The timing and sequence of events in the development of the human urinary system during the embryonic period proper

Summary A documented scheme of the early development of the human urinary system is presented. It is based on (1) reports of workers who personally studied staged embryos, and (2) personal observations and confirmations. The necessity of studying staged embryos in order to determine the precise sequence of developmental events is stressed.Supported in part by National Institutes of Health (U.S.A.) General Research Support Grant, School of Medicine, Wayne State University.     

The timing and sequence of events in the development of the human vertebral column during the embryonic period proper

Summary A documented scheme of the early development of the human vertebrae is presented. It is based on (1) reports of workers who personally studied staged human embryos, and (2) personal observations and confirmations. The necessity of studying staged embryos in order to determine the precise sequence of developmental events is stressed.Supported by research programme project grant No. HD-08658, Institute of Child Health and Human Development, National Institutes of Health (U.S.A.)     

The timing and sequence of events in the development of the human nervous system during the embryonic period proper

Summary A documented scheme of the early development of the human nervous system is presented. It is based on (I) reports of workers who personally studied staged embryos, and (2) personal observations and confirmations. The necessity of staged embryos in determining the precise sequence of developmental events is stressed.Supported in part by National Institutes of Health (U.S.A.) General Research Support Grant, School of Medicine, Wayne State University.     

The timing and sequence of events in the development of the human respiratory system during the embryonic period proper

Summary A documented scheme of the early development of the human respiratory system is presented. It is based on (1) reports of workers who personally studied staged embryos, and (2) personal observations and confirmations. The necessity of studying staged embryos in order to determine the precise sequence of developmental events is stressed.     

The timing and sequence of events in the development of the limbs in the human embryo.

A documented scheme of the early development of the human limbs is presented. It is based on (1) published and unpublished personal observations, and (2) reports of other workers who personally studied staged human embryos. The necessity of studying staged embryos in determining the precise sequence of developmental events is stressed.     

The development of the elbow joint of the chick and its correlation with embryonic staging

Summary The development of the elbow joint was examined in 67 staged chick embryos. It proved possible to correlate the internal limb development with the external embryonic staging. A summary of the chief events in the development of the chick elbow joint is given in the Table, which also provides comparative data on the human elbow joint and the corresponding features of the chick knee joint. A close similarity exists between the morphogenesis of these synovial joints in the chick and in the human, in contrast to noticeable differences in osteogenesis between the two species.This study was supported by research grants A-1644 and A-532 from the National Institutes of Health, United States Public Health Service, and was aided by a grant from the Michigan Chapter of the Arthritis and Rheumatism Foundation.     

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.     

Staging of the early embryonic brain in the baboon (Papio cynocephalus) and rhesus monkey (Macaca mulatta)

Summary Early morphogenesis of the brain and its derivatives was studied in sixty-nine baboon and rhesus monkey embryos representing developmental stages 8–16, and compared with the staged human embryo. The baboon and rhesus monkey embryos develop in a similar temporal sequence when compared with human embryos with the following exceptions: 1) The respective developmental events for otic disc, adenohypophyseal pouch, and hippocampal internal sulcus formation in the baboon and rhesus monkey occur at stage 10, stages 11–12, and after stage 16, while the comparable stages in humans are 9, 10, and 16; 2) Alternatively, formation of the trigeminal primordium and the motor root of the trigeminal nerve and evagination of the neurohypophysis occur earlier in the baboon and rhesus monkey (i.e., stages 12–13, stage 14, and stage 15, respectively) than observed in the human embryo (stage 14, stage 15, and stage 16, respectively); and 3) Lens pore closure in baboon and human embryos takes place during stage 14, while in the rhesus monkey closure occurs during stage 15.Supported by NIH Grants HD08658 and RR00169     

Reduced number of brain cells in so-called neural overgrowth

Patten described as neural overgrowth a folding of brain tissue into the ventricles in abnormal human embryos. Intubation of chick embryo brains release cerebrospinal fluid pressure resulting in a similar folding. These folded brains have 2.5 times less tissue volume than control embryos of identical stage. This study shows, with total DNA measurements, that brain cell number is 50% less in folded brains (intubated embryos) as compared to control brain of identical staged embryos.     

