Epidermis mitosis

Eehner We haven t done these experiments. But we have looked in string mutants where cells arrest in G2 before mitosis 14 and in cyclinAl cyclinB double mutants where cells arrest in G2 before mitosis 15. The timing of dacapo expression in the epidermis appears to be normal in these mutants. 

Eehner In the epidermis it is quite reproducible. After mitosis 13, when the syncytial division cycle is stopped, cellularization occurs followed by a pulse of string expression that allows cells to go through mitosis 14. Then they go immediately into S phase and wait in the next G2 phase until the next pulse of string comes up, driving mitosis 15. After mitosis 15, they go again immediately into S phase and wait in G2 until string comes up, triggering the final division. 

The innermost layer of the epidermis, the stratum basale, consists of a single layer of columnar-shaped, undifferentiated stem cells. Mitosis of these cells constantly renews the epidermis and this proliferation compensates for the loss of dead stratum corneum cells (corneocytes) from the skin surface. As the cells produced by the basal layer move upward, they alter morphologically as well as histochemically to form the outermost layer, the stratum corneum. Over a 4- to 5-week period the entire epidermis is renewed [5]. 

Inhibition of root meristem mitosis, rapid elongation of epidermis - short, pitted trachea with lesions, root hairs at root tip only, considerable vacuolation and lignification. 

After a resorcinol peel, the superficial stratum corneum comes away from the germinative layer in the stratum granulosum. The basal layer shows increased mitosis and accelerated turnover. The total thickness of the epidermis therefore increases, to the detriment of the stratum corneum, and the skin appears more hydrated. 

F7. Fisher, L. B., Determination of the normal rate and duration of mitosis in human epidermis. Brit. J. Dermatol. 80, 24-28 (1968). 

After oral administration, griseofulvin is specifically localized in a patient s keratinized cells, namely the epidermis, hair, and nails, and is used to injure fungi parasitizing these tissues. Griseofulvin blocks fungal mitosis, causing multinucleate cells to be formed (Gull and Trinci, 1973) mammalian (and plant) cells suffer similarly, so the selectivity depends on the initial distribution. 

Malpighian layer (stratum germina-tivum) The iimermost layer of the epidermis of mammalian skin, separated from the underlying dermis by a fibrous basement membrane. It is only in this layer of the epidermis that active cell division ( mitosis) occurs. As the cells produced by these divisions age and mature, they migrate upwards through the layers of the epidermis to replace the cells being continuously worn away at the surface. 

A chalone extracted from the skin inhibits epidermal mitosis it is tissue-specific in that it inhibits cell division in the epidermis but not in other tissues, but it is not species specific. 

Effect of Adrenochrome and Adrenalin Tartrate on Mitosis Average numbers of mitoses arrested by colchicine in 4 hr. in unit lengths (1 cm.) of sections 7 M thick of mouse ear epidermis incubated at 38°C. in 4 ml. saline medium and an oxygen gas phase. Each figure is the average of 5 observations. 

Apart from the light which this sheds on the relation of the hormone complex to growth by mitosis, confirmation is given for the theory that the process of energy production is a highly important, if not critical, factor in the mitotic activity of tissues such as epidermis. 

The feet of rats raised from weaning on EFA-deficient diet are scaly and cracked and this occurs generally within 2 weeks. The tail also exhibits scaliness and ringing , and later, necrosis of the tip. Microscopically the dorsal epidermis is thickened and hyperplastic, with a greater than normal number of cells in mitosis, an elaborated stratum granulosum, increased keratohyalin, and a highly compacted stratum corneum ... 

The mechanism of action of 13-cis retinoic acid in normal and diseased human skin has not been studied. Many biological effects of vitamin A, especially its ability to labilize biological membranes and release lysosomal enzymes, have been described in detail. Vitamin A and its derivatives control cell growth and differentiation in epithelial tissues. Retinoic acid, in particular, is a potent stimulator of mitosis in the epidermis. Excess vitamin A and its derivatives also have been demonstrated to inhibit keratinization and induce a mucous metaplasia with enhanced glycoprotein synthesis in several laboratory models, such as embryonic chick skin in organ culture . The mode of action of topical retinoic acid in acne is thought to be the increased production of nonadherent surface scales, which prevents follicular occlusion and comedo formation . None of the known effects, however, can fully explain the apparent disease and individual specificity of the clinical response to 13-cis retinoic acid nor do they explain its ability to reduce the erythema in these diseases. 

At the end of the S period, the cell enters in the G2 period. It is believed that condensation of chromosomes occurs as a result of synthesis of a number of uncharacterized factors as the cell enters the D phase from the G2 phase. This is the beginning of the prophase of mitosis. The HeLa cell in mitosis can cause premature chromosome condensation (chromosomal pulverization) of an interphase nucleus that enters the cell by cell fusion (Johnson and Rao, 1970 Matsui et al., 1972). The chromosomal condensation factor is not species specific (Johnson et al., 1970). Arrest of the G2 phase may occur but usually involves only a few percent of the cells. It has been studied best in the mouse ear epidermis (Gelfant, 1963). Cyclic AMP may mediate the reversible arrest of cells in the G2 phase (Nose and Katsuta, 1975 Willingham et al., 1972). Fusion of a HeLa cell in the G2 phase with a cell in an earlier phase can arrest the G2 phase and prevent progression into the D phase (Rao et al., 1975 Rao and Johnson, 1970). Protein synthesis is necessary until 10 min before prophase in order for cells to enter into mitosis (Tobey et al., 1966). RNA synthesis is also required but is completed before the protein synthesis requirement (Tobey et al., 1966). 

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