Immunohistochemistry of phosphotyrosine residues: identification of distinct intracellular patterns in epithelial and steroidogenic tissues.

Tyrosine kinases are thought to play a major role in the control of cell growth and differentiation. Most of the work on the phosphorylated product was performed, however, on isolated proteins or cultured cell lines. To assess the overall involvement of tyrosine phosphorylation in vivo, a monoclonal antibody (MAb) against phosphotyrosine was applied to conventional histological sections of various tissues. With the immunoperoxidase staining method, two unique patterns of intracellular distribution of phosphotyrosine were identified among a large variety of normal tissues. (a) In many of the epithelia examined, a peripheral staining was observed, either at the apical aspect alone or at the entire contact region between neighboring cells. This pattern of staining seems to coincide with the distribution of a subset of cytoskeletal elements and requires pre-treatment with proteinase K. (b) In most steroidogenic tissues examined, vesicular cytoplasmic staining was evident, which seems to represent steroid-containing granules. In this case, proteolytic pretreatment is not essential and can be harmful. An extensive survey of human ovarian carcinoma biopsies failed to reveal any consistent staining pattern. These findings might indicate the involvement of tyrosine phosphorylation in basic cellular activities such as the assembly of the specialized cytoskeletal components.

Identification of programmed cell death in situ via specific labeling of nuclear DNA fragmentation.

Programmed cell death (PCD) plays a key role in developmental biology and in maintenance of the steady state in continuously renewing tissues. Currently, its existence is inferred mainly from gel electrophoresis of a pooled DNA extract as PCD was shown to be associated with DNA fragmentation. Based on this observation, we describe here the development of a method for the in situ visualization of PCD at the single-cell level, while preserving tissue architecture. Conventional histological sections, pretreated with protease, were nick end labeled with biotinylated poly dU, introduced by terminal deoxy-transferase, and then stained using avidin-conjugated peroxidase. The reaction is specific, only nuclei located at positions where PCD is expected are stained. The initial screening includes: small and large intestine, epidermis, lymphoid tissues, ovary, and other organs. A detailed analysis revealed that the process is initiated at the nuclear periphery, it is relatively short (1-3 h from initiation to cell elimination) and that PCD appears in tissues in clusters. The extent of tissue-PCD revealed by this method is considerably greater than apoptosis detected by nuclear morphology, and thus opens the way for a variety of studies.