Transcriptional regulatory regions of testis-specific PGK2 defined in transgenic mice

A native, highly active Tc1/mariner transposon from zebrafish (ZB) offers an efficient genetic manipulation tool for vertebrates

New genetic tools and strategies are currently under development to facilitate functional genomics analyses. Here, we describe an active member of the Tc1/mariner transposon superfamily, named ZB, which invaded the zebrafish genome very recently. ZB exhibits high activity in vertebrate cells, in the range of those of the widely used transposons piggyBac (PB), Sleeping Beauty (SB) and Tol2. ZB has a similar structural organization and target site sequence preference to SB, but a different integration profile with respect to genome-wide preference among mammalian functional annotation features. Namely, ZB displays a preference for integration into transcriptional regulatory regions of genes. Accordingly, we demonstrate the utility of ZB for enhancer trapping in zebrafish embryos and in the mouse germline. These results indicate that ZB may be a powerful tool for genetic manipulation in vertebrate model species.

Evaluation of seminal plasma proteomics and relevance of FSH in identification of nonobstructive azoospermia: A preliminary study

Nonobstructive azoospermia (NOA) patients present with high levels of serum FSH. At the protein level, the aetiology and pathways underlying different subtypes of NOA are unclear. The aim was to evaluate quantitatively differences in proteomic profiles of NOA patients presenting with normal serum FSH and normal testicular volume and high serum FSH and small testicular volume. The study comprised of 14 nonobstructive azoospermic men (N = 4; normal FSH and normal testicular volume and N = 10; high FSH and small testicular volume) and seven normozoospermic men. Proteomic analysis was done using LC-MS. GSTM3 and PGK2 were less abundant in the normal and high FSH group compared to controls. HSPA4L and HSPA4 were exclusively present in control group whereas HSP90AB1, HSPA1B, HSP90AA1 and HSPA2 were less abundant and exclusive to the normal and high FSH group. We have identified six heat-shock proteins that may have a role in the pathology of NOA. FSH and testicular volume by itself are not good markers of NOA. The inverse association of GSTM3 and PGK2 regulation with FSH levels along with 12 proteins exclusively in NOA groups suggests further evaluation of their predictive potential in a larger cohort of patients.

Wt1 deficiency causes undifferentiated spermatogonia accumulation and meiotic progression disruption in neonatal mice

Spermatogenesis is a complex process involving the regulation of multiple cell types. As the only somatic cell type in the seminiferous tubules, Sertoli cells are essential for spermatogenesis throughout the spermatogenic cycle. The Wilms tumor gene, Wt1, is specifically expressed in the Sertoli cells of the mouse testes. In this study, we demonstrated that Wt1 is required for germ cell differentiation in the developing mouse testes. At 10 days post partum, Wt1-deficient testes exhibited clear meiotic arrest and undifferentiated spermatogonia accumulation in the seminiferous tubules. In addition, the expression of claudin11, a marker and indispensable component of Sertoli cell integrity, was impaired in Wt1−/flox; Cre-ERTM testes. This observation was confirmed in in vitro testis cultures. However, the basal membrane of the seminiferous tubules in Wt1-deficient testes was not affected. Based on these findings, we propose that Sertoli cells' status is affected in Wt1-deficient mice, resulting in spermatogenesis failure.

Sequence-specific promoter elements regulate temporal-specific changes in chromatin required for testis-specific activation of the Pgk2 gene

The phosphoglycerate kinase-2 (Pgk2) gene is regulated in a tissue-, cell type-, and developmental stage-specific manner during spermatogenesis and is required for normal sperm motility and fertility in mammals. Activation of Pgk2 transcription is regulated by testis-specific demethylation of DNA and binding of testis-specific transcription factors to enhancer and core promoter elements. Here, we show that chromatin remodeling including reconfiguration of nucleosomes and changes in histone modifications is also associated with transcriptional activation of the Pgk2 gene during spermatogenesis. Developmental studies indicate that the order of events involved in transcriptional activation of the Pgk2 gene includes demethylation of DNA in T₁- and T₂-prospermatogonia, binding of a factor to the CAAT box in type A and B spermatogonia, followed by recruitment of chromatin remodeling factors, displacement of a nucleosome from the Pgk2 promoter region, binding of factors to the Pgk2 core promoter and enhancer regions, and, finally, initiation of transcription in primary spermatocytes. Transgene studies show that Pgk2 core promoter elements are required to direct demethylation of DNA and reconfiguration of nucleosomes, whereas both enhancer and core promoter elements are required to direct changes in histone modifications and initiation of transcription. These results provide novel insight into the developmental order of molecular events required to activate tissue-specific transcription of the Pgk2 gene, the distinct elements in the 5'-regulatory region of the Pgk2 gene that regulate each of these events, and the relationship among these events in that each step in this process appears to be a necessary prerequisite for the subsequent step.

