Graphic and movie illustrations of human prenatal development and their application to embryological education based on the human embryo specimens in the Kyoto collection

Species Choice and Model Use: Reviving Research on Human Development

While model organisms have had many historians, this article places studies of humans, and particularly our development, in the politics of species choice. Human embryos, investigated directly rather than via animal surrogates, have gone through cycles of attention and neglect. In the past 60 years they moved from the sidelines to center stage. Research was resuscitated in anatomy, launched in reproductive biomedicine, molecular genetics, and stem-cell science, and made attractive in developmental biology. I explain this surge of interest in terms of rivalry with models and reliance on them. The greater involvement of medicine in human reproduction, especially through in vitro fertilization, gave access to fresh sources of material that fed critiques of extrapolation from mice and met demands for clinical relevance or "translation." Yet much of the revival depended on models. Supply infrastructures and digital standards, including biobanks and virtual atlases, emulated community resources for model organisms. Novel culture, imaging, molecular, and postgenomic methods were perfected on less precious samples. Toing and froing from the mouse affirmed the necessity of the exemplary mammal and its insufficiency justified inquiries into humans. Another kind of model-organoids and embryo-like structures derived from stem cells-enabled experiments that encouraged the organization of a new field, human developmental biology. Research on humans has competed with and counted on models.

Animated teaching improves student learning of human gastrulation and neurulation

Human embryology is a complex topic that brings together core components of anatomy and physiology to describe the developmental process from fertilisation to birth. Embryonic development is a challenging topic of study that is core to the curricula for health science students. There are challenges ingrained in teaching and learning embryology, due to the three-dimensional dynamic processes that occur as the embryo develops. This study aimed to develop and assess two newly developed animations depicting key processes in embryology, namely gastrulation and neurulation, as supplemental learning aids for students. Indeed, animated teaching tools to enhance the learning of gastrulation and neurulation are not widely available. A multi-disciplinary team of physiologists, biochemists, anatomists, and a computer scientist developed the animation sets. A student cohort of 81 first-year health science students were enrolled in this study over a period of three academic years. Both animations are in line with the course content of the first-year health science students undertaking the Human Health and Disease BSc at Trinity College Dublin, who were the study participants. Participants were randomly assigned to a non-animation control group and an animation group. Each set of animated teaching aids was broken down into individual clips which were given identifiable headings to allow the user to interchange between clips to facilitate a more personal learning experience. The animation group had open access to the animations for a three-week period. Questionnaires were designed to assess participants' attitude to the animations and their knowledge of embryology, both at the start of the study and three weeks later following access to the animations. Data presented herein indicate that students incorporated the animated teaching aids into digital home study and that the use of the animations acted as a supplemental tool that increased student knowledge in key areas of human embryology. From a qualitative point of view, students described the animations as enjoyable and helpful in visualising complex processes. This study indicates that the development of gastrulation and neurulation animated learning tools allow for a more engaging learning experience, facilitating student's engagement with academically challenging concepts in human embryology.

Recent advances in understanding cell types during human gastrulation

Gastrulation is a fundamental process during embryonic development, conserved across all multicellular animals [1]. In the majority of metazoans, gastrulation is characterised by large scale morphogenetic remodeling, leading to the conversion of an early pluripotent embryonic cell layer into the three primary 'germ layers': an outer ectoderm, inner endoderm and intervening mesoderm layer. The morphogenesis of these three layers of cells is closely coordinated with cellular diversification, laying the foundation for the generation of the hundreds of distinct specialized cell types in the animal body. The process of gastrulation has for a long time attracted tremendous attention in a broad range of experimental systems ranging from sponges to mice. In humans the process of gastrulation starts approximately 14 days after fertilization and continues for slightly over a week. However our understanding of this important process, as it pertains to human, is limited. Donations of human fetal material at these early stages are exceptionally rare, making it nearly impossible to study human gastrulation directly. Therefore, our understanding of human gastrulation is predominantly derived from animal models such as the mouse [2,3] and from studies of limited collections of fixed whole samples and histological sections of human gastrulae [4-7], some of which date back to over a century ago. More recently we have been gaining valuable molecular insights into human gastrulation using in vitro models of hESCs [8-12] and increasingly, in vitro cultured human and non-human primate embryos [13-16]. However, while methods have been developed to culture human embryos into this stage (and probably beyond), current ethical standards prohibit the culture of human embryos past 14 days again limiting our ability to experimentally probe human gastrulation. This review discusses recent molecular insights from the study of a rare CS 7 human gastrula obtained as a live sample and raises several questions arising from this recent study that it will be interesting to address in the future using emerging models of human gastrulation.

