Parameters determining isotretinoin teratogenicity in rat embryo culture

At the in vitro threshold serum concentration of 500 ng/ml, isotretinoin induces defects of visceral arch development in 9.5-day rat embryos grown in culture for 48 h. Experiments were performed to determine the minimum period of exposure necessary to induce these arch defects and whether an increase in concentration of isotretinoin could compensate for reduced exposure time. The results showed that a minimum 6-h exposure to 500 ng/ml immediately prior to cranial neural crest migration was necessary to induce severe defects of the second visceral arch in a majority of embryos. Maximal increase in isotretinoin concentration to 16,000 ng/ml did not compensate for shorter exposure periods. These results suggest that to cause malformations of the visceral arches, the embryo must be exposed to isotretinoin for a minimum period of time regardless of the concentration of isotretinoin above the threshold.     

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.     

Improved growth and development of presomite mouse embryos in whole embryo culture

A rotator whole embryo culture system was used to assess the growth and development of late-primitive-streak-stage (Theiler stage 9-10) mouse embryos to the limb-bud stage of organogenesis in a variety of media containing combinations of mouse serum (MS), rat serum (RS), and Tyrode's buffer (TB). The results demonstrate that embryonic growth and morphogenesis to the early limb-bud stage (20 somite pairs; 48-h total culture period) mimicked that in vivo when embryos were grown for 24 h in combinations of MS:RS:TB 1:2:1 or 2:1:1 (v/v/v) and then were transferred to fresh medium containing RS:TB 3:1 at the early somite stage. When the culture period was extended for an additional 24 h (total 72-h culture period) embryonic growth retardation was observed. Regardless of the medium employed, superior growth was observed in embryos transferred at the early somite stage when compared to embryos cultured continuously in the same medium for the entire 48- or 72-h culture period.     

Tissue-specific RNA interference in post-implantation mouse embryos using directional electroporation and whole embryo culture

In mammals, embryonic development is more difficult to analyze than in non-mammalian species because this development occurs in utero. Interestingly, whole embryo culture allows the normal development of mouse post-implantation embryos for up to 2 days in vitro. One limitation of this technology has been the difficulty of performing loss-of-gene function studies in this system. RNA interference (RNAi), whereby double-stranded RNA molecules suppress the expression of complementary genes, has rapidly become a widely used tool for gene function analyses. We have combined the technologies of mouse whole embryo culture and RNAi to allow the molecular dissection of developmental processes. Here, we review the manipulation by topical injection followed by directional electroporation of endoribonuclease-prepared siRNA to demonstrate that this technology may be useful to knock down genes in a tissue- and region-specific manner in several organs of the developing mouse embryo.     

Evaluation of the embryotoxic potential of ten chemicals in the whole mouse embryo culture

Ten widely different chemicals, actinomycin D, mithramycin, podophyllotoxin, vincristine sulfate, triaziquone, chlorambucil, mercaptopurine riboside, methyl-mercaptopurine riboside, dimethylsulfoxide, and L-lysine were tested in the whole mouse embryo culture system. The highest concentration was always the concentration that induced 100% lethality (ELC100). The lowest concentration varied from 1/2 to 1/10 of the ELC100. The chemicals that had the most noxious effect on embryonic growth and differentiation were actinomycin D, triaziquone, and mercaptopurine riboside. Podophyllotoxin, methyl-mercaptopurine riboside, and L-lysine were the less embryotoxic. As a whole, no significant discrepancies were observed between the results and the teratological data obtained from the literature. These observations support the assumption that the whole murine embryo culture system can give valuable information on the teratogenicity of chemicals.     

Targeting gene expression in the mouse somite: adenovirus-mediated gene delivery and whole embryo culture

We report here a novel approach to direct gene expression in the mouse somite based on the combined application of adenovirus-mediated gene delivery and whole embryo ex vivo culture. As proof of principle, we show functional analysis of somites microinjected with an engineered virus expressing an activated form of Smoothened, the signaling receptor for Sonic Hedgehog (SHH). As adenovirus can infect many embryonic tissues in the mouse, this method may provide an effective alternative to conventional transgenesis for targeted spatial and temporal gene expression.     

