Sbds ablation results in the down-regulation of multiple genes important in OCG. (A) Quantitative real-time PCR was used to quantify gene expression on days 2, 4, and 6 of osteoclast cultures. Results are expressed as fold versus glyceraldehyde-3-phosphate dehydrogenase expression used as internal control. Sbds-null cells expressed significantly lower transcript levels of DC-STAMP and Rac2 on day 2 compared with WT cells, whereas expression of c-Fms, TRAF6, and Rac1 was unchanged. RANK expression was mildly increased in Sbds-null cells on day 2. All 6 genes were down-regulated by day 6 in Sbds-null cells; however, Rac1 was least affected at approximately 80% of WT levels (n = 3): *P < .01. (B) To examine whether Rac1 and Rac2 gene expression is RANKL-dependent, cells were cultured for 6 days in M-CSF alone or in combination with RANKL, and quantitative RT-PCR was performed. Results are expressed as fold activation in the presence of RANKL versus M-CSF alone, and compared with DC-STAMP expression, which is known to be RANKL-dependent. As expected, DC-STAMP was highly up-regulated by RANKL in WT cells, but this up-regulation was much less pronounced in Sbds-null cells. Rac1 gene expression was RANKL-independent; however, Rac2 was up-regulated 3.2-fold in WT cells but not in Sbds-null cells. Thus, Sbds-null cells exhibit defective RANK-mediated up-regulation of Rac2 and DC-STAMP (n = 3): *P < .05.