 The investigators have data showing that RANKL, RANK and OPG are expressed at both RNA and protein level in the human testis. The Sertoli cells express RANKL, while the germ cells express RANK and the peritubular cells express OPG. Normally, RANKL activates NFKB and activation of this pathway in the male gonad appears to regulate whether the testicular cells proliferate or undergo apoptosis in the testis. The investigators in vitro, ex vivo and in vivo data from functional models support this suggestion and this pathway appears therefore to be a novel regulator of germ cell proliferation. 