Activator Of cAMP-responsive Element Modulator Research Articles

Dynamic Expression and Chromatin Incorporation of ACT and CREM Transcription Factors in Testis Tissues of Infertile Men.

ObjectiveActivator of CREM in the testis (ACT) is a tissue specific transcription factor which activates cAMP responsive element modulator (CREM), a key transcription factor in differentiation of round spermatids into mature spermatozoa. They bind to CRE region in the promoters of transition protein genes (TNP1, TNP2) and protamine genes (PRM1 and PRM2), which are essential for sperm chromatin compaction, and regulates their transcription. This study was conducted to consider the expression of ACT and CREM and their regulatory roles on the expression of PRM1, PRM2, TNP1 and TNP2 genes in testis tissues of infertile men.Materials and MethodsIn this case-control study, testicular biopsies were collected from 40 infertile men and classified into three groups: obstructive azoospermia (OA, n=10, positive control), round spermatid maturation arrest (SMA, n=20), Sertoli cell-only syndrome (SCOS, n=10, negative control group). Using quantitative real-time polymerase chain reaction (PCR), the expression profile of ACT, CREM, TNP1, TNP2, PRM1 and PRM2 genes were assessed in testicular samples and incorporation of ACT and CREM proteins on the promoters of PRM1, PRM2, TNP1 and TNP2 genes were also evaluated by ChIP-real time PCR. ResultsOur results demonstrated significant decrease in the expression levels of ACT, CREM and in their incorporations on their target genes in SMA group in comparison to control groups (P<0.05).ConclusionThese data confirm that there is low expression and incorporation of ACT and CREM and of their target genes in infertilities which are associated with post-meiotic arrest.

Abnormal spermatogenesis following sodium fluoride exposure is associated with the downregulation of CREM and ACT in the mouse testis.

cAMP response element modulator (CREM) is involved in regulating gene expression in normal spermatogenesis. The transcriptional activity of CREM is partly regulated by activator of CREM in the testis (ACT). To investigate the effects of different concentrations of sodium fluoride (NaF) on the gene and protein expression of CREM and ACT in the mouse testis, sexually mature male Kunming mice were exposed to 50, 100, or 150 mg/L NaF in their drinking water for 90 days. NaF reduced the sperm count and viability and increased the percentage of malformed sperm in a dose-dependent manner. The mRNA expression of CREM and ACT was markedly downregulated in the NaF-treated groups. Furthermore, immunohistochemistry revealed that CREM and ACT proteins were decreased significantly in the 50, 100, and 150 mg/L NaF-treated groups compared to the control group. These findings indicate that the decreased gene and protein expression of CREM and ACT in the testis is associated with an impairment of reproductive functions by NaF.

1,2-Dichloroethane Induces Reproductive Toxicity Mediated by the CREM/CREB Signaling Pathway in Male NIH Swiss Mice.

1,2-Dichloroethane (1,2-DCE) is a widely used chlorinated organic toxicant but little is known about the reproductive disorders induced by its excessive exposure. To reveal 1,2-DCE-induced male reproductive toxicity and to elucidate the underlying mechanisms, we exposed male National Institutes of Health Swiss mice to 1,2-DCE by inhalation at 0, 100, 350, and 700 mg/m3 for 6 h/day, for 1 and 4 weeks. Our findings showed a significant decrease in body weight with increased testis/body weight ratio, reduced sperm concentration and induced malformation of spermatozoa, and vacuolar degeneration of germ cells in the seminiferous tubules of testes in mice exposed to 1,2-DCE. Cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) and cAMP-response element modulator (CREM) were significantly inhibited by 1,2-DCE. This is consistent with the declines in the transducer of regulated CREB activity 1 and activator of CREM in testis, which results in the decrease in lactate dehydrogenase C and testis-specific kinase 1 in the testes. Moreover, the activation of p53 and Bax with the inhibition of Bcl-2 might be the reason for the upregulation of caspase-3 in the apoptosis, as detected by TdT-mediated dUTP nick-end labeling assay in the testes induced by 1,2-DCE. Finally, elevated testosterone levels were found along with increased levels of gonadotropin-releasing hormone, cAMP, luteinizing hormone (LH), and LH receptors in the testes. These findings suggest that 1,2-DCE inhibits CREM/CREB signaling cascade and subsequently induces apoptosis associated with p53 activation and mitochondrial dysfunction. This also results in induced malformation of spermatozoa, reduced sperm concentration, and pathological impairment of the testes.