Exploring Visualisation for Embryology Education: A Twenty-First-Century Perspective

Embryology and congenital malformations play a key role in multiple medical specialties including obstetrics and paediatrics. The process of learning clinical embryology involves two basic principles; firstly, understanding time-sensitive morphological changes that happen in the developing embryo and, secondly, appreciating the clinical implications of congenital conditions when development varies from the norm. Visualising the sequence of dynamic events in embryonic development is likely to be challenging for students, as these processes occur not only in three dimensions but also in the fourth dimensions of time. Consequently, features identified at any one timepoint can subsequently undergo morphological transitions into distinct structures or may degenerate and disappear. When studying embryology, learners face significant challenges in understanding complex, multiple and simultaneous events which are likely to increase student cognitive load. Moreover, the embryology content is very nonlinear. This nonlinear content presentation makes embryology teaching challenging for educators. Embryology is typically taught in large groups, via didactic lecture presentations that incorporate two-dimensional diagrams or foetal ultrasound images. This approach is limited by incomplete or insufficient visualisation and lack of interactivity.It is recommended that the focus of embryology teaching should instill an understanding of embryological processes and emphasise conceptualising the potential congenital conditions that can occur, linking pre-clinical and clinical disciplines together. A variety of teaching methods within case-based and problem-based curricula are commonly used to teach embryology. Additional and supplementary resources including animations and videos are also typically utilised to demonstrate complex embryological processes such as septation, rotation and folding.We propose that there is a need for embryology teaching in the twenty-first century to evolve. This is particularly required in terms of appropriate visualisation resources and teaching methodologies which can ensure embryology learning is relevant to real-world scenarios. Here we explore embryology teaching resources and methodologies and review existing evidence-based studies on their implementation and impact on student learning. In doing so, we aim to inform and support the practice of embryology educators and the learning of their students.

External surface anatomy of the postfolding human embryo: Computer-aided, three-dimensional reconstruction of printable digital specimens

Opportunities for clinicians, researchers, and medical students to become acquainted with the three‐dimensional (3D) anatomy of the human embryo have historically been limited. This work was aimed at creating a collection of digital, printable 3D surface models demonstrating major morphogenetic changes in the embryo's external anatomy, including typical features used for external staging. Twelve models were digitally reconstructed based on optical projection tomography, high‐resolution episcopic microscopy and magnetic resonance imaging datasets of formalin‐fixed specimens of embryos of developmental stages 12 through 23, that is, stages following longitudinal and transverse embryo folding. The reconstructed replica reproduced the external anatomy of the actual specimens in great detail, and the progress of development over stages was recognizable in a variety of external anatomical features and bodily structures, including the general layout and curvature of the body, the pharyngeal arches and cervical sinus, the physiological gut herniation, and external genitalia. In addition, surface anatomy features commonly used for embryo staging, such as distinct steps in the morphogenesis of facial primordia and limb buds, were also apparent. These digital replica, which are all provided for 3D visualization and printing, can serve as a novel resource for teaching and learning embryology and may contribute to a better appreciation of the human embryonic development.

Latest developments in post-mortem foetal imaging

A sustained decline in parental consent rates for perinatal autopsies has driven the development of less-invasive methods for death investigation. A wide variety of imaging modalities have been developed for this purpose and include post-mortem whole body magnetic resonance imaging (MRI), ultrasound, computed tomography (CT) and micro-focus CT techniques. These are also vital for "minimally invasive" methods, which include potential for tissue sampling, such as image guidance for targeted biopsies and laparoscopic-assisted techniques. In this article, we address the range of imaging techniques currently in clinical practice and those under development. Significant advances in high-field MRI and micro-focus CT imaging show particular promise for smaller and earlier gestation foetuses. We also review how MRI biomarkers such as diffusion-weighted imaging and organ volumetric analysis may aid diagnosis and image interpretation in the absence of autopsy data. Three-dimensional printing and augmented reality may help make imaging findings more accessible to parents, colleagues and trainees.

Learning Cardiac Embryology-Which Resources Do Students Use, and Why?

