Comparison of staging systems for the gastrulation and early neurulation period in rodents: a proposed new system

Phenotypic Analysis: Assessing Timing of Recessive Prenatal Lethality in Mice

Once a recessive mutation has been established in a mouse strain in the heterozygous state, the task of phenotypic analysis of the homozygous mutants can begin. This overview leads you through a sequence of steps to determine whether the homozygous mutants are present at birth or whether the mutation causes prenatal lethality. In the case of a prenatal lethality, the time of death of the mutants, which could occur at any time during pre- or postimplanation development, must be firmly established before further phenotypic analysis. Here, we present a detailed plan to efficiently determine the time of prenatal death of the mutants and provide a guide for developmental landmarks to establish how far they progress during gestation. To determine whether or not homozygous mutants are present or normal at any given time point, it is important to recover a sufficient number of embryos. Examples of a simple Chi square test for Mendelian segregation is provided to establish statistical significance for the genotype/phenotype distribution.

Developmental Genes and Malformations in the Hypothalamus

The hypothalamus is a heterogeneous rostral forebrain region that regulates physiological processes essential for survival, energy metabolism, and reproduction, mainly mediated by the pituitary gland. In the updated prosomeric model, the hypothalamus represents the rostralmost forebrain, composed of two segmental regions (terminal and peduncular hypothalamus), which extend respectively into the non-evaginated preoptic telencephalon and the evaginated pallio-subpallial telencephalon. Complex genetic cascades of transcription factors and signaling molecules rule their development. Alterations of some of these molecular mechanisms acting during forebrain development are associated with more or less severe hypothalamic and pituitary dysfunctions, which may be associated with brain malformations such as holoprosencephaly or septo-optic dysplasia. Studies on transgenic mice with mutated genes encoding critical transcription factors implicated in hypothalamic-pituitary development are contributing to understanding the high clinical complexity of these pathologies. In this review article, we will analyze first the complex molecular genoarchitecture of the hypothalamus resulting from the activity of previous morphogenetic signaling centers and secondly some malformations related to alterations in genes implicated in the development of the hypothalamus.

Collection and preparation of rodent embryonic samples for transcriptome study

The need for large-scale collection of rodent embryos and individual embryonic tissues for genomic and proteomic studies requires modification of traditional practices of embryo necropsy. The sample intended for transcriptome study should be rapidly dissected and stabilized to preserve its molecular integrity. The retrieval of high-quality RNA, DNA, and proteins from the target tissue is crucial for informative molecular analysis (e.g., gene profiling on microarray platform). We present a reliable method of collection and preparation of rodent embryos for genomic studies supported by detailed protocols and RNA extraction results for different stages of mouse embryonic development.

Rat whole embryo culture system as a tool to investigate developmental mechanisms of left/right body axis

The rat whole embryo culture (WEC) system is a suitable experimental tool for the study of the mechanisms of development of the left/right body axis (L/R axis) because embryos can be cultured from before and during the development of several asymmetric structures including the heart. This paper reviews the development of asymmetric structures in rat embryos during the culture period and the literature on abnormal development of the L/R axis studied using the WEC system. In addition, the author suggests the following guideline for investigators who use this system to study the development of the L/R axis. (1) Precisely stage the embryos according to a modified Theiler's system. (2) Examine the sidedness of three asymmetric structures whose sidedness is controlled by different mechanisms [i.e. the heart, chorioallantoic placenta and the lower part of the embryo (the so-called 'tail')]. (3) Establish the background incidences of inversion of the above structures in control groups cultured from different stages. (4) Perform dose-response studies if testing a chemical. (5) Examine antagonists or inactive isoforms to confirm the pharmacological effects of the test chemical.