Sulfur dioxide inhalation lowers sperm quality and alters testicular histology via increasing expression of CREM and ACT proteins in rat testes.

Sulfur dioxide (SO2) is one of the main atmospheric pollutants worldwide, and is reported to be responsible for the formation of severe haze in China. Some studies have demonstrated a potential harmful effect of SO2 on the male reproductive system; however the underlying mechanism is still unknown. The purpose of this study is to investigate the roles of cytochrome P450 (P450), cAMP-responsive element modulator (CREM), and activator of CREM (ACT) in SO2-induced toxicity. Forty-eight male Wistar rats were randomly divided into an experimental and control group. The experiment group was exposed to SO2 in ambient air (10ppm, 4h/day), and the control group was treated with filtered air in the same conditions. After 2 weeks, the results showed a significant decrease in body weight and sperm motility, and an increase in the testis weight-to-body weight ratio as compared to the control group. Histological investigation suggested that SO2 exposure led to loose arrangement of the spermatogenic cells and local structural damage in the seminiferous tubules. Moreover, the expressions of P450, CREM and ACT proteins increased in the testes by 0.22%, 47.26% and 23.38%, respectively. Taken together, SO2 inhalation lowered sperm quality, altered testicular histology, and increased expressions of CREM and ACT proteins in the testes of rats. Overall, these results could contribute to a better understanding of SO2-induced male reproductive toxicity.

Effects of Fluoride on Expression of P450, CREM and ACT Proteins in Rat Testes.

Fluoride (F) is an essential trace element that humans and animals ingest from water, air, and fluoride-containing products; however, excessive fluoride absorption can damage a variety of organs and tissues, including the male reproductive system. Our previous studies found that fluoride exposure lowered sperm quality and interfered with spermatogenesis; however, the exact mechanism remained unclear. Proteins cytochrome P450 (P450), cAMP-responsive element modulator (CREM), and activator of CREM in testis (ACT) play the key roles in spermatogenesis and sperm motility. To investigate whether fluoride affects the expression of P450, CREM, and ACT, we used immunohistochemical techniques to determine expression levels of these proteins in testes of rats administered 100mg NaF/L for 2weeks via drinking water. The results showed that P450 expression was decreased while CREM and ACT expression was increased in the fluoride group, compared to the control. These data suggest that fluoride can impair male reproduction by affecting expression of P450, CREM, and ACT in the testes.

Astragalus membranaceus augment sperm parameters in male mice associated with cAMP-responsive element modulator and activator of CREM in testis

Astragalus membranaceus BUNGE (AM; 黃芪 huáng qí) has been widely used as a medicinal herb for different kinds of diseases. AM treatment in vitro enhance sperm motility and ameliorates testicular toxicity, it has demonstrated the ability as a potential treatment for male infertility. In order to gain further insights on the molecular understanding of how AM enhances spermatogenesis, this study investigated whether AM has an affect on sperm parameters associated with cAMP response element modulator (CREM) and activator of CREM in testis (ACT) expression. Five-week-old male ICR mice were divided into four groups; control group and three different concentrations of AM treated groups. Each group was treated for 5 days a week for 5 weeks. Testis samples were collected for real time quantitative PCR and western blot analysis. Epididymis was taken out and used for sperm analysis using the computer assisted semen analysis (CASA) system. To facilitate expression of genes required for spermatogenesis, it is controlled by fine-tuning of CREM and its coactivator, ACT. AM treatment promotes CREM and ACT mRNA expression and also protein expression compared to control. AM enhances sperm values such as sperm count and motility compared to control. Overall, the study highlights, the ability of AM to increases CREM and ACT expression to facilitate sperm development and semen quality.

EXPRESSION PROFILING OF CREM GENE IN TESTIS WITH NORMAL AND IMPAIRED SPERMATOGENESIS IN EGYPTIAN MALES

cAMP responsive element modulator (CREM) is one of the most important transcription factors expressed in male testes which connect the extra cellular signals to gene regulation. CREM expression switches from a repressor to an activator in testes during spermatogenesis. Any alteration in this switch leads to different testicular patterns. Methods: Total RNA was extracted from Eighty eight testicular biopsy and analyzed for CREM expression profiling. Normal spermatogenesis showed expression of CREM2and gamma repressor, the same finding was detected in Hypospermatogenesis group but with another longer repressor belong to alpha repressor type, 95% of Round spermatid maturation arrest group showed two repressor patterns, and 5% showed two activator transcripts of CREM2 activator. Sertoli cells only group didn’t show any activator transcripts of CREM. In conclusion studying the mechanisms of interaction between CREM repressors and activators in the normal and impaired spermatogenesis may lead to better understanding of genetic control of the spermatogenesis and consequently to better treatment options.