Developmental toxicity research of ginsenoside Rb1 using a whole mouse embryo culture model

BACKGROUND: Ginseng has been widely used around the world for many years. Knowledge is limited, however, on its effects on embryonic development. METHODS: Whole embryo culture was used to explore the developmental toxicity of ginsenoside Rb1 (GRb1) on mouse embryos. All embryos were exposed to different concentrations of GRb1, and scored for their growth and differentiation at the end of the 48-hr culture period. RESULTS: Total morphological score decreased significantly at the concentration of GRb1 of 30 microg/ml and was further reduced at 50 microg/ml. Yolk sac was affected at the lower concentration of 15 microg/ml. Developments of midbrain, forebrain, and optic system were relatively sensitive to GRb1 and were affected at the concentration of 30 microg/ml. Allantois, flexion, branchial arch, and limb buds were affected at 50 microg/ml. At this concentration, the embryonic crown-rump length, head length, and somite number were also reduced significantly compared to the control group. CONCLUSIONS: These results suggest that GRb1 has teratogenic effect during the mouse organogenetic period. We suggest that before more data in humans is available, ginseng should be used with caution by pregnant women in the first trimester.     

A dysmorphology score system for assessing embryo abnormalities in rat whole embryo culture

BACKGROUND: The rodent whole embryo culture (WEC) system is a well‐established model for characterizing developmental toxicity of test compounds and conducting mechanistic studies. Laboratories have taken various approaches in describing type and severity of developmental findings of organogenesis‐stage rodent embryos, but the Brown and Fabro morphological score system is commonly used as a quantitative approach. The associated score criteria is based upon developmental stage and growth parameters, where a series of embryonic structures are assessed and assigned respective scores relative to their gestational stage, with a Total Morphological Score (TMS) assigned to the embryo. This score system is beneficial because it assesses a series of stage‐specific anatomical landmarks, facilitating harmonized evaluation across laboratories. Although the TMS provides a quantitative approach to assess growth and determine developmental delay, it is limited to its ability to identify and/or delineate subtle or structure‐specific abnormalities. Because of this, the TMS may not be sufficiently sensitive for identifying compounds that induce structure or organ‐selective effects. METHOD: This study describes a distinct morphological score system called the “Dysmorphology Score System (DMS system)” that has been developed for assessing gestation day 11 (approximately 20–26 somite stage) rat embryos using numerical scores to differentiate normal from abnormal morphology and define the respective severity of dysmorphology of specific embryonic structures and organ systems. This method can also be used in scoring mouse embryos of the equivalent developmental stage. RESULT AND CONCLUSION: The DMS system enhances capabilities to rank‐order compounds based upon teratogenic potency, conduct structure‐ relationships of chemicals, and develop statistical prediction models to support abbreviated developmental toxicity screens. Birth Defects Res (Part B) 89:485–492, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of VLA-4 antagonists in rat whole embryo culture

BACKGROUND: Pharmacological antagonism of VLA-4 (Very Late Antigen 4, alpha(4)beta(1) integrin) has become an attractive target for the treatment of predominantly eosinophil mediated disease states such as asthma, allergic rhinitis, multiple sclerosis, rheumatoid arthritis, diabetes, and inflammatory bowel disease. Gene knockouts of the alpha(4)-integrin subunit of VLA-4 or its cell surface ligand, VCAM-1, however, have been shown to result in embryo-lethality in homozygous null mice due to defects in chorio-allantoic or epi-myocardial fusion. Although gene knockout phenotypes are not always manifested by pharmacological antagonism, those studies suggested that VLA-4 antagonists might cause embryo-lethality or drug-induced malformations. METHODS: To test these concepts, early neurulating rat embryos were cultured by the methods of New ('78) after intra-coelomic microinjection of a VLA-4 blocking antibody or in the presence of small molecule VLA-4 antagonists. RESULTS: Defects in chorio-allantoic fusion were induced after microinjection of VLA4 blocking antibody and after continuous exposure to small molecule antagonists. In a minority of affected embryos chorio-allantoic fusion was completely blocked whereas the majority of affected embryos had only superficial chorio-allantoic fusion and the allantois was enlarged and edematous. Although the allantoic mesoderm covered the trophoblasts of the chorionic plate and contained blood vessels there was only minimal invasion of the trophoblasts by the allantoic mesoderm. The lowest observed effect level generally correlated with the IC(approximately 95), as determined in 90% plasma. DISCUSSION: Based on these data, VLA-4 antagonism might represent a significant risk to the developing embryo/fetus. In vitro exposure, however, is "constant" and does not take into account the elimination phase of these xenobiotics in vivo. Given the high concentrations required to elicit an effect, therapeutic blood levels in vivo may be several fold lower than those that affect the conceptus, depending on the tissue penetration of the compound and the route of administration. VLA-4 also exists in a range of conformations and activation states in vivo and the gene KOs and present studies do not define whether these developmental processes are dependent upon a particular activation state of VLA-4. Therefore, state-selective antagonists may have an improved embryonic safety profile. Additional studies will be required to determine potential effects of VLA-4 antagonists on embryo/fetal development in vivo.     

