Dissection of 6.5 dpc mouse embryos

Analysis of gene expression patterns during early stages of mammalian embryonic development can provide important clues about gene function, cell-cell interaction and signaling mechanisms that guide embryonic patterning. However, dissection of the mouse embryo from the decidua shortly after implantation can be a challenging procedure, and detailed step-by-step documentation of this process is lacking. Here we demonstrate how post-implantation (6.5 dpc) embryos are isolated by first dissecting the uterus of a pregnant mouse (detection of the vaginal plug was designated day 0.5 poist coitum) and subsequently dissecting the embryo from maternal decidua. The dissection of Reichert's membrane is described as well as the removal of the ectoplacental cone.     

Growth and proliferation in mouse parietal yolk sac during whole embryo culture

Use of the culture techniques for postimplantation rodent embryos, modified by explanting Day 9 or Day 10 embryos with the trophoblast cells removed but the remainder of the parietal yolk sac left intact, resulted in significant expansion of Reichert's membrane, accompanied by a marked increase in the numbers of the adherent parietal endoderm cells which synthesize the membrane. The surface area of the parietal endoderm/Reichert's membrane complex roughly doubled during culture, and the combined protein content of the cells and their basement membrane was also raised after incubation. Parietal endoderm cell numbers, calculated from area and cell density measurements on flattened membranes, increased by 54-190%, depending on the age of the embryo.     

Possible mechanisms of cadmium fetotoxicity in golden hamsters and mice: uptake by the embryo, placenta and ovary.

Pregnant golden hamsters and mice of different gestational ages were injected intravenously with 109CdCl(2). The whole animal or the uterus and embryos were submitted to autoradiography. Cadmium administered on the 8th day accumulated in the primitive gut of the embryos. No cadmium was detected in the embryos after administration on or after the 9th day (hamster) and 11th day (mouse). This finding can be explained by the ability of cadmium to pass from the yolk-sac cavity into the primitive gut (where it is absorbed) before the closure of the vitelline duct but not later. This uptake by the embryo might explain the severe malformations produced by cadmium given on the 8th day as compared with the 9th day in the hamster. Cadmium is also heavily accumulated in the decidua (mainly the antimesometrial part), the yolk sac, the ectoplacental cone, and later in the chorioallantoic placenta-possibly disturbing the maternal-embryonic relationship and fetal nutrition. A high accumulation in the CL and the follicles and in the pituitary may also disturb reproductive function.     

小鼠外胎盘锥次级滋养层巨细胞的分离、培养与鉴定

目的：建立小鼠外胎盘锥次级滋养层巨细胞的分离、培养方法.方法：在小鼠妊娠第8 d,通过机械分离和组织块翻转干涸法分离、培养小鼠外胎盘锥次级滋养层巨细胞;免疫细胞化学鉴定细胞来源与纯度;酶谱方法检测其所分泌基质金属蛋白酶2和9（matrix metalloproteinase-2,9,MMP-2,9）结果：利用机械分离法分离外胎盘锥可生长于Matrigel包被的培养板上,并生长出次级滋养层巨细胞,表达特异性标志物Cytokeratin;体外培养24 h、48 h后,外胎盘锥滋养层巨细胞的粘附率分别为（83.3±9.1）%和（92.4±7.3）%;扩展率分别为（45.5±5.3）%和（56.4±6.8）%;及其所分泌的MMP-2,9的24 h光密度值分别为（87±4.7）和（351.5±25.2）;48 h分别为（186±40.2）和（556.5±61.5）.结论：采用机械分离和组织块翻转干涸法,可简单、快捷地获得高纯度小鼠外胎盘锥次级滋养层巨细胞.     

Expression of v-src induces aberrant development and twinning in chimaeric mice

The role of the proto-oncogene c-src in mouse development has been investigated by studying the consequences of expressing its viral homologue, v-src. Embryonic stem (ES) cell lines with differing levels of v-src tyrosine kinase activity have been used to generate chimaeric mice. Whereas a low level of v-src expression is compatible with embryogenesis, chimaeras derived from ES clones with high levels of v-src activity develop abnormally and die on the 8th-9th day of gestation. These abnormalities are characterized by the formation of twin or multiple embryos within the same Reichert's membrane, and by the arrest of embryonic development at the late egg cylinder stage, accompanied by relative expansion of the visceral yolk sac (VYS) and hyperplasia of the VYS endoderm. These results demonstrate for the first time that deregulated expression of the src protooncogene product can induce developmental abnormalities during early embryogenesis.     

