cAMP-response element modulator tau is a positive regulator of testis angiotensin converting enzyme transcription

Characterization of the promoter region of the murine Catsper2 gene

CATSPER2 (Cation channel sperm-associated protein 2) protein, which is part of the calcium CATSPER channel located in the membrane of the flagellar principal piece of the sperm cell, is only expressed in the testis during spermatogenesis. Deletions or mutations in the Catsper2 gene are associated with the deafness-infertility syndrome (DIS) and non-syndromic male infertility. However, the mechanisms by which Catsper2 is regulated are unknown. Here, we report the characterization of the promoter region of murine Catsper2 and the role of CTCF and CREMτ in its transcription. We report that the promoter region has transcriptional activity in both directions, as determined by observing luciferase activity in mouse Sertoli and GC-1 spg transfected cells. WGBS data analysis indicated that a CpG island identified in silico is non-methylated; Chromatin immunoprecipitation (ChIP)-seq data analysis revealed that histone marks H3K4me3 and H3K36me3 are present in the promoter and body of the Catsper2 gene respectively, indicating that Catsper2 is subject to epigenetic regulation. In addition, the murine Catsper2 core promoter was delimited to a region between -54/+189 relative to the transcription start site (TSS), where three CTCF and one CRE binding site were predicted. The functionality of these sites was determined by mutation of the CTCF sites and deletion of the CRE site. Finally, ChIP assays confirmed that CREMτ and CTCF bind to the Catsper2 minimal promoter region. This study represents the first functional analysis of the murine Catsper2 promoter region and the mechanisms that regulate its expression.

cAMP Response Element Modulator α Induces Dual Specificity Protein Phosphatase 4 to Promote Effector T Cells in Juvenile-Onset Lupus

Effector CD4⁺ T cells with increased IL-17A and reduced IL-2 production contribute to tissue inflammation and organ damage in systemic lupus erythematosus (SLE). Increased expression of the transcription factor cAMP response element modulator (CREM) α promotes altered cytokine expression in SLE. The aim of this study was to investigate CREMα-mediated events favoring effector CD4⁺ T cells in health and disease. Using CRISPR/Cas9 genome editing and lentiviral transduction, we generated CREMα-deficient and CREMα-overexpressing Jurkat T cells. Gene expression and regulatory events were assessed using luciferase reporter assays and chromatin immunoprecipitation. Interaction between CREMα and p300 was investigated using proximity ligation assays, coimmunoprecipitation, and knockdown of p300. Gene expression profiles of modified cells were compared with CD4⁺ T cells from patients with juvenile-onset SLE. We show that CREMα induces dual specificity protein phosphatase (DUSP) 4 in effector CD4⁺ T cells through corecruitment of p300. The transcriptional coactivator p300 mediates histone acetylation at DUSP4, prompting increased gene expression. Using DUSP4 transfection models and genetically modified CREM-deficient and CREMα-overexpressing T cells, we demonstrate the molecular underpinnings by which DUSP4 induces IL-17A while limiting IL-2 expression. We demonstrate that CD4⁺ T cells from patients with juvenile-onset SLE share phenotypical features with CREMα-overexpressing CD4⁺ T cells, including increased DUSP4 expression and imbalanced IL-17A and IL-2 production. Taken together, we describe CREMα-mediated mechanisms that involve the transcriptional upregulation of DUSP4, leading to imbalanced cytokine production by effector T cells. Our findings identify the CREMα/DUSP4 axis as a promising candidate in the search for biomarkers and therapeutic targets in SLE.

Two novel ligand-independent variants of the VEGFR-1 receptor are expressed in human testis and spermatozoa, one of them with the ability to activate SRC proto-oncogene tyrosine kinases

The vascular endothelial growth factor receptor 1 (VEGFR-1) family of receptors is preferentially expressed in endothelial cells, with the full-length and mostly the soluble (sVEGFR-1) isoforms being the most expressed ones. Surprisingly, cancer cells (MDA-MB-231) express, instead, alternative intracellular VEGFR-1 variants. We wondered if these variants, that are no longer dependent on ligands for activation, were expressed in a physiological context, specifically in spermatogenic cells, and whether their expression was maintained in spermatozoa and required for human fertility. By interrogating a human library of mature testis cDNA, we characterized two new truncated intracellular variants different from the ones previously described in cancer cells. The new isoforms were transcribed from alternative transcription start sites (aTSS) located respectively in intron-19 (i₁₉VEGFR-1) and intron-28 (i₂₈VEGFR-1) of the VEGFR-1 gene (GenBank accession numbers JF509744 and JF509745) and expressed in mature testis and spermatozoa. In this paper, we describe the characterization of these isoforms by RT-PCR, northern blot, and western blot, their preferential expression in human mature testis and spermatozoa, and the elements that punctuate their proximal promoters and suggest cues for their expression in spermatogenic cells. Mechanistically, we show that i₁₉VEGFR-1 has a strong ability to phosphorylate and activate SRC proto-oncogene non-receptor tyrosine kinases and a significant bias toward a decrease in expression in patients considered infertile by WHO criteria.

Seasonal Variation of the Intraepithelial Gland in Camel Epididymis with Special Reference to Autophagosome

The key role of the epididymis is contributing to sperm storage, maturation, and survival. The epididymis of camel has a unique structure called the intraepithelial gland. The present work aimed to investigate the structure of the epididymal intraepithelial gland with special references to the seasonal variation. The samples were collected from the distal part of the corpus epididymes of completely healthy mature camels (Camelus dromedarius) in the breeding and nonbreeding seasons. Tomato lectin-positive material had been demonstrated within the epididymal spermatozoa. Here, we provide the first transmission electron microscopic study for the intraepithelial gland of camel epididymis detecting the autophagy during the nonbreeding season. The autophagosomes originated from the endoplasmic reticulum, surrounding mitochondria, and located mainly next to the basement membrane. This location is probably valuable for subsequent passing of their contents into the interstitium for possible recycling. The histochemical and ultrastructural characteristics of the gland in the breeding season indicated a hyperactive secretory microenvironment enriched with the glycoprotein-producing machinery, which could be controlled by androgens. The present data suggest that the camel intraepithelial gland has a significant impact on the reproductive activity through their secretory microenvironment during the breeding season. Moreover, it recycles the unused organelles or proteins for reuse or to supply energy under stress conditions in the nonbreeding season.

Human CATSPER1 Promoter Is Regulated by CREB1 and CREMτ Transcriptional Factors In Vitro

BACKGROUND

The CATSPER1 gene encodes a CATSPER channel protein that selectively permeates Ca²⁺ ions, and CATSPER expression in sperm is essential for flagellum hyperactivation and, thus, male fertility. Little is known regarding the transcriptional regulation of CATSPER1, but previous studies have performed in silico analyses of transcription factor binding sites, including three CRE sites designated 0-2, in which CRE0 is located near the transcription start site.

OBJETIVES

We investigate if overexpression of CREB-A and CREMτ transcription factors might regulate CATSPER1 expression.

MATERIAL AND METHODS

In this study, the transcriptional regulation of the CATSPER1 gene by CREB-A and CREMτ transcriptions factors was determined by dual-luciferase assays in HEK293 and GC1-spg cells, and important CRE sites were mutated and analyzed for transcriptional regulation.

RESULTS

The deletion of the CRE1 site dramatically increased the transcriptional activity of the CATSPER1 promoter in HEK293 and GC1-spg cells. In HEK293 cells, the CREB-A transcription factor positively regulated CATSPER1 gene expression, while the presence of CREB-A and CREMτ factors synergistically enhanced promoter activity in these cells. In contrast, deletion of CRE0 prevented any transcriptional activity of the CATSPER1 promoter in GC1-spg spermatogonial cells, but expression of either CREB-A or CREMτ restored such transcriptional activity.