A 5'-flanking region of gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) gene directs its cell-specific androgen-regulated gene expression in testicular germ cells

Gonadotropin-regulated testicular RNA helicase (GRTH/Ddx25) is a posttranscriptional regulator of genes that are essential for spermatid elongation and completion of spermatogenesis. It also prevents Leydig cells (LCs) from gonadotropin overstimulation of androgen production. In transgenic (Tg) mice carrying deletions of the GRTH 5'-flanking regions, we previously demonstrated that the -1085 bp to ATG contains the elements for basal and androgen-induced LC-specific expression. No expression in germ cells (GCs) was found with sequences extended up to -3.6 kb. To define regulatory regions of GRTH required for expression in GC, Tg mice were generated with 5'-flanking sequence 6.4 kb (6.4 Kb-Tg) and/or deletion using green fluorescent protein (GFP) as reporter gene in the present study. GFP was expressed in all lines. Immunohistochemistry analysis showed that 6.4 Kb-Tg directed GFP expression in both GCs and LCs. Deletion of the sequence -205 bp to -3.6 kb (6.4 Kb/del-Tg) directs GFP expression only in meiotic and haploid GCs. This indicated that the distal region -6.4 kb/-3.6 kb is required for GRTH cell-specific expression in GC. Also, it inhibits the expression of GRTH in LC directed by the 205-bp promoter, an effect that is neutralized by the -3.6-kb/-205-bp sequence. Androgen receptor antagonist, flutamide treatment prevents GFP/GRTH expression in Tg lines, demonstrating in vivo direct and indirect effects of endogenous androgen on LCs and GCs, respectively. Our studies have generated and characterized Tg lines that can be used to define requirements for cell-specific expression of the GRTH gene and to further advance our knowledge on the regulation of GRTH by androgen in GCs.

Nuclear factor-κB (NF-κB) regulates the expression of human testis-enriched Leucine-rich repeats and WD repeat domain containing 1 (LRWD1) gene

The human Leucine-rich Repeats and WD repeat Domain containing 1 (LRWD1) gene was originally identified by cDNA microarray as one of the genes down-regulated in the testicular tissues of patients with severe spermatogenic defects. Human LRWD1 is a testicular-enriched protein that is present predominantly in the cytoplasm of spermatocytes and spermatids and colocalizes with the centrosome at the base of sperm tail. Reporter assay, Chromatin immunoprecipitation (ChIP) analysis, and gel electrophoretic mobility shift assay (EMSA) were used to identify the core promoter region of LRWD1. A 198 bp segment upstream of the LRWD1 transcription initiation site exhibited promoter activity. The LRWD1 core promoter lacked a TATA box but contained a NF-κB binding site. Chromatin immunoprecipitation (ChIP) analysis and gel electrophoretic mobility shift assay (EMSA) showed basal binding of the NF-κB subunit to the LRWD1 promoter. LRWD1 promoter activity was positively regulated by NF-κB, and this regulation was dependent on the presence of the conserved κB site in the LRWD1 promoter region. Our data suggest that NF-κB is an important regulator for the expression of LRWD1. This is the first study showing that the expression of the testis-enriched LRWD1 gene is regulated by NF-κB.

Overexpression of human SPATA17 protein induces germ cell apoptosis in transgenic male mice

SPATA17 is a new testis-specific-expressed gene that is involved in Spermatogenesis process. Previous studies show that SPATA17 was involved in acceleration of cell apoptosis in GC-1 cell lines. To further investigate specific roles of SPATA17 in Spermatogenesis in vivo, we generated transgenic mice in which the human SPATA17 gene was expressed specifically in spermatocytes using the human phosphoglycerate kinase 2 (PGK2) promoter. The SPATA17 transgenic mice did not show any significant defect in gross testicular anatomy as well as in fertility. However, a significant increase was observed in defective spermatogenic cells, such as apoptotic cells in the SPATA17 transgenic mice. These results revealed that elevated production of the SPATA17 protein disturbed the normal development of male germ cells.

Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2) regulates axon integrity in the mouse embryo

Using transposon-mediated gene-trap mutagenesis, we have generated a novel mouse mutant termed Blad (Bloated Bladder). Homozygous mutant mice die perinatally showing a greatly distended bladder, underdeveloped diaphragm and a reduction in total skeletal muscle mass. Wild type and heterozygote mice appear normal. Using PCR, we identified a transposon insertion site in the first intron of Nmnat2 (Nicotinamide mononucleotide adenyltransferase 2). Nmnat2 is expressed predominantly in the brain and nervous system and has been linked to the survival of axons. Expression of this gene is undetectable in Nmnat2^blad/blad mutants. Examination of the brains of E18.5 Nmnat2^blad/blad mutant embryos did not reveal any obvious morphological changes. In contrast, E18.5 Nmnat2^blad/blad homozygotes showed an approximate 60% reduction of spinal motoneurons in the lumbar region and a more than 80% reduction in the sensory neurons of the dorsal root ganglion (DRG). In addition, facial motoneuron numbers were severely reduced, and there was virtually a complete absence of axons in the hind limb. Our observations suggest that during embryogenesis, Nmnat2 plays an important role in axonal growth or maintenance. It appears that in the absence of Nmnat2, major target organs and tissues (e.g., muscle) are not functionally innervated resulting in perinatal lethality. In addition, neither Nmnat1 nor 3 can compensate for the loss of Nmnat2. Whilst there have been recent suggestions that Nmnat2 may be an endogenous modulator of axon integrity, this work represents the first in vivo study demonstrating that Nmnat2 is involved in axon development or survival in a mammal.

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.

Overexpression of peroxisomal testis-specific 1 protein induces germ cell apoptosis and leads to infertility in male mice

Peroxisomal testis-specific 1 gene (Pxt1) is the only male germ cell-specific gene that encodes a peroxisomal protein known to date. To elucidate the role of Pxt1 in spermatogenesis, we generated transgenic mice expressing a c-MYC-PXT1 fusion protein under the control of the PGK2 promoter. Overexpression of Pxt1 resulted in induction of male germ cells' apoptosis mainly in primary spermatocytes, finally leading to male infertility. This prompted us to analyze the proapoptotic character of mouse PXT1, which harbors a BH3-like domain in the N-terminal part. In different cell lines, the overexpression of PXT1 also resulted in a dramatic increase of apoptosis, whereas the deletion of the BH3-like domain significantly reduced cell death events, thereby confirming that the domain is functional and essential for the proapoptotic activity of PXT1. Moreover, we demonstrated that PXT1 interacts with apoptosis regulator BAT3, which, if overexpressed, can protect cells from the PXT1-induced apoptosis. The PXT1-BAT3 association leads to PXT1 relocation from the cytoplasm to the nucleus. In summary, we demonstrated that PXT1 induces apoptosis via the BH3-like domain and that this process is inhibited by BAT3.

Zmynd15 encodes a histone deacetylase-dependent transcriptional repressor essential for spermiogenesis and male fertility

Spermatogenesis is a complex process through which male germ line stem cells undergo a multi-step differentiation program and sequentially become spermatogonia, spermatocytes, spermatids, and eventually spermatozoa. In this process, transcription factors act as switches that precisely regulate the expression of genes that in turn control the developmental program of male germ cells. Transcription factors identified to be essential for normal haploid gene expression all display transcription-activating effects and thus serve as the "on" switch for haploid gene expression. Here, we report that ZMYND15 acts as a histone deacetylase-dependent transcriptional repressor and controls normal temporal expression of haploid cell genes during spermiogenesis. Inactivation of Zmynd15 results in early activation of transcription of numerous important haploid genes including Prm1, Tnp1, Spem1, and Catpser3; depletion of late spermatids; and male infertility. ZMYND15 represents the first transcriptional repressor identified to be essential for sperm production and male fertility.

Turnover and lineage-specific broadening of the transcription start site in a testis-specific retrogene

Proteasomes are large multisubunit complexes responsible for regulated protein degradation. Made of a core particle (20S) and regulatory caps (19S), proteasomal proteins are encoded by at least 33 genes, of which 12 have been shown to have testis-specific isoforms in Drosophila melanogaster. Pros28.1A (also known as Prosalpha4T1), a young retroduplicate copy of Pros28.1 (also known as Prosalpha4), is one of these isoforms. It is present in the D. melanogaster subgroup and was previously shown to be testis-specific in D. melanogaster. Here, we show its testis-specific transcription in all D. melanogaster subgroup species. Due to this conserved pattern of expression in the species harboring this insertion, we initially expected that a regulatory region common to these species evolved prior to the speciation event. We determined that the region driving testis expression in D. melanogaster is not far from the coding region (within 272 bp upstream of the ATG). However, different Transcription Start Sites (TSSs) are used in D. melanogaster and D. simulans, and a "broad" transcription start site is used in D. yakuba. These results suggest one of the following scenarios: (1) there is a conserved motif in the 5' region of the gene that can be used as an upstream or downstream element or at different distance depending on the species; (2) different species evolved diverse regulatory sequences for the same pattern of expression (i.e., "TSS turnover"); or (3) the transcription start site can be broad or narrow depending on the species. This work reveals the difficulties of studying gene regulation in one species and extrapolating those findings to close relatives.