A null mutation in the inflammation-associated S100 protein S100A8 causes early resorption of the mouse embryo.

S100A8 (also known as CP10 or MRP8) was the first member of the S100 family of calcium-binding proteins shown to be chemotactic for myeloid cells. The gene is expressed together with its dimerization partner S100A9 during myelopoiesis in the fetal liver and in adult bone marrow as well as in mature granulocytes. In this paper we show that S100A8 mRNA is expressed without S100A9 mRNA between 6.5 and 8. 5 days postcoitum within fetal cells infiltrating the deciduum in the vicinity of the ectoplacental cone. Targeted disruption of the S100A8 gene caused rapid and synchronous embryo resorption by day 9. 5 of development in 100% of homozygous null embryos. Until this point there was no evidence of developmental delay in S100A8-/- embryos and decidualization was normal. The results of PCR genotyping around 7.5-8.5 days postcoitum suggest that the null embryos are infiltrated with maternal cells before overt signs of resorption. This work is the first evidence for nonredundant function of a member of the S100 gene family and implies a role in prevention of maternal rejection of the implanting embryo. The S100A8 null provides a new model for studying fetal-maternal interactions during implantation.     

Effect of 32/67 kDa laminin-binding protein antibody on mouse embryo implantation

Mouse embryo implantation depends on the complex interaction between the embryo trophoblast cells and the uterine environment, which deposits an extracellular matrix with abundant amounts of laminin. Intrauterine injection and blastocyst or ectoplacental cone culture models were used to study the effect of 32/67 kDa laminin-binding protein antibody on mouse embryo implantation in vivo and in vitro. Intrauterine injection of 32/67 kDa laminin-binding protein antibody (0.4 mg in 1 ml Ham's F-10 medium, 5 microl per mouse) into the left uterine horns of mice (n = 22) on day 3 of pregnancy inhibited embryo implantation significantly (P < 0.001) compared with the contralateral horns that had been injected with normal rabbit IgG. A continuous section study on day 5 after injection showed that the embryos in the control uteri implanted normally and developed healthily, but there were no embryos or the remaining embryos had disintegrated in the uteri injected with 32/67 kDa laminin-binding protein antibody. Blastocysts or ectoplacental cones were cultured in media containing 32/67 kDa laminin-binding protein antibody (0.2 mg ml(-1)) on laminin-coated dishes with normal rabbit IgG at the same concentration as in the controls. The 32/67 kDa laminin-binding protein had no effect on blastocyst or ectoplacental cone attachment, but prohibited the blastocyst or ectoplacental cone outgrowth and primary or secondary trophoblast giant cell migration. These results indicate that 32/67 kDa laminin-binding protein antibody blocked mouse embryo implantation by preventing embryo trophoblast cell invasion and migration through the uterine decidual basement membrane-like extracellular matrix which has a high laminin content.     

Protein synthesis in embryonic tissues during mouse postimplantation development

Mouse embryos of the NMRI strain between the 7th and 9th day of gestation were isolated from the uterus and dissected into the various tissue derivatives in order to investigate newly synthesized proteins during morphogenesis. The day 7 embryo was fragmented into trophoblast and ectoplacental cone, distal and proximal endoderm, extraembryonic and embryonic ectoderm. The day 8 and day 9 embryos were divided into trophoblast and placental anlage, yolk sac, amnion, and allantois, as well as cranial, central, and caudal embryonic tissue. The intact embryos were incubated in Dulbecco's minimum essential medium in the presence of 35S-methionine for 4 h, then dissected into the various fragments, and further processed for two-dimensional gel electrophoresis. Protein synthesis of the isolated tissue derivatives was analyzed and compared for the three developmental stages. Concerning the proteins with isoelectric points in the range of 4.5 to 8.0 and molecular weight ratio (M(r)) values between 20,000 and 200,000, we found several significant quantitative and qualitative differences in the various tissue fragments. In addition, we observed further quantitative and qualitative differences in protein synthesis during the postimplantation period investigated. We propose that the differences reflect some of the cell lineage- and developmental stage-specific changes in gene expression during early mammalian differentiation.     