Evolution of Cyclin B3 Shows an Abrupt Three-Fold Size Increase, due to the Extension of a Single Exon in Placental Mammals, Allowing for New Protein–Protein Interactions

Cyclin B3 evolution has the unique peculiarity of an abrupt 3-fold increase of the protein size in the mammalian lineage due to the extension of a single exon. We have analyzed the evolution of the gene to define the modalities of this event and the possible consequences on the function of the protein. Database searches can trace the appearance of the gene to the origin of metazoans. Most introns were already present in early metazoans, and the intron-exon structure as well as the protein size were fairly conserved in invertebrates and nonmammalian vertebrates. Although intron gains are considered as rare events, we identified two cases, one at the prochordate-chordate transition and one in murids, resulting from different mechanisms. At the emergence of mammals, the gene was relocated from chromosome 6 of platypus to the X chromosome in marsupials, but the exon extension occurred only in placental mammals. A repetitive structure of 18 amino acids, of uncertain origin, is detectable in the 3,000-nt mammalian exon-encoded sequence, suggesting an extension by multiple internal duplications, some of which are still detectable in the primate lineage. Structure prediction programs suggest that the repetitive structure has no associated three-dimensional structure but rather a tendency for disorder. Splice variant isoforms were detected in several mammalian species but without conserved pattern, notably excluding the constant coexistence of premammalian-like transcripts, without the extension. The yeast two-hybrid method revealed that, in human, the extension allowed new interactions with ten unrelated proteins, most of them with specific three-dimensional structures involved in protein-protein interactions, and some highly expressed in testis, as is cyclin B3. The interactions with activator of cAMP-responsive element modulator in testis (ACT), germ cell-less homolog 1, and chromosome 1 open reading frame 14 remain to be verified in vivo since they may not be expressed at the same stages of spermatogenesis as cyclin B3.

The kinesin superfamily protein KIF17: one protein with many functions

Kinesins are ATP-dependent molecular motors that carry cargos along microtubules, generally in an anterograde direction. They are classified into 14 distinct families with varying structural and functional characteristics. KIF17 is a member of the kinesin-2 family that is plus end-directed. It is a homodimer with a pair of head motor domains that bind microtubules, a coiled-coil stalk, and a tail domain that binds cargos. In neurons, KIF17 transports N-methyl-D-aspartate receptor NR2B subunit, kainate receptor GluR5, and potassium Kv4.2 channels from cell bodies exclusively to dendrites. These cargos are necessary for synaptic transmission, learning, memory, and other functions. KIF17's interaction with NXF2 enables the transport of mRNA bidirectionally in dendrites. KIF17 or its homolog OSM-3 also mediates intraflagellar transport of cargos to the distal tips of flagella or cilia, thereby aiding in ciliogenesis. In many invertebrate and vertebrate sensory cells, KIF17 delivers cargos that contribute to chemosensory perception and signal transduction. In vertebrate photoreceptors, KIF17 is necessary for outer segment development and disc morphogenesis. In the testis, KIF17 (KIF17b) mediates microtubule-independent delivery of ACT from the nucleus to the cytoplasm and microtubule-dependent transport of Spatial-ε, both are presumably involved in spermatogenesis. KIF17 is also implicated in epithelial polarity and morphogenesis, placental transport and development, and the development of specific brain regions. The transcriptional regulation of KIF17 has recently been found to be mediated by nuclear respiratory factor 1 (NRF-1), which also regulates NR2B as well as energy metabolism in neurons. Dysfunctions of KIF17 are linked to a number of pathologies.

