Relationship of epidermal melanocytes and langerhans cells with epidermal cambial cells.

Studies of mouse ear epidermis showed that proliferative activity of basal epidermal cells has two active and two passive phases throughout 24 h. Active phases consist of two subphases: long (proliferation of cambial cell descendants) and very short (cambial cell proliferation). Cambial cells proliferate at the boundary between active and passive phases; this results in an increase in the counts of epidermal melanocytes and Langerhans cells resultant from division of epidermal cambial cells. The count of Langerhans cells almost 2-fold surpasses melanocyte count, because melanocytes gradually transform into epidermal basal cells.

On the common mechanisms of cambial somatic and sex cells proliferation and the notion of the cambial cells.

Study of the early embryogenesis process based on the previously suggested scheme of epithelial cambial cell work has shown that cambial (or stem) cells originate from the primary ectoderm and intensely express RhoA protein and slightly express Src kinase. This explains their stem properties and the absence of differentiation. Primary sex cells are separated stem cells getting into an environment which expresses (to a certain measure) Src kinase in them and causes their polarization and specialization. In order to induce differentiation of cambial cells in a certain direction, expression of Src kinase should be stimulated to the needed degree in each tissue.

[Participation of morphofunctional zones in aging processes].

There are morphofunctional zones in organism tissues, where proliferation and differentiation processes occur. Daughter cells are differentiated in the electric field excited by 12 mother and daughter cell pairs, turned out at cambial cell division. With aging, the cambial cell number is reduced to 7, close to thresholds level (6 cells), at which the differentiation of daughter cells is absent. The depression of cambial cell number with aging is connected with the work of another morphofunctional zone--the hypothalamus, which is the major center of vegetative regulation and initially has very high RhoA activity, which has been established in embryogenesis. Estrogens, influencing over the hypothalamus and activating Src kinase in its nuclei, reduce the level of RhoA activity, including SCN, responsible for many biorhythms of an organism. As a result, the hyperestrogenemia and therefore a connective tissue at first occur. Then there happens a hypoestrogenemia that leads to sharp falling of proliferative activity of cells, causing the depression of cambial cell number and possibility of a malignant tumor development. Along with this, there are the deep lesions of hormone regulation, leading to some lethal diseases. Thus, the RhoA increasing in hypothalamus and especially in SCN circadian rhythm can counteract the Src kinase intensifying and prevent the processes connected with this.

Peculiarities of proliferation and differentiation of cambial and daughter cells of epidermal-dermal morphofunctional zone in normal epithelium and in cancer.

The cambial and daughter cells of normal epithelium function in the morphofunctional zone consisting of two subunits with 12 cambial cells in each. Daughter cells are differentiated in an electrical field created by 12 pairs of maternal and daughter cells, products of division of cambial cells located in the same subunit. The differentiation requires relaxation of the cortex of daughter cells via expression of SH3 domain of Src kinase by dermal daughter cells, which leads to a decrease in activity of RhoA in epidermal cells, their stretching, and activation of SH2 domain of Src responsible for differentiation. Reduction of the number of cambial cells to 6 and, consequently, weakening of electrical field produced by them to a threshold value corresponding to very weak stretching of daughter epithelial cells results in a decrease in SH2 domain expression in these cells and its kinase contribution in Src. This leads to an increase in RhoA relative to Src, enhances cell contraction, impairs formation of stress fibrils and focal contacts, reduces cell flattening, and increases cell mobility. The decrease in the number of microtubules, intermediate filaments, and stress-fibrils changes the major cell axis direction, which, in turn, sharply reduces nucleus stretching and leads to impaired chromosome looping out near the centromeres and telomeres; the cells acquires signs of an epitheliocyte and a fibroblast, protein transcription is impaired, and daughter cells are transformed into malignant cell.

[Characteristics of proliferation and differentiation of cambial and daughter cells in morphofunctional zones in the normal epithelium and cancer using age aspect].

Work of cambial cells of normal epithelium occurs in morphofunctional zone consisting of two subunits with 12 cells in each. 12 pairs of maternal and daughter cells which have turned out at their division, create the electric field making a differentiation of daughter cells. But it is necessary to relax the cortex of epidermal daughter cells by expression of the SH3 domain of Src-kinase in them with the help of dermal cells that leads to depression of RhoA activity in epidermal cells and the further activation of the SH2 domain of Src in them responsible for a differentiation. With the years, the number of epidermal cambial cells falls from 12 in 20 years to 7 in 75+ in consequence of depression of influence of dermal cells on cambial epidermal cells, which results in dropping of expression of SH2 domain and change of a differentiation of epidermal daughter cells. The reduction of the number of cambial cells to threshold size (6) leads to sharp falling of expression of SH2 domain of Src in daughter cells. This involves augmentation RhoA in relation to Src, falling of formation of stresses-fibrils, microtubules. The stretching of nucleus is sharply decreased, which conducts to formation of incomplete loops of chromosomes, simultaneously nearby a centromere and telomere, thus the cell gets features of an epitheliocyte and a fibroblast, the transcription of proteins is broken, and the daughter epithelial cell becomes malignant.