With increasing class sizes, small group activities for learning embryology are present in few institutions. How then do students supplement their lectures in order to ask and answer questions, or delve into concepts in detail? Arguably, animations and videos are ideal for visualizing four-dimensional anatomy, but how do students find and filter these? First-year medical students were surveyed with respect to the cardiac embryology component of their course and asked their opinions regarding the clinical relevance of this content and the resources they used to enhance learning. Students indicated that they considered cardiac embryology to be of relevance to clinical practice and that videos are a useful resource in helping them to learn this material. However, when seeking videos or resources, it emerged that students tended to Google information in preference to accessing online resources (or textbooks) specifically recommended by their instructor, despite students' recognition that "accuracy of information" was paramount when choosing what resource to use. While all students seemed reluctant to contact a staff member with questions, those with less proficiency in English were less likely to approach faculty for assistance. While acknowledging students as adult learners, self-regulated learning skills do not develop automatically and the development of these skills should be viewed as a "shared responsibility" between students and staff. Likewise, students also need to be taught critical appraisal of learning resources, especially in the complex online environment, with design of their bespoke institutional virtual learning environment facilitating easy identification and access of recommended resources.

Creating a 3D Learning Tool for the Growth and Development of the Craniofacial Skeleton

Advances in technology are facilitating wider access to delicate, and often irreplaceable, anatomy specimens for teaching. Moreover, 3-dimensional (3D) models and interactive applications may help students to understand the spatial arrangement of complex 3D anatomical structures in a way not afforded by the 2-dimensional (2D) textbook images of traditional teaching.Historical specimens from the University of Glasgow's Museum of Anatomy were digitised for the creation of a 3D learning tool to help students better understand the growth and development of the juvenile skull. The overarching goal of this project was to assess whether interactive 3D applications can provide a useful tool for teaching more complex, non-static, anatomy subjects such as growth and development.The application received positive feedback from the small test group of 12 anatomy students. The majority of participants strongly agreed that the application helped them learn more about the human skull and they positively rated the use of 3D models in helping them learn about the position and structure of anatomical features, and in comparing skulls at different stages of development. Following on from this positive feedback, further tests could be conducted to assess if this 3D application confers an advantage in student learning over traditional teaching methods.

Ethical Rationales and Guidelines for the Continued Use of Archival Collections of Embryonic and Fetal Specimens

Benefits from the use of cadavers in anatomical education are well described. Historically, human embryos and fetal cadavers were used in anatomy education to understand development and congenital malformations. Recently, three-dimensional printed models produced from archival fetal specimens, and online repositories of images from archival collections of embryos and fetuses, have been used as an educational tool in human development courses. Given that the archival specimens were likely obtained prior to the era of informed consent, this raises questions about their appropriate and ethical use. Because some institutions in the United States retain archival collections of embryonic and fetal specimens that were once used as educational tools, their existence and utility require frequent reexamination against contemporary ethical frameworks to guide appropriate use or utilization. Four ethical rationales for uses of these collections are examined, including destruction, indefinite storage, use in research, and use in health professions education. Guidelines for the use of archival collections of human embryos and fetuses are presented. Indefinite storage and use in health professions education are supported, while use in research is also permitted, however, such use is limited and dependent on circumstance and purpose. The development of current digital repositories and three-dimensionally printed models based on archival collections that were collected without informed consent, or those promoting commercial opportunity, are not supported. New embryonic and fetal donations obtained with informed consent should include reference to potential uses with new technology and virtual, genetic, or imaging applications.

Videos for embryology teaching, power and weakness of an innovative tool

BACKGROUND AND AIM

Difficulties are encountered in embryology learning such as imagining embryo modifications in three-dimensions and time. We provided an experimentation to evaluate if short videos during magisterial lecture could increase the quality and the efficiency of embryology teaching.

METHODS

The study was conducted amongst students in first year of medical studies in France. It is an intense and highly competitive year at the end of which students can engage in medical or paramedical specialties depending on their rank. In a first step, pre-implantation embryo development and microscopic videos of in vitro Fertilization were presented during a course of medical ethics. Three months later, students gave their opinion on this presentation in a satisfaction survey using a Likert scale. In a second step (the two following years), similar videos were integrated in the regular embryology lectures and the results of the subsequent embryology test were analyzed.