Developmental effects of serum from flaxseed-fed rats on cultured rat embryos

Gestation day 9.5 rat embryos were cultured for 45 h in serum obtained from pregnant rats that had been fed throughout gestation with either a control diet (based on the AIN-93 formulation), a diet supplemented with flaxseed (20% or 40%, w/w), or a diet supplemented with de-fatted flaxseed ("flaxseed meal", 13 or 26%, w/w). The embryos were fixed in neutral formalin at the end of culture. Overall growth and development was assessed, and the presence of abnormalities was noted. A significant inhibition of growth (as determined by crown-rump length) relative to control was observed in embryos cultured in serum from rats fed the 20% flaxseed diet. The incidence of spontaneous heart inversions was increased significantly in the embryos cultured in serum from the 20% flaxseed and 26% flaxseed meal fed rats. The incidence of flexion defects was increased significantly in embryos cultured in serum from 20% flaxseed-fed rats. The lack of an apparent dose response in any of the statistically significant effects suggests that the observed anomalies were chance occurrences unrelated to the treatment group from which serum was obtained. It is therefore concluded that diets high in flaxseed or flaxseed meal do not result in serum factors that are directly embryotoxic to organogenesis-staged rat embryos. This finding is consistent with the findings of a parallel in vivo rat teratology study where no significant embryotoxicity attributable to flaxseed exposure was observed.

alpha(1)-Adrenergic stimulation perturbs the left-right asymmetric expression pattern of nodal during rat embryogenesis

BACKGROUND

Normal development of the left/right (L/R) body axis leads to the characteristic sidedness of asymmetric body structures, e.g., the left-sided heart. Several genes are now known to be expressed with L/R asymmetry during embryogenesis, including nodal, a member of the transforming growth factor-beta (TGF-beta) family. Mutations or experimental treatments that affect L/R development, such as those that cause situs inversus (reversal of the sidedness of asymmetric body structures), have been shown to alter or abolish nodal's asymmetric expression.

METHODS

In the present study, we examined the effects on nodal expression of alpha(1)-adrenergic stimulation, known to cause a 50% incidence of situs inversus in rat embryos grown in culture, using reverse transcription-polymerase chain reaction assay and whole-mount in situ hybridization assay.

RESULTS

In embryos cultured with phenylephrine, an alpha(1)-adrenergic agonist, nodal's normal asymmetric expression only in the left lateral plate mesoderm was altered. In some treated embryos, nodal expression was detected in either the left or right lateral plate mesoderm. However, most treated embryos lacked lateral plate mesoderm expression. In addition, the embryos that did show expression were at a later stage than when nodal expression is normally found.

CONCLUSIONS

Our results demonstrate that alpha(1)-adrenergic stimulation delays the onset and perturbs the normal asymmetric pattern of nodal expression. Either of these effects might contribute to situs inversus.

Assessment of developmental toxicity of antiretroviral drugs using a rat whole embryo culture system

BACKGROUND

Previous guidelines for HIV-infected pregnant women have recommended zidovudine (ZDV) monotherapy during the second and third trimesters of pregnancy to prevent fetal HIV infection. New guidelines suggest that women should continue or be offered combination antiretroviral therapy (including protease inhibitors) during pregnancy. Nevertheless, little animal or human toxicity data underlie these recommendations.

METHODS

We used an in vitro rat whole embryo culture system to assess the embryo toxicity of various nucleoside analogues, namely, ZDV, dideoxyinosine (ddI), and 2', 3'-dideoxycytidine (ddC), and the HIV-1 protease inhibitor, indinavir, both alone and in combination.

RESULTS

Although human fetal concentrations of these compounds are unknown, no gross abnormalities were detected after incubation with these agents, either alone or in combination at concentrations that would be expected to be achievable in human maternal serum (1-50 microM). ZDV in combination with ddC at >100 microM, resulted in severe growth retardation and morphologic abnormalities not seen with either agent singly.

CONCLUSIONS

We conclude that the combination of ZDV/ddC results in severe concentration-dependent embryo toxicity. No growth retardation or gross morphologic abnormalities were found for any of the agents, either singly or in combination, at clinically relevant concentrations.