Sperm associated antigen 8 (SPAG8), a novel regulator of activator of CREM in testis during spermatogenesis

cAMP response element modulator (CREM)-mediated gene expression is an essential regulatory mechanism for germ cell differentiation. CREM and its coactivator in testis, ACT, activate the transcription of many essential genes for spermatogenesis. Sperm associated antigen 8 (SPAG8) is a testis-specific component that is expressed during germ cell differentiation. In this study, we found the pattern of SPAG8 expression largely overlapped with that of ACT during spermatogenesis and verified the association of SPAG8 with ACT. Furthermore, we showed that SPAG8 enhanced the transcriptional activation of ACT-mediated CREMτ by strengthening the binding of ACT to CREMτ. These results indicate that SPAG8 acts as a regulator of ACT and plays an important role in CREM-ACT-mediated gene transcription during spermatogenesis. Structured summaryMINT-7892874: CREM tau (uniprotkb:P27699-1) physically interacts (MI:0915) with ACT (uniprotkb:Q9WTX7) by anti tag coimmunoprecipitation (MI:0007)MINT-7892809: ACT (uniprotkb:Q9WTX7) physically interacts (MI:0915) with SPAG8 (uniprotkb:B9EKF1) by pull down (MI:0096)MINT-7892820, MINT-7892840, MINT-7892987, MINT-7892854: ACT (uniprotkb:Q9WTX7) physically interacts (MI:0915) with SPAG8 (uniprotkb:B9EKF1) by anti tag coimmunoprecipitation (MI:0007)

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

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: CREMtheta1, CREMtheta2 and CREMt2 + Ex-gamma 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 gamma (CREMtau2 + Exgamma) in normal human spermatogenesis. Among the three CREM isoforms, CREMtheta1 was expressed in its highest level in the male gonads. In comparison, CREMtheta2 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 CREMtheta1 isoform in the regulation of transcription during post-meiotic germ cell differentiation.

Sequencing and haplotype analysis of the Activator of CREM in the Testis (ACT) gene in populations of fertile and infertile males

cAMP-responsive element modulator (CREM) is a key transcription factor in the differentiation of round spermatids into mature spermatozoa. During spermiogenesis, CREM is regulated in part by activator of CREM in the testis (ACT), which activates CREM in a phosphorylation-independent fashion. We hypothesized that the ACT gene, which is expressed exclusively in the testis, could be involved in male factor infertility in patients with idiopathic-impaired spermatogenesis. To test this hypothesis, we sequenced the coding regions and flanking intronic regions of the ACT gene in 96 azoo- or oligospermic patients and 69 fertile controls. A total of 12 single-nucleotide polymorphisms (SNPs) was identified, and four of them leading to amino acid substitutions. An association study was performed based on calculated haplotype frequencies, and statistically significant differences were found between the patient and control populations for some haplotypes. To help establish the evolutionary relationships between the haplotypes, the coding regions of both the chimpanzee and the gorilla ACT gene were sequenced and evaluated. To test whether the different haplotypes conferred a functional change to the ACT protein, a yeast two-hybrid assay was designed to test the interaction between the two most divergent ACT haplotypes and their known binding partners, CREM and KIF17b. We identified one ACT haplotype that had a 45% reduction in its interaction with CREM. Our results suggest that different haplotypes within the ACT gene may contribute to male factor subfertility.

Microtubule-independent and Protein Kinase A-mediated Function of Kinesin KIF17b Controls the Intracellular Transport of Activator of CREM in Testis (ACT)

Kinesins are motor proteins that transport their cargos along microtubules in an ATP-dependent manner. The testis-specific kinesin KIF17b was shown to directly regulate cAMP-response element modulator (CREM)-dependent transcription by determining the subcellular localization of the activator of CREM in testis (ACT), the testis-specific coactivator of CREM in postmeiotic male germ cells. CREM is a crucial transcriptional regulator of many important genes required for spermatid maturation, as demonstrated by the complete block of sperm development at the first steps of spermiogenesis in crem-null mice. To better understand the complex regulation of postmeiotic germ cell differentiation, we further characterized the ACT-KIF17b interaction, the function of KIF17b, and the signaling pathways governing its action. In this study, we demonstrated that the abilities of KIF17b to shuttle between the nuclear and the cytoplasmic compartments and to transport ACT are neither dependent on its motor domain nor on microtubules, thus revealing a novel microtubule-independent function for kinesins. We also showed that the cyclic AMP-dependent protein kinase A mediates the phosphorylation of KIF17b, and this modification is important for its subcellular localization. These results indicate that cyclic AMP signaling controls CREM-mediated transcription in male germ cells through modification of KIF17b function.