Development of olfactory and related structures in staged human embryos

Summary The staged sequence of development of the olfactory and related structures has been established from the serially sectioned human embryos of the Carnegie collection, from stage 11 to stage 23.The nasal epiblastic thickening appears at stage 11 and the nasal field is well outlined at stage 12. At stage 15, a continuous cellulovascular strand is observed between the nasal groove and the olfactory field. The vomeronasal groove appears at stage 16 (O'Rahilly 1967). During stage 17, the olfactory nerve is organized into two plexuses, lateral and medial, the latter mingled with the terminal-vomeronasal complex. The olfactory bulb begins to appear at stage 18. Stage 19 is characterized by the individualization of the olfactory bulb and nuclei. In addition, the distinction between olfactory structures and terminal and vomeronasal ones begins to be clear. The structure of the olfactory bulb is evident at stage 21. At stage 23, the olfactory strands are well individualized, and olfactory and terminal-vomeronasal fibers are easily distinguishable.The terminal ganglion is rather terminal-vomeronasal with an autonomic terminal contingent and a sensory one attached to the vomeronasal system.Supported by research programme project grant No. HD-08658, Institute of Child Health and Human Development, National Institutes of Health (USA)     

The first appearance of the human nervous system at stage 8

Summary Eleven embryos of stage 8 (18 days), including a set of twins, were studied in detail and graphic reconstructions were prepared. This is the first report based on more than two specimens, as well as the first account of embryos of excellent histological quality at this developmental stage. Detailed measurements of the embryos are provided. It is found that the neural groove, which is the first morphological manifestation of the nervous system, is present in one quarter of embryos of stage 8. The neural folds are very largely cerebral rather than spinal. Correlations with other developmental features suggest that the neural groove is seen only when a certain degree of size and maturity has been reached by embryos of this important stage.Supported by research programme project grant No. HD-08658, Institute of Child Health and Human Development, National Institutes of Health (U.S.A.)     

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. © 2007 Wiley‐Liss, Inc.     

Computer ranking of the sequence of appearance of 100 features of the brain and related structures in staged human embryos during the first 5 weeks of development

The sequence of events in the development of the brain in staged human embryos was investigated in much greater detail than in previous studies by listing 100 features in 165 embryos of the first 5 weeks. Using a computerized bubble-sort algorithm, individual embryos were ranked in ascending order of the features present. This procedure made feasible an appreciation of the slight variation found in the development features. The vast majority of features appeared during either one or two stages (about 2 or 3 days). In general, the soundness of the Carnegie system of embryonic staging was amply confirmed. The rhombencephalon was found to show increasing complexity around stage 13, and the postoptic portion of the diencephalon underwent considerable differentiation by stage 15. The need for similar investigations of other systems of the body is emphasized, and the importance of such studies in assessing the timing of cogenital malformations and in clarifying syndromic clusters is suggested.     

Transient retinofugal pathways in the developing chick

Summary The central retinal projections have been examined in normal chick embryos early in development to determine if a transient ipsilateral projection is present. Anterograde transport of HRP identified using tetramethyl benzidine as a chromogen and degeneration techniques were used on embryos of successive ages between 6 and 16 days of incubation to show the central distribution of the retinal axons from one eye. Besides the anticipated contralateral projection, a small projection was identified to primary visual nuclei on the side of the brain ipsilateral to the injected or lesioned eye in embryos between days 6 and 12 of incubation. A projection from the injected eye into the contralateral optic nerve was also identified in a number of embyos. By embryonic day 15 the retinal projection to the ipsilateral side of the brain and into the contralateral optic nerve had disappeared. This loss of the anomalous projections coincides with a period of substantial cell death in the retinal ganglion cell layer. It appears, therefore, that in the chick, like the rat, the ipsilateral retinofugal projection resulting from an embryonic enucleation may in part be due to retention of a normal ipsilateral projection.Supported by grants EY 03713 and EY 03326 from the National Institutes of Health and by the Medical University of South Carolina Biomedical Research Appropriation     

Embryonic length and cerebral landmarks in staged human embryos

The greatest length (GL) and the crown-rump (C-R) length were compared in 43 staged human embryos. It was found that point C, which overlies the middle of the midbrain, was sometimes difficult to locate and that point R is not precise. These disadvantages render the C-R measurement unsatisfactory. At 4 weeks (stage 13) the GL comes to exceed the C-R and continues to do so until about 7 weeks (stages 17-19). The maximum difference is approximately 1.5 mm. Thereafter, the two lengths are basically equal and coincide from about stages 18 and 19 onward. In a series of 100 embryos of stages 19-23, female embryos at stages 21 and 22 were found to be shorter (by a mean of 1 mm) than male embryos, but not at stages 19, 20, and 23. The greatest length, which is independent of fixed points, is much simpler to measure than the C-R length, and it is recommended that it be used instead. It is pointed out that Streeter had already made that substitution. The greatest length has the further advantage of being a practicable measurement from two postovulatory weeks (stage 6) throughout the remainder of the embryonic and also in the fetal period. The lower limbs are excluded from measurement.     

