The ultrastructure of osteoclasts in microphthalmic mice.

Osteoclasts in microphthalmic (mi/mi) mice were significantly smaller than in their heterozygous (mi/+) or normal (+/+) littermates as measured by electronmicroscopic morphometry. Clear zones were also significantly smaller and normal ruffled borders were absent. The cytoplasm was not fully differentiated. No differences were seen between osteoclasts from mi/+ and +/+ mice. The number of osteoclasts was not different in mi/mi, mi/+ or +/+ mice. Lysosomal enzymes and collagenase content of bones in the three genotypes did not show marked differences.