Distribution of F-actin during mouse facial morphogenesis and its perturbation with cytochalasin D using whole embryo culture.

Histological and experimental studies were performed in mouse embryos to elucidate possible roles of actin filaments in the nasal epithelium during facial morphogenesis. C57BL/6 mouse embryos (8.5-11.5 days of gestation) were fixed and frozen sections were stained with rhodamine-phalloidin. Before formation of the nasal placode, there was no specific localization of F-actin. After the nasal placode was formed, intense staining of F-actin was observed at the apical side of the placode. Conversely, it was located at the basal side of the epithelium of developing nasal prominences. By using the whole embryo culture system, perturbation experiments were conducted with cytochalasin D (CD), which inhibits the polymerization of actin filaments. When day-10 embryos were exposed to CD at several concentrations for 24 hr, fusion of nasal prominences was inhibited in a dose-dependent manner. Treatment with a high dose of CD for 2 hr also prevented the same development irreversibly. In contrast, when day-9 embryos were exposed to CD at several concentrations for 24 hr, invagination of the nasal placode was not perturbed at all. The results suggest that apical F-actin plays an essential role in maintaining the close apposition state of the nasal prominences and in the following fusion. During the invagination stage, F-actin might be important in maintaining the epithelial structure, but is not crucial to the initiation of placode invagination.     

Dynamic in vivo imaging of postimplantation mammalian embryos using whole embryo culture

Due to the internal nature of mammalian development, much of the research performed is of a static nature and depends on interpolation between stages of development. This approach cannot explore the dynamic interactions that are essential for normal development. While roller culture overcomes the problem of inaccessibility of the embryo, the constant motion of the medium and embryos makes it impossible to observe and record development. We have developed a static mammalian culture system for imaging development of the mouse embryo. Using this technique, it is possible to sustain normal development for periods of 18-24 h. The success of the culture was evaluated based on the rate of embryo turning, heart rate, somite addition, and several gross morphological features. When this technique is combined with fluorescent markers, it is possible to follow the development of specific tissues or the movement of cells. To highlight some of the strengths of this approach, we present time-lapse movies of embryonic turning, somite addition, closure of the neural tube, and fluorescent imaging of blood circulation in the yolk sac and embryo.     

Alterations in craniofacial growth induced by isotretinoin (13-cis-retinoic acid) in mouse whole embryo and primary mesenchymal cell culture

Recent evidence has demonstrated that 13-cis-retinoic acid (13-cis-RA, or isotretinoin) is responsible for various craniofacial malformations in the rodent and human embryo. Our studies have been directed toward understanding this effect using mouse whole embryo and primary cell cultures. In whole embryo culture, 13-cis-RA caused significant overall embryonic growth retardation, especially in the primary and secondary palatal processes. In embryos explanted on day 10 of gestation and exposed for 24 or 48 hr, the mesenchyme beneath the epithelium of the nasal and maxillary processes contained pyknotic nuclei as well as a dramatically reduced number of nuclei incorporating 3H-thymidine. The secondary palatal processes and the roof of the oral-nasal cavity had fewer mesenchymal cells than control embryos. The incorporation of 3H-thymidine into TCA-insoluble macromolecules was 30% less in the retinoid-treated heads. In primary cell cultures from day-12 mouse secondary palatal mesenchyme, subsequent cell growth was decreased at concentrations of 13-cis-RA greater than 1 X 10(-5) M. After a 40-hr treatment period, labeling indices in retinoid-treated cells were significantly lower than control values (25% compared with 40%). Retinoic acid also caused a significant, concentration-dependent decrease in 3H-thymidine incorporation. The inhibitory effect of 13-cis-RA on proliferation of oral-nasal mesenchymal cells appears to be related to the production of craniofacial malformations.     

