Crem activator isoforms in normal and impaired human spermatogenesis analyzed by real time RT-PCR

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

Spermatogenesis is a very complex process with an intricate transcriptional regulation. The transition from the diploid to the haploid state requires the involvement of specialized genes in meiosis, among other specific functions for the formation of the spermatozoon. The transcription factor cAMP-response element modulator (CREM) is a key modulator that triggers the differentiation of the germ cell into the spermatozoon through the modification of gene expression. CREM has multiple repressor and activator isoforms whose expression is tissue-cell-type specific and tightly regulated by various factors at the transcriptional, post-transcriptional and post-translational level. The activator isoform CREMτ controls the expression of several relevant genes in post-meiotic stages of spermatogenesis. In addition, exposure to xenobiotics negatively affects CREMτ expression, which is linked to male infertility. On the other hand, antioxidants could have a positive effect on CREMτ expression and improve sperm parameters in idiopathically infertile men. Therefore, CREM expression could be used as a biomarker to detect and even counteract male infertility. This review examines the importance of CREM as a transcription factor for sperm production and its relevance in male fertility, infertility and the response to environmental xenobiotics that may affect CREMτ expression and the downstream regulation that alters male fertility. Also, some health disorders in which CREM expression is altered are discussed.

A comprehensive review of genetics and genetic testing in azoospermia

Azoospermia due to obstructive and non-obstructive mechanisms is a common manifestation of male infertility accounting for 10-15% of such cases. Known genetic factors are responsible for approximately 1/3 of cases of azoospermia. Nonetheless, at least 40% of cases are currently categorized as idiopathic and may be linked to unknown genetic abnormalities. It is recommended that various genetic screening tests are performed in azoospermic men, given that their results may play vital role in not only identifying the etiology but also in preventing the iatrogenic transmission of genetic defects to offspring via advanced assisted conception techniques. In the present review, we examine the current genetic information associated with azoospermia based on results from search engines, such as PUBMED, OVID, SCIENCE DIRECT and SCOPUS. We also present a critical appraisal of use of genetic testing in this subset of infertile patients.

Differential expression of cyclic-AMP responsive element modulator (CREM) mRNA isoforms during testicular development of boars

The cyclic-AMP responsive element modulator (CREM) transcription factor, a key regulator of spermatogenesis, can activate or repress gene expression by differential expression of alternatively spliced mRNA isoforms. The objective of this study was to report the sequences of the predominant CREM mRNA isoforms with leader exons B, θ1, θ2, in addition to the relative expression of these transcripts, in immature and adult boar testes. Activator CREM isoforms τγ (containing the B exon), θ1τγ and θ2τγ, were expressed in the adult boar testes, but not in immature testes. The CREM θ2τγ isoform had the highest expression levels in the adult boar testes compared to the τγ and θ1τγ isoforms (θ2τγ = 4.94 ± 1.49 in contrast to τγ = 1.66 ± 0.79 and θ1τγ = 2.32 ± 0.72; mean ± SD; P < 0.01). Interestingly, the predominant CREM mRNA isoforms in adult boar testes contained the C and γ exons; these exons are not present in human and rodent CREM mRNA, demonstrating species-specific expression. In contrast to the adult CREM isoforms, only CREM mRNA isoforms with the B exon (τ1 and α) were amplified in the 21 d (immature) boar testes. Further understanding of CREM mRNA isoform expression and regulation during boar spermatogenesis could contribute to our knowledge of spermatogenic efficiency in this species.