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Biomedical subjects

R E Poelmann

Publications and source records attributed to R E Poelmann.

90 records · Page 5Linked to original sources
PubMed1987

6.5-mm human embryo with a single nasal placode: cyclopia or hypotelorism?

A macroscopic study on the missing elements in cyclopia (a single eye or closely approximated eyes with all intergrades in a single orbit) with or without proboscis and hypotelorism was performed on 12 human fetuses and 2 human fetal skulls. In addition, microscopic investigations were carried out on the orbital contents of the cyclops with a single eye without proboscis, crown-heel length (C-HL) 37 cm, and on the 6.5-mm-crown-rump length (C-RL) human embryo with a single nasal placode localized in front of two eye cups. In the embryo and in all 14 fetal cases the midfacial region was more-or-less deficient. In the two cyclopia cases without proboscis the nasal placode(s) had not developed at all during the embryonic period. In cases with proboscis, consisting of a single tube localized above both eyes, and in the hypotelorismic specimens, there could only have been a single nasal placode during development: a situation evident in the 6.5-mm-C-RL human embryo. In this holoprosencephalic embryo the single nasal placode was undulated, as if formed from two fused nasal placodes, and flanked by the prospective areas for the lateral nasal processes. Caudally, it was bordered by the maxillary processes. In view of the position of the single placode in this embryonic face, as described above, it is most likely that this is a preliminary stage of hypotelorism. Moreover, both medial nasal processes with the internasal groove in between, i.e., the interplacodal area, were missing.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Multiple↗
PubMed1987

The formation of mesoderm and mesectoderm in presomite rat embryos cultured in vitro, using WGA-Au as a marker.

Presomite rat embryos cultured in vitro were injected with the cell marker wheat germ agglutinin-gold in order to find out whether the ectoderm already formed mesodermal cells. These labelled so-called mesectodermal cells were found in all embryos studied, ranging in age from 8.7 to 9.3 days post coitum. In embryos younger than 9.0 days, the entire head fold ectoderm produced mesectodermal cells. From 9.0 days onwards, the neural crest and surface ectoderm placodes were recognizable as separate entities, both producing mesectodermal cells. The early onset of mesectodermal cell formation and the numerous and continuous manufacture led us to the conclusion that mesectodermal cells are deposited at their definitive location and that subsequent long-distance migration is unnecessary.

Animals↗
PubMed1987

Axial rotation of murine embryos, a study of asymmetric mitotic activity in the neural tube of somite stages.

Axial rotation is an important event during a certain period of development of Amniote embryos. In murine embryos a sharp lordosis changes into a kyphosis. The result is the typical fetal position. In this study a temporal and topological relation is found between an asymmetric mitotic activity in the neural tube and the rotation process. The mitotic asymmetry is lost when rotation is completed. A causal relationship between mitotic activity and rotation is postulated.

Animals↗
PubMed1986

The cell surface coat in neurulating mouse and rat embryos, studied with lectins.

Carbohydrates in the surface coat of cells are thought to have a function in cell adhesion. The surface coat of cells, located in the fusion zone of the neural walls is investigated during neural tube closure in mammalian embryos. The presence of alpha-D-mannose, alpha-D-glucose and N-acetyl-D-glucosamine is quantified with the help of the lectins concanavalin A and wheat germ agglutinin in absence or after enzymic treatment. A two-step incubation is used, in which the second step consists of a protein-gold conjugate. A high incidence of these sugar residues was found in the fusion zone, indicating a relation to the specific capacity of these cells in establishing cell contacts.

Animals↗
PubMed1986

Wheat germ agglutinin-gold as a novel marker for mesectoderm formation in mouse embryos cultured in vitro.

The routes of movement of mesectoderm cells in mammalian embryos have not yet been investigated experimentally due to technical problems. However, the recent development of in vitro culture methods have made an experimental approach to this problem in mouse and rat embryos possible. We have used combined lectin and colloidal-gold (WGA-Au) probe as a nontraumatic, easily detectable mesectoderm marker. The probe is introduced into the amniotic cavity by microinjection. All of the cells lining the cavity, including the mesectoderm precursors, phagocytose the colloidal gold, which is then stored in membrane-bound vesicles. The probe remains inside the target mesectoderm cells after their migration into the mesoderm compartment. Vesicles containing gold are detectable in both ultrathin and semithin sections. The applicability of WGA-HRP as a probe was also assessed because of the many properties it shares with WGA-Au, but it proved to be unsatisfactory for this purpose because it is transferred between cells and also to the extracellular spaces.

