Sperm-specific expression of angiotensin-converting enzyme (ACE) is mediated by a 91-base-pair promoter containing a CRE-like element

Regulation of Male Fertility by the Renin-Angiotensin System

The renin-angiotensin system (RAS) is a peptidic system known mainly for its roles in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, several tissues and cells have been described to possess an intrinsic RAS that acts locally through different paracrine and autocrine mechanisms. In the male reproductive system, several components of this system have been observed in various organs and tissues, such as the testes, spermatozoa and seminal fluid. Some functions attributed to this local RAS are maintenance of seminal plasma electrolytes, regulation of steroidogenesis and spermatogenesis, and sperm functions. However, their specific actions in these locations are not fully understood. Therefore, a deep knowledge of the functions of the RAS at both the testicular and seminal levels could clarify its roles in male infertility and sperm physiology, and the different RAS elements could be used to design tools enabling the diagnosis and/or treatment of male infertility.

A 50-bp enhancer of the mouse acrosomal vesicle protein 1 gene activates round spermatid-specific transcription in vivo†

Enhancers are cis-elements that activate transcription and play critical roles in tissue- and cell type-specific gene expression. During spermatogenesis, genes coding for specialized sperm structures are expressed in a developmental stage- and cell type-specific manner, but the enhancers responsible for their expression have not been identified. Using the mouse acrosomal vesicle protein (Acrv1) gene that codes for the acrosomal protein SP-10 as a model, our previous studies have shown that Acrv1 proximal promoter activates transcription in spermatids; and the goal of the present study was to separate the enhancer responsible. Transgenic mice showed that three copies of the -186/-135 fragment (50 bp enhancer) placed upstream of the Acrv1 core promoter (-91/+28) activated reporter expression in testis but not somatic tissues (n = 4). Immunohistochemistry showed that enhancer activity was restricted to the round spermatids. The Acrv1 enhancer failed to activate transcription in the context of a heterologous core promoter (n = 4), indicating a likely requirement for enhancer-core promoter compatibility. Chromatin accessibility assays showed that the Acrv1 enhancer assumes a nucleosome-free state in male germ cells (but not liver), indicating occupancy by transcription factors. Southwestern assays (SWA) identified specific binding of the enhancer to a testis nuclear protein of 47 kDa (TNP47). TNP47 was predominantly nuclear and becomes abundant during the haploid phase of spermatogenesis. Two-dimensional SWA revealed the isoelectric point of TNP47 to be 5.2. Taken together, this study delineated a 50-bp enhancer of the Acrv1 gene for round spermatid-specific transcription and identified a putative cognate factor. The 50-bp enhancer could become useful for delivery of proteins into spermatids.

Two isoforms of the RAC-specific guanine nucleotide exchange factor TIAM2 act oppositely on transmission ratio distortion by the mouse t-haplotype

Transmission ratio distortion (TRD) by the mouse t-haplotype, a variant region on chromosome 17, is a well-studied model of non-Mendelian inheritance. It is characterized by the high transmission ratio (up to 99%) of the t-haplotype from t/+ males to their offspring. TRD is achieved by the exquisite ability of the responder (Tcr) to trigger non-Mendelian inheritance of homologous chromosomes. Several distorters (Tcd1-Tcd4), which act cumulatively, together promote the high transmission ratio of Tcr and the t-haplotype. Molecularly, TRD is brought about by deregulation of Rho signaling pathways via the distorter products, which impair sperm motility, and the t-sperm specific rescue of sperm motility by the responder. The t-sperm thus can reach the egg cells faster than +-sperm and fertilize them. Previously we have shown that the responder function is accomplished by a dominant negative form of sperm motility kinase (SMOKTCR), while the distorter functions are accomplished by the Rho G protein regulators TAGAP, FGD2 and NME3 proposed to function in two oppositely acting pathways. Here we identify the RAC1-specific guanine nucleotide exchange factor TIAM2 as modifier of t-haplotype TRD. Tiam2 is expressed in two isoforms, the full-length (Tiam2l) and a short transcript (Tiam2s). Tiam2s expression from the t-allele is strongly increased compared to the wild-type allele. By transgenic approaches we show that Tiam2s enhances t-haplotype transmission, while Tiam2l has the opposite effect. Our data show that a single modifier locus can encode different gene products exerting opposite effects on a trait. They also suggest that the expression ratio of the isoforms determines if the outcome is an enhancing or a suppressive effect on the trait.

