Immunohistochemical staining of bromodeoxyuridine-labelled cells in the mouse embryo

Light and electron microscopic immunohistochemical detection of bromodeoxyuridine-labeled cells in the brain: different fixation and processing protocols

Bromodeoxyuridine (BrdU) immunohistochemistry is the method of choice for labeling newly generated cells in the brain. Most BrdU studies utilize paraformaldehyde-fixed brain tissue because of its compatibility with both BrdU and other immunohistochemical methods. However, stronger fixation is required for electron microscopic studies, and unfixed tissue is needed for biochemical and molecular studies. Because there are no systematic studies comparing the effects of different fixatives on BrdU immunohistochemistry in brain tissue, we compared BrdU immunohistochemical methods in brain tissue fixed with 4% paraformaldehyde, a mixed glutaraldehyde-paraformaldehyde fixative for electron microscopy, and unfixed tissue from brains perfused only with buffer and flash frozen. After optimizing immunostaining protocols, qualitative assessments of light microscopic diaminobenzidine labeling and of double-label immunofluorescence with confocal microscopy demonstrated excellent BrdU labeling in each of the three groups. Quantitative stereological assessment of the number of BrdU-labeled cells in rat dentate gyrus showed no significant difference in the number of labeled cells detected with each perfusion protocol. Additionally, we developed a protocol to visualize BrdU-labeled cells in the electron microscope with adequate preservation of fine structure in both rat and monkey brain.

Expression of the proliferation-related Ki-67 mRNA in the early development of murine embryo

In a search for early lymphoid-specific genes, we isolated a cDNA clone (LL7) encoding a murine homologue of Ki-67 protein, a proliferation-related nuclear antigen. LL7 transcript appears preferentially in lymphoid organs as the bone marrow, spleen, and the thymus. Here, we studied the expression of murine Ki-67 (mKi-67) mRNA among various organs or tissues during the early development of fetus. In fetus, mKi-67 mRNA appears developmentally as early as day 11 and is expressed maximally at day 15. In situ hybridization on the section revealed that the expression of mKi-67 mRNA is preferential in the area of active organ formation such as neurological system and the fetal liver. These results suggest that mKi-67 plays an important role in the proliferation of early embryonic precursor cells of neurological and immune systems.

Hypertrophic chondrocytes undergo further differentiation to osteoblast-like cells and participate in the initial bone formation in developing chick embryo

Differentiation of hypertrophic chondrocytes to an osteoblast-like phenotype occurs in vivo in the hypertrophic cartilage of chick embryo tibiae underneath early or prospective periosteum and in cartilage around vascular canals. Synthesis of type I collagen by hypertrophic chondrocytes was shown by immunolocalization of the C propeptide. By enzyme cytochemistry it was instead shown that, in vivo, further differentiating hypertrophic chondrocytes express alkaline phosphatase at the time of initial mineral deposition. Evidence that hypertrophic chondrocytes may resume proliferation was obtained by BrdU labeling. A monoclonal antibody (LA5) was isolated and characterized that recognizes a hypertrophic chondrocyte membrane protein. In addition to staining hypertrophic chondrocytes surrounded by a type II and type X collagen-stainable matrix, the LA5 antibodies also stained elongated chondrocytes at the cartilage/bone collar interface and cells incorporated in the first layer of bone and osteoid matrix.

Periodic acid incubation can replace hydrochloric acid hydrolysis and trypsin digestion in immunogold--silver staining of bromodeoxyuridine incorporation in plastic sections and allows the PAS reaction

We have examined the possibility of improving the present methods of detecting bromodeoxyuridine (BrdU) and for combining the PAS reaction with the BrdU detection by means of immunogold-silver staining (IGSS). This was done in testes fixed in Carnoy or Bouin, and in parts of the small intestine which were fixed in Carnoy or periodate-lysine-paraformaldehyde (PLP). All tissues were embedded in a mixture of glycol methacrylate and butanediol-monoacrylate. It was found to be impossible to carry out BrdU detection using HCl hydrolysis and trypsin digestion in combination with a PAS reaction. However, incubation of the plastic sections in periodic acid for a period of 30 minutes appeared to make it possible to eliminate the HCl denaturation step and to carry out a specific PAS reaction. Moreover, after incubation in periodic acid, trypsin digestion was no longer required to make the BrdU label accessible in GMA-embedded sections, nor to re-expose the antigenic sites in plastic sections of tissues fixed with cross-linking fixatives. In this way the loss of cell structures, which is inevitable when trypsin is used, can be avoided. Now a BrdU detection with improved morphology can be combined with the PAS reaction in the same plastic section in order to stain tissue carbohydrates. This is important for tumour diagnosis, where the PAS reaction can be very useful.