The ultrastructural study of rare cells within their niche
in situis very difficult. We have developed a method for locating individual transplanted cells and simultaneously identifying and analyzing the molecules and cellular phenotypes surrounding them in situusing transmission electron microscopy. This innovative method involves triple immunogold labeling combined with serial ultrathin sectioning. We demonstrate the validity of this approach by examining the niche of individual transplanted cells from a population highly enriched for hemopoietic stem cells and the ultrastructural expression of two key stem cell regulatory molecules, hyaluronic acid and osteopontin. In addition, we describe the phenotypes of the surrounding cells.