CONCLUSIONS

The human CATSPER1 promoter is positively regulated in vitro by CREB-A in HEK293 and GC1-spg cells. Both lines showed differential transcriptional regulation, which was defined by the factors and coactivators present in each cell line as well as the context in which the CRE sites were found in the promoter.

Sox30 initiates transcription of haploid genes during late meiosis and spermiogenesis in mouse testes

Transcription factors of the Sox protein family contain a DNA-binding HMG box and are key regulators of progenitor cell fate. Here, we report that expression of Sox30 is restricted to meiotic spermatocytes and postmeiotic haploids. Sox30 mutant males are sterile owing to spermiogenic arrest at the early round spermatid stage. Specifically, in the absence of Sox30, proacrosomic vesicles fail to form a single acrosomal organelle, and spermatids arrest at step 2-3. Although most Sox30 mutant spermatocytes progress through meiosis, accumulation of diplotene spermatocytes indicates a delayed or impaired transition from meiotic to postmeiotic stages. Transcriptome analysis of isolated stage-specific spermatogenic cells reveals that Sox30 controls a core postmeiotic gene expression program that initiates as early as the late meiotic cell stage. ChIP-seq analysis shows that Sox30 binds to specific DNA sequences in mouse testes, and its genomic occupancy correlates positively with expression of many postmeiotic genes including Tnp1, Hils1, Ccdc54 and Tsks These results define Sox30 as a crucial transcription factor that controls the transition from a late meiotic to a postmeiotic gene expression program and subsequent round spermatid development.

CREM-transgene mice: An animal model of atrial fibrillation and thrombogenesis

BACKGROUND

The molecular pathomechanisms underlying atrial thrombogenesis are multifactorial and still require detailed investigations. Transgenic mice with cardiomyocyte-directed expression of the transcriptional repressor CREM-IbΔC-X (CREM-TG) represent an experimental model of atrial fibrillation (AF) that shows a gradual, age-dependent progression from atrial ectopy to persistent AF. Importantly, this model develops biatrial thrombi. The molecular characteristics related to the thrombogenesis in CREM-TG mice have not been studied, yet.

METHODS

The inflammatory and prothrombotic state was evaluated at the transcriptional (qRT-PCR) and protein level in the left (LA) and right atria (RA) from CREM-TG mice at the age of 20weeks and compared to wild-type controls. Moreover, histological analyses of atrial thrombi were performed.

RESULTS

The endocardial dysfunction was mirrored by diminished levels of eNOS-mRNA in both atria (RA: 0.79±0.04, LA: 0.72±0.06; each P<0.05). Moreover, the PAI-1/t-PA mRNA ratio was significantly increased in both atria (RA: 3.6±0.6; P<0.01, LA: 4.0±1.0; P<0.05) indicating a high risk of thrombus formation. However, the inflammatory phenotype was more pronounced in the RA and was reflected by a significant increase in the mRNA levels encoding adhesion molecules ICAM-1 (2.1±0.2; P<0.01), VCAM-1 (2.3±0.5; P<0.05), and selectin P (3.6±0.5: P<0.05).

CONCLUSIONS

CREM-TG mice represent a valuable model for studying atrial thrombogenesis and assessing therapeutic approaches preventing embolic events in the systemic and pulmonary circulation.

Protective regulation of the ACE2/ACE gene expression by estrogen in human atrial tissue from elderly men

Data from animal experiments and clinical investigations suggest that components of the renin-angiotensin system are markedly affected by sex hormones. However, whether estrogen affects human atrial myocardium has not been investigated yet. In this study, we determined the effects of estrogen on key components of atrial renin-angiotensin system: angiotensin-converting enzyme, responsible for generation of angiotensin II and angiotensin-converting enzyme 2, counteracting majority of AngII effects, and different renin-angiotensin system receptors, AT1R, AT2R, and MAS. First, the expression levels of estrogen receptors mRNA were determined in right atrial appendages obtained from patients undergoing heart surgery. The amounts of estrogen receptor α and estrogen receptor β mRNA were similar between women ( n = 14) and men ( n = 10). Atrial tissue slices (350 µm) were prepared from male donors which were exposed to estrogen (1-100 nM; n = 21) or stimulated at 4 Hz for 24 h in the presence or absence of 100 nM estrogen ( n = 16), respectively. The administration of estrogen did not change mRNA levels of estrogen receptors, but activated MAP kinases, Erk1/2. Furthermore, estrogen increased the amounts of angiotensin-converting enzyme 2-mRNA (1.89 ± 0.23; P < 0.05) but reduced that of angiotensin-converting enzyme-mRNA (0.78 ± 0.07, P < 0.05). In addition, the transcript levels of AT2R and MAS were upregulated by estrogen. Pacing of tissue slices significantly increased the angiotensin-converting enzyme/angiotensin-converting enzyme 2 ratio at both the mRNA and protein level. During pacing, administration of estrogen substantially lowered the angiotensin-converting enzyme/angiotensin-converting enzyme 2 ratio at the transcript (0.92 ± 0.21 vs. 2.12 ± 0.27 at 4 Hz) and protein level (0.94 ± 0.20 vs. 2.14 ± 0.3 at 4 Hz). Moreover, estrogen elicited anti-inflammatory and anti-oxidative effects on renin-angiotensin system-associated downstream effectors such as pro-oxidative LOX-1 and pro-inflammatory ICAM-1. An antagonist of estrogen receptor α reversed these anti-inflammatory and anti-oxidative effects of estrogen significantly. Overall, our results demonstrated that estrogen modifies the local renin-angiotensin system homeostasis and achieves protective effects in atrial myocardium from elderly men. Impact statement The present study demonstrates that estrogen affects the human atrial myocardium and mediates protective actions through estrogen receptors-(ER) dependent signaling. Estrogen substantially modulates the local RAS via downregulation of ACE and simultaneous upregulation of ACE2, AT2R and MAS expression levels. This is indicative of a shift of the classical RAS/ACE axis to the alternative, protective RAS/ACE2 axis. In support of this view, estrogen attenuated the expression of RAS-associated downstream effectors, LOX-1, and ICAM-1. A specific antagonist of ERα reversed the anti-inflammatory and anti-oxidative effects of estrogen in paced and non-paced atrial tissue slices. In summary, our data demonstrate the existence of protective effects of estrogen in atrial tissue from elderly men which are at least in part, mediated by the regulation of local RAS homeostasis.

Characterization of the cardiac renin angiotensin system in oophorectomized and estrogen-replete mRen2.Lewis rats

The cardioprotective effects of estrogen are well recognized, but the mechanisms remain poorly understood. Accumulating evidence suggests that the local cardiac renin-angiotensin system (RAS) is involved in the development and progression of cardiac hypertrophy, remodeling, and heart failure. Estrogen attenuates the effects of an activated circulating RAS; however, its role in regulating the cardiac RAS is unclear. Bilateral oophorectomy (OVX; n = 17) or sham-operation (Sham; n = 13) was performed in 4-week-old, female mRen2.Lewis rats. At 11 weeks of age, the rats were randomized and received either 17 β-estradiol (E2, 36 µg/pellet, 60-day release, n = 8) or vehicle (OVX-V, n = 9) for 4 weeks. The rats were sacrificed, and blood and hearts were used to determine protein and/or gene expression of circulating and tissue RAS components. E2 treatment minimized the rise in circulating angiotensin (Ang) II and aldosterone produced by loss of ovarian estrogens. Chronic E2 also attenuated OVX-associated increases in cardiac Ang II, Ang-(1–7) content, chymase gene expression, and mast cell number. Neither OVX nor OVX+E2 altered cardiac expression or activity of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and Ang II type 1 receptor (AT1R). E2 treatment in OVX rats significantly decreased gene expression of MMP-9, ACE2, and Ang-(1–7) mas receptor, in comparison to sham-operated and OVX littermates. E2 treatment appears to inhibit upsurges in cardiac Ang II expression in the OVX-mRen2 rat, possibly by reducing chymase-dependent Ang II formation. Further studies are warranted to determine whether an E2-mediated reduction in cardiac chymase directly contributes to this response in OVX rats.

