Metaplasia produced in cultures of chick ectoderm by high vitamin A / by Honor B. Fell and E. Mellanby.

  • Fell, Honor B.
Date:
[1953?]
Catalogue details

Licence: In copyright

Credit: Metaplasia produced in cultures of chick ectoderm by high vitamin A / by Honor B. Fell and E. Mellanby. Source: Wellcome Collection.

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    Number of cultures studied. In the first main group of experiments (section I), thirty-eight + A explants and twenty-eight controls grown in watch-glasses and nineteen +A and twenty- three controls from hanging-drop cultures were histologically examined after periods of cultivation ranging from 7 to 14 days. In the second group, eight .explants from watch-glasses and fourteen from hanging drops were fixed and sectioned after being grown in the -I-A medium for 7-14 days and then transferred to normal medium for 4-8 days. Histology The explants were fixed in 3 % acetic Zenker’s fluid; fixation for 30 min gave the best results. For comparison with the explants, the ectoderm, with underlying body wall, and the nasal regions of 7-, 10-, 13- and 18-day embryos, and also the skin and nasal mucosa from an adult cock were fixed in 5 % acetic Zenker’s fluid for periods varying according to the size of the tissue fragment. After being washed, dehydrated and cleared in Cedar wood oil in the usual way, the tissue was embedded in paraffin wax and sectioned at a thickness of 8 y. Sections were stained by one of the following procedures: Bauer’s and Bensley’s modification of the Periodic acid-Schiff reaction (PAS), after digestion with saliva, followed by Meyer’s haematoxylin or haemalum, or by mucicarmine followed by Meyer’s haematoxylin, by Delafield’s haematoxylin and chromotrop, or with azan and celestin blue, followed by haemalum and van Giesen’s stain. The sections were mounted in Depex. RESULTS I. The effect of cultivation in +A medium The structure of the original explants In the original explants (PL 1, fig. 3) the ectoderm consisted of an outer layer of flattened cells and a basal layer of columnar or cubical cells which varied in depth in different parts of the trunk and limbs. Feather papillae had not yet appeared. Below the ectoderm was loose mesenchymatons tissue. Watch-glass cultures Controls. During the first 48 hr in normal medium the tissue spread into a sheet composed of mesoderm, with a marginal fringe of amoeboid cells, and a superficial layer of ectoderm which often extended beyond the mesoderm as a thin membrane on the surface of the clot. By about the 4th day small, dome-shaped feather papillae had appeared. Between the 4th and 7th day the central region of the explants had greatly thickened and sometimes projected from the clot like a balloon, from the base of which epithelium and fibroblasts wandered over and into the medium. The epidermis increased in thickness, and by the 7th day was often much folded and, especially in the peripheral part of the tissue, had become opaque owing to cornification of the superficial layers. The feather germs had elongated and assumed a fairly symmetrical bottle-shape, the 4 neck5 being attached to the skin. In cultures of embryos from a pigmented breed, branched rnelano- phores differentiated and wandered into the epidermis and especially into the feather germs, which often looked nearly black to the naked eye. By the 9th day the controls were almost completely epithelialized, only a narrow gap
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