Crem Activator Isoforms in Normal and Impaired Human Spermatogenesis Analyzed by Real Time RT-PCR

Abstract

cAMP responsive element modulator (CREM) activator isoforms are involved in mammalian spermatogenesis and spermiogenesis. CREM proteins are highly expressed in postmeiotic germ cells of rodents and primates. Homozygous CREM inactivated mice exhibit round spermatid maturation arrest. The lack of CREM expression at both the mRNA and protein levels is associated with spermatid maturation arrest in infertile patients. Using real-time RT-PCR, we have examined the levels of CREM activator isoform mRNAs: CREMθ1, CREMθ2 and CREMt2 + Ex-γ in gametogenic and interstitial cell fractions from normal human testis, in homogenized tissue samples from spermatogenic arrest and from testicular tumors. We have shown for the first time the presence of CREM activator isoform containing exon γ (CREMτ2 + Exγ) in normal human spermatogenesis. Among the three CREM isoforms, CREMθ1 was expressed in its highest level in the male gonads. In comparison, CREMθ2 mRNA was significantly less suggesting that the P3 promoter is much more active in human testis than the P4 promoter. Minimal-nill levels of mRNA for either of the CREM activator isoforms were detected in lymphocytes or in gonadal tissues from patients with SCOS (Sertoli Cell Only Syndrome). This data underlines the significance of CREMθ1 isoform in the regulation of transcription during post-meiotic germ cell differentiation.

KEYWORDS:

• azoospermia
• CREM activators
• spermatogenesis
• testicular tumors

Notes

Abbreviations: CREM – cAMP responsive element modulator; ICER – inducible early repressor; bZIP – basic domain/leucin zipper motif; KID – kinase inducible domain; DBD1, DBD2 – DNA binding domains; GAPDH – glyceraldehyde-3-phosphate dehydrogenase; SCOS – Sertoli cell only syndrome; MA – maturation arrest; MAspc. – maturation arrest on spermatocyte stage; MAspd. – maturation arrest on spermatid stage; OA – obstructive azoospermia; PKA – protein kinase A.