Optimization of mouse embryo culture media using simplex methods

Culture media were developed for pronuclear-stage mouse embryos using simplex optimization, which has the benefit of being able to optimize several components simultaneously. Initially, several different media were generated. All media contained the same components, yet each medium was characterized by having a different component at a high concentration. The simplex procedure identified 4 components (NaCl, pyruvate, KH2PO4 and glucose) which at high concentrations were detrimental to embryo development, compared to the other components tested. For example, all embryos cultured in a medium with high NaCl blocked at the 2-cell stage. The optimization method then adjusted each medium by lowering the concentration of the component or removing it entirely, which resulted in a significant increase in development. In an experiment comparing 8 media generated from the simplex optimization, along with 7 other media, removal of KH2PO4 resulted in the largest increase in development; 88% of embryos were greater than or equal to 4 cells on Day 3 after hCG, and 53% developed into blastocysts by Day 5. Another experiment compared 4 of the best media generated from the simplex optimization. In 3 out of the 4 media, 90% or more of the embryos were greater than or equal to 4 cells on Day 3. In 3 of the media, approximately 60% or more of the embryos developed into blastocysts. The simplex optimization procedure is an efficient method for developing culture media and determining requirements for development in vitro.     

Histogenesis in 11-day mouse embryo limb buds explanted in organ culture

Fore- and hindlimb buds from 11-day mouse embryos with 40 to 52 somites (including the four occipital pairs) were explanted in organ culture and submitted to systematic histological analysis. Chondrogenesis occurs normally in culture in all preskeletal rudiments which were already represented by condensed blastemas before explantation. In the proximal territories, the progress of cartilage differentiation occurs according to the normal pattern and can be revealed histologically much earlier than in bulk preparations. In all explanted hindlimbs as well as in forelimbs from embryos with less than 50 somites, a primary coalescence occurs between the IId and IIId digital rays, leading to various fusions from soft tissue syndactyly to oligosyndactyly. This is the result of two combined unfavorable effects of the culture conditions: the lack of simultaneous volumetric growth of the foot- or handplate, which normally would provide the necessary space for the laying down of a pentadactylous pattern, and a loss of cells resulting from abnormal cell death affecting selective mesodermal sites in the zeugopod and in the marginal subridge area, the latter being more severely affected in hindlimb buds. Several observations suggest that the preferential sensitivity of the marginal mesoderm might be related to early changes in the apical ectoderm, which itself becomes excessively necrotic and rapidly looses its pseudostratified configuration. The forelimb buds from embryos with 50 somites and more usually develop a pentadactylous pattern with a better individuation of digital structures. In all explants, the prospective mesoderm of digit I exhibits stronger regulatory tendencies.     

