Biomedical subjects

Shigehito Yamada

Publications and source records attributed to Shigehito Yamada.

8 recordsLinked to original sources

PubMed2006

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.

Anatomy, Artistic↗

PubMed2006

Embryonic holoprosencephaly: pathology and phenotypic variability.

Holoprosencephaly (HPE) is one of the major brain anomalies caused by the failure of cleavage of the prosencephalon during the early stage of development. Over 200 cases of HPE in the Kyoto Collection of Human Embryos were observed grossly and histologically, with special emphasis on the anomalies of the brain, face and eye. The facial anomalies of HPE human embryos after Carnegie stage (CS) 18 could be classified into cyclopia, synophthalmia, ethmocephaly, cebocephaly, and premaxillary agenesis, similarly as the classical classification for postnatal cases. On the other hand, HPE embryos at CS 13-17 showed some characteristic facies which are different from those in older embryos. In the present paper, pathology and phenotypic variability in HPE embryos were discussed from the embryopathological point of view. Recently, the molecular mechanism of HPE has been clarified by the techniques of gene manipulation, and various HPE genes have been identified by gene analysis of familial HPE cases. HPE is one of the major CNS anomalies which have been extensively studied and provides a clue to the mechanisms of normal and abnormal development of craniofacial structures.

Animals↗

PubMed2005

Embryogenesis of fused umbilical arteries in human embryos.

OBJECTIVE: The objective of this study was to elucidate the embryologic basis of fused umbilical arteries in the human. STUDY DESIGN: Twenty-nine human embryo specimens at Carnegie stages 11 through 15 (4-5 weeks after fertilization) were examined histologically, with special reference to the development of umbilical arteries. RESULTS: All embryos at Carnegie stage 11 and 12 had fused umbilical arteries, and 66% of Carnegie stage 13 embryos and 29% of Carnegie stage 14 embryos still had the condition. None of the embryos at Carnegie stage 15 or older had fused umbilical arteries, but there were always 2 arteries present in their umbilical cords. CONCLUSION: Our data suggest that (1) a single umbilical artery splits into 2 as the developmental stage of the embryo advances, (2) that fused umbilical arteries represent a remnant of the embryonic phenotype, and (3) that fused umbilical arteries are embryologically distinct from true single umbilical artery.

Cadaver↗

PubMed2005

Assisted reproductive technologies and birth defects.

In vitro fertilization (IVF) and other assisted reproductive technologies (ART) are effective treatments for infertility and are widely provided at infertility clinics. Although IVF and related ART procedures are generally considered safe, some studies have suggested an excess occurrence of major malformations, low birth-weight and other perinatal complications in babies conceived by ART. Further, it was recently reported that IVF and intracytoplasmic sperm injection (ICSI) are associated with imprinting disorders in the offspring such as Beckwith-Wiedemann syndrome and Angelman syndrome. Here we review the human and animal studies investigating the potential risks of ART, and discuss the need for further investigation.

Animals↗

PubMed2005

Spontaneous regression of congenital cystic adenomatoid malformation of the lung: longitudinal examinations by magnetic resonance imaging.

We report a case of large cystic adenomatoid malformation of the lung (CCAM), which occupied almost the entire left lung with a prominent mediastinal shift at 24 weeks of gestation. The volume of the lesion, determined by magnetic resonance imaging (MRI), was 27.0 cm3. Subsequent MRI and ultrasound examinations revealed a spontaneous resolution of the lesion at 32 and 36 weeks of gestation without a mediastinal shift, when the lesion volume was 12.8 cm3 and 5.6 cm3, respectively. At 37 weeks of gestation, a mature male baby weighing 2638 g with an Apgar score of 7 was delivered by elective cesarean section. A lobectomy of the left upper lobe of the lung was carried out at 3 days of age, due to an enlargement of the CCAM after birth.

Adult↗

PubMed2004

Development of the posterior neural tube in human embryos.

