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: CREMh1, CREMh2 and CREMt2 þ Ex-c 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 c (CREMs2 þ Exc) in normal human spermatogenesis. Among the three CREM isoforms, CREMh1 was expressed in its highest level in the male gonads. In comparison, CREMh2 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 CREMh1 isoform in the regulation of transcription during post-meiotic germ cell differentiation.

Novel Aspects of cAMP-Response Element Modulator (CREM) Role in Spermatogenesis and Male Fertility

“…Furthermore, the presence of alternative promoters P3 and P4 allows for the expression of different Cremθ1 and 2 isoforms, along with alternative splicing and translation initiation, which contribute to the generation of various isoforms of the gene, including Cremα , β , γ and Crem-S [ 7 , 21 , 22 , 23 ]. In low-bred sheep, alterations in Crem alternative RNA splicing were observed, resulting in phenotypic changes associated with infertility.…”

A comprehensive review of genetics and genetic testing in azoospermia

“…Fourth, the cell cycle in mitosis or meiosis should pass through four important phases: G1, S, G2 and M. A defect in any of these phases can result in cell cycle arrest or apoptosis (244-249). Fifth, impaired signal transduction may undermine the response of testicular cells to activating factors, such as hormones and growth factors (248-257). Finally, selective defects in the genes encoding transcription factors in germ and/or supporting cells, such as DAX-1 and nuclear export factor (NF2), have been implicated in NOA (283,284).…”