While Nanos2 prevents differentiation, the TATA-box Binding Protein Associated Factor-4b (TAF4B) controls the expression of genes promoting differentiation and self-renewal of SSCs, and TAF4B deletion results in nonobstructive azoospermia (NOA) or oligozoospermia in mice and men (Fig. 2) [40]. This evidence concerns the gene TAF4B and Azoospermia.