Toxicity of heparin in postimplantation whole-embryo culture

Cranial neural tube defects occur when heparin is added to the culture media of postimplantation rat embryos undergoing organogenesis in vitro. Timed-exposure studies were undertaken to determine whether the defects caused by heparin were the result of defective folding and fusion of the neural folds, or due to reopening of a closed neural tube. Experiments were also undertaken to elucidate whether the in vitro toxicity of heparin was due to an effect of heparin at the level of the culture medium, at the level of the visceral yolk sac, or at the level of the embryo proper. Heparin was found to cause defective folding and closure of the neural folds at between 9.5 and 10.5 days' gestation. Neural tube defects did not occur when embryos were cultured in media prepared using a culture medium depleted of heparin ligands by heparin-agarose affinity chromatography. However, studies with [G-(3)H]heparin demonstrated visceral yolk sac uptake and transfer of the radiolabel to the embryo proper. In addition, microinjection of heparin directly into the amniotic cavity of early head-fold embryo explants resulted in cranial neural tube defects similar to those caused by the addition of heparin to culture medium. These data indicate that heparin causes closure defects of cranial neurulation, primarily by an effect at the tissue level of the embryo proper.

Detecting potential teratogenic alkaloids from blue cohosh rhizomes using an in vitro rat embryo culture

The novel alkaloid thalictroidine (1), as well as the known alkaloids taspine (2), magnoflorine (3), anagyrine (4), baptifoline (5), 5,6-dehydro-alpha-isolupanine (6), alpha-isolupanine (7), lupanine (8), N-methylcytisine (9), and sparteine (10), were identified from an extract of Caulophyllum thalictroides rhizomes. N-Methylcytisine exhibited teratogenic activity in the rat embryo culture (REC), an in vitro method to detect potential teratogens. The structure of 1 was elucidated using various spectroscopic methods, primarily by NMR techniques. Thalictroidine, anagyrine, and alpha-isolupanine were not teratogenic in the REC at tested concentrations. Taspine (2) showed high embryotoxicity, but no teratogenic activity, in the REC.

Hypoxic microenvironment within an embryo induces apoptosis and is essential for proper morphological development

Recent studies have suggested the importance of hypoxia-inducible transcription factors in development, yet the questions of whether hypoxia actually exists in a developing embryo in vivo and, if so, what role it plays in development remain unanswered. In this study, we directly demonstrate that regions of hypoxia, most prominently the hindbrain, otic vesicle, and first branchial arch, exist in a gestational day (GD) 11 rat embryo grown in utero. We also show that varying the oxygen environment of an embryo affects its morphological development. Rat embryos which were grown at 45% oxygen from GD 9-11 showed gross morphological abnormalities, including defective cranial neural tube closure, incomplete otic vesicle invagination, and abnormal somite formation and embryo turning. These embryos, in addition, exhibited reduced cell death. On the other hand, embryos which were grown at 5% oxygen during the same period were stunted in overall growth, yet morphologically normal, and displayed prominent areas of apoptosis. In this study, we propose that embryonic development, like tumor development, requires two different but interactive sets of signals. One set exists in the genetic program for development; the other set arises from changes in the microenvironment of the embryo. Therefore, it is the interplay between these two sets of cues that drives normal embryonic development. The requirement for hypoxia to activate apoptotic cell death is but one example of such interactions.

Mechanism of hyperthermia effects on CNS development: rostral gene expression domains remain, despite severe head truncation; and the hindbrain/otocyst relationship is altered

To study the mechanism of hyperthermia on the development of the rostral neural tube, we used a model in which closely-staged presomite 9.5-day rat embryos were exposed in culture to 43 degrees C for 13 min, and then cultured further for 12-48 hr. This treatment had little effect on the development of the rest of the embryo, but resulted in a spectrum of brain defects, the most severe being a lack of all forebrain and midbrain structures. Whole-mount in situ hybridisation was used to monitor the expression domains of Otx2, Emx2, Krox20, and hoxb1. These showed that there were no ectopic expression patterns, for any gene at any stage examined. Even in those embryos which apparently lacked all forebrain and midbrain structures, there were expression domains of Otx2 and Emx2 in the most rostral neural tissue, and these retained their nested dorso-ventral boundaries, showing that cells fated to form rostral brain were not wholly eliminated. Thus, heat-induced rostral neural tube truncation is of a quite different mechanism from the respecification proposed for retinoic acid, despite their very similar phenotypes. In the hindbrain region of treated embryos, we observed decreased intensity of Krox20, staining and an abnormal relationship developed between the position of hoxb1 expression and the otocyst and pharyngeal arches. In the most extreme cases, this domain was shifted to be more caudal than the rostral edge of the otocyst, while the otocyst retained its normal position relative to the pharyngeal arches. We interpret this as a growth imbalance between neuroepithelium and overlying tissues, perhaps due to a disruption of signals from the midbrain/hindbrain boundary.