RESULTS

In the first step, students declared that movies could increase their interest in embryology and significantly help to the comprehension and memorization of embryologic processes. In the second step, we found that students answered better to the video-related questions of the test even if globally in the first year, results were weaker compared to previous years.

DISCUSSION

The effects of movies in pedagogy are discussed, especially the accelerated rhythm imposed by this medium. Adverse consequences could be balanced by traditional drawing.

CONCLUSIONS

The association of complementary pedagogic methods like movies and drawing could allow an optimization of embryo teaching.

Relationship Between Physiological Umbilical Herniation and Liver Morphogenesis During the Human Embryonic Period: A Morphological and Morphometric Study

It is widely hypothesized that physiological umbilical herniation (PUH) in humans occurs, because the liver occupies a large space in the abdominal cavity, which pushes the intestine into the extraembryonic coelom during the embryonic period. We have recently shown the presence of the intestinal loop in the extraembryonic coelom in embryos with liver malformation. Here, we analyzed the relationship between the liver and the PUH at Carnegie stage 21 of four embryos with liver malformation, including two with hypogenesis (HY1, HY2) and two with agenesis (AG1, AG2), using phase-contrast X-ray computed tomography and compared them with two control embryos. The intestinal loop morphology in the malformed embryos differed from that in the control embryos, except in HY1. The length of the digestive tract in the extraembryonic coelom of the embryos with liver malformation was similar to or longer than that of the controls. The rate of intestinal loop lengthening in the extraembryonic coelom compared with that of the total digestive tract in all embryos with liver malformation was similar to or higher than that of the controls. The estimated total abdominal cavity volume in the embryos with liver malformation was considerably smaller than that of the controls, while the intestinal volume was similar. The cardia and proximal portion of the pancreas connecting to the duodenum were located at almost identical positions in all the embryos, whereas other parts of the upper digestive tract deviated in the embryos with abnormal livers. Thus, our results provided evidence that PUH occurred independently of liver volume. Anat Rec, 302:1968-1976, 2019. © 2019 American Association for Anatomy.

Impact of cardiovascular embryology animations on short-term learning

An understanding of human embryology is essential for students to better understand the subjects of human anatomy and physiology. However, human embryology is a challenging subject for many, since they must learn how anatomic structures and physiological processes develop over a period of time. Embryology texts typically use static, two-dimensional images to illustrate the dynamic three-dimensional developmental processes, making it difficult for a student to understand spatial relationships and sequential steps. To help students conceptualize these series of complex dynamic developmental events that occur over time, two of the authors and a graphic artist developed six web-based cardiovascular embryology animations and housed them on an Indiana University website. This research study examines knowledge gains and user satisfaction of students, faculty, and laypeople around the world who accessed these six website animations. Data collection spanned 6 yr, and pretest/posttest assessments (ranging from 4 to 7 multiple-choice questions each) were used to determine immediate knowledge gains of cardiovascular embryology. The total number of completed pretest/posttest assessments ranged from 555 to 1,449 per animation. The number of correct posttest scores was significantly improved over matched pretest scores (confidence interval range 1.3-3.2, depending on the animation, P < 0.001), suggesting the animations are useful for embryology learning (at least in the short term). Demographic and user satisfaction information was gathered with an anonymous survey at the end of each animation. Survey data from all animations indicated participants found the animations easy to use and very effective for their learning. This research highlights the positive impacts of web-based animations on learning complicated events of cardiovascular embryology.

Critical Growth Processes for the Midfacial Morphogenesis in the Early Prenatal Period

BACKGROUND

Congenital midfacial hypoplasia often requires intensive treatments and is a typical condition for the Binder phenotype and syndromic craniosynostosis. The growth trait of the midfacial skeleton during the early fetal period has been assumed to be critical for such an anomaly. However, previous embryological studies using 2-dimensional analyses and specimens during the late fetal period have not been sufficient to reveal it.

OBJECTIVE

To understand the morphogenesis of the midfacial skeleton in the early fetal period via 3-dimensional quantification of the growth trait and investigation of the developmental association between the growth centers and midface.

METHODS

Magnetic resonance images were obtained from 60 human fetuses during the early fetal period. Three-dimensional shape changes in the craniofacial skeleton along growth were quantified and visualized using geometric morphometrics. Subsequently, the degree of development was computed. Furthermore, the developmental association between the growth centers and the midfacial skeleton was statistically investigated and visualized.

