Transcription Factors, cAMP-responsive Element Modulator (CREM) and Tisp40, Act in Concert in Postmeiotic Transcriptional Regulation

CAG repeat expansion in the Huntington's disease gene shapes linear and circular RNAs biogenesis

Alternative splicing (AS) appears to be altered in Huntington's disease (HD), but its significance for early, pre-symptomatic disease stages has not been inspected. Here, taking advantage of Htt CAG knock-in mouse in vitro and in vivo models, we demonstrate a correlation between Htt CAG repeat length and increased aberrant linear AS, specifically affecting neural progenitors and, in vivo, the striatum prior to overt behavioral phenotypes stages. Remarkably, a significant proportion (36%) of the aberrantly spliced isoforms are not-functional and meant to non-sense mediated decay (NMD). The expanded Htt CAG repeats further reflect on a previously neglected, global impairment of back-splicing, leading to decreased circular RNAs production in neural progenitors. Integrative transcriptomic analyses unveil a network of transcriptionally altered micro-RNAs and RNA-binding proteins (Celf, hnRNPs, Ptbp, Srsf, Upf1, Ythd2) which might influence the AS machinery, primarily in neural cells. We suggest that this unbalanced expression of linear and circular RNAs might alter neural fitness, contributing to HD pathogenesis.

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

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

Tisp40 prevents cardiac ischemia/reperfusion injury through the hexosamine biosynthetic pathway in male mice

The hexosamine biosynthetic pathway (HBP) produces uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) to facilitate O-linked GlcNAc (O-GlcNAc) protein modifications, and subsequently enhance cell survival under lethal stresses. Transcript induced in spermiogenesis 40 (Tisp40) is an endoplasmic reticulum membrane-resident transcription factor and plays critical roles in cell homeostasis. Here, we show that Tisp40 expression, cleavage and nuclear accumulation are increased by cardiac ischemia/reperfusion (I/R) injury. Global Tisp40 deficiency exacerbates, whereas cardiomyocyte-restricted Tisp40 overexpression ameliorates I/R-induced oxidative stress, apoptosis and acute cardiac injury, and modulates cardiac remodeling and dysfunction following long-term observations in male mice. In addition, overexpression of nuclear Tisp40 is sufficient to attenuate cardiac I/R injury in vivo and in vitro. Mechanistic studies indicate that Tisp40 directly binds to a conserved unfolded protein response element (UPRE) of the glutamine-fructose-6-phosphate transaminase 1 (GFPT1) promoter, and subsequently potentiates HBP flux and O-GlcNAc protein modifications. Moreover, we find that I/R-induced upregulation, cleavage and nuclear accumulation of Tisp40 in the heart are mediated by endoplasmic reticulum stress. Our findings identify Tisp40 as a cardiomyocyte-enriched UPR-associated transcription factor, and targeting Tisp40 may develop effective approaches to mitigate cardiac I/R injury.

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.

The concentration of testosterone, pituitary adenylate cyclase-activating polypeptide, and protamine 1 in the serum of male chicken following administration of epididymis and testicular extracts and their combination

Bakcground and Aim

Testis and epididymis are male reproductive organs that play an important role in spermatogenesis. These two organs are rich in the content of hormones and other molecules needed in the process of spermatogenesis which affect the quality of the spermatozoa. The objective of this study was to examine the effect of the administration of epididymis and testicular extracts and their combination on testosterone, pituitary adenylate cyclase-activating polypeptide (PACAP), and protamine 1 (PRM1) concentrations in the serum of male chicken.

Materials and Methods

Twenty male chickens (broiler strain Cp707), aged 3 weeks and weighing 800-1000 g, were randomly divided into four different groups including a control group (T0) = injected with 1 ml normal saline and treatment groups: T1 = injected with 1 ml epididymis extract, T2 = injected with 1 ml testicular extract, and T3 = injected with a combination of 1 ml epididymis + 1 ml testicular extract. The experiment was conducted for 13 days and at the end of the study (day 14), the chickens were sacrificed to obtain the serum. Furthermore, the concentrations of testosterone, PACAP, and PRM1 were then measured by using an enzyme-linked immunosorbent assay technique.

Results

The concentrations of PACAP and PRM1 did not show a significant difference between treatment groups (T1, T2, and T3) and control group (T0) (p>0.05). However, the concentration of testosterone showed a significantly higher difference in a group injected with a combination of 1 ml epididymis and 1 ml testicular extracts (T3) compared to the control group (T0) (p<0.05).