Blastocyst attachment and morphogenesis of ectoplacental cone in mouse

Mouse blastocyst attaches on the antimesometrial side of the uterus through mural trophoblasts. Later the polar trophoblasts begin proliferation, and rapid multiplication towards the mesometrial side of the uterus occurs resulting in the formation of an excrescence designated as ectoplacental cone. The morphogenesis of ectoplacental cone, viewedin utero, initiates on day 6post-coitum when microvilli of the trophoblast and the uterine epithelial cells are lost and as a result of this opposing membranes appear interlocked with each other. Soon following the invasion by surrounding trophoblasts the necrosis of the epithelial cells starts. Mitochondriae of the epithelial cells, at this stage, are shrunken and lack well defined cristae. Several leucocytes are seen at the site and few electron dense structures appear wedged between the trophoblasts and epithelial cells. At places the cell membrane is studded with the basement membrane of the uterine epithelium giving an impression of a bristle coated membrane. By day 7post-coitum the basement membrane has almost disappeared leaving trophoblast cells to develop close contact with stromal cells. Collagen fibres appeared between the trophoblasts and the stromal cells, many large inclusions of high electron density representing engulfed necrotic epithelial cells are discernible. On day 8post-coitum the ectoplacental cone is fully developed. Four types of trophoblast cells can be identified in it: (i) basal cells lying on the base of the cone, are polyhedral and compactly arranged. They have a large nucleus and well developed nucleoli, (ii) central cells forming the middle area of the cone are of two types; one contained several osmiophilic granules enclosing translucent area (eccentric) and a well developed golgi complex around the nucleus, while the other has many heterophagosomes, vacuoles and residual bodies and (iii) peripheral cells contained several pleomorphic structures resembling secondary lysosomes. Minute dense granules and band of microfibrils on the apical region of these cells are seen. Dense granules probably release lytic proteins at the site and microfibrils help in forming cytoplasmic projections.     

Ultrastructural localization of carbohydrates in Reichert's membrane of the mouse

In the present investigation, we examined the role of trophoblast and parietal endoderm cells in the synthesis of carbohydrate-containing components of Reichert's membrane. To eliminate the function of Reichert's membrane as a filter between maternal and embryonal tissues we carried out our examination under in vitro conditions. Parietal yolk sac from mouse embryos on day 9 post coitum (p.c.) were cultivated for 0 to 5 days. Because tannic acid enables a complex formation between carbohydrates and osmium we chose the fixation with this acid for the ultrastructural study. Electron microscopy showed that for assembly of Reichert's membrane, trophoblast cells produce and then release components that were detected as tannic acid-positive granules both in the Reichert's membrane and in the vacuoles of the trophoblast cells. To localize specific carbohydrates we used postembedding-gold-lectin histochemistry on LR-Gold^R-embedded tissues. Strong binding sites for the lectins WGA (Triticum vulgare), RCA I (Ricinus communis) and Con A (Canavalia ensiformis) were observed in Reichert's membrane and trophoblast cells but not in the parietal endoderm cells. The LTA (Lotus tetragonolobus)-binding pattern was positive in the membrane and its adjacent cells but that of the LFA (Limax flavus) was negative in the parietal endoderm cells and very weak in Reichert's membrane and trophoblast cells. Our results demonstrate that trophoblast cells are involved in the construction of Reichert's membrane through the production and release of specific glycoconjugates.     

