Morphological changes during survival, cellular transformation, and calcification of the embryonic mouse: Meckel's...

Meckel's cartilages obtained from 18-day-old embryonic mice were transplanted into heterotopic sites to examine their site-specific effects on cellular modification, calcification, and long-term survival. The explants were isografted into the liver, subcutaneous tissue, anterior chamber of the eye, kidney, peritoneal cavity, and intrafemoral muscle of mouse for up to 2 weeks. In addition, Meckel's cartilages were wrapped in a Nucleopore filter and transplanted into the spleen. Grafted Meckel's cartilages were observed by light and electron microscopy, including application of von Kossa's reaction and osmium-potassium ferrocyanide fixation. It was demonstrated by von Kossa's reaction that when Meckel's cartilage was grafted in liver parenchyma, initial calcification appeared on the territorial matrix as spotted deposits. The chondrocytes gradually transformed into small ovoidal cells and showed a morphology closely resembling that of osteocytes. Transplants in the kidney subcapsular site contained active surviving chondrocytes, and subcutaneously grafted Meckel's cartilage revealed three types of chondrocytes: nonhypertrophic and calcification-inducing hypertrophic chondrocytes, as well as cells showing osteocytelike phenotypes. Intraocular and Nucleopore filter-wrapped explants showed degenerative changes, and peritoneal-cavity transplants showed cellular hypertrophy, but calcified precipites were not observed. The present investigation demonstrated that in blood-rich tissues Meckel's cartilage showed long-term survival and could modulate calcified precipitation. Thus, this adaptation of Meckel's cartilage to the environment of various heterotopic sites suggests that it has the ability to induce calcification.