Epidermis regulators

The veins of skin are organized along the same lines as the arteries in that there are both subpapillary and subdermal plexuses [11]. The main arteriole communication to these is the capillary bed. Copious blood is passed through capillaries when the core body is either feverish or overheated, far more than needed to sustain the life force of the epidermis, and this rich perfusion lends a red coloration to skin. When there is opposite physiological need, the capillary bed is short-circuited as blood is passed directly into the venous drainage by way of the arteriovenous anastomoses. Fair skin noticeably blanches when this occurs. These mechanisms act in part to regulate body temperature and blood pressure. 

Temperature influences skin permeability in both physical and physiological ways. For instance, activation energies for diffusion of small nonelectrolytes across the stratum corneum have been shown to lie between 8 and 15 kcal/mole [4,32]. Thus thermal activation alone can double the rate skin permeability when there is a 10°C change in the surface temperature of the skin [33], Additionally, blood perfusion through the skin in terms of amount and closeness of approach to the skin s surface is regulated by its temperature and also by an individual s need to maintain the body s 37° C isothermal state. Since clearance of percuta-neously absorbed drug to the systemic circulation is sensitive to blood flow, a fluctuation in blood flow might be expected to alter the uptake of chemicals. No clear-cut evidence exists that this is so, however, which seems to teach us that even the reduced blood flow of chilled skin is adequate to efficiently clear compounds from the underside of the epidermis. 

FIG. 3. Stopping the cell division cycles. In Drosophila embryos, the timely arrest of cell proliferation in the epidermis requires the transcriptional activation of dacapo (Lane et al 1996, de Nooij et al 1996) and fi y-related (Sigrist Lehner 1997) which occurs during the final division cycle in parallel to down-regulation of cyclin E expression. 

The stratum corneum consists of separated, nonviable, cornified, almost nonpermeable corneocytes embedded into a continuous lipid bilayer made of various classes of lipids, for example, ceramides, cholesterol, cholesterol esters, free fatty acids, and triglycerides [6], Structurally, this epidermis layer is best described by the so-called brick-and-mortar model [7], The stratum corneum is crucial for the barrier function of the skin, controlling percutaneous absorption of dermally applied substances and regulating fluid homeostasis. The thickness of the stratum corneum is usually 10-25 /an, with exceptions at the soles of the feet and the palms, and swells several-fold when hydrated. All components of the stratum corneum originate from the basal layer of the epidermis, the stratum germinativum. 

Much of the FLS biochemical and structure/fimction analysis has focused on a protein from C. unshiu (mandarin). A cDNA was isolated based on sequence homology to an Arabidopsis FLS EST (153O10T7) and used as a probe to determine regulation of gene expression [92]. Higher expression was observed in young leaf, flower, peel, and juice sac/segment epidermis tissues. Expression decreased with tissue age, as has been observed for citrus CHS, CHI, and F3H [57]. Southern analysis... 

Resing, K. A., Thulin, C., Whiting, K., al-Alawi, N., and Mostad, S. (1995). Characterization of profilaggrin endoproteinase 1. A regulated cytoplasmic endoproteinase of epidermis./. Biol. Chem. 270, 28193-28198. 

Gibbs, S., and M. Ponec. 2000. Intrinsic regulation of differentiation markers in human epidermis, hard palate and buccal mucosa. Arch Oral Biol 45 149. 

The absence of an epidermal Ca2+ gradient in the epidermis in HHD may have direct effects on the expression of SPCA1. Extracellular Ca2+ may up regulate the expression of SPCA1 in keratinocytes (Kawada et al., 2005 Mayuzumi et al., 2005). According to one view, a rise in extracellular [Ca2+] would, at least in normal keratinocytes, result in a concomitant increase in [Ca2+]c followed by the... 

Toxic epidermal necrolysis occurs when the skin epidermis is destroyed by the action of toxicants and becomes detached from the dermis. This condition severely disrupts the ability of skin to regulate the release of heat, fluids, and electrolytes. Metabolites of the anticonvulsive drug carbamazepine have been implicated in toxic epidermal necrolysis. 

In most insects, pheromones are synthesized in specialized cells or tissues associated with the epidermis (Tillman et al., 1999). Biochemical analyses traced the localization of Scolytid pheromone accumulation to portions of the alimentary canal, particularly the hindgut (e.g. Borden et al., 1969 Byers, 1983), but the actual tissue source of pheromone components was unknown. Fortunately, the tight correlation of HMG-R gene expression with pheromone component biosynthesis meant that hybridization techniques could be used to map the location of pheromone biosynthesis. Northern blots provided the first maps, while in situ hybridizations definitively showed which tissues were elevating HMG-R mRNA in response to feeding or JH III treatment. As with endocrine regulation studies, the molecular and biochemical data complemented each other. 

It is not yet clear whether the calcium gradient leads to the formation of a mature barrier or the barrier caused the gradient. It may even be both, if the regulation uses a feedback mechanism, as the differentiation will eventually form a barrier leading to the accumulation of calcium ions in the upper epidermis. This high level of calcium will, in turn, guarantee the ongoing process of differentiation toward the formation of corneocytes (horny cells in the SC). The mechanism is thus almost completely autonomous, perpetual, and, if it runs smoothly, requires little correction from the body. 

Lee, S.H., Elias, P.M., Proksch, E. etal. Calcium and potassium are important regulators of barrier homeostasis in murine epidermis. J. Clin. Invest. 1992, 89 530-8. 

In situ expression of the HAS-1 and -2 genes are up-regulated in skin by TGF-/3, in both dermis and epidermis, but there are major differences in the kinetics of the TGF-/3 response between HAS-1 and -2, and between the two compartments, suggesting that the two genes are independently regulated. This also suggests that HA has a different function in dermis and epidermis. 

Dlugosz, A.A., and Yuspa, S.H., Coordinate changes in gene expression which mark the spinous to granular cell transition in epidermis are regulated by protein kinase C, J. Cell Biol., 120, 217, 1993. 

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