RESULTS

The zygoma expanded drastically in the anterolateral dimension, and the lateral part of the maxilla developed forward until approximately 13 weeks of gestation. The growth centers such as the nasal septum and anterior portion of the sphenoid were highly associated with the forward growth of the midfacial skeleton (RV = 0.589; P < .001).

CONCLUSIONS

The development of the midface, especially of the zygoma, before 13 weeks of gestation played an essential role in the midfacial development. Moreover, the growth centers had a strong association with midfacial forward growth before birth.

Quantitation of nasal development in the early prenatal period using geometric morphometrics and MRI: a new insight into the critical period of Binder phenotype

OBJECTIVES

Disturbance of the development of the nasal septum in the early prenatal period causes congenital facial anomalies characterized by a flat nose and defects of the anterior nasal spine (ANS), such as Binder phenotype. The present research aimed to assess the development of the nasal septum and the ANS with growth in the early prenatal period.

METHODS

Magnetic resonance images were obtained from 56 specimens. Mid-sagittal images were analyzed by using geometric morphometrics for the development of the nasal septum, and angle analysis was performed for the development of the ANS. Additionally, we calculated and visualized the ontogenetic allometry of the nasal septum.

RESULTS

Our results showed that the nasal septum changed shape in the anteroposterior direction in smaller specimens, while it maintained an almost isometric shape in larger specimens. Furthermore, mathematical evidence revealed that the maturation periods of the shapes of the ANS and the nasal septum were around 12 and 14 weeks of gestation, respectively.

CONCLUSION

The anteroposterior development of the nasal septum is specific until 14 weeks of gestation, and it is important for nasal protrusion and the development of the ANS. Therefore, the disturbance of such development could induce low nasal deformity, including Binder phenotype. © 2017 John Wiley & Sons, Ltd.

Formation of duodenal atresias in fibroblast growth factor receptor 2IIIb-/- mouse embryos occurs in the absence of an endodermal plug

PURPOSE

Duodenal atresia in humans has been hypothesized to arise from a failure of the duodenal lumen to recanalize after formation of an endodermal plug. Recently, mutations in the fibroblast growth factor receptor 2 gene (Fgfr2IIIb) have been shown to cause atretic defects of the duodenum in mice. However, work in rats suggests that murine species do not form an endodermal plug during normal duodenal development. These lines of data led us to hypothesize that mice are able to form a duodenal atresia in the absence of an endodermal plug. To test this hypothesis, we examined duodenal development in wild-type and Fgfr2IIIb-/- embryos.

METHODS

Paraffin sections were generated for H&E, E-cadherin, or terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling staining from Fgfr2IIIb-/- and wild-type embryos between embryonic days (E) 10.5 and E14.5. Sections were photographed and reconstructed into 3-dimensional display using Adobe Photoshop and Amira Visage software.

RESULTS

Normal mouse duodenum does not form an endodermal plug, although a plug does form in the pyloric region of the stomach at E14.5. Fgfr2IIIb-/- embryos experience significant apoptosis in the duodenal region at E10.5, followed by the disappearance of the endoderm in the atretic precursor by E11.5. Thereafter, the mesoderm of the atretic precursor involutes over the next 2 days in the absence of further apoptosis. Interestingly, an endodermal plug was not observed at any point during the formation of a duodenal atresia.

CONCLUSIONS

These results suggest that duodenal atresia in the Fgfr2IIIb-/- model does not arise from persistence of an epithelial plug. Rather it appears to result from the loss of the endoderm because of apoptosis very early in development.

Towards a 3-dimensional atlas of the developing human embryo: the Amsterdam experience

Knowledge of complex morphogenetic processes that occur during embryonic development is essential for understanding anatomy and to get insight in the pathogenesis of congenital malformations. Understanding these processes can be facilitated by using a three-dimensional (3D) developmental series of human embryos, which we aim to create in this project. Digital images of serial sections of 34 human embryos of the Carnegie Collection between Carnegie stages 7 (15-17 days) and 23 (56-60 days) are used to create 3D reconstructions of different organ systems. The software package Amira is used to align the sections and to create the 3D reconstructions. In this midway evaluation we show the first results of the atlas, containing 34 embryos with more than 13.500 manually annotated sections. The 3D models can be interactively viewed within a 3D-pdf. This will be the first complete digital 3D human embryology atlas of this size, containing all developing organ systems.