cAMP responsive element modulator: a critical regulator of cytokine production

T lymphocytes from patients with systemic lupus erythematosus (SLE) display a complex array of cellular, molecular, and signaling anomalies, many of which have been attributed to increased expression of the transcriptional regulator cAMP responsive element modulator α (CREMα). Recent evidence indicates that CREMα, in addition to its regulatory functions on gene promoters in T lymphocytes, alters the epigenetic conformation of cytokine genes by interacting with enzymes that control histone methylation and acetylation as well as cytosine-phosphate-guanosine (CpG) DNA methylation. This review summarizes the most recent findings on CREM protein expression in various cell types, in particular its effects on T lymphocyte biology in the context of both health and SLE. We emphasize CREMα as a key molecule that drives autoimmunity.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Novel insights into the downstream pathways and targets controlled by transcription factors CREM in the testis

The essential role of the Crem gene in normal sperm development is widely accepted and is confirmed by azoospermia in male mice lacking the Crem gene. The exact number of genes affected by Crem absence is not known, however a large difference has been observed recently between the estimated number of differentially expressed genes found in Crem knock-out (KO) mice compared to the number of gene loci bound by CREM. We therefore re-examined global gene expression in male mice lacking the Crem gene using whole genome transcriptome analysis with Affymetrix microarrays and compared the lists of differentially expressed genes from Crem−/− mice to a dataset of genes where binding of CREM was determined by Chip-seq. We determined the global effect of CREM on spermatogenesis as well as distinguished between primary and secondary effects of the CREM absence. We demonstrated that the absence of Crem deregulates over 4700 genes in KO testis. Among them are 101 genes associated with spermatogenesis 41 of which are bound by CREM and are deregulated in Crem KO testis. Absence of several of these genes in mouse models has proven their importance for normal spermatogenesis and male fertility. Our study showed that the absence of Crem plays a more important role on different aspects of spermatogenesis as estimated previously, with its impact ranging from apoptosis induction to deregulation of major circadian clock genes, steroidogenesis and the cell-cell junction dynamics. Several new genes important for normal spermatogenesis and fertility are down-regulated in KO testis and are therefore possible novel targets of CREM.

Psoralea corylifolia protects against testicular torsion/detorsion-induced ischemia/reperfusion injury

ETHNOPHARMACOLOGICAL RELEVANCE

The pathophysiology of testicular torsion-detorsion is ischemia-reperfusion injury of the testis. In the course of testicular ischemia and reperfusion, overgeneration of reactive oxygen species is a major initiating component of the testicular spermatogenic injury. Reactive oxygen species regulate many genes whose expression affects cell-cycle regulation, cell proliferation, and apoptosis. The transcription factor cAMP-responsive element modulator-τ (CREMτ) plays an essential role in spermatogenesis. Psoralea corylifolia, a medicinal herb with anti-oxidative activity, has been used to treat male reproductive dysfunction in traditional Chinese medicine. In this study, we investigated the effect of Psoralea corylifolia on testicular torsion/detorsion-induced injury.

MATERIALS AND METHODS

Sixty adult male Sprague-Dawley rats were randomly divided into 3 groups, each containing 20 rats. Rats in the control group underwent a sham operation of the left testis. In the torsion-detorsion group, the left testis was rotated 720° for 2h. Rats in the treatment group received the same surgical procedure as the torsion-detorsion group, but Psoralea corylifolia was administered orally. Bilateral orchiectomy was performed on half of the rats in each experimental group at 4h after detorsion for measurement of malondialdehyde which is an indicator of intratesticular reactive oxygen species content. Orchiectomy was performed on the remaining rats at 3 months after detorsion for analysis of testicular CREMτ expression and spermatogenesis.

RESULTS

Unilateral testicular torsion-detorsion caused a significant increase in malondialdehyde level and caused significant decreases in CREMτ expression and spermatogenesis in ipsilateral testes. Psoralea corylifolia treatment significantly decreased malondialdehyde level and significantly increased CREMτ expression and spermatogenesis in ipsilateral testes, compared with torsion-detorsion group.

CONCLUSIONS

These results suggest that Psoralea corylifolia may protect testicular spermatogenesis by enhancing CREMτ expression by scavenging reactive oxygen species.

Cell-specific occupancy of an extended repertoire of CREM and CREB binding loci in male germ cells

Background

CREB and CREM are closely related factors that regulate transcription in response to various stress, metabolic and developmental signals. The CREMτ activator isoform is selectively expressed in haploid spermatids and plays an essential role in murine spermiogenesis.

Results

We have used chromatin immunoprecipitation coupled to sequencing (ChIP-seq) to map CREM and CREB target loci in round spermatids from adult mouse testis and spermatogonia derived GC1-spg cells respectively. We identify more than 9000 genomic loci most of which are cell-specifically occupied. Despite the fact that round spermatids correspond to a highly specialised differentiated state, our results show that they have a remarkably accessible chromatin environment as CREM occupies more than 6700 target loci corresponding not only to the promoters of genes selectively expressed in spermiogenesis, but also of genes involved in functions specific to other cell types. The expression of only a small subset of these target genes are affected in the round spermatids of CREM knockout animals. We also identify a set of intergenic binding loci some of which are associated with H3K4 trimethylation and elongating RNA polymerase II suggesting the existence of novel CREB and CREM regulated transcripts.

Conclusions

We demonstrate that CREM and CREB occupy a large number of promoters in highly cell specific manner. This is the first study of CREM target promoters directly in a physiologically relevant tissue in vivo and represents the most comprehensive experimental analysis of CREB/CREM regulatory potential to date.

Functional cooperation between CREM and GCNF directs gene expression in haploid male germ cells

Cellular differentiation and development of germ cells critically depend on a coordinated activation and repression of specific genes. The underlying regulation mechanisms, however, still lack a lot of understanding. Here, we describe that both the testis-specific transcriptional activator CREMτ (cAMP response element modulator tau) and the repressor GCNF (germ cell nuclear factor) have an overlapping binding site which alone is sufficient to direct cell type-specific expression in vivo in a heterologous promoter context. Expression of the transgene driven by the CREM/GCNF site is detectable in spermatids, but not in any somatic tissue or at any other stages during germ cell differentiation. CREMτ acts as an activator of gene transcription whereas GCNF suppresses this activity. Both factors compete for binding to the same DNA response element. Effective binding of CREM and GCNF highly depends on composition and epigenetic modification of the binding site. We also discovered that CREM and GCNF bind to each other via their DNA binding domains, indicating a complex interaction between the two factors. There are several testis-specific target genes that are regulated by CREM and GCNF in a reciprocal manner, showing a similar activation pattern as during spermatogenesis. Our data indicate that a single common binding site for CREM and GCNF is sufficient to specifically direct gene transcription in a tissue-, cell type- and differentiation-specific manner.

