Chigako Uwabe

Neural tube closure in humans initiates at multiple sites: evidence from human embryos and implications for the pathogenesis of neural tube defects

The closure of the neural tube (NT) in the human embryo has generally been described as a continuous process that begins at the level of the future cervical region and proceeds both rostrally and caudally. On the other hand, multiple initiation sites of NT closure have been demonstrated in mice and other animals. In humans, based on the study of neural tube defects (NTD) in clinical cases, van Allen et al. (1993) proposed a multi-site NT closure model in which five closure sites exist in the NT of human embryos. In the present study, we examined human embryos in which the NT was closing (Congenital Anomaly Research Center, Kyoto University) grossly and histologically, and found that NT closure in human embyos initiates at multiple sites but that the mode of NT closure in humans is different from that in many other animal species. In addition to the future cervical region that is widely accepted as an initiation site of NT closure (Site A), the mesencephalic-rhombencephalic boundary was found to be another initiation site (Site B). The second closure initiating at Site B proceeds bidirectionally and its caudal extension meets the first closure from Site A over the rhombencephalon, and the rostral extension of the second closure meets another closure extending from the rostral end of the neural groove (Site C) over the prosencephalon, where the anterior neuropore closes. The caudal extension of the first closure initiating at Site A was found to proceed all the way down to the caudal end of the neural groove where the posterior neuropore is formed, indicating that in humans, NT closure does not initiate at the caudal end of the neural groove to proceed rostrally. Since there is a considerable species difference in the mode of NT closure, we should be careful when extrapolating the data from other animals to the human. It seems that the type of NTD affects the intrauterine survival of abnormal embryos. Almost all the embryos with total dysraphism appear to die by 5 weeks of gestation, those with an opening over the rhombencephalon by 6.5 weeks, and those with a defect at the frontal and parietal regions survive beyond 7 weeks.

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. Developmental Dynamics 239:1585–1595, 2010.

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

Morphogenesis in the developing embryo takes place in three dimensions, and in addition, the dimension of time is another important factor in development. Therefore, the presentation of sequential morphological changes occurring in the embryo (4D visualization) is essential for understanding the complex morphogenetic events and the underlying mechanisms. Until recently, 3D visualization of embryonic structures was possible only by reconstruction from serial histological sections, which was tedious and time‐consuming. During the past two decades, 3D imaging techniques have made significant advances thanks to the progress in imaging and computer technologies, computer graphics, and other related techniques. Such novel tools have enabled precise visualization of the 3D topology of embryonic structures and to demonstrate spatiotemporal 4D sequences of organogenesis. Here, we describe a project in which staged human embryos are imaged by the magnetic resonance (MR) microscope, and 3D images of embryos and their organs at each developmental stage were reconstructed based on the MR data, with the aid of computer graphics techniques. On the basis of the 3D models of staged human embryos, we constructed a data set of 3D images of human embryos and made movies to illustrate the sequential process of human morphogenesis. Furthermore, a computer‐based self‐learning program of human embryology is being developed for educational purposes, using the photographs, histological sections, MR images, and 3D models of staged human embryos. Developmental Dynamics 235:468–477, 2006.

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.

Embryonic hydromyelia: cystic dilatation of the lumbosacral neural tube in human embryos

Abstract. In a large collection of human embryos (the Kyoto Collection of Human Embryos, Kyoto University), we encountered five cases with abnormal dilatation of the neural tube at the lumbosacral level. In these examples, the central canal was enlarged, and the roof plate of the neural tube was extremely thin and expanded. The mesenchymal tissue was scarce or lacking between the roof plate and the surface ectoderm. This type of anomaly was assumed to be formed after neural tube closure and may be an early form of spina bifida. In two of the cases, some abnormal cells were found ectopically between the thin roof plate and the surface ectoderm. Morphologically, these cells resembled those forming spinal ganglia and could be of the neural crest origin. Since neural crest cells are pluripotent and can differentiate into a variety of tissues, such ectopic cells might undergo abnormal differentiation into teratomatous tumors and/or lipomas, which are frequently associated with spina bifida. We also discuss the definition of spina bifida and the classification of neural tube defects from the embryological and pathogenic viewpoints and propose a new classification of neural tube defects.

Movement of the external ear in human embryo

IntroductionExternal ears, one of the major face components, show an interesting movement during craniofacial morphogenesis in human embryo. The present study was performed to see if movement of the external ears in a human embryo could be explained by differential growth.MethodsIn all, 171 samples between Carnegie stage (CS) 17 and CS 23 were selected from MR image datasets of human embryos obtained from the Kyoto Collection of Human Embryos. The three-dimensional absolute position of 13 representative anatomical landmarks, including external and internal ears, from MRI data was traced to evaluate the movement between the different stages with identical magnification. Two different sets of reference axes were selected for evaluation and comparison of the movements.ResultsWhen the pituitary gland and the first cervical vertebra were selected as a reference axis, the 13 anatomical landmarks of the face spread out within the same region as the embryo enlarged and changed shape. The external ear did move mainly laterally, but not cranially. The distance between the external and internal ear stayed approximately constant. Three-dimensionally, the external ear located in the caudal ventral parts of the internal ear in CS 17, moved mainly laterally until CS 23. When surface landmarks eyes and mouth were selected as a reference axis, external ears moved from the caudal lateral ventral region to the position between eyes and mouth during development.ConclusionThe results indicate that movement of all anatomical landmarks, including external and internal ears, can be explained by differential growth. Also, when the external ear is recognized as one of the facial landmarks and having a relative position to other landmarks such as the eyes and mouth, the external ears seem to move cranially.