CREM activator and repressor isoform expression in human male germ cells

The transcription factor cAMP-responsive element modulator (CREM) is known to play a vital role for male fertility as it has been demonstrated that male mice lacking a functional CREM gene are infertile. The CREM gene consists of 14 exons. Owing to alternative exon splicing, CREM gene expression results in the production of functionally different CREM proteins with either activating or repressing potential on target gene expression. Infertile men have been reported to reveal a substantial reduction of CREM activators and additional inaccurately spliced CREM transcripts. In the present study, we analysed the expression of CREM transcripts with the recently reported leader exons theta1 and theta2 and identified a new putative CREM repressor, namely theta1-F-H, in patients with impaired spermatogenesis. In addition, we applied single cell microdissection followed by RT-PCR with leader exons B, theta1 and theta2 to assign the expressed CREM activator and repressor isoforms to specific germ cell types within the seminiferous epithelium. Contrary to dogma, we demonstrated CREM activator and repressor isoforms in all germ cell types, but not in Sertoli cells. However, the percentage of germ cell samples that revealed positive RT-PCR signals for these CREM activators was higher in spermatocytes and round spermatids than in spermatogonia and elongated spermatids. It remains unknown whether these activator transcripts are physiologically active. Our data suggest a fine-tuning between CREM activator and repressor isoforms in normal germ cells that might be disturbed during impaired spermatogenesis.

Specialized rules of gene transcription in male germ cells: the CREM paradigm*

Specialized transcription complexes that coordinate the differentiation programme of spermatogenesis have been found in germ cells, which display specific differences in the components of the general transcription machinery. The TATA-binding protein family and its associated cofactors, for example, show upregulated expression in testis. In this physiological context, transcriptional control mediated by the activator cAMP response element modulator (CREM) represents an established paradigm. Somatic cell activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CREB-binding protein. In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, activator of CREM in the testis (ACT), which confers a powerful, phosphorylation-independent activation capacity. The function of ACT was found to be regulated by the testis-specific kinesin KIF17b. Here we discuss some aspects of the testis-specific transcription machinery, whose function is essential for the process of spermatogenesis.

Abnormal sperm in mice with targeted deletion of the act (activator of cAMP-responsive element modulator in testis) gene.

ACT [activator of cAMP-responsive element modulator (CREM) in testis] is a LIM-only protein that interacts with transcription factor CREM in postmeiotic male germ cells and enhances CREM-dependent transcription. CREM regulates many crucial genes required for spermatid maturation, and targeted mutation of the Crem gene in the mouse germ-line blocks spermatogenesis. Here we report the phenotype of mice in which targeted disruption of the act gene was obtained by homologous recombination. Whereas the seminiferous tubules of the act(-/-) mice contain all of the developmental stages of germ cells and the mice are fertile, the amount of mature sperm in the epididymis is drastically reduced. The residual sperm display severe abnormalities, including fully folded tails and aberrant head shapes. These results indicate that numerous postmeiotic genes under CREM control require the coactivator function of ACT. Thus, the fine-tuning of sperm development is achieved by the coordinated action of two transcriptional regulators.

Expression of activator of CREM in the testis (ACT) during normal and impaired spermatogenesis: correlation with CREM expression.

The cAMP-responsive element modulator (CREM) is involved in regulating gene expression in haploid spermatids. Transcriptional activity of the CREM protein is thought to be regulated by activator of CREM in the testis (ACT). Applying RT-PCR and in situ hybridization, cell-specific gene expression of ACT was demonstrated in man, cynomolgus monkey and mouse. During normal spermatogenesis, RT-PCR revealed a strong signal in all three species. We sequenced monkey ACT cDNA and demonstrated that the putative amino acid sequence is highly conserved between these species. In situ hybridization demonstrated ACT mRNA in mid and late pachytene spermatocytes and in round spermatids. Among four infertile men with round spermatid maturation arrest (RSMA), only one patient revealed a strong signal for ACT, while three patients displayed a weak signal for both RT-PCR and in situ hybridization, although germ cells normally expressing ACT were present in these patients. In addition, CREM knockout mice known to be infertile due to RSMA also exhibited only a weak amplification product for ACT cDNA. ACT mRNA was barely detectable in some round spermatids, but was completely absent in pachytene spermatocytes. Database search revealed two and one CRE within the putative human and mouse ACT promoters respectively. Our findings indicate a conserved function of ACT during the evolution of mammalian spermatogenesis and suggest a role for CREM in ACT transcriptional regulation.