Role of basic leucine zipper proteins in transcriptional regulation of the steroidogenic acute regulatory protein gene

The regulation of steroidogenic acute regulatory protein (StAR) gene transcription by cAMP-dependent mechanisms occurs in the absence of a consensus cAMP response element (CRE, TGACGTGA). This regulation is coordinated by multiple transcription factors that bind to sequence-specific elements located approximately 150 bp upstream of the transcription start site. Among the proteins that bind within this region, the basic leucine zipper (bZIP) family of transcription factors, i.e. CRE binding protein (CREB)/CRE modulator (CREM)/activating transcription factor (ATF), activator protein 1 (AP-1; Fos/Jun), and CCAAT enhancer binding protein beta (C/EBPbeta), interact with an overlapping region (-81/-72 bp) in the StAR promoter, mediate stimulus-transcription coupling of cAMP signaling and play integral roles in regulating StAR gene expression. These bZIP proteins are structurally similar and bind to DNA sequences as dimers; however, they exhibit discrete transcriptional activities, interact with several transcription factors and other properties that contribute in their regulatory functions. The 5'-flanking -81/-72 bp region of the StAR gene appears to function as a key element within a complex cAMP response unit by binding to different bZIP members, and the StAR promoter displays variable states of cAMP responsivity contingent upon the occupancy of these cis-elements with these transcription factors. The expression and activities of CREB/CREM/ATF, Fos/Jun and C/EBPbeta have been demonstrated to be mediated by a plethora of extracellular signals, and the phosphorylation of these proteins at several Ser and Thr residues allows recruitment of the transcriptional coactivator CREB binding protein (CBP) or its functional homolog p300 to the StAR promoter. This review will focus on the current level of understanding of the roles of selective bZIP family proteins within the complex series of processes involved in regulating StAR gene transcription.

Role of cAMP-responsive element modulator-τ (CREMτ) in ipsilateral testicular injury after unilateral testicular torsion-detorsion

OBJECTIVE

To investigate the role of cAMP-responsive element modulator-tau (CREMtau), an essential transcription factor for spermatogenesis, in ipsilateral testicular injury after unilateral testicular torsion-detorsion.

DESIGN

Controlled experimental study using rats.

SETTING

Research laboratory.

ANIMAL(S)

Twenty adult male Sprague-Dawley rats.

INTERVENTION(S)

Ten rats in the control group underwent a sham operation of the left testes. Ten rats in the torsion-detorsion group received 1 hour of left testicular torsion. Orchiectomy was performed on all rats 3 months after detorsion.

MAIN OUTCOME MEASURE(S)

Testicular spermatogenesis was evaluated by measuring testicular weight, mean seminiferous tubular diameter, number of germ cell layers, and mean testicular biopsy score. The expressions of CREMtau mRNA and protein in testes were detected by reverse transcription-polymerase chain reaction and Western blot, respectively.

RESULT(S)

Unilateral testicular torsion-detorsion caused significant spermatogenic damage in the ipsilateral testes, including reductions in testicular weight, mean seminiferous tubular diameter, number of germ cell layers, and mean testicular biopsy score. In ipsilateral testes with spermatogenic damage, the expressions of CREMtau mRNA and protein were also significantly reduced.

CONCLUSION(S)

Reduction in testicular CREMtau expression may be one of the mechanisms responsible for impairment of spermatogenesis in ipsilateral testes after unilateral testicular torsion-detorsion.

Transcriptional regulation of the bovine leukemia virus promoter by the cyclic AMP-response element modulator tau isoform

Bovine leukemia virus (BLV) expression is controlled at the transcriptional level through three Tax(BLV)-responsive elements (TxREs) responsive to the viral transactivator Tax(BLV). The cAMP-responsive element (CRE)-binding protein (CREB) has been shown to interact with CRE-like sequences present in the middle of each of these TxREs and to play critical transcriptional roles in both basal and Tax(BLV)-transactivated BLV promoter activity. In this study, we have investigated the potential involvement of the cAMP-response element modulator (CREM) in BLV transcriptional regulation, and we have demonstrated that CREM proteins were expressed in BLV-infected cells and bound to the three BLV TxREs in vitro. Chromatin immunoprecipitation assays using BLV-infected cell lines demonstrated in the context of chromatin that CREM proteins were recruited to the BLV promoter TxRE region in vivo. Functional studies, in the absence of Tax(BLV), indicated that ectopic CREMtau protein had a CRE-dependent stimulatory effect on BLV promoter transcriptional activity. Cross-link of the B-cell receptor potentiated CREMtau transactivation of the viral promoter. Further experiments supported the notion that this potentiation involved CREMtau Ser-117 phosphorylation and recruitment of CBP/p300 to the BLV promoter. Although CREB and Tax(BLV) synergistically transactivated the BLV promoter, CREMtau repressed this Tax(BLV)/CREB synergism, suggesting that a modulation of the level of Tax(BLV) transactivation through opposite actions of CREB and CREMtau could facilitate immune escape and allow tumor development.

The transcription factor CREMtau and cAMP regulate promoter activity of the Na,K-ATPase alpha4 isoform

The Na,K-ATPase is an essential enzyme of the plasma membrane that plays a key role in numerous cell processes that depend on the transcellular gradients of Na(+) and K(+). Among the various isoforms of the catalytic subunit of the Na,K-ATPase, alpha4 exhibits the most limited pattern of expression, being restricted to male germ cells. Activity of alpha4 is essential for sperm function, and alpha4 is upregulated during spermatogenesis. The present study addressed the transcriptional control of the human Na,K-ATPase alpha4 gene, ATP1A4. We describe that a 5' untranslated region of the ATP1A4 gene (designated -339/+480 based on the ATP1A4 transcription initiation site) has promoter activity in luciferase reporter assays. Computer analysis of this promoter region revealed consensus sites (CRE) for the cyclic AMP (cAMP) response element modulator (CREM). Accordingly, dibutyryl cAMP (db-cAMP) and ectopic expression of CREMtau, a testis specific splice variant of CREM were able to activate the ATP1A4 promoter driven expression of luciferase in HEK 293 T, JEG-3 and GC-1 cells. Further characterization of the effect of db-cAMP and CREMtau on deleted constructs of the ATP1A4 promoter (-339/+80, and +25/+480), and on the -339/+480 region carrying mutations in the CRE sites showed that db-cAMP and CREMtau effect required the CRE motif located 263 bp upstream the transcription initiation site. EMSA experiments confirmed the CRE sequence as a bonafide CREMtau binding site. These results constitute the first demonstration of the transcriptional control of ATP1A4 gene expression by cAMP and by CREMtau, a transcription factor essential for male germ cell gene expression.

Views of the renin-angiotensin system: brilling, mimsy, and slithy tove

The renin-angiotensin system plays a role in many physiological systems, as proven by the phenotype of angiotensin-converting enzyme (ACE) knockout mice. We have used homologous recombination to create novel lines of mice with limited and unusual expression patterns of ACE. These mice show that, as long as an animal can regulate renin, they can tolerate both unusual patterns and reduced expression of ACE. We have also created mice in which one of the two ACE catalytic sites is nonfunctional. These new lines of mice give great insight into the function of the renin-angiotensin system in blood pressure control, response to stress, hematopoiesis, and reproduction.

Genetic control of spermiogenesis: insights from the CREM gene and implications for human infertility

Male germ cell differentiation requires a highly cell-specific gene expression programme that is achieved by unique chromatin remodelling, transcriptional control, and the expression of testis-specific genes or isoforms. The regulatory processes governing gene expression in spermatogenesis have fundamentally unique requirements, including meiosis, ongoing cellular differentiation and a peculiar chromatin organization. The signalling cascades and the downstream effectors contributing to the programme of spermatogenesis are currently being unravelled, revealing the unique features of germ cell regulatory circuits. This paper reports on the unique role that CREM exerts as a master regulator. Targeted inactivation of the genes encoding CREM and ACT has been achieved. ACT selectively associates with KIF17b, a kinesin motor protein highly expressed in germ cells. It has been found that KIF17b directly determines the intracellular localization of ACT. Thus, the activity of a transcriptional co-activator is intimately coupled to the function of a kinesin via tight regulation of its intracellular localization. The conservation of these elements and of their regulatory functions in human spermatogenesis indicates that they are likely to provide important insights into understanding the molecular mechanisms of human infertility.