Animals↗
PubMed1985

Cell degeneration and mitosis in the buccopharyngeal and branchial membranes in the mouse embryo.

The frequencies of cell degeneration and mitosis were investigated in the rupturing buccopharyngeal membrane (BPM) and in the persistent first branchial membrane (BM). In the BPM, cell degeneration starts many hours before rupture is visible, but mitotic figures are absent. In the BM this situation is reversed: mitotic figures are regularly observed, but a degenerating cell only occasionally. It is concluded that the ratio between the numbers of degenerating and dividing cells regulates the fate of both the BPM and the BM.

Animals↗
PubMed1985

Histologic studies on normal and persistent ductus arteriosus in the dog.

The process of anatomic closure of the ductus arteriosus was studied at the ultrastructural level in 15 normal beagles (age 0 hour to 13 days) and in 18 specimens from a strain of dogs with hereditary persistent ductus arteriosus (age 4 hours to 27 days). Normal ductal closure takes place from the pulmonary artery to the aortic end. It is accompanied by a series of histologic changes: 1) separation of the endothelial cells from the internal elastic lamina resulting in a wide region of subendothelial edema; 2) ingrowth and infolding of endothelial cells and migration of undifferentiated smooth muscle cells from the inner media into the subendothelial region; 3) apposition of endothelial cells bordering the lumen; and 4) degenerative changes. In persistent ductus arteriosus, these changes do not occur. The endothelial cells remain closely adhered to the internal elastic lamina and the underlying media is abnormal in structure. In the case of partial persistent ductus arteriosus (ductus diverticulum), both the normal and the abnormal type of wall are found in a single ductus arteriosus. The histologic features of the normal and the persistent ductus arteriosus in the dog resemble those of the normal and the persistent ductus arteriosus in humans, suggesting a similar pathogenesis.

Animals↗
PubMed1985

The neural crest in presomite to 40-somite murine embryos.

The production of cells by the neural crest is studied light-microscopically in 10 microns and 1 micron serially sectioned mouse and rat embryos, ranging in age from presomite to 40-somite stages. In the head region, mesectoderm formation starts in a pre-neural plate stage. It continues to the 20-somite stage. This implies that the contribution of the neural crest to the head mesoderm must be considerable. In the trunk, the neural crest only produces cells after adhesion of the neural walls. Mesectoderm formation continues for a long time, slowly retreating in a caudal direction. At the 40-somite stage, mesectoderm formation still occurs in the most caudal part of the trunk. Compared to the head, the contribution of the neural crest in the trunk seems to be less important than that of the primitive streak.

Animals↗
PubMed1984

Hypertelorism and the median cleft face syndrome. An embryological analysis.

A microscopical study of the early and late development of the face was performed in 77 human embryos and fetuses. After the transformation of both nasal placodes, via nasal grooves, into the nasal tubes the ectoderm of the face is closed superficially and the early development of the face (less than or equal to 17 mm crown-rump length (C-RL)) is terminated. Between the nasal tubes the internasal groove is present. Furthermore these embryos show physiologically a flat nose and hypertelorism. During the late development (greater than or equal to 17 mm C-RL) of the face the internasal groove disappears due to the outgrowth and differentiation of the nasal septum in the frontocaudal direction. Simultaneously (17-27 mm C-RL) the distance between the eyes decreases relatively, because of a relative lag in transverse growth. The differentiation of the facial mesenchyme into bone centres starts in the same period. From this embryological point of view the major anomalies of the median cleft face syndrome (hypertelorism--orbital as well as interorbital--and cranium bifidum occultum, median cleft nose, median cleft prolabium and median cleft premaxilla), can be classified as secondary or late, i.e., differentiation, defects.

Bone Diseases, Developmental↗
PubMed1981

The formation of the embryonic mesoderm in the early post-implantation mouse embryo.