Imaging of the human embryo with magnetic resonance imaging microscopy and high-resolution transvaginal 3-dimensional sonography: human embryology in the 21st century

OBJECTIVE

This article illustrates early human development, demonstrated by magnetic resonance (MR) microscopy and computer graphics on human embryo specimens, and advanced 3-dimensional (3D) sonography in clinical obstetrics.

STUDY DESIGN

Fixed human embryo specimens were imaged by MR microscopy coupled with computer graphics technology. Transvaginal 3D sonography was used to examine embryos in ongoing gestations and compare embryological findings.

RESULTS

Advances in MR microscopy allowed detailed visualization of embryo specimens. Computational techniques allowed reconstruction of tomographic images to render them as 3D structures. High-resolution transvaginal 3D sonography produced images that demonstrated the neural tube from week 6; brain anatomy and vasculature from week 8; and craniofacial morphology and other structures from week 11.

CONCLUSION

MR microscopy is a novel technique that enables nondestructive, high-resolution imaging of embryo specimens. On the other hand, 3D sonoembryology allows detailed anatomical visualization in vivo and is the basis for the assessment of anomalies as well as human development.

Developmental atlas of the early first trimester human embryo

Rapid advances in medical imaging are facilitating the clinical assessment of first-trimester human embryos at increasingly earlier stages. To obtain data on early human development, we used magnetic resonance (MR) imaging and episcopic fluorescence capture (EFIC) to acquire digital images of human embryos spanning the time of dynamic tissue remodeling and organogenesis (Carnegie stages 13 to 23). These imaging data sets are readily resectioned digitally in arbitrary planes, suitable for rapid high-resolution three-dimensional (3D) observation. Using these imaging datasets, a web-accessible digital Human Embryo Atlas (http://apps.devbio.pitt.edu/humanatlas/) was created containing serial 2D images of human embryos in three standard histological planes: sagittal, frontal, and transverse. In addition, annotations and 3D reconstructions were generated for visualizing different anatomical structures. Overall, this Human Embryo Atlas is a unique resource that provides morphologic data of human developmental anatomy that can accelerate basic research investigations into developmental mechanisms that underlie human congenital anomalies.

Epithelial and muscular regionalization of the human developing anorectum

In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial "closure" in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.

Visualization of human prenatal development by magnetic resonance imaging (MRI)

It is essential to visualize the structures of embryos and their internal organs three-dimensionally to analyze morphogenesis; this used to rely solely on serial histological sectioning and solid reconstruction, which were tedious and time-consuming. We have applied imaging with a magnetic resonance (MR) microscope equipped with a 2.35 T superconducting magnet to visualize human embryos; we were successful in acquiring high-resolution sectional images and in identifying the detailed structures of major organs. The imaging process was facilitated by using a super-parallel MR microscope. A dataset of MR images of more than 1,000 human embryos, now collected, will be important for future biomedical research and for education.

Early human development

Human development in the first 8 weeks is potentially one of the most exciting areas of biologic research. Beyond historic staging of fixed human embryos, it is also one of the least understood. In contrast, detailed information exists for the embryonic period of several other species, from which human development information is extrapolated. This period is also the most sensitive to system abnormalities generated by teratogens. This review combines the human embryo Carnegie stages, available online at UNSW Embryology (http://embryology.med.unsw.edu.au), with teratogen-sensitive information. Integrating this data with current molecular, imaging, and online tools will provide insights to this period.

Computerized three-dimensional analysis of the heart and great vessels in normal and holoprosencephalic human embryos

The developing heart and great vessels undergo drastic morphogenetic changes during the embryonic period. To analyze the normal and abnormal development of these organs, it is essential to visualize their structures in three and four dimensions, including the changes occurring with time. We have reconstructed the luminal structure of the hearts and great vessels of staged human embryos from serial histological sections to demonstrate their sequential morphological changes in three dimensions. The detailed structures of the embryonic heart and major arteries in normal and holoprosencephalic (HPE) human embryos could be reconstructed and visualized, and anatomical structures were analyzed using 3D images. By 3D analysis, cardiac anomalies such as double-outlet right ventricle and malrotation of the heart tube were identified in HPE embryos, which were not easily diagnosed by histological observation. Reconstruction and analysis of 3D images are useful for the study of anatomical structures of developing embryos and for identifying their abnormalities.