Germ Cell Nuclear Factor Relieves cAMP-response Element Modulator τ-mediated Activation of the Testis-specific Promoter of Human Mitochondrial Glycerol-3-phosphate Dehydrogenase

Mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) is an essential component of the glycerol phosphate shuttle that transfers reduction equivalents from the cytosol into the mitochondrion. Within the testis, immunohistological analysis localized human mGPDH to late spermatids and to the midpiece of spermatozoa. The expression of human mGPDH is regulated by two somatic promoters, and here, we describe a third testis-specific promoter of human mGPDH. The usage of this testis-specific promoter correlates with the expression of a shortened mGPDH transcript of approximately 2.4 kb in length, which is solely detectable from testicular RNA. Within the testis-specific promoter, we detected a cAMP-response element (CRE) site at -51, which binds the testis-specific transcriptional activator CRE modulator tau (CREMtau) in electrophoretic mobility shift assays. This recognition site overlaps with a nuclear receptor binding half-site at -49, which binds the testis-specific transcriptional repressor germ cell nuclear factor (GCNF). Both factors compete for binding to the same DNA response element. Ectopic expression of CREMtau in HepG2 cells activated a promoter-driven luciferase construct in transient transfection experiments. Additional cotransfection of GCNF relieved this activity, suggesting a down-regulation of CREMtau-mediated activation by GCNF. This effect was preserved by introducing the CRE/nuclear receptor-binding element into a heterologous promoter context. Our data suggest a down-regulation of CREMtau-mediated gene expression by GCNF, which might be a general regulation mechanism for several postmeiotically expressed genes with a temporal expression peak during early spermatid development.

Expression of the soluble adenylyl cyclase during rat spermatogenesis: evidence for cytoplasmic sites of cAMP production in germ cells

To gain insight into the mechanisms of cAMP signaling in germ cells, the expression and subcellular localization of the full-length form of the soluble adenylyl cyclase (sAC) was investigated during rat spermatogenesis and in spermatozoa. A full-length sAC-specific antibody was generated by using a glutathione S-transferase (GST)-sAC carboxyl-terminal region (1399aa-1608aa) fusion protein as the antigen. The selectivity of the purified antibody was confirmed by immunoblotting with lysates from HEK293 cells overexpressing full-length sAC or truncated sAC. Western blot analysis demonstrated that full-length sAC protein appeared on day 25 during testis development. The expression levels increased progressively on days 30 and 35 and remained elevated in adult testis. Full-length sAC protein is retained in spermatozoa from the cauda epididymis. Consistent with the timing of the appearance of the Western blot signal, immunohistochemistry with testis sections at different stages of development detected sAC in late pachytene spermatocytes as well as round and elongating spermatids. Further experiments on the subcellular localization of native or recombinant enzymes revealed that full-length sAC is not only recovered in soluble fractions but also in particulate fractions of testis extracts. Immunofluorescence detection showed localization of the protein in the cytoplasm as well as in organelles of pachytene spermatocytes and spermatids. These findings indicate that cAMP production in spermatids and spermatozoa may occur at sites other than the plasma membrane and suggest that full-length sAC may play a role during spermatid differentiation.

Analysis of CREM-dependent gene expression during mouse spermatogenesis

The transcription factors CREM, CREB, and ATF-1 constitute a subfamily of beta-Zip transcription factors. Several different kinase cascades regulate the activity of these proteins. The activator splice-isoform CREMtau is specifically and highly expressed in post-meiotic germ cells during mouse spermatogenesis. Male mice lacking CREMtau expression are sterile because of stage-specific arrest of sperm maturation as the spermatids undergo apoptosis. In order to characterize the genes that are controlled by CREM during post-meiotic differentiation of round spermatids, we compared the expression levels of mRNA prepared from testes of wild-type and CREM-deficient mice by suppression subtractive hybridization (SSH) and affymetrix oligonucleotide arrays. A set of 956 unique sequences found in the CREM SSH library was further characterized by generating stage-specific expression profiles during spermatogenesis by hybridization with cDNA from pre-pubertal mice at defined stages of spermatogenesis using nylon DNA arrays. The resulting expression profiles were arranged in a linear order according to similarity in their profile shapes to find co-regulation of functionally related genes. Our data shows that a large number of genes are transcriptionally activated in round spermatids when CREM activity is maximal, including functional groups like transcription factors, proteins involved in signal transduction, and metabolic enzymes, therefore providing novel information of post-meiotic expression of many known as well as novel genes that are either directly or indirectly influenced by CREM expression.

Control of mouse hils1 gene expression during spermatogenesis: identification of regulatory element by transgenic mouse

Histone H1-like protein in spermatids 1 (Hils1) is a testis- specific histone H1-like protein exclusively expressed in haploid spermatids and should be involved in chromatin remodeling during mouse spermatogenesis. Spatial and temporal regulation of the hils1 gene expression would be critical for the formation of functional sperm, controlled at both transcriptional and translational levels. Previously, we reported that transcripts of the hils1 gene are exclusively expressed in mouse testis from 23 days of age whereas the Hils1 protein is not detected until 28 days of age, suggesting that hils1 is a member of a class of translationally regulated genes. By analyzing transgenic mice, we could demonstrate that 318-base pair (bp) 5'-proximal region corresponding to the first 70-bp proximal TATA-less promoter, and 248 bp of 5'-untranslated region is sufficient to confer testis- and spermatid-specific transcription as well as posttranscriptional control of the mouse hils1 gene in vivo.

Testis-specific expression of rat mitochondrial glycerol-3-phosphate dehydrogenase in haploid male germ cells

Mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) is regulated by multiple promoters in a tissue-specific manner. We characterized the testis-specific promoter C of the mGPDH gene and investigated the cellular localization of mGPDH within the testis. Electrophoretic mobility shift experiments identified a cAMP-response element (CRE) site at -57 that was active in the testis. An in vitro-translated CRE modulator (CREM) protein was able to bind this CRE site, and an anti-CREM antibody interfered with this complex. Ectopic expression of the testis-specific transcriptional activator CREMtau and protein kinase A in human hepatocarcinoma HepG2 cells activated a promoter C-driven luciferase construct in transient transfection experiments. Furthermore, mGPDH expression was undetectable in testis of CREM-deficient mice. The cellular localization of mGPDH expression and translation in adult rat testis was determined by in situ hybridization and immunohistochemistry techniques. The mGPDH transcripts were detected solely in postmeiotic germ cells. Expression of mGPDH was restricted from round spermatids to early elongating spermatids. The mGPDH protein was delayed in postmeiotic germ cells, restricted from late elongating spermatids to mature spermatids. Our results indicate that rat mGPDH is expressed by a testis-specific promoter from haploid male germ cells in a stage-specific manner.

Isoforms of angiotensin I-converting enzyme in the development and differentiation of human testis and epididymis

Angiotensin I-converting enzyme (ACE; CD143, Kininase II, EC 3.4.15.1) is known to be crucial for male fertility in animal models. We therefore studied its testicular (tACE) and somatic (sACE) isoforms in foetal and adult human testis and epididymis using monoclonal antibodies and cRNA probes. During spermatogenesis, tACE was found only in differentiating germ cells and was the only isoform within the seminiferous tubules of adult men. Although tACE mRNA was present in spermatocytes, tACE protein was initially found in post-meiotic step 3 spermatids and increased markedly during further differentiation. The enzyme was strictly confined to the adluminal membrane site of elongating spermatids and was localized at the neck and midpiece region of released and ejaculated spermatozoa. In contrast, sACE was expressed heterogeneously in Leydig cells and endothelial cells of the testicular interstitium, and homogeneously along the luminal surface of epithelial cells lining the ductuli efferents, corpus and cauda of epididymis, and vas deferens. The cell- and site-restricted pattern of sACE corresponded to that found in foetal tissues except an additional and transient expression of sACE in foetal germ cells and foetal Sertoli cells. Our study documents for the first time in humans the regulation and unique cellular distribution of ACE isoforms during the ontogenesis of the lower male genital tract.