Specification of left-right asymmetry in mammals: embryo culture studies of stage of determination and relationships with morphogenesis and growth

The internal mammalian body plan is laterally asymmetric with a consistent handedness such that some organs are placed on one side (stomach on the left, for example) and paired organs are not symmetric (for example, there are more lung lobes on the right). Some chemical teratogens can affect the development of asymmetry, and some can cause asymmetric defects in overtly symmetric structures, but the mechanisms are unknown. We have used chemical treatment of rat embryos in culture to examine the stage at which the left-right axis is determined and show that all effective treatments can affect left-right axis development up to the early headfold stage, but not from late headfold onwards. This suggests that the left-right axis is determined by the late headfold stage, even though the embryo is overtly symmetric at this stage. It appears to be much easier to induce an abnormal left-right axis from late allantoic bud and early headfold stages than the early allantoic bud stage, but we have not established the earliest stage at which a response can be induced. Complete situs inversus was the most common chemically induced abnormality, although heart looping and body turning could be inverted separately, suggesting that the two phenomena are linked but not wholly interdependent. The treatments appeared to cause a loss of handedness, rather than inducing inversion, since the incidence of an abnormal left-right axis never exceeded 50%. All treatments except methoxamine, an alpha1 adrenergic agonist, induced an abnormal left-right axis in association with other morphologic defects and growth retardation. However, there was no relationship between the severity or incidence of dysmorphology, nor growth retardation, and left-right abnormality, suggesting that although the process that specifies lateral asymmetry is labile, it is independent of general growth and morphogenesis.

Assessment of the embryotoxic potential of the total hydrolysis product of fumonisin B1 using cultured organogenesis-staged rat embryos

Aminopentol (AP1) is the total hydrolysis product of fumonisin B1 (FB1), the major and best characterized of the fumonisins, which are mycotoxins that are common contaminants of corn and corn meal. Some human populations expected to have significant exposure to AP1 have a high incidence of babies born with neural tube defects (NTD). The embryotoxicity of AP1 was evaluated in cultured rat embryos. Gestation day 9.5 embryos were exposed to 0, 3, 10, 30, 100 or 300 microM AP1 throughout the entire 45-hr culture period. At 100 microM AP1, growth and overall development were reduced significantly. There was also a significant increase in the incidence of abnormal embryos. 29% of the embryos had NTD, and 36% of the embryos had other abnormalities. At 300 microM AP1, the incidence of NTD was 15%, and 85% of the embryos had other abnormalities. These findings suggest that AP1, at concentrations of 100 microM and above, can induce NTD in organogenesis-stage cultured rat embryos. However, these NTD are in conjunction with significant overall retardation of growth and development as well as significant increases in the incidence of other defects. These studies also showed, when compared with previous findings, that AP1 is over 100-fold less toxic than FB1 to cultured rat embryos.

