Morphodynamics of the epidermis of axolotl (Sideron mexicanum Shaw) under the influence of exogenously administered thyroxine. II. Epidermis during metamorphosis
Fährmann, W.
Zeitschrift für Mikroskopisch-Anatomische Forschung 83(4): 535-568
1971
ISSN/ISBN: 0044-3107 PMID: 5166123 Document Number: 5511
In order to bring about metamorphosis, neotenic axolotls were kept in a 0.05% thyroxine solution. Upon light and electron microscopical investigation the epidermis was found to show the following characteristics: Changes produced up to the 7th experimental day are not very noticeable and primarily of a gradual kind (Fig. 21a). To be noted is a reduction of the epithelial height, which has an average value of 120 µm (controls 140 µm). The epidermal cells increase their rate of mitosis. No more mitoses may be found among the Leydig cells. In the perinuclear area restructuring of the endoplasmic reticulum may be observed, which is now almost entirely vesicularised. The cover cells are much flattened and have only a very narrow mucous zone. Whilst X-cells are commonly seen, mitochondria-rich cells are absent. The next stage of metamorphosis, up to the 18th day, is characterized by major rebuilding and breakdown processes. The epidermal height is reduced to an average of 80 µm. The figures of Eberth can no longer be demonstrated in the epidermal cells. A new distribution of granular elements, leading to a concentration in the upper stratum intermedium becomes obvious. Certain changes in cell synthesis and hence in the chemistry of the granules can be observed. Further, scattered epidermal cells in the stratum intermedium now contain glycogen. During this period the Leydig cells almost completely disappear. In detail the breakdown processes, with dislocations, shrinkages and dissolutions may be extraordinarily varied. The X-cells serve to remove cell fragments. This brings about an increased activity of these cells during this phase. The most prominent alteration in the cover cells is the absence of the mucous zone. In their apical cytoplasm the cells contain only few granular elements of mainly oblong shape, which are obviously identical with those of the upper epidermis cells. There is further conformity in the histochemical characteristics, as far as the granules are concerned. By contrast, only the cytoplasm of the cover cells can be stained a homogeneous blue with alcian blue at low pH values (1.0 or 0.5). The later stage of metamorphosis (up to the 21st experimental day) is typified by the formation of a first stratum corneum. Here it must be emphasized that the keratinised layer is initially very incomplete, so that the epidermis is partly covered by a non-keratinised stratum superficiale and partly by a stratum corneum. In the epidermal cells of the upper stratum intermedum, tonofibrils may be Seen somewhat more clearly. In the deeper layers of the stratum intermedium one may now also find granules which may be stained with chrome-alum hematoxylin or aldehyde-fuchsin. Leydig cells can only be found in extremely degenerated forms and are very rarely seen. The number of X-cells is reduced again. In electron microscopical investigations the greatest changes are to be seen in the cells of the stratum superficiale. The varying aspects of the cover cells are brought about by the first keratinisation process. Hereby one initially finds swelling and dissolution processes, which do not affect the tonofibrils and granules. The terminal product, the keratinised cell, is greatly shrunk; in a relatively electrondense matrix lie tonofibrils and now swollen and disrupted granules. The desmosomes between the stratum intermedium and the stratum corneum are also modified.
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