Expression of Veratrum alkaloid teratogenicity in the mouse

Jervine, a steroidal alkaloid found as a minor constituent in the teratogenic range plant Veratrum californicum, has produced similar terata in sheep, rabbit, hamster, and chick, although the sensitivity to the alkaloid varies in the different species. Sprague Dawley rats and Swiss Webster mice are relatively insensitive. The aim of this study was to determine the teratogenic potential of jervine in three strains of mice and to ascertain if the response is strain dependent. One strain, Swiss N:GP(S), was retested since a Swiss Webster strain had been found previously to be jervine-resistant. In addition, we tested C57BL/6J and A/J, which are known to differ in their response to the teratogenic action of steroids and vitamin A. Mice were treated by gavage with single doses of jervine (70, 150, or 300 mg/kg body weight) on either day 8, 9, or 10 of gestation. Jervine was teratogenic to C57BL/6J and A/J mice but not to N:GP(S). The induced terata included cleft lip with or without cleft palate, isolated cleft palate, mandibular micrognathia or agnathia, and limb malformations. Fetal teratogenicity and maternal and fetal toxicity were highly correlated. The prevalence of each defect and fetal death was a function of strain, dose, and time of treatment. Maternal death was higher in C57BL/6J than in A/J mice. Although some of the terata were similar, the response pattern between strains was different from corticosteroids and vitamin A for both sensitive period and the strain dose response. An effect on differentiation of chondrocyte precursors may account for many of the defects, but an earlier lethal effect on differentiation of neural crest cells or precordal mesenchyme may also occur.     

Expression of virally transduced mouse tyrosinase in tyrosinase-negative chick embryo melanocytes in culture

A cDNA encoding mouse tyrosinase was inserted into a plasmid containing the provirus of a replication competent avian leukosis virus (ALV). A viral stock produced from the plasmid was used to infect cultured tyrosinase-negative (ca/ca) unpigmented chick embryo melanocytes. Five days after infection many cells were producing very dark discrete melanosomes.     

Comparative studies of embryotoxic action of ethylenethiourea in rat whole embryo and embryonic cell culture

The effects of ethylenethiourea (ETU) were investigated using rat (Wistar-imamichi) embryos cultured from days 11 to 13 of gestation or cultured rat embryonic cells extracted on day 11. Malformations in cultured embryos at the concentration of 30 micrograms/ml of ETU were found in the head and tail, which were severely affected, as well as the limb and face. All embryos exposed to 150 and 300 micrograms/ml of ETU had malformed heads, tails, limbs, and facial configurations. Protein contents of the cultured embryos were decreased dose-dependently at the concentrations ranging from 30 to 300 micrograms/ml. In the histological studies of the cultured embryos with ETU, thinner neuroepithelium in head was observed. In the embryonic cells extracted on day 11 of gestation, ETU dose-dependently inhibited the differentiation of midbrain (MB) cells into neurons and that of limb bud (LB) cells into chondrocytes at the concentrations ranging from 30 to 600 micrograms/ml of ETU. The concentrations of ETU that inhibited the production of differentiated foci by 50% (IC50) were 170 micrograms/ml in LB cells of day 11, and greater than 600 micrograms/ml in LB cells on day 12 of development. Therefore, differentiation of MB cells was more sensitive to ETU than the differentiation of LB cells. These results indicated that there was a reasonable correlation of ETU induced changes in cultured whole embryos and embryonic cells.     

Derivation of functional insulin-producing cell lines from primary mouse embryo culture

We have previously described the derivation of insulin-producing cell lines from mouse embryonic stem cells (mESCs) by differentiation of an intermediate lineage-restricted E-RoSH cell line through nutrient depletion in the presence of nicotinamide followed by limiting dilution. Here we investigated whether insulin-producing cell lines could be similarly derived directly from mouse embryo cells or tissues. Using a similar approach, we generated the RoSH2.K and MEPI-1 to -14 insulin-producing cell lines from the 5.5-dpc embryo-derived E-RoSH-analogous RoSH2 cell line and a 6.0-dpc mouse embryo culture, respectively. Insulin content was ～8 μg/10⁶ MEPI-1 cells and 0.5 μg/10⁶ RoSH2.K cells. Like insulin-producing mESC-derived ERoSHK cell lines, both MEPI and RoSH2.K lines were amenable to repeated cycles of freeze and thaw, replicated for months with a doubling time of 3–4 days, and exhibited genomic, structural, biochemical, and pharmacological properties of pancreatic β-cells, including storage and release of insulin and C-peptide in an equimolar ratio. Transplantation of these cells also reversed hyperglycemia in streptozotocin-treated SCID mice and did not induce teratoma. Like ERoSHK cells, both RoSH2.K and MEPI-1 cells also induced hypoglycemia in the mice. Therefore, our protocol is robust and could reproducibly generate insulin-producing cell lines from different embryonic cell sources.