Gene expression of catecholamine synthesizing enzymes and beta adrenoceptor subtypes during rat embryogenesis

Timed-pregnant Sprague-Dawley rats were killed between gestational day (GD) 8 and 10, and embryos were explanted and separated into developmental stages according to a modified Theiler's system. Total RNA from each stage was isolated and subjected to reverse transcription-polymerase chain reaction (RT-PCR) assays to examine gene expression of catecholamine synthesizing enzymes and three subtypes of beta adrenoceptors. Expression of these genes was detected at much earlier stages than previously reported, and each enzyme and receptor subtype showed a different pattern of gene expression. For example, mRNA for tyrosine hydroxylase, the rate-limiting enzyme for catecholamine synthesis, was detected as early as stage 10a, late GD 8, before the neural crest cells appear (stage 12, mid GD 10). This contradicts the common belief that catecholamines are produced only in the cells of sympathoadrenal lineage which originate from the neural crest cells and the cells of central nervous system. Results from the present study indicate that catecholamine synthesis is not limited to the cells of sympathoadrenal lineage.

Cell proliferation in mammalian gastrulation: the ventral node and notochord are relatively quiescent

During gastrulation, the node of the mammalian embryo appears to be an organising centre, homologous to Hensen's node in the chick and the dorsal lip of the amphibian blastopore. In addition, the node serves as a precursor population for the head process, notochord and foregut endoderm. We have studied node architecture and cell morphology by electron microscopy, and cell proliferation using bromodeoxyuridine incorporation and mitotic counts. The dorsal (ectodermal) and ventral (endodermal) components of the node are two distinct populations, separated by a basement membrane. The ventral node, contiguous with the head process, is characterised by a relatively low proliferation rate, with only approximately 10% of cells incorporating BrdU over 4 hr, compared to > 95% in surrounding mesodermal and ectodermal tissues. This is the case from the beginning of node formation, at the no-allantoic-bud stage, until the 7 somite stage, and is not compatible with the idea that the ventral node is a stem cell population. The dorsal node is highly proliferative, its rate of division being indistinguishable from the neurectoderm, with which it is contiguous. In the ventral node, two regions can be recognised: cells in the "pit" are columnar and all monociliated; around them lies a "crown" of cells arranged radially in a horseshoe shape and less often ciliated. Node derivatives share common features with the ventral node; the head process and the notochord are relatively quiescent; and some head process cells are also monociliated. Node and head process monocilia are immotile and appear to be associated with non-proliferation. We suggest that the ventral node contains all the properties of the organiser, while the dorsal node is indistinct from the surrounding epiblast. The cranial end of the foregut pouch, the thyroid diverticulum, and the promyocardium of early somite stage embryos are also areas of low cell division. All the described regions of relative quiescence are sites of expression of members of the TGF beta family, which may be involved in maintaining non-proliferation.

Role of formate in methanol-induced exencephaly in CD-1 mice

Mouse embryos develop exencephaly when dams are exposed by inhalation to high concentrations (> or = 10,000 ppm) of methanol on gestational day 8 (GD8; copulation plug = GD0). The present study examined the role of formate, an oxidative metabolite of methanol, in the development of methanol-induced exencephaly in CD-1 mice and cultured mouse embryos. The pharmacokinetics and developmental toxicity of sodium formate (750 mg/kg by gavage), a 6-hr methanol inhalation (10,000 or 15,000 ppm), or methanol gavage (1.5 g/kg) in pregnant CD-1 mice on GD8 were determined. Gross morphological evaluations for neural tube closure status in embryos or exencephaly in near-term fetuses were performed. Decidual swellings and maternal plasma were analyzed for methanol and formate. The mean (+/- S.E.M.) end-of-exposure plasma methanol concentration was 223 +/- 23 mM following the 6-hr, 15,000 ppm methanol inhalation. There were no changes in blood or decidual swelling formate concentrations under any of the methanol exposure conditions. Peak formate levels in plasma (1.05 +/- 0.2 mM; control 0.5 +/- 0.3 mM) and decidual swelling (2.0 +/- 0.2 mM; control 1.1 +/- 0.2 mM) from pregnant mice (GD8) given sodium formate (750 mg/kg, po) were similar to those observed following a 6-hr methanol inhalation of 15,000 ppm (plasma = 0.75 +/- 0.1 mM; decidual swelling = 2.2 +/- 0.3 mM) but did not result in exencephaly.(ABSTRACT TRUNCATED AT 250 WORDS)

