Regional variations in mouse skin: quantitation of epidermal compartments in two different body sites

Increased interstitial pressure improves nucleic acid delivery to skin enabling a comparative analysis of constitutive promoters

Nucleic acid-based therapies hold great promise for treatment of skin disorders if delivery challenges can be overcome. To investigate one mechanism of nucleic acid delivery to keratinocytes, a fixed mass of expression plasmid was intradermally injected into mouse footpads in different volumes, and reporter expression was monitored by intravital imaging or skin sectioning. Reporter gene expression increased with higher delivery volumes, suggesting that pressure drives nucleic acid uptake into cells after intradermal injections similar to previously published studies for muscle and liver. For spatiotemporal analysis of reporter gene expression, a dual-axis confocal (DAC) fluorescence microscope was used for intravital imaging following intradermal injections. Individual keratinocytes expressing hMGFP were readily visualized in vivo and initially appeared to preferentially express in the stratum granulosum and subsequently migrate to the stratum corneum over time. Fluorescence microscopy of frozen skin sections confirmed the patterns observed by intravital imaging. Intravital imaging with the DAC microscope is a noninvasive method for probing spatiotemporal control of gene expression and should facilitate development and testing of new nucleic acid delivery technologies.

Cell proliferation kinetics of epidermis and sebaceous glands in relation to chalone action

Median S-phase lengths of pinna epidermis and sebaceous glands, and of epithelia from the oesophagus and under surface of the tongue of Albino Swiss S mice were estimated by the percentage labelled mitoses method (PLM). The 18.4 and 18,8 hr for the median length of S-phase for pinna epidermis and sebaceous glands respectively made it possible for these two tissues to be used experimentally for testing tissue specificity in chalone assay experiments. The 10.0 and 11.5 hr for oesophagus ang tongue epithelium respectively made experimental design for chalone assay difficult when pinna epidermis was the target tissue. The results of the Labelling Index measured each hour throughout a 24-hr period showed no distinct single peaked diurnal rhythm for pinna epidermis and sebaceous glands. Instead a circadian rhythm with several small peaks occurred which would be expected if an S-phase of approximately 18 hr was imposed on the diurnal rhythm. This indicates that there may be very little change in the rate of DNA synthesis. The results are given for the assay in vivo of purified epidermal G1 and G2 chalones, and the 72--81% ethanol precipitate of pig skin from which they could be isolated. These experiments were performed over a time period which took into account the diurnal rhythm of activity of the mice as well as the S-phase lengths. Extrapolating the results with time of action of the chalone shows that the G1 chalone acts at the point of entry into DNA synthesis and that the S-phase length was approximately 17 hr for both the pinna epidermis and sebaceous glands. This may be a more correct value since the PLM method overestimates the median S-phase length as it is known that in pinna skin the [3H]TdR is available to the tissues for 2 hr and true flash labelling does not take place. The previous reports that epidermal G1 chalone acts some hours prior to entry into S-phase resulted from experiments on back skin where the S-phase is shorter and there is a pronounced diurnal rhythm which could mask the chalone effect. The epidermal G2 chalone had no effect on DNA synthesis even at different times in the circadian rhythm. Thus the circadian rhythms and S-phase lengths of the test tissues need to be considered when experiments are performed with chalones. Ideally, the target tissues selected for cell line specificity tests should have the same cell kinetics for the easier and more accurate assessment and interpretation of results. When the tissues have markedly different cell kinetics, experimental procedures and results need to be evaluated accordingly. The point of action of G1 chalone can only be assessed if the effect is measured over the peak of incorporation of [3H]TdR into DNA. The results of the effects of skin extracts are analysed in relation to changes in the availability of [3H]TdR for the incorporation into DNA and to the possibility of there being two distinct populations of proliferating cells.

Cytochemical identification of ATPase-positive langerhans cells in EDTA-separated sheets of mouse epidermis

Sheets of epidermis for incubation to demonstrate ATPase activity were obtained from specimens of mouse footpad using EDTA as the separation medium. The use of EDTA in place of the NaBr method previously described, resulted in a greatly reduced incubation time, precise localization of reaction product and preservation of ultrastructural detail. A population of closely and regularly spaced ATPase-positive dendritic cells was demonstrated by light microscopy. Electron microscopy demonstrated that, with short incubation times, reaction product was found only in the extracellular space adjacent to dendritic cells, the majority of which possessed the typical ultrastructural features of Langerhans cells.