Spz1, a novel bHLH-Zip protein, is specifically expressed in testis

We isolated a novel bHLH-Zip gene designated Spz1 from a mouse testis cDNA library. Spz1 is expressed specifically in the testis and epididymis. Immun ofluorescence staining detected Spz1 protein in the nuclei of LFG6 Leydig c ells. The ability of Spz1 protein to bind to the bHLH consensus-binding sit e, the E-box, was confirmed by EMSA, and a 9-bp asymmetric target site was identified by random selection and PCR amplification. Hormonal regulation o f Spz1 was investigated and downregulation of Spz1 expression by testostero ne and retinoic acid was found. This nuclear transcription factor may play a crucial role in spermatogenesis by regulating cell proliferation or diffe rentiation through binding to specific DNA sequences like other bHLH-Zip mo lecules. (C) 2001 Elsevier Science Ireland Ltd. Ail rights reserved.