Teratoid Tumors Derived from Mouse Embryos Grown in an Immunologically Privileged Site

Mouse early embryos and embryo fragments were transplanted into an immunologically privileged site, consisting of a glass cylinder previously implanted under the skin of adult mice in order to test their tumor producing potential, in allogeneic adult recipients. The highest yield of tumors was obtained upon transplantation of 6 1/2 day old embryos in toto. i.e., including the embryonic and extraembryonic areas. Histological examination showed teratomas composed of differentiated tissues derived from the three germ layers containing isolated foci of undifferentiated cells and nodules of trophoblast giant cells. Areas exhibiting the histological appearance of yolk sac carcinoma were also observed. Transplantation of the whole 6 1/2 day old egg cylinder, including the ectoplacental cone, and the isolated embryonic area produced a lower incidence of teratomas with a reduced variety of differentiated tissues. No yolk sac carcinoma was found in these grafts. The ectoplacental cone of 6 1/2 day embryos produced no tumors. Grafts of genital ridges from 12 1/2 day embryos gave rise to teratomas with well differentiated tissues of embryonic and extraembryonic origin. Areas ressembling yolk sac carcinoma were also observed. The life span of trophoblastic giant cells within the glass cylinder was significantly longer than in other experimental systems.     

Monoclonal antibodies to laminin reveal the heterogeneity of basement membranes in the developing and adult mouse tissues

Two monoclonal antibodies raised against laminin isolated from a mouse parietal yolk sac cell line were used for immunohistochemical studies of basement membranes of the mouse embryo and various fetal and adult tissues. No immunoreactivity with either of the two monoclonal antibodies could be detected in the preimplantation-stage embryos, although it has been shown that these embryos contain extracellular laminin reactive with the conventional polyclonal antilaminin antibodies. Reichert's membrane in early postimplantation stages of development reacted with the monoclonal antibody LAM-I but not with the antibody LAM-II. However, from day 8 of pregnancy onward the Reichert's membrane reacted with both antibodies. Basement membranes of the embryo proper were unreactive with both monoclonal antibodies until day 12 of pregnancy. By day 14 some basement membranes of the fetal tissues became reactive with one or both monoclonal antibodies, whereas others remained still unreactive. In the 17-d fetus and the newborn mouse most of the basement membranes reacted with both monoclonal antibodies, whereas others still reacted with only one. Similar heterogeneity in the immunoreactivity of basement membranes of various tissues was noted in the adult mouse as well. These results indicate that the immunoreactivity of laminin in the extracellular matrix changes during development and that the basement membranes in various anatomic locations display heterogeneity even in the adult mouse.     

Variation in development of rat embryos at the presomite period.

Rat embryos at a single gestational time in the presomite period were studied for their variation in development and their fate after culture. They were explanted at 8 A.M. on day 9 of gestation from timed-pregnant Sprague-Dawley rats which were obtained by mating between 8 and 10 A.M. (plug day = day 0). In the first experiment, a total of 203 embryos from 20 litters were examined for their variation in development. Several dimensions of embryo/egg cylinder were measured and development of various embryonic/extraembryonic structures were assessed using a scoring system that we developed for the present study. Embryos were then divided into different stages of development based on their scores using the staging system that we developed previously. A large variation in developmental stage was demonstrated; the youngest embryo was at the early primitive streak stage with no signs of amniotic folds and the oldest one was at the late neural plate stage with a foregut pocket but without visible somites. No strong correlation was demonstrated between developmental stage and size of embryo/egg cylinder, nor between developmental stage and development of the proamniotic tube, ectoplacental cavity, or allantois. In the second experiment, embryos were explanted at the same time and those at different stages were cultured separately in rotating bottles and their outcomes were compared after 49 hours. The difference in mean somites number of embryos cultured from the mid primitive streak and late neural plate stages was 6.1. This difference corresponds to approximately 10 hours based on the known linear increase of somites number on day 11 of approximately 0.6 somites per hour. These results indicate a large variation in development of presomite period embryos supposedly of the same gestational age and suggest the importance of careful staging at the time of explantation if precision is needed for whole embryo culture experiments.     