Conclusion

The administration of epididymis and testicular extracts and their combination did not affect the increase of PACAP and PRM1 concentration. However, a combination of these extracts significantly affects the increase of testosterone concentration in the serum of male chicken.

Testis Transcriptome Modulation in Klinefelter Patients with Hypospermatogenesis

The main genetic cause of male infertility is represented by the Klinefelter Syndrome (KS), a condition accounting for 3% of all cases of infertility and up to15% of cases of azoospermia. KS is generally characterized by azoospermia; approximately 10% of cases have severe oligozoospermia. Among these, the 30-40% of patients show hypospermatogenesis. The mechanisms leading to adult testis dysfunctions are not completely understood. A microarray transcriptome analysis was performed on testis biopsies obtained from three KS patients with hypospermatogenesis and three control subjects. KS testis showed a differential up- and down-regulation of 303 and 747 transcripts, respectively, as compared to controls. The majority of down-regulated transcripts were involved in spermiogenesis failure and testis morphological defects, whereas up-regulated genes were responsible for testis apoptotic processes. Functional analysis of the transcriptionally altered genes indicated a deregulation in cell death, germ cell function and morphology as well as blood-testis-barrier maintenance and Leydig cells activity. These data support a complex scenario in which spermatogenic impairment is the result of functional and morphological alterations in both germinal and somatic components of KS testis. These findings could represent the basis for evaluating new markers of KS spermatogenesis and potential targets of therapeutic intervention to preserve residual spermatogenesis.

The expression of cyclic adenosine monophosphate responsive element modulator in rat sertoli cells following seminal extract administration

Aim:

This study aims to determine the effect of seminal vesicle extract on cyclic adenosine monophosphate responsive element modulator (CREM) expression in rat Sertoli cells.

Materials and Methods:

This study examined the expression of CREM on 20 male rats (Rattus norvegicus) at 4 months of age, weighing 250-300 g. The rats were divided into four groups: K0, KP1, KP2, and KP3. K0 group was injected with 0.2 ml normal saline; KP1 was injected with 25 mg cloprostenol (Prostavet C, Virbac S. A); KP2 and KP3 were injected with 0.2 and 0.4 ml seminal vesicle extract, respectively. The treatments were conducted 5 times within 12-day interval. At the end of the study, the rats were euthanized by cervical dislocation; then, the testicles were necropsied and processed for histology observation using immunohistochemistry staining.

Results:

CREM expression in rat Sertoli cells was not altered by the administration of either 0.2 or 0.4 ml seminal vesicle extract.

Conclusion:

The administration of seminal vesicle extract is unable to increase CREM expression in rat Sertoli cells.

The essential biology of the endoplasmic reticulum stress response for structural and computational biologists

The endoplasmic reticulum (ER) stress response is a cytoprotective mechanism that maintains homeostasis of the ER by upregulating the capacity of the ER in accordance with cellular demands. If the ER stress response cannot function correctly, because of reasons such as aging, genetic mutation or environmental stress, unfolded proteins accumulate in the ER and cause ER stress-induced apoptosis, resulting in the onset of folding diseases, including Alzheimer's disease and diabetes mellitus. Although the mechanism of the ER stress response has been analyzed extensively by biochemists, cell biologists and molecular biologists, many aspects remain to be elucidated. For example, it is unclear how sensor molecules detect ER stress, or how cells choose the two opposite cell fates (survival or apoptosis) during the ER stress response. To resolve these critical issues, structural and computational approaches will be indispensable, although the mechanism of the ER stress response is complicated and difficult to understand holistically at a glance. Here, we provide a concise introduction to the mammalian ER stress response for structural and computational biologists.

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.

Transcriptional regulation of human novel gene SPATA12 promoter by AP-1 and HSF

Human SPATA12 is a spermatogenesis associated gene and is supposed to function as an inhibitor during male germ cell development. SPATA12 is specifically expressed in spermatocytes, spermatids, and spermatozoa of human testis. In order to understand the regulation mechanism of SPATA12 gene expression, we identified and characterized the SPATA12 gene core promoter region and transcription factor binding sites by using reporter gene assays. AP-1 is founded to be a potential transcriptional activator of SPATA12. The promoter activity of SPATA12 was drastically declined after AP-1 binding site mutation or deletion. We also demonstrated that AP-1 combined with Smad3/4 contributes to the transcriptional regulation of SPATA12 in response to TGF-β1. The expression of SPATA12 could be induced by TGF-β1 in a dose-dependent manner, suggesting that AP-1 as an activator plays a role in the regulation of SPATA12 promoter. We have also shown that heat shock treatment could activate the expression of SPATA12 and transcription factor HSF binding sites in the SPATA12 promoter might be responsible for this heat-induction. These results suggested that AP-1 and HSF may play an important role in regulating SPATA12 promoter activity.