Development of the posterior neural tube (PNT) in human embryos is a complicated process that involves both primary and secondary neurulation. Because normal development of the PNT is not fully understood, pathogenesis of spinal neural tube defects remains elusive. To clarify the mechanism of PNT development, we histologically examined 20 human embryos around the stage of posterior neuropore closure and found that the developing PNT can be divided into three parts: 1) the most rostral region, which corresponds to the posterior part of the primary neural tube, 2) the junctional region of the primary and secondary neural tubes, and 3) the caudal region, which emerges from the neural cord. In the junctional region, the axially-condensed mesenchyme (AM) intervened between the neural plate/tube and the notochord at the stage of posterior neuropore closure, while the notochord was directly attached to the neural plate/tube in the most rostral region. A single cavity was found to be formed in the AM as the presumptive luminal surface cells were radially aligned in the junctional region prior to the formation of the neural cord. The single cavity was continuous with the central cavity of the primary neural tube. In contrast, multiple or isolated cavities were frequently observed in the caudal region of the PNT. Our observation suggests that the junctional region of the PNT is distinct from other regions in terms of the relationship with the notochord and the mode of cavitation during secondary neurulation.

Cauda Equina↗

PubMed2004

Palatal shelf movement during palatogenesis: a fate map of the fetal mouse palate cultured in vitro.

Day-13 fetal mouse palates (plug day=day 0) were labeled with carbon particles at various sites of palatal shelves and cultivated in a chemically defined medium for up to 48 h. During the culture period, the bilateral palatal shelves came in contact and fused with each other, which simulated in vivo palatogenesis. The carbon study revealed that at the midpalatal region, the medial edge of the palatal shelf elevated to the horizontal plane, elongated toward the midline, and made contact with the medial edge of the opposing shelf. On the other hand, near the anterior and posterior ends of the shelf, some new tissue was formed at the medial edge of the shelf by remodeling and this newly formed tissue took part in palatal fusion. The results of the present study indicate that during mouse palatogenesis, the anterior and posterior regions of the palatal shelf behave differently from the midpalatal region. It seems that in the fetal mouse palate, the midpalate closes mainly by means of rotation and medial elongation of the shelf, whereas the anterior and posterior parts of the palate close mainly by tissue remodeling of the medial edge and partly by medial elongation of the shelf.

Animals↗

PubMed2004

Phenotypic variability in human embryonic holoprosencephaly in the Kyoto Collection.

BACKGROUND: Holoprosencephaly (HPE) is one of the most common developmental disorders of the brain associated with specific craniofacial dysmorphogenesis. Although numerous postnatal cases have been reported, early phases of its pathogenesis are not well understood. We examined over 200 cases of HPE human embryos both grossly and histologically, and studied their phenotypic variability and stage-specific characteristics. METHODS: Among over 44,000 human embryos in the Kyoto Collection of Human Embryos, 221 embryos have been diagnosed as HPE. Their developmental stages ranged from Carnegie stage (CS) 13 to CS 23. They were examined grossly and were also serially sectioned for detailed histological analysis. RESULTS: HPE embryos after CS 18 were classified into complete (true) cyclopia, synophthalmia (partially fused eyes in a single eye fissure), closely apposed separate eyes (possible forerunners of ethmocephaly and cebocephaly), and milder HPE with median cleft lip (premaxillary agenesis). At CS 13-17, when facial morphogenesis is not completed, HPE embryos had some facial characteristics that are specific to these stages and different from those in older HPE embryos. The midline structures of the brain, including the pituitary gland, were lacking or seriously hypoplastic in HPE embryos. Complete cyclopia was found in two cases after CS 18 but none at earlier stages. CONCLUSIONS: The early development of HPE in human embryos was systematically studied for the first time. The pathogenesis of craniofacial abnormalities, especially eye anomalies, in HPE was discussed in the light of recent studies with mutant laboratory animals.

Embryonic Development↗