SOX30 is required for male fertility in mice

Male infertility is a major and growing problem and, in most cases, the specific root cause is unknown. Here we show that the transcription factor SOX30 plays a critical role in mouse spermatogenesis. Sox30-null mice are healthy and females are fertile, but males are sterile. In the absence of Sox30 meiosis initiates normally in both sexes but, in males, germ cell development arrests during the post-meiotic round spermatid period. In the mutant testis, acrosome and axoneme development are aberrant, multinucleated germ cells (symplasts) form and round spermatids unable to process beyond step 3 of spermiogenesis. No elongated spermatids nor spermatozoa are produced. Thus, Sox30 represents a rare example of a gene for which loss of function results in a complete arrest of spermatogenesis at the onset of spermiogenesis. Our results suggest that SOX30 mutations may underlie some instances of unexplained non-obstructive azoospermia in humans.

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.

Classical Renin-Angiotensin system in kidney physiology

The renin-angiotensin system has powerful effects in control of the blood pressure and sodium homeostasis. These actions are coordinated through integrated actions in the kidney, cardiovascular system and the central nervous system. Along with its impact on blood pressure, the renin-angiotensin system also influences a range of processes from inflammation and immune responses to longevity. Here, we review the actions of the "classical" renin-angiotensin system, whereby the substrate protein angiotensinogen is processed in a two-step reaction by renin and angiotensin converting enzyme, resulting in the sequential generation of angiotensin I and angiotensin II, the major biologically active renin-angiotensin system peptide, which exerts its actions via type 1 and type 2 angiotensin receptors. In recent years, several new enzymes, peptides, and receptors related to the renin-angiotensin system have been identified, manifesting a complexity that was previously unappreciated. While the functions of these alternative pathways will be reviewed elsewhere in this journal, our focus here is on the physiological role of components of the "classical" renin-angiotensin system, with an emphasis on new developments and modern concepts.

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.

The nucleoside diphosphate kinase gene Nme3 acts as quantitative trait locus promoting non-Mendelian inheritance

The t-haplotype, a variant form of the t-complex region on mouse chromosome 17, acts as selfish genetic element and is transmitted at high frequencies (> 95%) from heterozygous (t/+) males to their offspring. This phenotype is termed transmission ratio distortion (TRD) and is caused by the interaction of the t-complex responder (Tcr) with several quantitative trait loci (QTL), the t-complex distorters (Tcd1 to Tcd4), all located within the t-haplotype region. Current data suggest that the distorters collectively impair motility of all sperm derived from t/+ males; t-sperm is rescued by the responder, whereas (+)-sperm remains partially dysfunctional. Recently we have identified two distorters as regulators of RHO small G proteins. Here we show that the nucleoside diphosphate kinase gene Nme3 acts as a QTL on TRD. Reduction of the Nme3 dosage by gene targeting of the wild-type allele enhanced the transmission rate of the t-haplotype and phenocopied distorter function. Genetic and biochemical analysis showed that the t-allele of Nme3 harbors a mutation (P89S) that compromises enzymatic activity of the protein and genetically acts as a hypomorph. Transgenic overexpression of the Nme3 t-allele reduced t-haplotype transmission, proving it to be a distorter. We propose that the NME3 protein interacts with RHO signaling cascades to impair sperm motility through hyperactivation of SMOK, the wild-type form of the responder. This deleterious effect of the distorters is counter-balanced by the responder, SMOK(Tcr), a dominant-negative protein kinase exclusively expressed in t-sperm, thus permitting selfish behaviour and preferential transmission of the t-haplotype. In addition, the previously reported association of NME family members with RHO signaling in somatic cell motility and metastasis, in conjunction with our data involving RHO signaling in sperm motility, suggests a functional conservation between mechanisms for motility control in somatic cells and spermatozoa.