ELOVL2 controls the level of n-6 28:5 and 30:5 fatty acids in testis, a prerequisite for male fertility and sperm maturation in mice

ELOVL2 is a member of the mammalian microsomal ELOVL fatty acid enzyme family, involved in the elongation of very long-chain fatty acids including PUFAs required for various cellular functions in mammals. Here, we used ELOVL2-ablated (Elovl2(-/-)) mice to show that the PUFAs with 24-30 carbon atoms of the ω-6 family in testis are indispensable for normal sperm formation and fertility in male mice. The lack of Elovl2 was associated with a complete arrest of spermatogenesis, with seminiferous tubules displaying only spermatogonia and primary spermatocytes without further germinal cells. Furthermore, based on acyl-CoA profiling, heterozygous Elovl2(+/-) male mice exhibited haploinsufficiency, with reduced levels of C28:5 and C30:5n-6 PUFAs, which gave rise to impaired formation and function of haploid spermatides. These new insights reveal a novel mechanism involving ELOVL2-derived PUFAs in mammals and previously unrecognized roles for C28 and C30 n-6 PUFAs in male fertility. In accordance with the function suggested for ELOVL2, the Elovl2(-/-) mice show distorted levels of serum C20 and C22 PUFAs from both the n-3 and the n-6 series. However, dietary supplementation with C22:6n-3 could not restore male fertility to Elovl2(+/-) mice, suggesting that the changes in n-6 fatty acid composition seen in the testis of the Elovl2(+/-) mice, cannot be compensated by increased C22:6n-3 content.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Comparative genomics reveals gene-specific and shared regulatory sequences in the spermatid-expressed mammalian Odf1, Prm1, Prm2, Tnp1, and Tnp2 genes

The comparative genomics of the Odf1, Prm1, Prm2, Tnp1, and Tnp2 genes in 13-21 diverse mammalian species reveals striking similarities and differences in the sequences that probably function in the transcriptional and translational regulation of gene expression in haploid spermatogenic cells, spermatids. The 5' flanking regions contain putative TATA boxes and cAMP-response elements (CREs), but the TATA boxes and CREs exhibit gene-specific sequences, and an overwhelming majority of CREs differ from the consensus sequence. The 5' and 3' UTRs contain highly conserved gene-specific sequences including canonical and noncanonical poly(A) signals and a suboptimal context for the Tnp2 translation initiation codon. The conservation of the 5' UTR is unexpected because mRNA translation in spermatids is thought to be regulated primarily by the 3' UTR. Finally, all of the genes contain a single intron, implying that retroposons are rarely created from mRNAs that are expressed in spermatids.

NSSR1 is regulated in testes development and cryptorchidism and promotes the exon 5-included splicing of CREB transcripts

Neural salient serine/arginine rich protein 1 (NSSR1, alternatively SRp38) is a newly identified splicing factor that is highly expressed in neural and reproductive tissues. We showed that the expression of testicular NSSR1 increased significantly during mouse testes development. NSSR1 was mainly expressed in germ cells, but barely detected in Sertoli cells. Testicular NSSR1 was mostly phosphorylated and cytosolic in germ cells. In comparison, pituitary NSSR1 was mostly dephosphorylated and nuclear. In the cryptorchid testes, the dephosphorylated NSSR1 was significantly increased. RT-PCR analysis demonstrated that the alternative splicing of CREB and CREM genes was altered in the cryptorchid testes. In addition, CREB transcripts were associated with NSSR1 either in testes tissues or cultured GC-1 cells. Moreover, the studies with NSSR1 over-expression or silence demonstrated that NSSR1 promoted the exon 5 inclusion of CREB, indicating that NSSR1 is a new factor that regulates the alternative exon 5 inclusion of CREB transcripts. The findings for the first time provide the evidence indicating the potential importance of NSSR1 in testes development, spermatogenesis and cryptorchidism.

