RXRA and RXRB are both instrumental to spermatogonia differentiation.

<p>Mean percentages of tubule sections showing normal cellular associations (white bars), abnormal associations resembling the VAD situation with either one or two generations of germ cells lacking (grey bars), and degenerated epithelium containing only spermatogonia and Sertoli cells (black bars) in testes of 12 month-old mice (n = 5) with the indicated genotype. Mice lacking <i>Rxrg</i> and either <i>Rxra</i> (<i>Rxra;g</i>^{<i>Sgp–/–</i>} mutants) or <i>Rxrb</i> (<i>Rxrb;g</i>^{<i>Sgp–/–</i>} mutants) are marginally affected. In contrast, mice simultaneously lacking <i>Rxra</i> and <i>Rxrb</i> (<i>Rxra;b</i>^{<i>Sgp–/–</i>} mutant) displayed a high proportion of affected tubule sections. Additional ablation of <i>Rxrg</i> does not worsen the pathological phenotype (<i>Rxra;b</i>^{<i>Sgp–/–</i>} mutant). This indicates that RXRG is dispensable, whereas RXRA and RXRB are both required and exert redundant functions in spermatogonia.