A-MYB (MYBL1) stimulates murine testis-specific Ldhc expression via the cAMP-responsive element (CRE) site

Generally, knowledge of the mechanism regulating gene expression in primary spermatocytes is incomplete. We have used the lactate dehydrogenase gene (Ldhc) as a model to explore these mechanisms during spermatogenesis. Its 100-bp core promoter contained two essential elements common to many genes, a GC box and a CRE site. Here we report results that support a model in which transcription factor MYBL1 acts as a coactivator directing tissue-specific expression via the CRE cis element. We hypothesize that this is a common mechanism involving activation of multiple genes in the primary spermatocyte. MYBL1 is expressed predominantly as a tissue-specific transcription factor in spermatocytes and breast epithelial cells. Our finding that LDHC expression is lost in 21-day testes of MYBL1 mutant mice supports our hypothesis. In the GC1-spg germ cell line exogenous MYBL1 induces activity 4- to 8-fold, although extracts from these cells do not show MYBL1 binding activity for the Myb consensus sequences in the Ldhc promoter by EMSA. Rather, MYBL1 stimulates expression from a synthetic promoter containing only CRE elements, suggesting MYBL1 activates the promoter by interacting with protein that binds to a CRE element. Mutation of three Myb sites does not affect Ldhc promoter activity significantly (P > 0.05). CREB-binding protein (CBP) is a coactivator that interacts with CRE-binding protein CREB. We show that the transactivation domain (TAD) in MYBL1 interacts with the KIX domain in CBP, and the TAD domain and DNA binding domain in MYBL1 each interact with the CREB N-terminal domain. MYBL1 also stimulated expression from testis-specific genes Pgk2 (phosphoglycerate kinase 2) and Pdha2 (pyruvate dehydrogenase alpha 2) promoters, each of which contains CRE promoter elements and is expressed in primary spermatocytes. We propose that MYBL1 directs germ cell-specific activation via the CRE site of certain genes that are activated specifically in the primary spermatocyte, although other, more indirect effects of MYBL1 remain a possible explanation for our results.

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.

Tissue-specific regulation of ACE/ACE2 and AT1/AT2 receptor gene expression by oestrogen in apolipoprotein E/oestrogen receptor-alpha knock-out mice

Angiotensin-converting enzyme (ACE) and ACE2 and the AT1 and AT2 receptors are pivotal points of regulation in the renin-angiotensin system. ACE and ACE2 are key enzymes in the formation and degradation of angiotensin II (Ang II) and angiotensin-(1-7)(Ang-(1-7)). Ang II acts at either the AT1 or the AT2 receptor to mediate opposing actions of vasoconstriction or vasodilatation respectively. While it is known that oestrogen acts to downregulate ACE and the AT(1) receptor, its regulation of ACE2 and the AT2 receptor and the involvement of a specific oestrogen receptor subtype are unknown. To investigate the role of oestrogen receptor-alpha (ERalpha) in the regulation by oestrogen of ACE/ACE2 and AT1/AT2 mRNAs in lung and kidney, ovariectomized female mice lacking apolipoprotein E (ee) with the ERalpha (AAee) or without the ERalpha (alphaalphaee) were treated with 17beta-oestradiol (6 microg day(-1)) or placebo for 3 months. ACE, ACE2, AT1 receptor and AT2 receptor mRNAs were measured using reverse transcriptase, real-time polymerase chain reaction. In the kidney, 17beta-oestradiol showed 1.7-fold downregulation of ACE mRNA in AAee mice, with 2.1-fold upregulation of ACE mRNA in alphaalphaee mice. 17beta-Oestradiol showed 1.5- and 1.8-fold downregulation of ACE2 and AT1 receptor mRNA in AAee mice; this regulation was lost in alphaalphaee mice. 17beta-Oestradiol showed marked (81-fold) upregulation of the AT(2) receptor mRNA in AAee mice. In the lung, 17beta-oestradiol treatment had no effect on AT1 receptor mRNA in AAee mice, but resulted in a 1.5-fold decreased regulation of AT1 mRNA in alphaalphaee mice. There was no significant interaction of oestrogen with ERalpha in the lung for ACE, ACE2 and AT2 receptor genes. These studies reveal tissue-specific regulation by 17beta-oestradiol of ACE/ACE2 and AT1/AT2 receptor genes, with the ERalpha receptor being primarily responsible for the regulation of kidney ACE2, AT1 receptor and AT2 receptor genes.

