Histopathology of Bone.

<p>S1PL^+/+ Bone (A, B, and C): In Wt mice, the majority of the marrow cavity is filled with hematopoietic elements. Widely spaced trabeculae in long bones (A) and sternum (B) extend a relatively short distance from the physeal growth plate. At higher magnification (C), normal osteoclasts appear as multinucleated cells that are usually tightly adherent and flattened against bone surfaces. S1PL^−/− Bone (D, E, and F): In marked contrast, there is a diffuse increase in the volume and extent of trabecular bone in the long bones (D) and sternum (E) S1PL^−/− mice. The bony trabeculae extend throughout the marrow farther than normal into the diaphysis of long bones (D) and sternum (E). At higher magnification (F), the more numerous osteoclasts of S1PL^−/− mice are distended by abundant pale and granular eosinophilic cytoplasm that displaces cell nuclei to the periphery. These large rounded S1PL^−/− osteoblasts (arrows) have reduced direct contact with bone surfaces. H&E stain.