Biomedical subjects
Publications and source records attributed to M A England.
Experimental primary neural induction was studied by transmission electron microscopy and compared with normal primary neural induction studies. A change was observed in the ectoderm cytoplasm and the ribosomes formed polysomes in the same way as previously described in normal induction.
Wound closure in the ectoderm of Xenopus early neurulae and chick primitive-streak embryos has been studied by scanning electron microscopy (SEM). Initial gaping of the wound and a cobble-stone appearance of cells peripheral to the wound in both Xenopus and chick confirm that the ectoderm is under lateral tension at these stages. Healing is rapid: in Xenopus embryos wound closure has started within 5 min of wounding; in chick healing is almost complete within 30 min in some cases. The SEM observations suggest that in Xenopus embryos changes in cell shape are the major mechanism for wound closure. In chick embryos wound healing is also accompanied by changes in the shape of the marginal cells, but evidence is presented that in this system cell proliferation is important. The mechanisms of wound healing in Xenopus and chick embryonic ectoderm are compared with those of wound healing in other tissues.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Chick embryo mesoderm cells were explanted to culture systems in vivo and in vitro and their subsequent movements were correlated with the external morphology as studied by SEM. In vitro cell movements are exaggerations of normal in vivo movements where a 2-dimensional substrate is encountered rather than a 3-dimensional environment.
The effects of cytochalasin B (CCB) on chick mesoderm cells in vivo was examined by scanning electron microscopy (SEM). The embryos were mounted for New Culture and the mesoderm exposed by dissecting off the endoderm. Cytochalasin B was suspended in saline and the embryos flooded with the suspension. Control embryos were treated with saline alone. The embryos were reincubated for varying times at 37 degrees C. In the treated embryos the mesoderm cells were rounded and separated from each other. Many had long branched processes and rough surfaces. These changes became more pronounced as treatment time was increased. They were also reversible on reincubating treated embryos in the absence of cytochalasin B. The morphological changes produced by CCB are thought to be due to an effect on the cytoskeleton, either a direct disruptive effect or detachment of skeletal microfilaments from the cell membrane. There may also be a direct removal of cell surface materials leading to the observed surface roughening of treated cells.
Changes in cell shape during the formation of the head process and regression of Hensen's node have been examined by scanning electron microscopy in a series of chick embryos from stage -5 to stage -8. The endoderm was removed from embryos mounted for New culture so that the mesoderm could be viewed from the ventral surface. As the primitive streak shortens its cells flatten and lose the flap-like processes characteristic of earlier stages. The notochord differentiates and its cells become transversely orientated, then re-align along the embryonic axis between stage 6 and stage -8. At the same time a split or cleft appears between notochord and head mesoderm, and extracellular fibrils are formed which are the first sign of the formation of a notochordal sheath.
Regeneration of the area pellucida endoderm of the chick embryo was studied by scanning electron microscopy (SEM). A new endoderm was formed by in situ changes in the shape and relationships of mesoderm cells. Initially the cells flattened and lost their processes except along cell boundaries. Later even these processes were lost and an epithelium was formed. The area of regenerated endoderm coincided with the area of mesoderm at the time of endoderm removal, confirming the mesodermal origin of the new layer. Remnants of the original endoderm did not contribute to the regenerated layer. Contact inhibition was observed at the boundary between original and regenerated endoderms.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A simple incision was made in the early chich embryo (stages 3-5) are pellucida endoderm and its subsequent healing studied by scanning electron microscopy (SEM). Initially the wounded edges of the endoderm layer curl towards the ectoderm creating a gaping slit. The endoderm cells adjacent to the slit from large mounds probably in response to a loss of substrate and the trauma of the incision. Healing begins as the endoderm cells direct processes across the underlying cell layers and the two cut edges move towards one another. Many intervening mesoderm cells have cup-shaped processes. As the two endoderm edges meet in the corners of the wound, the wound outline changes to an oval shape. After 2 hours the wound outline is changed to a slit with the cut edges contracting in one or two areas. The cup-shaped mesoderm processes remain in the slit until the wound is healed primarily by endoderm cell movement.
The distribution of mesoderm, the structure of mesoderm cells and relationship between mesoderm and ectoderm were examined by SEM in embryos at stages 3 to 5. The mesoderm was displayed by removal of the endoderm and by fracturing the embryos through mesoderm containing regions. Within the mesoderm layer four zones could be distinguished by their cell shape and arrangement--the primitive streak, a multilayered compact area around the margins of the area pellucida, multilayered and loosely arranged cells near the primitive streak and a flattened monolayer of cells around the advancing lateral and anterior edges of the mesoderm sheet. Secretion of basement membrane by the ectoderm was seen to precede the arrival of mesoderm cells. This suggests that ectoderm alone can synthesize basement membrane without mesodermal contribution.
The structure of the cells forming the primitive streak was examined by SEM in a series of embryos at Hamburger and Hamilton's stages 2--5. Specimens were prepared by stripping the endoderm from fresh embryos in New Culture and by fracturing whole fixed embryos along and at right angles to the primitive streak. At all stages of examination the SEM appearance of cells within the privitive streak was quite different from that of ectodermal, endodermal or mesodermal cells away from the streak. Streak cells were closely packed, lay with their long axes directed from ectoderm to endoderm and possessed many flat leaf-like processes. By contrast the ectoderm formed a columnar epithelium, the endoderm a flat epithelium and the mesoderm was a layer of loosely arrangedcells with long. thin processes. Within the streak SEM did not show any differences between cells that could identify them specifically as future endoderm or mesoderm cells. It was concluded that during gastrulation all the cells migrating through the primitive streak have the same appearance regardless of their eventual destination in the embryo. This structure may be attributable to the type of movement made by cells during invagination.
Normal primary neural induction has been further studied by TEM and SEM. A single mesoderm cell is usually in contact with several ectoderm cells. The mesoderm cells are also contacting other mesoderm cells. It is suggested that ectoderm cells are induced in groups and that induction is synchronized by these contacts. At the points of contact between mesoderm and ectoderm cells cytoplasmic changes are present in the induced tissue.
Normal primary neural induction has been studied by scanning electron microscopy and the results compared with those obtained by TEM. Mesoderm cells are usually in contact with several other cells, both mesodermal and endodermal in origin. By SEM the ectoderm layer has been shown to be in contact with the underlying mesoderm cells. Tufts of fibrous basement membrane are also present between the two cell types. TEM specimens also show an intermediate basement membrane.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.