Regulation of murine lactate dehydrogenase C (Ldhc) gene expression

Expression of Ldhc begins with the onset of meiosis in male germ cells and continues throughout spermatogenesis. Transcriptional regulatory mechanisms, especially in primary spermatocytes, are poorly described because of the lack of a reliable cell culture system. We constructed mouse transgenics and transfected germ cells in situ to study expression of the testis-specific isozyme of lactate dehydrogenase (LDH). From previous work, we determined that a 100-bp Ldhc core promoter contained potential cis regulatory elements, including a palindrome (-21 to +10), GC box (-70 to -65), and cAMP-responsive element (CRE) sites (-53 to -49, -39 to -35). We provide here the demonstration of a functional role for these sequences by expression of mutated transgenes in vivo. Our results reveal for the first time that mutation of the GC box does not abolish promoter activity, which remains testis-specific. Mutation of GC box or CRE sites resulted in a 73% and 74% reduction in promoter activity, respectively, in a transient transfection of germ cells in vivo by electroporation; the combination of GC box and CRE site mutations eliminates promoter activity. Therefore, we conclude that simultaneous occupancy of the GC box and CRE sites in the core promoter is necessary for full expression of Ldhc in the testis.

cAMP-responsive element in TATA-less core promoter is essential for haploid-specific gene expression in mouse testis

Promoters, including neither TATA box nor initiator, have been frequently found in testicular germ cell-specific genes in mice. These investigations imply that unique forms of the polymerase II transcription initiation machinery play a role in selective activation of germ cell-specific gene expression programs during spermatogenesis. However, there is little information about testis-specific core promoters, because useful germ cell culture system is not available. In this study, we characterize the regulatory region of the haploid-specific Oxct2b gene in detail by using in vivo transient transfection assay in combination with a transgenic approach, with electrophoretic mobility shift and chromatin immunoprecipitation assays. Expression studies using mutant constructs demonstrate that a 34 bp region, which extends from -49 to -16, acts as a core promoter in an orientation-dependent manner. This promoter region includes the cAMP-responsive element (CRE)-like sequence TGACGCAG, but contains no other motifs, such as a TATA box or initiator. The CRE-like element is indispensable for the core promoter activity, but not for activator in testicular germ cells, through the binding of a testis-specific CRE modulator transcription factor. These results indicate the presence of alternative transcriptional initiation machinery for cell-type-specific gene expression in testicular germ cells.

Bimodal regulation of mPeriod promoters by CREB-dependent signaling and CLOCK/BMAL1 activity

Circadian rhythmicity in mammals is under the control of a molecular pacemaker constituted of clock gene products organized in transcriptional autoregulatory loops. Phase resetting of the clock in response to light involves dynamic changes in the expression of several clock genes. The molecular pathways used by light to influence pacemaker-driven oscillation of clock genes remain poorly understood. We explored the functional integration of both light- and clock-responsive transcriptional regulation at the promoter level of the Period (Per) genes. Three Per genes exist in the mouse. Whereas mPer1 and mPer2 are light-inducible in clock neurons of the hypothalamic suprachiasmatic nucleus, mPer3 is not. We have studied the promoter structure of the three mPer genes and compared their regulation. All three mPer promoters contain E-boxes and respond to the CLOCK/brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein 1 (BMAL1) heterodimer. On the other hand, only mPer1 and mPer2 promoters contain bona fide cAMP-responsive elements (CREs) that bind CRE-binding protein (CREB) from suprachiasmatic nucleus protein extracts. The mPer1 promoter is responsive to synergistic activation of the cAMP and mitogen-activated protein kinase pathways, a physiological response that requires integrity of the CRE. In contrast, activation of mPer promoters by CLOCK/BMAL1 occurs regardless of an intact CRE. Altogether, these results constitute strong evidence that CREB acts as a pivotal endpoint of signaling pathways for the regulation of mPer genes. Our results reveal that signaling-dependent activation of mPer genes is distinct from the CLOCK/BMAL1-driven transcription required within the clock feedback loop.