Effects of hormone replacement therapy on serum angiotensin-converting enzyme activity and plasma bradykinin in postmenopausal women according to angiotensin-converting enzyme-genotype

An insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene determines serum ACE levels. The D allele is associated with increased ACE activity and is linked to cardiovascular disease. Hormone replacement therapy (HRT) in postmenopausal women (PMW) decreases serum ACE activity and concomitantly increases plasma bradykinin. We investigated the effect of HRT on these parameters in PMW according to ACE-genotype. We assessed 68 PMW during 12-month oral HRT (0.625 mg conjugated estrogen +2.5 mg medroxyprogesterone acetate). ACE genotype was determined at baseline, and serum ACE activity and plasma bradykinin were measured at baseline and after 3-, 6-, and 12-month HRT. We divided the PMW into three groups according to ACE genotype: groups I/I (n = 26), I/D (n = 33), and D/D (n = 9). HRT resulted in a significant reduction in the genotype-associated increase in ACE activity in the ACE I/D and D/D groups after 6-month (p < 0.001 and p < 0.05, respectively) and 12-month HRT (p < 0.001 and p < 0.01, respectively), but not in the I/I group. While the reduction of ACE activity was expected to increase bradykinin in the ACE I/D and D/D groups, HRT significantly increased the bradykinin levels not only in these two groups but also in the ACE I/I group at both 6 months (p < 0.01, p < 0.05, and p < 0.001, respectively) and 12 months after the start of HRT (p < 0.01, p < 0.01, and p < 0.01, respectively). These results suggest that the increased plasma bradykinin of PMW by HRT might not be induced solely by the reduction in serum ACE activity.

Structure and promoter activity of the gene encoding ornithine decarboxylase antizyme expressed exclusively in haploid germ cells in testis (OAZt/Oaz3)

Ornithine decarboxylase antizyme 1 and 2 (OAZ1 and OAZ2) are expressed ubiquitously, and control the intracellular concentration of polyamines. Their testicular isoform, OAZt/Oaz3, is specifically expressed in differentiated haploid germ cells. We have identified and characterized the gene encoding OAZt in mice. The mouse OAZt gene contains, as does the human ortholog and paralogs, five exons and four introns. Comparison of the mouse OAZt with the human ortholog gene revealed that exon sizes are identical and nucleotide sequences in exons are highly homologous (83% identity). The major transcriptional start site was determined by primer extension assay. Promoter activity was confirmed by transgenic mouse assays, using the upstream region of the mouse OAZt gene fused to a EGFP reporter gene. The OAZt essential promoter located between -133 and +242, has two CREs and an Inr, and lacks a TATA box. These elements are conserved in the human ortholog but not in the paralogs, indicating that such a short upstream region including two CREs and Inr is sufficient to drive endogenous OAZt mRNA expression in the haploid testicular germ cells.

miwi, a murine homolog of piwi, encodes a cytoplasmic protein essential for spermatogenesis

The piwi family genes are crucial for stem cell self-renewal, RNA silencing, and translational regulation in diverse organisms. However, their function in mammals remains unexplored. Here we report the cloning of a murine piwi gene (miwi) essential for spermatogenesis. miwi encodes a cytoplasmic protein specifically expressed in spermatocytes and spermatids. miwi(null) mice display spermatogenic arrest at the beginning of the round spermatid stage, resembling the phenotype of CREM, a master regulator of spermiogenesis. Furthermore, mRNAs of ACT (activator of CREM in testis) and CREM target genes are downregulated in miwi(null) testes. Whereas MIWI and CREM do not regulate each other's expression, MIWI complexes with mRNAs of ACT and CREM target genes. Hence, MIWI may control spermiogenesis by regulating the stability of these mRNAs.

Identification and functional analysis of splice variants of the germ cell soluble adenylyl cyclase

In mammalian germ cells, cAMP signaling is dependent on two forms of adenylyl cyclase, the conventional membrane-bound ACIII and a soluble form of adenylyl cyclase (sAC). Recent elucidation of the sAC sequence indicates that this enzyme is phylogenetically distinct from the membrane-bound AC, does not interact with G proteins, and its activity is regulated by bicarbonate ions. Here we have investigated the properties and regulation of this enzyme during spermatogenesis. Two different transcripts encoding a full-length and truncated sAC were identified by reverse transcriptase-polymerase chain reaction and RNase protection analysis. The truncated sAC transcript lacks exon 11 with a premature termination of the open reading frame after the catalytic domain. Reverse transcriptase-polymerase chain reaction with testis RNA from adult mouse and rat of different ages, as well as RNase protection, showed that both transcripts are absent at 11 days of age, appear between 20 and 30 days of age, and are retained in the adult testis. The presence of corresponding proteins in testis, germ cells, and spermatozoa was demonstrated by fast protein liquid chromatography and differential immunoprecipitation with full-length sAC-specific antibodies. Bicarbonate ions activated both sAC forms and increased cAMP levels in germ cells isolated from 25- and 50-day-old rats and adult rats in a concentration-dependent manner. These findings provide evidence that full-length and truncated sAC are generated by alternate splicing. Both forms are active in spermatids, and the bicarbonate present in the seminiferous tubule may be a signal that regulates cAMP levels in these cells.

Assessment of promoter elements of the germ cell-specific proacrosin gene

The testis-specific proacrosin gene encodes for a fertilization-promoting protein. In mouse and rat it is first transcribed in late pachytene spermatocytes and revealed to be translationally regulated. Former proacrosin promoter studies demonstrated that elements necessary for conducting a stage and temporal-specific expression of the gene are located within 0.9 kb upstream of the translational start codon. In the present study we analyzed putative cis-acting elements located in this promoter region for their specific binding properties to nuclear factors assumed to be involved in proacrosin gene regulation. Supplement of specific antibodies in electrophoretic mobility shift assays (EMSA) revealed that two Y-box proteins and the transcription factors CREM and YY1 interact with proacrosin promoter elements. The Y-box proteins, antigenically related to the frog Y-box proteins FRGY1 and FRGY2, bound to the Y-box (55-66 bp upstream of the ATG initiation codon) in brain and testis nuclear extracts, respectively. CREM bound to three elements (30-37, 252-259, and 717-724 bp upstream of ATG). The ubiquitous transcription factor YY1 bound to a conserved element in the central proacrosin promoter (457-473 bp upstream of ATG) and showed almost germ cell-specific truncates in EMSA. These results suggest that the identified factors are involved in proacrosin gene regulation.

Transcriptional cascades during spermatogenesis: pivotal role of CREM and ACT

The gene CREM plays key physiological and developmental roles within the hypothalamic--pituitary--gonadal axis. We have previously shown that CREM is highly expressed in male postmeiotic cells. Spermiogenesis is a complex process by which postmeiotic male germ cells differentiate into mature spermatozoa. CREM regulates the expression of a number of post-meiotic genes involved in the process of spermiogenesis. Using homologous recombination we have generated CREM-mutant mice that display a complete block at the first step of spermiogenesis. The molecular mechanism by which CREM elicits its regulatory function involves ACT (Activator of CREM in Testis), a testis-specific coactivator constituted by a repeat of four and half LIM domains. ACT is coordinately expressed with CREM, associates with it and confers a powerful transcriptional activation function. It is able to bypass the classical requirement of CREM phosphorylation and recruiting of CBP.

cAMP response element modulator (CREM): an essential factor for spermatogenesis in primates?

