MORPHOLOGICAL-CHANGES DURING SURVIVAL, CELLULAR-TRANSFORMATION, AND CALCIFICATION OF THE EMBRYONIC MOUSE - MECKELS CARTILAGE TRANSPLANTED INTO HETEROTOPIC SITES

Meckel's cartilages obtained from 18-day-old embryonic mice were trans planted into heterotopic sites to examine their site-specific effects on cellular modification, calcification, and long-term survival. The e xplants 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 wra pped in a Nucleopore filter and transplanted into the spleen. Grafted Meckel's cartilages were observed by light and electron microscopy, in cluding application of von Kossa's reaction and osmium-potassium ferro cyanide fixation. It was demonstrated by von Kossa's reaction that whe n Meckel's cartilage was grafted in liver parenchyma, initial calcific ation appeared on the territorial matrix as spotted deposits. The chon drocytes gradually transformed into small ovoidal cells and showed a m orphology closely resembling that of osteocytes. Transplants in the ki dney subcapsular site contained active surviving chondrocytes, and sub cutaneously grafted Meckel's cartilage revealed three types of chondro cytes: nonhypertrophic and calcification-inducing hypertrophic chondro cytes, as well as cells showing osteocytelike phenotypes. Intraocular and Nucleopore filter-wrapped explants showed degenerative changes, an d peritoneal-cavity transplants showed cellular hypertrophy, but calci fied precipites were not observed. The present investigation demonstra ted that in blood-rich tissues Meckel's cartilage showed long-term sur vival and could modulate calcified precipitation. Thus, this adaptatio n of Meckel's cartilage to the environment of various heterotopic site s suggests that it has the ability to induce calcification.