The kinesin KIF17b and RNA-binding protein TB-RBP transport specific cAMP-responsive element modulator-regulated mRNAs in male germ cells.

Testis brain RNA-binding protein (TB-RBP), the mouse orthologue of the human protein Translin, is a widely expressed and highly conserved protein with proposed functions in chromosomal translocations, mitotic cell division, and mRNA transport, stabilization, and storage. Targeted inactivation of TB-RBP leads to abnormalities in fertility and behavior. A testis-enriched kinesin KIF17b coimmunoprecipitates with TB-RBP in a RNA-protein complex containing specific cAMP-responsive element modulator (CREM)-regulated mRNAs. The specificity of this interaction is confirmed by in vivo RNA-protein crosslinking and transfections of hippocampal neurons. Combining in situ hybridization and immunohistochemistry at the electron microscope level, a temporally sequential dissociation of KIF17b and TB-RBP from specific mRNAs is detected with TB-RBP release coincident with the time of mRNA translation, indicating a separation of the processes of transport and translation. We conclude that KIF17b serves as a molecular motor component of a TB-RBP-mouse ribonucleoprotein complex transporting a group of specific CREM-regulated mRNAs in mammalian male postmeiotic germ cells. Because KIF17b has been reported to control CREM-dependent transcription in male germ cells by regulating the intracellular location of the transcriptional coactivator activator of CREM in testis, this indicates that one kinesin links the processes of transcription and transport of specific mRNAs in mammalian male germ cells.

Transcriptional control in male germ cells: general factor TFIIA participates in CREM-dependent gene activation.

Regulation of gene expression in haploid male germ cells follows a number of specific rules that differ from somatic cells. In this physiological context, transcriptional control mediated by the activator CREM (cAMP-responsive element modulator) represents an established paradigm. In somatic cells activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CBP (cAMP response element binding protein-binding protein). In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, ACT (activator of CREM in testis), which confers a powerful, phosphorylation-independent activation capacity. In addition to specialized transcription factors and coactivators, a variety of general factors of the basal transcriptional machinery, and their distinct tissue-specific isoforms, are highly expressed in testis, supporting the general notion that testis-specific gene expression requires specialized mechanisms. Here, we describe that CREM interacts with transcription factor IIA (TFIIA), a general transcription factor that stimulates RNA polymerase II-directed transcription. This association was identified by a two-hybrid screen, using a testis-derived cDNA library, and confirmed by coimmunoprecipitation. The interaction is restricted to the activator isoforms of CREM and does not require Ser117. Importantly, CREM does not interact with TFIIAtau-ALF, a testis-specific TFIIA homolog. CREM and TFIIA are expressed in a spatially and temporally coordinated fashion during the differentiation program of germ cells. The two proteins also colocalize intracellularly in spermatocyte and spermatid cells. These findings contribute to the understanding of the highly specialized rules of transcriptional regulation in haploid germ cells.

Different CREM-isoform gene expression between equine and human normal and impaired spermatogenesis

Histone-to-protamine exchange causes chromatin condensation ceasing gene expression in elongating spermatids. Gene expression of protamines is regulated by the transcription factor cAMP-responsive element modulator (CREM). Altered CREM expression results in male infertility, as shown by CREM-knock-out mice being sterile due to round spermatid maturation arrest and patients exhibiting round spermatid maturation arrest revealing a lack or substantial reduction of both CREM-mRNA and CREM-protein. Similar defects in histone-to-protamine exchange have been suggested in infertile stallions exhibiting enlarged sperm heads. The CREM-gene consists of 14 exons. Alternative exon splicing results in the production of both activator and repressor proteins. To further clarify the role of different CREM-isoforms for male infertility, the expression pattern of various CREM-isoforms during equine and human normal and impaired spermatogenesis was investigated by RT-PCR. Stallions with normal spermatogenesis expressed six activators and three repressors. In men three activators and seven different repressors were detected. In one stallion and patients with impaired spermatogenesis, only repressors were found. It is concluded that (i) stallion and man reveal a different CREM expression pattern, (ii) the expression of CREM activators is a prerequisite for normal spermatogenesis, and (iii) the lack of CREM activator expression results in male infertility.