Transmembrane bZIP transcription factors in ER stress signaling and the unfolded protein response

Regulated intramembrane proteolysis (RIP) of the transmembrane transcription factor ATF6 represents a key step in effecting adaptive response to the presence of unfolded or malfolded protein in the endoplasmic reticulum. Recent studies have highlighted new ATF6-related transmembrane transcription factors. It is likely that current models for ER stress signaling are incomplete and that the expansion of the bZIP transmembrane family reflects selectivity in many aspects of these responses, including the type and duration of any particular stress, the cell type in which it occurs, and the integration with other aspects of cell-type-specific organization or additional intrinsic pathways, and the integration and communication between these pathways, not only in a cell-type-specific manner, but also between different tissues and organs. This review summarizes current information on the bZIP-transmembrane proteins and discusses outstanding questions on the elucidation of the stress signals, the repertoire of components involved in regulating different aspects of the forward transport, cleavage, nuclear import, transcriptional activity, and turnover of each of these factors, and dissection of the integration of the various outputs into broad coordinated responses.

The essential role of Drosophila HIRA for de novo assembly of paternal chromatin at fertilization

In many animal species, the sperm DNA is packaged with male germ line–specific chromosomal proteins, including protamines. At fertilization, these non-histone proteins are removed from the decondensing sperm nucleus and replaced with maternally provided histones to form the DNA replication competent male pronucleus. By studying a point mutant allele of the Drosophila Hira gene, we previously showed that HIRA, a conserved replication-independent chromatin assembly factor, was essential for the assembly of paternal chromatin at fertilization. HIRA permits the specific assembly of nucleosomes containing the histone H3.3 variant on the decondensing male pronucleus. We report here the analysis of a new mutant allele of Drosophila Hira that was generated by homologous recombination. Surprisingly, phenotypic analysis of this loss of function allele revealed that the only essential function of HIRA is the assembly of paternal chromatin during male pronucleus formation. This HIRA-dependent assembly of H3.3 nucleosomes on paternal DNA does not require the histone chaperone ASF1. Moreover, analysis of this mutant established that protamines are correctly removed at fertilization in the absence of HIRA, thus demonstrating that protamine removal and histone deposition are two functionally distinct processes. Finally, we showed that H3.3 deposition is apparently not affected in Hira mutant embryos and adults, suggesting that different chromatin assembly machineries could deposit this histone variant.

Chromatin is composed of basic units called nucleosomes, in which DNA wraps around a core of histone proteins. HIRA is a histone chaperone that is specifically involved in the assembly of nucleosomes containing H3.3, a universally conserved type of histone 3. To understand the function of HIRA in vivo, the authors generated mutant fruit flies with a non-functional Hira gene. Surprisingly, mutant flies were viable, but females were completely sterile. By analysing the female fruit flies' eggs, the authors found that in the absence of HIRA protein, the sperm nucleus was unable to participate in the formation of the zygote. In Drosophila, as in many animals, the condensed sperm chromatin contains protamines instead of histones. The authors found that the only crucial role of HIRA in flies was to assemble nucleosomes containing H3.3 in the male pronucleus, after the removal of protamines. This fundamental process, which is presumably also controlled by HIRA in vertebrates, allows the paternal DNA to reconstitute its chromatin and participate in the development of the embryo.

Oleamide derivatives suppress the spontaneous metastasis by inhibiting connexin 26

We previously reported that overexpressing connexin 26 (Cx26) enhances the spontaneous metastasis of mouse BL6 melanoma cells. In contrast, daily intraperitoneal injections of an oleamide derivative named MI-18 potently inhibits the spontaneous metastasis of BL6 cells. In the present study, we chemically synthesized a novel oleamide derivative named MI-22 and found that it also efficiently suppressed the spontaneous metastasis of BL6 cells. Both MI-18 and MI-22 inhibited the gap junction-mediated intercellular communications (GJIC) that are formed between HeLa cells by the ectopic expression of the hCx26 and hCx32 human connexin subtypes; however, they had no effect on GJIC mediated by hCx40, hCx43 or hCx45. Fluorescently labeled MI-18 primarily localized not only at plasma membrane but also at Golgi/endosome. This suggests that this oleamide derivative may also act on the Cx26 molecules that accumulate in the Golgi/endosome because of their overexpression. Notably, neither derivative had a cytotoxic effect on HeLa cells when they were added into the tissue culture medium. Taken together, we propose that the MI-18 and MI-22 oleamide derivatives may serve as prototypes for novel and clinically important anticancer drugs.

