Transcription factor that binds to the DNA sequence 5'-CANNTG-3'(E box) and the G-box motif. May play an important role in the regulation of cell proliferation and differentiation during spermatogenesis (By similarity). Phosphorylated by MAPK1/ERK2 and MAPK3/ERK1. The helix-loop-helix and basic motifs form a SPZ1 specific bHLH different from the classical one.