Embryonic Liver Morphology and Morphometry by Magnetic Resonance Microscopic Imaging

Embryonic liver has a unique external morphology and quantitative morphometry, based on magnetic resonance imaging data of human embryos from the Kyoto Collection of Human Embryos. Liver morphogenesis is strongly affected by the adjacent organs and tissues. The left ventricle develops to the left medial‐caudal side, which results in the formation of a depression at left medial region and a prominence bilaterally at the cranial surface of the liver between Carnegie Stage (CS)17 and CS19. An imprint of the stomach that formed at the dorsal left‐medial region of the liver became more marked with development until CS23. A depression induced by the umbilicus formed at the ventral region of the liver between CS16 and CS19. An indentation caused by the right adrenal gland formed at the dorsal‐caudal region of the liver surface from CS20. Morphometric analysis revealed that the volume of the liver increased exponentially from CS14 through CS23. The liver developed preferentially along the dorsoventral axis and right/left axis until CS17, along the craniocaudal axis between CS17 and CS19, and then in all directions after CS19. Several important developmental phenomena, such as differentiation of the diaphragm, the extension of the body axis of the embryo, and the physiologic herniation of the intestine into the umbilical cord, may affect morphometric data. These data contribute to a better understanding of liver development as well as the morphogenesis of adjacent organs, both temporally and spatially, and serve as a useful reference for fetal medicine and prenatal diagnosis. Anat Rec, 2012.

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. Anat Rec, 2007.

Morphometric analysis of the brain vesicles during the human embryonic period by magnetic resonance microscopic imaging

The development of the brain vesicles between Carnegie stages (CS) 17 and 23 was analyzed morphometrically using 177 magnetic resonance image data derived from the Kyoto Collection of Human Embryos. Whole embryonic volume was 106.55 ± 21.08 mm3 at CS17, exponentially increasing to CS23 when it reached 1357.28 ± 392.20 mm3. Length of brain vesicles was 29.83 ± 2.52 mm at CS17, increased almost linearly and reached 49.31 ± 6.66 mm at CS23. The rate of increase was approximately 4.2 times higher on the dorsal side than on the ventral side. The increase in the length of the brain vesicles resulted mainly from that of the prosencephalon, and the rate of increase was three times higher on the dorsal side than on the ventral side of the prosencephalon.

Morphology and morphometry of the human embryonic brain: A three-dimensional analysis.

The three-dimensional dynamics and morphology of the human embryonic brain have not been previously analyzed using modern imaging techniques. The morphogenesis of the cerebral vesicles and ventricles was analyzed using images derived from human embryo specimens from the Kyoto Collection, which were acquired with a magnetic resonance microscope equipped with a 2.35-T superconducting magnet. A total of 101 embryos between Carnegie stages (CS) 13 and 23, without apparent morphological damage or torsion in the brain ventricles and axes, were studied. To estimate the uneven development of the cerebral vesicles, the volumes of the whole embryo and brain, prosencephalon, mesencephalon, and rhombencephalon with their respective ventricles were measured using image analyzing Amira™ software. The brain volume, excluding the ventricles (brain tissue), was 1.15 ± 0.43 mm(3) (mean ± SD) at CS13 and increased exponentially to 189.10 ± 36.91 mm(3) at CS23, a 164.4-fold increase, which is consistent with the observed morphological changes. The mean volume of the prosencephalon was 0.26 ± 0.15 mm(3) at CS13. The volume increased exponentially until CS23, when it reached 110.99 ± 27.58 mm(3). The mean volumes of the mesencephalon and rhombencephalon were 0.20 ± 0.07 mm(3) and 0.69 ± 0.23 mm(3) at CS13, respectively; the volumes reached 21.86 ± 3.30 mm(3) and 56.45 ± 7.64 mm(3) at CS23, respectively. The ratio of the cerebellum to the rhombencephalon was approximately 7.2% at CS20, and increased to 12.8% at CS23. The ratio of the volume of the cerebral vesicles to that of the whole embryo remained nearly constant between CS15 and CS23 (11.6-15.5%). The non-uniform thickness of the brain tissue during development, which may indicate the differentiation of the brain, was visualized with surface color mapping by thickness. At CS23, the basal regions of the prosencephalon and rhombencephalon were thicker than the corresponding dorsal regions. The brain was further studied by the serial digital subtraction of layers of tissue from both the external and internal surfaces to visualize the core region (COR) of the thickening brain tissue. The COR, associated with the development of nuclei, became apparent after CS16; this was particularly visible in the prosencephalon. The anatomical positions of the COR were mostly consistent with the formation of the basal ganglia, thalamus, and pyramidal tract. This was confirmed through comparisons with serial histological sections of the human embryonic brain. The approach used in this study may be suitable as a convenient alternative method for estimating the development and differentiation of the neural ganglia and tracts. These findings contribute to a better understanding of brain and cerebral ventricle development.