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.

Selective restoration of male fertility in mice lacking angiotensin-converting enzymes by sperm-specific expression of the testicular isozyme

Although angiotensin-converting enzyme (ACE) has been studied primarily in the context of its role in blood pressure regulation, this widely distributed enzyme has many other physiological functions. The ACE gene encodes two isozymes. The somatic isozyme is expressed in many tissues, including vascular endothelial cells, renal epithelial cells, and testicular Leydig cells, whereas the testicular or germinal angiotensin-converting enzyme is expressed only in sperm. The ACE gene knockout mice lack both isozymes and they exhibit low blood pressure, kidney dysfunctions, and male infertility. Here, we report the use of a sperm-specific promoter and interbreeding of transgenic and gene knockout mice for generating a mouse strain that expressed ACE only in sperm. The experimental mice maintained the kidney defects of ACE-/- mice, but unlike the knockout strain, the males were fertile. Thus, we established that the role of ACE in male fertility is completely dependent on its exclusive expression in sperm. Our study clearly demonstrated how transgenic and knockout techniques can be combined for ascribing a specific physiological function to the expression of a multifunctional protein in a given tissue.

Angiotensin-converting enzyme and male fertility

The angiotensin-converting enzyme (ACE; EC 3.4.15.1) gene (Ace) encodes both a somatic isozyme found in blood and several other tissues, including the epididymis, and a testis-specific isozyme (testis ACE) found only in developing spermatids and mature sperm. We recently used gene targeting to disrupt the gene coding for both ACE isozymes in mice and reported that male homozygous mutants mate normally but have reduced fertility; the mutant females are fertile. Here we explore the male fertility defect. We demonstrate that ACE is important for achieving in vivo fertilization and that sperm from mice lacking both ACE isozymes show defects in transport within the oviducts and in binding to zonae pellucidae. Males generated by gene targeting that lack somatic ACE but retain testis ACE are normally fertile, establishing that somatic ACE in males is not essential for their fertility. Furthermore, male and female mice lacking angiotensinogen have normal fertility, indicating that angiotensin I is not a necessary substrate for testis ACE. Males heterozygous for the mutation inactivating both ACE isozymes sire wild-type and heterozygous offspring at an indistinguishable frequency, indicating no selection against sperm carrying the mutation.

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

Testis angiotensin-converting enzyme (ACE) is a unique form of ACE, only produced by male germ cells, and results from a testis-specific promoter found within the ACE gene. We have investigated the role of cAMP-response element modulator (CREM)tau in testis ACE transcription. In gel shift experiments, testes nuclear proteins retard an oligonucleotide containing the cAMP-response element (CRE) found at position -55 in the testis ACE promoter. Anti-CREM antibody supershifts this complex. Competitive gel shift shows that recombinant CREM tau protein and testis nuclear proteins have a similar specificity of binding to the tests ACE CRE. Functional analysis using in vitro transcription and transfection studies also demonstrate that CREM tau protein is a transcriptional activator of the testis ACE promoter. Western blot analysis identifies CREM tau protein in the protein-DNA complex formed between nuclear proteins and the testis ACE CRE motif. This analysis also identified other CREM isoforms in the gel-shifted complex, which are thought to be CREM tau 1/2, CREM alpha/beta, and S-CREM. These data indicate that CREM tau isoforms play an important role as a positive regulator in the tissue-specific expression of testis ACE.

