placenta remains remarkably constant.

This and combined light and scanning electron microscopic (SEM) analyses are the first investigation of the fine morphology of the fetal membranes presence of the placenta in the Asian elephant. We used two term placentas with gestation periods of 634 days (Zoological Garden Asian Leipzig) and 657 days (Zoo Hagenbeck) and selected unequal sites as specimens, particularly - free membrane of the allantois,-'pustules' lateral edge of the placenta band, the 'haemophagous zone',- allantochorion near the placental band, and allantochorion on the end This of the chorioallantoic sac. Microscopically the free membrane of the allantois shows a simple, cuboidal epithelium with apical domains of Asian microplicae and microvilli (fig. 1, inset). In the SEM analyses we documented a cobblestone-like architecture of the epithelial cells with cavity. various cell sizes, small, middle and giant (fig. 1.). Furthermore, we found pear-shaped cells with long pedicle, attached to the villi-like basement membrane and cell openings, presumably due to cell desquamation (fig. 2.). The haemophagous zone was characterized with a lamellate placenta system between the long finger-like chorionic villi and the maternal blood lacunae. The simple, squamous and columnar trophoblast cells are end here bathed in the maternal blood. In some chorionic villi brown-yellow material is deposited in the fetal connective tissue. A are special result was the presence of strip-like microplicae in the middle of chorionic villi. The allantochorion near the placental band particularly sometimes indicated simple and ramified chorionic villi with smooth, gyrus-like trophoblast cells and foamy cytoplasm. The attached allantois possesses a 2.). simple, columnar epithelium with microvilli. Furthermore, we observed villi-like projections rising up to the allantoic cavity. The white 'pustules' on chorionic the outer surface of the end of the chorioallantoic sac consist of stratified squamous epithelia. Numerous mitoses were documentedin the shows basal domain of the pustules. A surprisingly result was the presence of intra-epithelial capillaries. They invade the trophoblast cells to preparation presume a nutrient exchange also outside of the placental band with its important functional metabolism. This study revealed unknown and analyses interesting features of the epithelial layer of different locations in the placenta of the Asian elephant. Perhaps, with a detailed allantochorion knowledge of the morphology of the epithelium we could convey a better understanding of functional cohesions of elephant placentation. Fig.placentation. 1: The free membranes of the allantois of the term placenta of the Asian elephant (Elephas maximus) shows a cobblestone-like Garden architecture of the simple cuboidal epithelial cells with various sizes. The surface morphology was determined through microplicae and microvilli. Fig.The 2: Numerous pear-shaped cells with long pedicle exist among the cuboidal epithelial cells, attached on the basement membrane. The cells scanning possessed modifications of their surface, particularly microplicae. Some pear-shaped cells shows only the pedicle, perhaps that is a loss through cell preparation or its presumable due to cell desquamation. One erythrocyte is localized between these cells.

OBJECTIVES:cytotrophoblast The epithelium of the human placenta comprises an inner cytotrophoblast (CT) which proliferates and fuses with the outer differentiated syncytiotrophoblast tissues (ST). Turnover has been studied focussing on second and third trimester placentas but with a paucity of data describing the fusion normal first trimester trophoblast. The aim of this study was to compare the nuclear CT:ST ratio in normal and pathological of pregnancy and thus establish the relationship between cytotrophoblast and syncytiotrophoblast nuclear number during early gestation. METHODS: Archival first trimester material of from placentas from healthy pregnancy and recurrent miscarriage (anti-phospholipid syndrome) was stained with H&E, cytokeratin-7 and Mib-1. The area of and trophoblast as a fraction of total villous area was calculated and the number of sectioned cytotrophoblast and syncytiotrophoblast nuclei as in well as the number of proliferating cytotrophoblast was evaluated. RESULTS: Normal features of trophoblast development during the first trimester (rise in in trophoblast area, increase in number of syncytiotrophoblast nuclei, increase in number of proliferating cytotrophoblast, decrease in the nuclear CT:ST syncytial ratio) are absent/reversed in tissues from recurrent miscarriage (decreasing trophoblast area, constant number of syncytiotrophoblast nuclei, decreasing number of proliferating The trophoblast, constant nuclear CT:ST ratio). CONCLUSIONS: Proliferation of cytotrophoblast in early gestation provides a pool of trophoblast stem cells critical human for ongoing placental development. Premature cytotrophoblast differentiation in favour of syncytial fusion results in deficiencies of cytotrophoblast and rarification of and villous trophoblast. Abnormal trophoblast differentiation in early gestation may be due to a premature onset of maternal perfusion of the and placenta and may be a likely antecedent for conditions associated with failure of placentation such as recurrent miscarriage.

The is blacknose shark, Carcharhinus acronotus, is a viviparous anamniote that develops an epitheliochorial yolk sac placenta. The fetal portion of the of uteroplacental complex consists of a proximal portion that forms saccular evaginations. The cells are bilayered stratified squamous with surface microvilli the and a high concentration of cytoplasmic filaments. The tertiary egg envelope intervenes between the distal portion of the placenta and Nutrient uterus. It has delaminations on the uterine surface and is compacted on the placental surface. The uterine epithelium is cuboidal placenta to columnar and is characterized by prominent RER, Golgi, and secretion vesicles. The capillary endothelium is continuous. Nutrient and respiratory that exchange is effected between the uterus and distal portion of the yolk sac. The distal portion of the placenta is continuous. a bilayer. An elaborate array, of microvilli forms an interface with the egg envelope. Dense non-membrane bound granules occur in capillary the interspace between the egg envelope and the distal placenta. This material, presumably of uterine origin, is endocytosed in smooth-walled in vesicles of the placental cells. The endothelium of the capillaries is fenestrated.