CREM is a cAMP-related transcription factor and alternate promotor usage and splicing generate repressor and activator transcripts of CREM within the testis. CREM activators are highly expressed in post-meiotic haploid germ cells and are essential for spermatid maturation in the mouse model as revealed by gene-targeting studies. Analysis of testicular CREM expression in rodent and monkey species, and in men yielded a highly comparable pattern thus suggesting that CREM is of general importance for spermatid development in the mammalian testis. Also, many CREM target genes have been identified in haploid germ cells. Studies in men with spermatogenic disturbance and spermatid maturation arrest demonstrated abnormal CREM expression and altered splicing events. Collectively, the data strongly argue for an essential role of CREM during spermatid maturation in primates.

Elevated levels of the polyadenylation factor CstF 64 enhance formation of the 1kB Testis brain RNA-binding protein (TB-RBP) mRNA in male germ cells

The single copy mouse Testis Brain RNA-Binding Protein (TB-RBP) gene encodes three mRNAs of 3.0, 1.7, and 1.0 kb which only differ in their 3' UTRs. The 1 kb TB-RBP mRNA predominates in testis, while somatic cells preferentially express the 3.0 kb TB-RBP mRNA. Here we show that the 1 kb mRNA is translated several-fold more efficiently than the 3 kb TB-RBP in rabbit reticulocyte lysates and cells with elevated levels of the 1 kB TB-RBP mRNA express high levels of TB-RBP. To determine if the cleavage stimulatory factor CstF 64 can modulate the alternative splicing of the TB-RBP pre-mRNA and therefore TB-RBP expression, CstF 64 levels and binding to alternative polyadenylation sites were examined. CstF 64 is abundant in the testis and preferentially binds to a distal site in the TB-RBP pre-mRNA that produces the 3 kb TB-RBP. Moreover, upregulation or overexpression of CstF 64 increases the poly(A) site selection for the 1 kb TB-RBP mRNA. We propose that the level of the polyadenylation factor CstF 64 modulates the level of TB-RBP synthesis in male germ cells by an alternative processing of the TB-RBP pre-mRNA.

Testis hormone-sensitive lipase expression in spermatids is governed by a short promoter in transgenic mice

A testicular form of hormone-sensitive lipase (HSL(tes)), a triacylglycerol lipase, and cholesterol esterase, is expressed in male germ cells. Northern blot analysis showed HSL(tes) mRNA expression in early spermatids. Immunolocalization of the protein in human and rodent seminiferous tubules indicated that the highest level of expression occurred in elongated spermatids. We have previously shown that 0.5 kilobase pairs of the human HSL(tes) promoter directs testis-specific expression of a chloramphenicol acetyltransferase reporter gene in transgenic mice and determined regions binding nuclear proteins expressed in testis but not in liver (Blaise, R., Grober, J., Rouet, P., Tavernier, G., Daegelen, D., and Langin, D. (1999) J. Biol. Chem. 274, 9327-9334). Mutation of a SRY/Sox-binding site in one of the regions did not impair in vivo testis-specific expression of the reporter gene. Further transgenic analyses established that 95 base pairs upstream of the transcription start site were sufficient for correct testis expression. In gel retardation assays using early spermatid nuclear extracts, a germ cell-specific DNA-protein interaction was mapped between -46 and -29 base pairs. The DNA binding nuclear protein showed properties of zinc finger transcription factors. Mutation of the region abolished reporter gene activity in transgenic mice, showing that it is necessary for testis expression of HSL(tes).

The CREM system in human spermatogenesis

Spermatogenesis is a multi-step process, regulated by endocrine, paracrine and autocrine signals, through which immature germ cells differentiate into spermatozoa. The cAMP-dependent transcription factor CREM directs in the testis the expression of genes related to the structuring of mature spermatozoa. CREM gene expression originates different isoforms, which in turn can be divided into activators or repressors of gene expression. Whereas only CREM repressors are expressed in pre-meiotic germ cells in mice, a switch to the expression of the CREM activator tau occurs in post-meiotic germ cells. In addition, mice lacking CREM gene are infertile and present an arrest of germ cell maturation at the stage of round spermatid. We have demonstrated that CREM gene is expressed also in human germ cells and that a switch from the expression of repressors to activators is present in normospermic men. In particular, CREM tau mRNA is located in the cytoplasm of round spermatids. Conversely, in patients showing a testicular pattern of round spermatid maturation arrest only CREM repressors are expressed. Other reports have confirmed our data, supporting the hypothesis that CREM plays a role also in human spermatogenesis and that the absence of "the CREM switch" can be associated to spermatogenic arrest.

Structure and expression of the mouse gene encoding the endozepine-like peptide from haploid male germ cells

The endozepine-like peptide (ELP) represents a testis-specific isoform of the ubiquitous acyl-CoA binding protein (ACBP) and is highly expressed in late haploid stages of male germ cell development. The genomic sequence of the functional ELP gene as well as that of a pseudogene were analysed from independent bacteriophage clones of a 129sv mouse genomic library. Unlike the ACBP gene, which comprises four exons, the ELP gene has only a single intron within the region of the 5' untranslated region, suggesting that, like some other haploid expressed genes, the ELP gene might have evolved by retroposon-mediated gene duplication. Primer extension analysis was used to define the start site for transcription and hence the 5' promoter region. Electrophoretic mobility shift analysis was carried out on this region comparing nuclear extracts from adult mouse testis with those from mouse liver. Several testis-specific DNA-protein complexes were observed throughout 700 bp upstream of the transcription start site. One of these could be identified as corresponding to a steroidogenic factor-1 (SF-1) binding element. Further analysis using pure transcription factors showed that this element at position -340 was able to bind specifically to both SF-1 and to the germ cell nuclear factor (GCNF). Immunohistochemical analysis using an ELP-specific antibody showed that expression was very restricted within the testis to the postmeiotic germ cells, and in the ovary to interstitial/luteal cells, cell-types known to express GCNF and SF-1, respectively. Testes of CREM-tau knockout mice, lacking all spermatogenic stages later than round spermatids, were devoid of ELP immunoreactivity, whereas in RAD6 knockout mice the few remaining elongated spermatids were clearly defined by this excellent late haploid marker product. The ELP gene and its product thus offer an ideal system with which to investigate the differentiation of late haploid stages of spermatogenesis.

Molecular and cellular mechanisms in spermatogenesis

Mammalian spermatogenesis shows a strict control of many specific molecular and cellular events. This control involves Sertoli cell-germ cell interaction, as well as a programmed performance of changes in chromatin structure and gene expression in the developing germ cells. In recent years, much knowledge about the functions of defined genes in spermatogenesis has been gained by making use of mouse transgenic and gene knockout models. Several of these models are discussed in this brief overview, with an emphasis on genes encoding proteins involved in the control of gene transcription, mRNA translation, DNA repair and protein ubiquitination. A better understanding of the molecular and cellular biology of spermatogenesis in the mouse may provide concepts that can improve our understanding of human male infertility and may also lead to the identification of novel targets for contraceptive intervention.

Pituitary adenylate cyclase-activating polypeptide gene expression regulated by a testis-specific promoter in germ cells during spermatogenesis

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the glucagon-related family of hormones that is widely expressed in various tissues. The PACAP messenger RNA (mRNA) and protein is expressed at high levels in the germ cells of the testis, where it locally activates cAMP-coupled receptors located in the somatic Sertoli cells. The PACAP mRNA expressed specifically in the testis is shorter than the mRNA expressed in hypothalamus and includes 127 nucleotides of novel sequence at the 5'-end, suggesting a different start site of transcription in the testes and the utilization of a tissue-specific promoter. Here we present evidence that a single PACAP gene uses a testis-specific promoter to express a mRNA containing a unique exon located 13.5 kb upstream from the first coding exon. As determined by RT-PCR analysis of testis mRNA, the expression of the first testis-specific exon is relatively specific for the testis, as no PACAP mRNA containing the testis-specific first exon was detected in hypothalamic mRNAs. The promoter for the testis-specific PACAP gene was cloned, and a start site for transcription was mapped by primer extension. The testis-specific promoter sequence directs germ cell-specific expression upon transfection of promoter-transcriptional reporter plasmids to populations of testicular cells in vitro and upon expression of a promoter-reporter transgene in mice. Analyses of PACAP gene expression during the spermatogenic cycle, accomplished by RT-PCR of segments of isolated seminiferous tubules, identified intense expression in the postmeiotic round spermatids during developmental stages I-VIII. These observations establish the existence of a specialized PACAP gene promoter whose activity is highly regulated during the spermatogenic cycle.