Molecular biological features of male germ cell differentiation

Somatic cell differentiation is required throughout the life of a multicellular organism to maintain homeostasis. In contrast, germ cells have only one specific function; to preserve the species by conveying the parental genes to the next generation. Recent studies of the development and molecular biology of the male germ cell have identified many genes, or isoforms, that are specifically expressed in the male germ cell. In the present review, we consider the unique features of male germ cell differentiation. (Reprod Med Biol 2007; 6: 1-9).

Altered protamine expression and diminished spermatogenesis: what is the link?

During the elongating spermatid stage of spermiogenesis, human sperm chromatin undergoes a complex transition in which histones are extensively replaced by protamines in a carefully regulated transition including histone modifications and intermediate and temporary replacement of the histones by sperm-specific transition proteins. The replacement of most histones by protamines 1 and 2 facilitates a high order of chromatin packaging necessary for normal sperm function and may also be necessary for DNA silencing and imprinting changes within the sperm cell. Protamines 1 and 2 are usually expressed in nearly equal quantities, but elevated or diminished protamine 1/protamine 2 ratios are observed in some infertile men and is often associated with severe spermatogenesis defects. Human and animal studies demonstrate that expression of the protamine proteins is uniquely regulated by transcription/translation factors, including storage of the mRNA in ribonucleoprotein (RNP) particles composed of the mRNA, transcription factors and a kinesin molecule necessary for transport of the RNP to the cytoplasm and removal of transcriptional activators from the nucleus. Recent studies indicate that most patients with abnormal protamine protein levels have elevated levels of protamine transcript in the mature sperm cell, indicating a possible defect in transcription or translation. The regulation of protamine expression is unique and includes several possible mechanisms which may be responsible for dysregulation of protamine expression and concurrent broad spectrum defects in spermatogenesis. We suggest two hypotheses: (i) that abnormal protamine expression is indicative of a generalized defect in mRNA storage and/or translation which affects other mRNA transcripts or (ii) that protamines may act as a checkpoint of spermatogenesis.

The testes-specific bZip type transcription factor Tisp40 plays a role in ER stress responses and chromatin packaging during spermiogenesis

We previously reported that the spermatid-specific transcription factor Tisp40 functions through UPRE and CRE. To investigate Tisp40 function in vivo, we generated TISP40(-/-) mice. TISP40(-/-) mice were born at expected ratios, were healthy, and mutant males bred normally. However, the ER stress-response protein Grp78/BiP accumulated in the TISP40(-/-) testis and RAMP4 (Ribosome-associated membrane protein 4) mRNA level was up-regulated. Disruption of TISP40 caused ER stress and activation of caspase 12 but not caspase 9, leading to apoptosis of meiotic/postmeiotic germ cells. On the other hand, DAPI staining and electron microscopy revealed that epididymal sperm nuclei were abnormally relaxed in the TISP40(-/-) testis, a phenotype that was independent of the expression and maturation of transition proteins and protamines but due to abnormally retained histones. Histones localized to the cytoplasm as well as to the nucleus and were also retained in epididymal sperm. Histones H2A and H4 were dramatically up-regulated and the acetylation of H2A, H2B and H4 was also enhanced in the TISP40(-/-) testis. Taken together, we conclude that Tisp40 plays an important role in the unfolded protein response of the testis and in regulating the maturation of sperm head nuclei.

Isolation and characterization of the TIGA genes, whose transcripts are induced by growth arrest

We report here the isolation of 44 genes that are upregulated after serum starvation and/or contact inhibition. These genes have been termed TIGA, after Transcript Induced by Growth Arrest. We found that there are two kinds of G0 phases caused by serum starvation, namely, the shallow G0 (or G0/G1) and the deep G0 phases. The shallow G0 is induced by only a few hours of serum starvation, while deep G0 is generated after 3 days of serum starvation. We propose that mammalian cells enter deep G0 through a G0 gate, which is only opened on the third day of serum starvation. TIGA1, one of the uncharacterized TIGA genes, encodes a homolog of cyanate permease of bacteria and localizes in mitochondria. This suggests that Tiga1 is involved in the inorganic ion transport and metabolism needed to maintain the deep G0 phase. Ectopic expression of TIGA1 inhibited not only tumor cell proliferation but also anchorage-independent growth of cancer cell lines. A microsatellite marker, ENDL-1, allowed us to detect loss of heterozygosity around the TIGA1 gene region (5q21-22). Further analysis of the TIGA genes we have identified here may help us to better understand the mechanisms that regulate the G0 phase.