Development of trophoblast and placenta of the mouse. A reinvestigation with regard to the in vitro culture of mouse trophoblast and placenta

At 5 days post conceptionem (p.c.) shortly after implantation, giant cell transformation starts at the abembryonic pole of the blastocyst, spreading over the mural trophoblast; 1 day later, the first ectoplacental giant cells appear at the base of the fast growing ectoplacental cone (derived from the polar trophoblast). Giant cell transformation expands over it periphery. Thus, by the 8th day p.c., the conceptus is separated from the maternal tissue by a continuous layer of giant cells, variable in thickness. Giant cells reach their greatest size by 10 days p.c. in the mural tophoblast and by 12 days p.c. in the chorioallantoic placenta. They are probably no longer formed after that stage. Around the 8th day p.c., the allantois reaches contact with the ectoplacental cone, which develops into the chorioallantoic (definitive) placenta. At 9 days p.c., its four zones can already be discriminated: chorionic plate, labyrinth, junctional zone (trophospongium), and zone of giant cells, respectively. Within the next day, the chorioallantoic placental circulation is established. The yolk sac placental circulation is established by the 9th day p.c. The villi of the proximal layer of the yolk sac increase in size and number, and their capillary network becomes more dense until the 12th to 14th day p.c. This provides evidence that the yolk sac placenta exerts its function--to a certain extent--beyond the establishment of the definitive placenta. Around the 14th day p.c., the placental labyrinth reaches its definitive features. Fetal capillaries in the labyrinth, branching from unbilical blood vessels within the septa of connective tissue are surrounded by trophoblast cells. They form a dense vascular network bathing in maternal blood. The structures of the placental zones remain almost the same during further development, the borders becoming sometimes little blurred. Adjacent to the chorionic plate, subchorionic clefts appear at the 14th day p.c. These clefts become confluent to form the intraplacental space, regularly communicating with the yolk sac cavity. At the end of gestation (19th day p.c.) there is a considerable amount of eosinophilic material ('fibrinoid') between the zone of giant cells and the decidua, probably produced by the giant cells.     

The shaping of the mesometrial proamniotic cavity in the mouse. Are there various mechanisms?

The existence of an alternative pathway of the shaping of the mesometrial proamniotic cavity (based upon the examination of several hundreds 6-day mouse embryos), which occurs more frequently than mentioned by other authors, is described. The observed pathway begins with the invagination of the mesometrial pole of the implanted blastocyst, the early proamniotic cavity thus communicating with the uterine lumen. Subsequently, it is occluded by the ectoplacental cone. The phylogenetic aspects of these observations are discussed.     

Compositional and structural requirements for laminin and basement membranes during mouse embryo implantation and gastrulation

Laminins are components of all basement membranes and have well demonstrated roles in diverse developmental processes, from the peri-implantation period onwards. Laminin 1 (alpha1beta1gamma1) is a major laminin found at early stages of embryogenesis in both embryonic and extraembryonic basement membranes. The laminin gamma1 chain has been shown by targeted mutation to be required for endodermal differentiation and formation of basement membranes; Lamc1(-/-) embryos die within a day of implantation. We report the generation of mice lacking laminin alpha1 and laminin beta1, the remaining two laminin 1 chains. Mutagenic insertions in both Lama1 and Lamb1 were obtained in a secretory gene trap screen. Lamb1(-/-) embryos are similar to Lamc1(-/-) embryos in that they lack basement membranes and do not survive beyond embryonic day (E) 5.5. However, in Lama1(-/-) embryos, the embryonic basement membrane forms, the embryonic ectoderm cavitates and the parietal endoderm differentiates, apparently because laminin 10 (alpha5beta1gamma1) partially compensates for the absent laminin 1. However, such compensation did not occur for Reichert's membrane, which was absent, and the embryos died by E7. Overexpression of laminin alpha5 from a transgene improved the phenotype of Lama1(-/-) embryos to the point that they initiated gastrulation, but this overexpression did not rescue Reichert's membrane, and trophoblast cells did not form blood sinuses. These data suggest that both the molecular composition and the integrity of basement membranes are crucial for early developmental events.     