A 1.3-kb upstream 5' region of the rat phosphoglycerate mutase m gene confers testis and skeletal muscle-specific expression in transgenic mice

Spermatogenesis is a complex process that occurs in successive mitotic, meiotic and post-meiotic phases and involves a highly regulated selective gene-expression pattern. However, this process has not been well characterised at the gene expression level due to the absence of germinal cell lines. We previously demonstrated that the rat skeletal muscle-specific gene for the glycolytic enzyme phosphoglycerate mutase is also specifically expressed in meiotic and haploid male germ cells from testis (12). To analyse the promoter elements that regulate the transcription of the phosphoglycerate mutase m gene (pgam-m)during spermatogenesis, we developed transgenic mice for a construct containing 1.3 kb from the pgam-m promoter linked to the Escherichia coli LacZ gene. RNA analysis by retrotranscription and PCR amplification of transgene expression showed transcriptional activity in the testis with a pattern during testis development that was identical to the endogenous gene. The transgene was also active in skeletal muscle but not in the adult heart in all the transgenic lines analysed. Collectively, these studies demonstrate that the 1.3 kb pgam-m promoter contains sufficient sequences to specify temporally regulated testis-specific expression as well as skeletal-muscle expression.

A novel 14-base-pair regulatory element is essential for in vivo expression of murine beta4-galactosyltransferase-I in late pachytene spermatocytes and round spermatids

During murine spermatogenesis, beginning in late pachytene spermatocytes, the beta4-galactosyltransferase-I (beta4GalT-I) gene is transcribed from a male germ cell-specific start site. We had shown previously that a 796-bp genomic fragment that flanks the germ cell start site and contains two putative CRE (cyclic AMP-responsive element)-like motifs directs correct male germ cell expression of the beta-galactosidase reporter gene in late pachytene spermatocytes and round spermatids of transgenic mice (N. L. Shaper, A. Harduin-Lepers, and J. H. Shaper, J. Biol. Chem. 269:25165-25171, 1994). We now report that in vivo expression of beta4GalT-I in developing male germ cells requires an essential and previously undescribed 14-bp regulatory element (5'-GCCGGTTTCCTAGA-3') that is distinct from the two CRE-like sequences. This cis element is located 16 bp upstream of the germ cell-specific start site and binds a male germ cell protein that we have termed TASS-1 (transcriptional activator in late pachytene spermatocytes and round spermatids 1). The presence of the Ets signature binding motif 5'-GGAA-3' on the bottom strand of the TASS-1 sequence (underlined sequence) suggests that TASS-1 is a novel member of the Ets family of transcription factors. Additional transgenic analyses established that an 87-bp genomic fragment containing the TASS-1 regulatory element was sufficient for correct germ cell-specific expression of the beta-galactosidase reporter gene. Furthermore, when the TASS-1 motif was mutated by transversion, within the context of the original 796-bp fragment, transgene expression was reduced 12- to 35-fold in vivo.

Testis expression of hormone-sensitive lipase is conferred by a specific promoter that contains four regions binding testicular nuclear proteins

The testicular isoform of hormone-sensitive lipase (HSLtes) is encoded by a testis-specific exon and 9 exons common to the testis and adipocyte isoforms. In mouse, HSLtes mRNA appeared during spermiogenesis in round spermatids. Two constructs containing 1.4 and 0.5 kilobase pairs (kb) of the human HSLtes gene 5'-flanking region cloned upstream of the chloramphenicol acetyltransferase gene were microinjected into mouse oocytes. Analyses of enzyme activity in male and female transgenic mice showed that 0.5 kb of the HSLtes promoter was sufficient to direct expression only in testis. Cell transfection experiments showed that CREMtau, a testis-specific transcriptional activator, does not transactivate the HSLtes promoter. Using gel retardation assays, four testis-specific binding regions (TSBR) were identified using testis and liver nuclear extracts. The testis-specific protein binding on TSBR4 was selectively competed by a probe containing a SRY/Sox protein DNA recognition site. Sox5 and Sox6 which are expressed in post-meiotic germ cells bound TSBR4. Mutation of the AACAAAG motif in TSBR4 abolished the binding. Moreover, binding of the high mobility group domain of Sox5 induced a bend within TSBR4. Together, our results showed that 0.5 kb of the human HSLtes promoter bind Sox proteins and contain cis-acting elements essential for the testis specificity of HSL.

CBP-independent activation of CREM and CREB by the LIM-only protein ACT

Transcriptional activation by CREB and CREM requires phosphorylation of a serine residue within the activation domain (Ser 133 in CREB; Ser 117 in CREM) which as a result interacts with the coactivator CBP. The activator CREM is highly expressed in male germ cells and is required for post-meiotic gene expression. Using a two-hybrid screen, we have isolated a testis-derived complementary DNA encoding a protein that we term ACT (for activator of CREM in testis), a LIM-only protein which specifically associates with CREM. ACT is expressed coordinately with CREM in a tissue- and developmentally regulated manner. It strongly stimulates CREM transcriptional activity in yeast and mammalian cells and contains an intrinsic activation function. As ACT bypasses the classical requirements for activation, namely phosphorylation of Ser 117 and interaction with CBP, it represents a new route for transcriptional activation by CREM and CREB. ACT may define a previously undiscovered class of tissue-specific coactivators whose function could be specific for distinct cellular differentiation programmes.

Estrogen regulation of angiotensin-converting enzyme mRNA

Estrogen replacement therapy is cardioprotective in postmenopausal women; however, the precise molecular mechanisms for this modulation are not fully elucidated. We previously showed that chronic estrogen replacement therapy reduced angiotensin-converting enzyme (ACE) activity in tissue extracts and serum with an associated reduction in plasma angiotensin II. A reverse transcriptase-polymerase chain reaction assay was developed to determine whether estrogen treatment regulates tissue ACE mRNA concentration. Total RNA was isolated from kidney cortex, kidney medulla, lung, and aorta of ovariectomized Sprague-Dawley rats after 21 days of chronic 17beta-estradiol replacement therapy (5 mg pellet per rat SC) or placebo. A marked decrease in densitometric intensity ratios of amplified ACE cDNA to elongation factor-1alpha control cDNA was observed in all tissues from placebo-treated rats compared with the estradiol-treated rats (renal cortex: 0.29+/-0.04 versus 0.14+/-0.02; renal medulla: 0. 37+/-0.04 versus 0.24+/-0.03; lung: 4.49+/-0.37 versus 2.49+/-0.59; and aorta: 0.41+/-0.04 versus 0.29+/-0.02; all P<0.05). A comparable reduction in ACE activity was detected in tissue extracts from kidney cortex, kidney medulla, and lung of hormone-treated animals. Incubation of purified rat lung ACE with 1 or 10 micromol/L 17beta-estradiol had no effect on enzyme activity. These results suggest that estrogen treatment regulates tissue ACE activity by reducing ACE mRNA concentrations. Thus, the beneficial cardiovascular effects of estrogen may be mediated in part by downregulation of ACE with a consequent reduction in the circulating levels of the vasoconstrictor angiotensin II, a decrease in the metabolism of the vasodilator bradykinin, and an increase in the production of the vasorelaxant angiotensin-(1-7).