The formation of the mesoderm in early post-implantation mouse embryos is described and analysed. The outgrowth of the mesoderm was found to depend on the changes in the shape of the embryonic ectoderm, which lead to a relative displacement of the primitive streak in the caudal direction. The primitive streak deposits its cells laterally in the case of the lateral mesoderm, and medially in the case of the headprocess. In doing so, the primitive streak leaves a trail of mesoderm cells. This means that mesoderm cells do not migrate actively from the caudally located primitive streak towards more frontal positions in the embryo. This is confirmed by the results of scanning electron microscopy, which revealed that mesoderm cells show no polarity at all in the caudofrontal direction. In may therefore be concluded that these cells probably do not migrate. Studies on the cell-cycle parameters of the embryonic ectoderm, showed that mesoderm cells-to-be are probably recruited not only from the proliferation zone, but also from the lateral ectoderm. It is postulated that the lateral ectoderm gives rise, via the largest part of the primitive streak, to most of the mesoderm cells, whereas the proliferation zone gives rise to the head-process mesoderm, via the anterior part of the primitive streak.

Animals↗
PubMed1981

The head-process and the formation of the definitive endoderm in the mouse embryo.

The formation of the secondary or definitive endoderm was studied by light microscopy (1-mu m sections) and (scanning) electron microscopy. The results show that the primary endoderm disappears axially, and a hiatus appears in this layer. The development of this hiatus may be caused by cell degeneration, which is observed in the primary endoderm, or by some activity of the underlying head-process. The apical parts of a number of head-process cells converge towards a hiatus. These cells are organized into a conical configuration which may participate in the formation of the hiatus. The cone cells reach through the hiatus into the yolk sac cavity, and comprise the secondary endoderm. The consequence is that in mice, the definitive endoderm develops from the head-process mesoderm rather than from the primary endoderm.

Animals↗
PubMed1980

Differential mitosis and degeneration patterns in relation to the alterations in the shape of the embryonic ectoderm of early post-implantation mouse embryos.

The shape of the embryonic ectoderm of early post-implantation mouse embryos changes greatly in the period of 6.2-7.3 days post coitum. The subcellular morphology of the embryonic ectoderm remains unchanged, except in the primitive-streak region. Cell kinetics differ between ectodermal regions. These differences may be related to the changes in the shape of the ectoderm. The increase in cell number in the lateral ectoderm (the prospective surface ectoderm) exceeds that in the frontal ectoderm (the future neurectoderm). This is not due to differences in the duration of the cell cycle. It can be explained, however, by the occurence of different relative numbers of dividing and non-dividing cells. These numbers vary between the two regions. The percentage of non-dividing cells in the frontal ectoderm may reach 45, whereas in the lateral ectoderm this percentage is not higher than 15. Autoradiography in tritiated thymidine-treated embryos combined with the mitotic indices gave us all of the parameters necessary to present a model capable of clarifying the growth of the ectoderm during gastrulation, as well as the changes in the shape of the ectoderm.

Animals↗
PubMed1975

An ultrastructural study of implanting mouse blastocysts: coated vesicles and epithelium formation.

Electron microscopial techniques were used to study mouse embryos at implantation stages (5 1/2 days post coitum). Evidence was obtained indicating that trophoblast cells remove uterine luminal epithelial cells by phagocytosis. Small coated vesicles very probably play an important role in the process of digestion of uterine cells by the trophoblast. Two types of endoderm cell were present: the embryonic endodermal cells contained organelles appropriate to a nutritive pathway; the extra-embryonic endodermal cells were relatively poorly developed compared with those of the embryonic endoderm, and remained as a discontinuous layer. The ectoderm contained few organelles. Epithelium formation is described. Junctions only develop between cells in the same germ layer except for occasional ones, including desmosomes, between trophoblast and uterine epithelial cells. The author wishes to thank Professors J.M.F. Landsmeer and W.T. Daems for their stimulating discussions during this research project and for their helpful comments during the preparation of the manuscript. The Laboratory for Electron Microscopy kindly provided full facilities. The assistance of Mr J. Tinkelenberg in the preparation of the drawing (Fig. 1) is acknowledged. Thanks are also due to Mrs 2. seeger for reading the English manuscript and to Miss Ria Stokman for typing it.

Animals↗