Axial rotation in rat embryos: morphological analysis and microsurgical study on the role of the allantois

In mouse and rat embryos, the embryonic disc develops within a cup-shaped "egg cylinder" and consists of an inner layer of ectoderm and an outer layer of endoderm. Because of this configuration, the embryo first develops in a dorsally flexed position and then undergoes "axial rotation" to a ventrally flexed position. In the present study, we first analyzed the morphological process of axial rotation in rat embryos using novel reference axes set in the egg cylinder that remained invariant during the process. Our new perspective allowed us to demonstrate that the process consists of three movements which start at different stages of development: twisting of the upper body at stage 12/s7-8, twisting of the middle body at stage 13/s11-12, and twisting of the lower body (so called "tail") at stage 14/s15-16. Axial rotation is an interesting developmental event not only because it is such a dynamic process but also because it is one of the earliest morphological signs of body asymmetry. This asymmetry is strongly biased in that the tail almost always finishes up on the right side of the embryo for reasons that are still unknown. In the second part of the study, we performed microsurgical experiments to extend our previous finding that removal of the allantois results in random determination of tail sidedness. We demonstrated that an allantois transplanted from another embryo can prevent this abnormal sidedness in an embryos whose allantois had been removed and that transecting the allantois did not lead to abnormal tail sidedness. A possible explanation is that the allantois produces a chemical factor that controls tail sidedness.

Staurosporine does not prevent adrenergic-induced situs inversus, but causes a unique syndrome of defects in rat embryos grown in culture

Staurosporine, an alkaloid isolated from Streptomyces species, is commonly used as a protein kinase C (PKC) inhibitor in animal investigations. In the present study, we used this compound to determine whether alpha 1-adrenergic stimulation-induced situs inversus in rats is mediated by PKC. Embryos were explanted at 8 A.M. on day 9 of gestation. Those with a neural groove but with no visible neural folds (Stage 11a) were selected and were cultured in medium containing various concentrations of staurosporine with or without 50 microM of phenylephrine, an alpha 1-adrenergic agonist. At 10 A.M. on day 11 of gestation, embryos were examined for situs inversus and other abnormalities. Staurosporine, tested at 0.0001, 0.001, 0.01, 0.1, 0.375, and 0.5 microM (lethal concentration), did not block phenylephrine-induced situs inversus at any concentration. However, staurosporine alone produced situs inversus at concentrations above 0.1 microM. At 0.5 and 1.0 microM, staurosporine also caused cyst-like lesions projecting dorsally from the mesencephalon that we named "mesencephalic vesicles" and the formation of secondary somites. To confirm and further examine these unique effects of staurosporine both grossly and histologically, we conducted additional experiments using staurosporine from another source. Embryos were explanted between 6 A.M. and 9 P.M. on day 9 of gestation and were placed in one of the following groups according to their stage of development: 10b, 11a, 11b, 11c, 12/s1-2, 12/s3-4, and 12/s5-6. Embryos were then cultured with various concentrations of staurosporine. Those cultured from Stage 11a exhibited similar lesions to those seen in the initial experiment but at somewhat higher concentrations of staurosporine. Embryos cultured from Stage 10b showed a similar pattern of lesions as seen at Stage 11a, except that higher concentrations of staurosporine were required to cause mesencephalic vesicles and secondary somites formation. Embryos cultured from Stage 11b showed similar effects to those cultured from younger stages except that maximum incidences of situs inversus were much lower. Those cultured from Stage 11c showed similar dose-response to those cultured from Stage 11b except that the incidence of secondary somites formation was much higher. In addition, in approximately 40% (n = 25) of embryos treated with greater than 1.0 microM of staurosporine, the growing end of the allantois did not reach the chorion and remained unattached in the exocoelomic cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

From gastrulation to neurulation: transition in retinoic acid sensitivity identifies distinct stages of neural patterning in the rat

