TRIM21 and osteoporosis: Estrogen deficiency-induced osteoporosis exhibits a typical phenotype characterized by low bone mass and excessive accumulation of adipose tissue in the bone marrow milieu;3,9 consistently, Trim21+/+ OVX-induced mice displayed thinned osteoporotic trabeculae with lost continuity, enlarged areolae, and increased fat cell density, whereas Trim21-deficient mice showed partial reversal of the OVX-induced phenotype (Fig. 6a and Fig. S9b).