Analysis of the role of c-Fos and Nfat in osteoclastogenesis by expression profiling of osteoclastogenic splenocytes lacking c-Fos but with an active Nfatc4. Active Nfatc4 introduced into cells by retroviral gene transfer. Osteoclastogenesis restored by active Nfatc4 in splenocytes lacking c-Fos.