Differential expression and regulation of the retinoblastoma family of proteins during testicular development and spermatogenesis: roles in the control of germ cell proliferation, differentiation and apoptosis

Normal spermatogenesis is highly dependent on well-balanced germ cell proli feration, differentiation, and apoptosis, However, the molecular mechanisms that govern these processes are largely unknown. Retinoblastoma family pro teins (pRb, p107 and p130) are potentially important regulators of cell gro wth, differentiation and apoptosis, pRb has been shown to be expressed in t he rat testis and involved in the regulation of spermatogenesis, In the pre sent study, the expression and localization of the other two pRb family mem bers, p107 and p130, were analysed at both mRNA and protein levels during t esticular development and spermatogenesis using Northern, Western blotting, immunohistochemistry, and in situ hybridization, Furthermore, changes of l evels and phosphorylation status of pRb family proteins in response to grow th suppression and/or apoptosis induction were investigated using a seminif erous tubule culture system and three animal models, Our data suggest that: (1) pRb family proteins are differentially expressed in the rat testis and they function in a cell-type-specific manner during testicular development and spermatogenesis; (2) they participate in the control of germ cell cycl e and act in a cell cycle-phase-specific fashion during germ cell prolifera tion, and (3) they are also involved in the regulation of apoptosis of germ cells and Leydig cells.