The sequence of events in the differentiation of the epidermis in fetal rats with particular reference to membrane-coating granules

Expression of keratin 18 in the periderm cells of the lingual epithelium of fetal rats: visualization by fluorescence immunohistochemistry and differential interference contrast microscopy

We examined the expression of keratin 18 (K18), by immunofluorescence staining, while monitoring morphological changes in the periderm on the lingual epithelium of rats by laser-scanning microscopy of epoxy resin-embedded, semi-ultrathin sections. We also examined differential interference contrast (DIC) images of the same sections to define the histology and morphology of the cells. It is difficult to visualize histological details of the fetal lingual epithelium of the rat on semi-ultrathin sections by light microscopy after immunohistochemical staining, because the histological structures in such sections cannot be distinguished by standard counterstaining. To solve this problem and to visualize keratin 18 (K18), we used a combination of immunofluorescence staining of semi-ultrathin sections and corresponding differential contrast (DIC) images, obtained by laser-scanning microscopy.

Use of a recombinant retrovirus to study post-implantation cell lineage in mouse embryos

We show that a gene introduced into cells of mouse embryos by a retrovirus can serve as a heritable marker for the study of cell lineage in vivo. We constructed a defective recombinant retrovirus in which the Escherichia coli beta-galactosidase (lacZ) gene is inserted in the genome of a Muloney murine leukemia virus (M-MuLV). Expression of lacZ was detected with a histochemical stain that can be applied to cultured cells and embryonic tissue. Infection of cultured cells showed that lacZ has no detectable deleterious effects on cell viability or growth, that the enzyme is stably expressed in the progeny of infected cells for many generations in the absence of selective pressure, and that the virus can induce lacZ in a variety of cell types. Following injection of the virus into mid-gestation mouse embryos, clones of lacZ-positive cells were detected in skin, skull, meninges, brain, visceral yolk sac, and amnion. We identified the cell types comprising a series of lacZ-positive clones in the visceral yolk sac and skin to learn the lineage relationships of the labelled cells. In each tissue, we obtained evidence that several cell types have a pluripotential ancestor and that cell fate is progressively restricted as development proceeds.

Identification and characterization of glycoproteins secreted by the skin of the day 16 fetal mouse

The secretion of tissue-specific proteins during mouse skin development, was investigated by incubating day 16 fetal skin explants in the presence of [35S]methionine and analyzing the medium electrophoretically. The medium was found to contain five proteins, which could be classified into two groups according to molecular weight. The kinetics of release of these proteins indicated that they were specifically secreted and not released by cytolysis. Mapping of the proteins by partial proteolytic digestion revealed that although the digestion patterns between the two molecular weight groups were different, within each group similar patterns were seen, suggesting that they were structurally related. Incubation in the presence of tunicamycin resulted in the decrease in molecular weight of the secreted proteins, indicating that the proteins were glycosylated. The results suggest that the two groups of structurally related glycoproteins were secreted by the peridermal layer of the fetal skin.