Deposition of fibronectin and laminin in the basement membrane of the rat parietal yolk sac: immunohistochemical and biosynthetic studies

Rat parietal yolk sacs (PYS) at gestational ages 7.5, 9.5, 11.5, 13.5, 14.5, and 16.5 d were reacted with antibodies against laminin or plasma fibronectin. At all times studied, laminin consistently gave a positive reaction with Reichert's membrane and with the cytoplasm of PYS cells. In contrast, fibronectin gave a negative reaction with Reichert's membrane at day 7.5, was weakly positive at day 9.5, and from then on was increasingly positive with maximum reactivity at 14.5 d. By electron microscopic immunohistochemistry, antilaminin reacted strongly with 14.5-d Reichert's membrane and with the contents of the rough endoplasmic reticulum RER cisternae of the PYS cells. Antifibronectin had some spotty reactivity with Reichert's membrane, but the cytoplasm of the PYS cells was negative. The contents of the vitelline vessels and the interface between trophoblast and Reichert's membrane were strongly positive. Metabolic labeling of PYS cells in organ culture clearly demonstrated the presence of laminin, type IV procollagen, and entactin both in the medium and in tissues, but fibronectin was absent. No component in the medium bound to gelatin-Sepharose columns. These studies demonstrate that PYS cells, which actively synthesize and secrete basement membrane components, do not synthesize any detectable fibronectin. Furthermore, the anti-fibronectin staining pattern in the vitelline vessels and trophoblast-Reichert's membrane interface strongly suggests that the fibronectin present in Reichert's membrane is derived from the maternal circulation and is merely "trapped" in the membrane.     

Effects of interleukin 11 (IL-11) on early post-implantation development of the rat

The development of embryos, trophoblast and decidua of IL-11-treated rats were examined in vivo, while ectoplacental cones (EPC) were studied in vitro. Female Wistar rats were injected daily with buffer (C), 1 mg/kg IL-11 (HD) daily or 30 microgram/kg (LD) IL-11 twice a week. On day 9 of pregnancy, embryonic tissue volume was reduced in IL-11-treated animals, but EPC volume was elevated, compared to controls. Mitotic indices were reduced in embryos (P<0.05 for LD, P<0.001 for HD) and in EPCs of both groups. Pycnotic indices were elevated in LD (NS) and HD (P<0.05) embryos, but decreased in EPCs of the LD group (P<0.01). Morphological abnormalities were observed in decidua, embryo and trophoblast. In HD, EPC attachment was impaired after 1 day culture but proliferation was stimulated after 5 days. Defective decidualization in IL-11 treated rats may therefore result in abnormal development of embryo and trophoblast.     

Endogenous peroxidase in the visceral endoderm of early mouse embryos

Endogenous peroxidase activity was demonstrated in early mouse embryos by means of the diaminobenzidine staining reaction. This enzyme was observed in visceral endoderm on the seventh to eighth day of gestation in vivo, but was no longer detected on the ninth day of development. In cell layers developing from blastocysts or isolated inner cell masses cultured for 96-144 h (developmental stage equivalent to 6-7.5-day-old embryos), diaminobenzidine product was also observed in visceral endodermal cells. Most of the endogenous peroxidase was localized inside or close to the numerous apical vacuoles in the endoderm. Ectoderm, mesoderm, ectoplacental cone, and trophoblast cells did not contain endogenous peroxidase.     

The peroxynitrite pathway in development: phenytoin and benzo[a]pyrene embryopathies in inducible nitric oxide synthase knockout mice

Nitric oxide generated by nitric oxide synthases (NOSs) can react with reactive oxygen species (ROS), forming peroxynitrite, which may contribute to the ROS-initiated macromolecular damage implicated in the embryopathic effects of both endogenous and drug-enhanced oxidative stress. Inducible NOS (iNOS) is nonconstitutive in most tissues, and its embryonic expression and developmental importance are unknown. Herein, during organogenesis (Gestational Days 9 and 10), wild-type B6129PF2 embryos in culture were highly susceptible to the ROS-initiating teratogens phenytoin and benzo[a]pyrene, whereas iNOS knockout embryos were substantially but not completely protected (p < .05), implicating iNOS in the embryopathic mechanism. However, in contrast to prostaglandin H synthase-catalyzed teratogen bioactivation and ROS formation, which occurs within the embryo, in vivo iNOS expression was limited to placental tissue. These results suggest that the diffusion of nitric oxide from placental progenitor tissue (ectoplacental cone) to embryonic target tissues contributes to the embryopathic effects of ROS-initiating teratogens in embryo culture, which may constitute a mechanism by which embryonic determinants of ROS-mediated teratogenesis can be modulated by maternal extra-embryonic processes.