Transcriptional regulation of the mouse alpha A-crystallin gene: activation dependent on a cyclic AMP-responsive element (DE1/CRE) and a Pax-6-binding site

Two cis-acting promoter elements (-108 to -100 and -49 to -33) of the mouse alpha A-crystallin gene, which is highly expressed in the ocular lens, were studied. Here we show that DE1 (-108 to -100; 5'TGACGGTG3'), which resembles the consensus cyclic AMP (cAMP)-responsive element sequence (CRE; 5'TGACGT[A/C][A/G]3'), behaves like a functional CRE site. Transfection experiments and electrophoretic mobility shift assays (EMSAs) using site-specific mutations correlated a loss of function with deviations from the CRE consensus sequence. Results of EMSAs in the presence of antisera against CREB, delta CREB, and CREM were consistent with the binding of CREB-like proteins to the DE1 sequence. Stimulation of alpha A-crystallin promoter activity via 8-bromo-cAMP, forskolin, or human T-cell leukemia virus type I Tax1 in transfections and reduction of activity of this site in cell-free transcription tests by competition with the somatostatin CRE supported the idea that DE1 is a functional CRE. Finally, Pax-6, a member of the paired-box family of transcription factors, activated the mouse alpha A-crystallin promoter in cotransfected COP-8 fibroblasts and bound to the -59 to -29 promoter sequence in EMSAs. These data provide evidence for a synergistic role of Pax-6 and CREB-like proteins for high expression of the mouse alpha A-crystallin gene in the lens.

Calspermin gene transcription is regulated by two cyclic AMP response elements contained in an alternative promoter in the calmodulin kinase IV gene

The transcript for the high-affinity Ca2+/calmodulin-binding protein calspermin is generated from the gene encoding Ca2+/calmodulin-dependent protein kinase IV only in postmeiotic germ cells during spermatogenesis. We demonstrate that this testis-specific calspermin transcript can be produced in heterologous cells by utilization of a promoter located in an intron of the calmodulin (CaM) kinase IV gene. Critical motifs within this promoter are two cyclic AMP response element (CRE)-like sequences located about -70 and -50 bp upstream of the transcriptional initiation site. Both CRE motifs are footprinted by the authentic testis-specific transcriptional activator CREM tau or by CREM tau present in adult testis nuclear extract. Whereas a 2.1-kb DNA fragment containing the calspermin promoter is inactive when transfected into NIH 3T3 cells, activity can be restored by cotransfection of CREM tau and protein kinase A or CaM kinase IV but not CaM kinase II alpha. Restoration of activity is greatly reduced by mutation of the two CRE motifs. Since CRE-like motifs have been identified in many genes uniquely expressed in postmeiotic germ cells, which contain abundant CREM tau protein, we suggest that CREM tau may function as one transcription factor responsible for the expression of postmeiotic germ cell-specific genes.

Molecular mechanism of transcriptional activation of angiotensinogen gene by proximal promoter

Angiotensinogen is shown to be produced by the liver and the hepatoma cell line HepG2. As a first step for understanding the molecular relationship between the transcriptional regulation of the angiotensinogen gene and the pathogenesis of hypertension, we have analyzed the basal promoter of the angiotensinogen gene. Chloramphenicol acetyltransferase (CAT) assays with 5'-deleted constructs showed that the proximal promoter region from -96 to +22 of the transcriptional start site was enough to express HepG2-specific CAT activity. Electrophoretic mobility shift assay and DNase I footprinting demonstrated that the liver- and HepG2-specific nuclear factor (angiotensinogen gene-activating factor [AGF2]) and ubiquitous nuclear factor (AGF3) bound to the proximal promoter element from -96 to -52 (angiotensinogen gene-activating element [AGE2]) and to the core promoter element from -6 to +22 (AGE3), respectively. The site-directed disruption of either AGE2 or AGE3 decreased CAT expression, and the sequential titration of AGF3 binding by in vivo competition remarkably suppressed HepG2-specific CAT activity. Finally, the heterologous thymidine kinase promoter assay showed that AGE2 and AGE3 synergistically conferred HepG2-specific CAT expression. These results suggest that the synergistic interplay between AGF2 and AGF3 is important for the angiotensinogen promoter activation.