Brain expansion in the chick embryo initiated by experimentally produced occlusion of the spinal neurocoel

The brain expands in the early chick embryo from pressure generated by accumulation of cerebrospinal fluid (CSF) in a closed neural tube. The sealing of the neural tube occurs as the result of occlusion of the spinal neurocoel rostral to and before closure of the posterior neuropore. We have previously demonstrated the dependence of normal brain expansion upon intraluminal pressure. We had yet to demonstrate, however, that brain expansion actually depends upon natural occlusion of the spinal neurocoel. To demonstrate such dependence, we experimentally occluded the spinal neurocoels of embryos 5 hr younger than stage 11 embryos (in which occlusion of the neurocoel occurs naturally). The stage 10 chick embryos were cultured ex ovo and critically staged, and their spinal neurocoels were occluded using microcautery. All embryos were photographed immediately and at 5, 12, and 24 hr after cautery. Serial sections were made of selected embryos, in which the areas of both the brain and the head were measured. Wilcoxon-Mann-Whitney rank-sum nonparametric tests, Hodges-Lehmann estimators, bootstrapping techniques, and resampling randomization tests were used to determine whether the increases in the brain and head areas for the experimental embryos were significantly different from those of the control embryos during three distinct intervals of expansion: 0-5, 5-12, and 0-12 hr. From 0 to 5 hr, the brains of the precociously occluded embryos expanded significantly more than the brains of the non-occluded controls. From 5 to 12 hr, the brains of the embryos with naturally occluded neurocoels grew significantly larger than the brains of the embryos with precociously occluded neurocoels. At 12 hr, there appeared to be no difference in brain size for these two groups. We conclude that the data support the hypothesis that brain expansion is directly dependent upon occlusion of the spinal neurocoel.     

Growth of dendrites in the optic tectum of the chick embryo following destruction of the eye primordium.

The consequences of depriving the optic tectum of axons from the contralateral eye have been studied in Golgi-impregnated brains from a staged series of chick embryos. Following enucleation at 2–5 days of age, measurements of dendritic length and the numbers of branches at all orders for three cell types were performed with an automated three-dimensional tracking system at various survival times. Dendritic lengths and the number of middle order branches of neurons from control animals, aged 12–14 days (stages 38–40), are greater than those from non-innervated embryos of the same ages. However, by Day 18 (stage 44), no significant differences in length or branching are seen between neurons from control and experimental embryos. Observations of these neurons revealed qualitative differences between experimental and control embryos. Growth cones, varicosities and filopodia, indicators of dendritic differentiation, are more commonly associated with neurons from control Day 12 and 14 embryos, than operated embryos of the same stages. However, at Days 16 and 18 these growth characteristics are more usually seen on neurons from deafferented embryos than from controls.The deleterious effects observed in experimental animals between Days 12 and 14 are presumably caused by the absence of optic fibers. The eventual growth during late embryogenesis, of the cells deprived of optic input, may reflect a trophic influence not acting in the earlier period.     

Insights Into Coronary Artery Development in Model of Maternal Protein Restriction in Mice

Programming of fetal development is considered to be an important risk factor for noncommunicable diseases of adulthood, including coronary heart disease (CHD). Aiming to investigate the association between maternal nutrition and the development of the coronary arteries (CAs) in staged mice embryos, C57BL/6 mice embryos from Stages 16 to 23 were taken from mothers fed a normal protein (NP) or low protein (LP) diet, and the CA were studied. Although the LP embryos had lower masses, they had faster heart growth rates when compared with the NP embryos. The subepicardial plexuses were observed earlier in the NP embryos (Stage 20) than in the LP ones (Stage 22; P < 0.01). Apoptotic nuclei were seen around the aortic peritruncal ring beginning at Stage 18 in the NP and LP embryos. FLK1⁺ (fetal liver kinase 1 = VEGF‐r2 or vascular endothelial growth factor receptor 2) cells had a homogeneous distribution in the NP embryos as early as Stage 18, whereas a similar distribution in the LP embryos was only seen at Stages 22 and 23. Maternal protein restriction in mice leads to a delay in the growth of the heart in the embryonic period modifying the development of the subepicardial peritruncal plexus and the apoptosis in the future coronary orifice region. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.