Age-specific morphofunctional changes in cambial cells and their derivatives in human skin.

The count of cambial cells decreases with age in the total morphofunctional zone of the skin. However, their number determines the stretching of the daughter cells, which, in turn, activates the Src domain of protein SH2. Twelve cambial cells is the optimal quantity, at which the SH2 domain (responsible later for full-value stretching and looping of chromosomes near telomeres in the region of epithelial cells formation) is sufficiently active, which is characteristic of the age of 20-40 and 41-59 years. If the number of cambial cells is less than 12, stretching of the nuclei and expression of SH2 domain reduce, this leading to looping of lesser sites of chromosomes, modulating the transcription; the expression of Src and RhoA proteins is imbalanced, which leads to reduction of cell proliferation, modification of the direction of the cell's basic axis, and to hyperdesquamation. This is characteristic of the age of over 60 years. After 75 years of age the number of cambial cells in both subunits of the epidermal basal layer decreased to 7 and is close to the threshold level (6 cells), when interactions between fields of the two subunits are weak or zero. Therefore, despite the involvement of both subunits (14 cells), cell stretching and expression of the Src protein SH2 domain in them drop sharply, while activity of RhoA protein increased, which leads to looping of chromosomes closer to the centromeres, that is, to active development of fibroblasts, which is characteristic of subjects over 75 years of age.

Interaction of cambial dermal cells (fibroblasts) and epidermis in morphofunctional area of mouse skin.

Epidermis and dermis form an integral morphofunctional area, where cambial cells proliferate and their first-division daughter cells differentiate. An important feature of this area is different rates of the development of daughter cells (fibroblasts) in the dermis and epidermis, which is greater in the epidermis. This asymmetry results in the prevalence of first epidermal daughter cells and, hence, their effect on cambial cells, and then of stromal daughter cells and their effects on cambial cells. The regulator factors of epidermal daughter cells promote unblocking of the major polarity axis of cambial (mother) cell, while stromal cells (fibroblasts) induce their polarization along the major axis and the onset of mitosis. In the dermis and epidermis, division of cambial cells is asymmetric; a prominent role in the formation of mother and daughter cells is given to the basal membrane as an elastic support. Mother and daughter cells form ring-like structures generating electric field that can promote differentiation of the daughter cells.

Comparative analysis of the work of morphofunctional zones in normal epithelium, fibroadenoma, and cancer of the breast.

Twenty-four rosettes (proliferative epidermal units) in epithelial tissue are united into morphofunctional zones, where cambial cells proliferate with the formation of maternal and daughter cells and these latter ones differentiate under the influence of electrical field generated by 12 maternal cells. The number of cambial cells in morphofunctional zone of a malignant tumor is reduced at least 2-fold. Hence, the number of maternal cells is reduced to 6, which is insufficient for electric field generation and stimulation of daughter cells differentiation. The percentage of cambial cells in a benign tumor decreases 1.5 times. Daughter cells are differentiated in an electric field whose strength is below optimal, but above the threshold value at which cells do not differentiate; hence, differentiation is incomplete.

Peculiarities of proliferation of epidermal cambial cells in mouse skin.

The long axis of epidermal cambial cells determining the direction of their division is determined before the beginning of division and is oriented perpendicularly, but not parallel, to the basal membrane, as in other basal cells. As a result, only one of the two newly formed cells adheres to the basal membrane and at the expense of traction forces detaching one cell from the other and elastic force of the basal membrane is formed as a maternal cell and stays in the focus of multiplication. The other cell, turning around under the effect of traction forces perpendicularly to the maternal cell, cardinally changes the direction of its long axis and is polarized parallel to the basal membrane like other cells. This cell becomes the daughter cell, its shape with the "head" and "tail" allows its rapid migration into other rosettes for differentiation.

Structural organization of the basal layer and morphofunctional characteristics of mouse epidermal cambial cells.

The basal layer of mouse skin epidermis consists of special structures - rosettes functionally arranged in zones including about 20 rosettes. The rosette contains a central cambial cell; after division of this cell the mother cell remains in the center of the rosette and the daughter cell migrated to the center of a free rosette. The mother and daughter cells are dipole cells (sources of electric field). If the disposition of mother cells is unidirectional and they predominate over daughter cells, the latter cells transform into other cells, i. e. are differentiated.