Early neural development is a multistep process with morphologically distinct stages; however, the molecular events that underlie morphologic development are poorly understood. Retinoic acid (RA) was chosen as a teratogen to perturb development because this endogenous molecule is thought to play an integral role in normal neuraxis formation in many vertebrate species. We have examined the effects of RA on early neural patterning in the rat at three morphologically distinct stages: late streak, foregut pocket, and early somite. In this model exogenous RA exposure during mid-gastrulation (late streak stage) leads to severe disruption of anterior neural development as determined by morphologic and molecular (Engrailed [En] gene expression) markers. This disruption in anterior neural development is associated with excessive cell death in the hindbrain posterior to the En expression domain. In contrast, at the time the neural folds begin to elevate (foregut pocket stage) there is a dramatic reduction in the sensitivity of anterior neural development to exogenous RA as reflected by En expression and cell death patterns. These results suggest that we have identified a major transition in the development of the anterior neuraxis that is reflected in a transition in sensitivity to RA. This transition in sensitivity demonstrates that the fundamental patterning mechanisms that separate fore- and midbrain from hindbrain occurs very early in neurogenesis.

Rat embryo culture to detect nutritional deficiency in women with poor reproductive histories

The cause of habitual early pregnancy loss is not known for most affected couples. It has been proposed that a deficiency of amino acids or other nutrients may contribute to early embryo loss, and an assay based on culture of rat embryos in human serum has been proposed to evaluate women with poor reproductive histories. We tested this assay in women with unexplained infertility (n = 27), habitual abortion (n = 15), and normal midtrimester pregnancies (n = 10) by examining the ability of subject's serum to support the normal development of rat embryos in culture with and without supplemental vitamins and amino acids. Nonpregnant women with nutrient deficiencies identified in this manner were given oral supplements or placebo and were retested. A similar proportion of women in each group had serum that was unable to support the normal development of rat embryos without supplemental vitamins and amino acids. When oral supplements were used, most sera were able to support normal embryo growth. There were no seroconversions on placebo. In spite of the apparent success in producing seroconversions on oral supplementation, only two women conceived, one on the placebo treatment and one on nutritional supplements. Because serum nutrient deficiencies identified by rat embryo culture could not distinguish normal pregnant women from women with unexplained infertility or habitual abortion, and because of the low pregnancy rates, we could not confirm the utility of this assay for the general population of women with habitual abortion.(ABSTRACT TRUNCATED AT 250 WORDS)

Staging of gastrulating mouse embryos by morphological landmarks in the dissecting microscope

We describe and illustrate a set of morphological landmarks for classifying mouse embryos by gross morphology from before gastrulation to the beginning of organogenesis. These landmarks are visible at the resolution of the dissecting microscope in embryos that are intact except for reflexion of Reichert's membrane. Adoption of these criteria should facilitate interpretation of both the expression patterns of genes and the consequences of experimental manipulation of embryos during early postimplantation development.

Microsurgical study on the mechanisms determining sidedness of axial rotation in rat embryos

Sidedness of left/right asymmetric body structures is strongly biased in most animals by mechanisms that are not well understood. In rat embryos, axial rotation starts at the 9-10 somite stage and is almost completed at the 17-18 somite stage. As a result, the ventrally flexed tail (caudal part of the body) and chorioallantoic placenta on the yolk sac take up their position normally on the right side of the embryo. Because the tail and chorion become connected via the allantois around the time when axial rotation takes place, we hypothesized that the allantois and possibly its connection to the chorion is important in determining sidedness of the tail. In the present study, we tested this hypothesis by surgically removing either the allantois or chorion before axial rotation started. Embryos were explanted at 8 AM on Day 9 of gestation (presomite stage), and either the allantois or chorion was removed using microforceps. Embryos were then cultured in rotating bottles, and sidedness of the tail, chorioallantoic placenta, and bulboventricular loop (heart) was determined after 50 hours (approximately 25-26 somite stage). Removal of the allantois (n = 55) resulted in absence of the umbilical cord and a 49.1% incidence of inverted tail; a chorioallantoic placenta-like structure developed on the yolk sac in the normal position.(ABSTRACT TRUNCATED AT 250 WORDS)