Characterization of a Dazl-GFP germ cell-specific reporter

In this study, we characterized the promoter activity of a 1.7 kb sequence in the 5' flanking region of the mouse Deleted in Azoospermia-Like (Dazl) gene. We found the 1.7 kb sequence sufficient to drive robust germ cell-specific expression of green fluorescent protein (GFP) in adult mouse testis and lower levels of expression in adult ovary and in fetal and newborn gonads of both sexes. This expression pattern was confirmed in two independently-derived transgenic mouse lines. In adult testis, Dazl-GFP exhibited a developmentally-regulated, stage-specific expression pattern during spermatogenesis. GFP was highly expressed in spermatocyte stages, with strongest expression in pachytene spermatocytes. Weaker expression was observed in round and elongating spermatids, as well as spermatogonial cells. In the fetal gonad, GFP transcript was detected by e12.5 in both sexes; however, GFP fluorescence was only detected during later embryonic stages. In addition, we produced mouse embryonic stem cell (ESC) lines harboring the Dazl-GFP reporter and used this reporter to isolate putative germ cell populations derived from mouse ESCs following embryoid body differentiation and fluorescence activated cell sorting.

Molecular and functional characterization of the murine ldh2 promoter region: Sp-binding GC-box domains are the key cis-elements regulating ldh2 gene expression during spermatogenesis

The goal of the present study was to elucidate the specific transcriptional mechanisms that regulate ldh2 gene expression during the early stages of spermatogenesis. DNA sequence analysis of the 1.0-kb ldh2 promoter region directly upstream of the transcriptional start site indicated the presence of three SP-protein binding GC-box elements and the absence of TATA and CAAT boxes. Functional characterization studies of the mouse ldh2 promoter were performed in the SV40 transformed mouse spermatogonial cell line, GC-1 spg. Transfection/transient expression studies using full-length and truncated ldh2 promoter/luciferase reporter constructs revealed that all three of the SP-binding cis-regulatory GC-box elements are required for optimal ldh2 promoter activity. Additional site-directed mutagenesis studies indicated that the two most proximal GC-box sites play essential regulatory roles in mediating basal ldh2 promoter activity. These studies suggest that the expression of the ldh2 gene in spermatogonia and early spermatocytes are regulated by SP-mediated transcriptional mechanisms.

A cytoplasmic variant of the KH-type splicing regulatory protein serves as a decay-promoting factor for phosphoglycerate kinase 2 mRNA in murine male germ cells

Phosphoglycerate kinase 2 (PGK2) is a germ cell-specific protein whose mRNA is translationally regulated in the mammalian testis. Using RNA affinity chromatography with the 3'-untranslated region (UTR) of Pgk2 mRNA and adult testis extracts, several associated proteins including a novel isoform of the AU-rich element RNA-binding protein and KH-type splicing regulatory protein (KSRP) were identified. KSRP, a protein of approximately 75 kDa, is widely expressed in somatic and germ cells where it is primarily nuclear. In addition to the approximately 75-kDa KSRP, a approximately 52-kD KSRP, t-KSRP, is present in the cytoplasm of a subpopulation of germ cells. t-KSRP binds directly to a 93-nt sequence (designated the F1 region) of the 3'-UTR of the Pgk2 mRNA and destabilizes Pgk2 mRNA constructs in testis extracts and in transfected cells. We conclude that this testicular variant of the multifunctional nucleic acid-binding protein, KSRP, serves as a decay-promoting factor for Pgk2 mRNA in male germ cells.

A conserved E2F6-binding element in murine meiosis-specific gene promoters

During gametogenesis, germ cells must undergo meiosis in order to become viable haploid gametes. Successful completion of this process is dependent upon the expression of genes whose protein products function specifically in meiosis. Failure to express these genes in meiotic cells often results in infertility, whereas aberrant expression in somatic cells may lead to mitotic catastrophe. The mechanisms responsible for regulating the timely expression of meiosis-specific genes have not been fully elucidated. Here we demonstrate that E2F6, a member of the E2F family of transcription factors, is essential for the repression of the newly identified meiosis-specific gene, Slc25a31 (also known as Ant4, Aac4), in somatic cells. This discovery, along with previous studies, prompted us to investigate the role of E2F6 in the regulation of meiosis-specific genes in general. Interestingly, the core E2F6-binding element (TCCCGC) was highly conserved in the proximal promoter regions of 19 out of 24 (79.2%) meiosis-specific genes. This was significantly higher than the frequency found in the promoters of all mouse genes (15.4%). In the absence of E2F6, only a portion of these meiosis-specific genes was derepressed in somatic cells. However, endogenous E2F6 bound to the promoters of these meiosis-specific genes regardless of whether they required E2F6 for their repression in somatic cells. Further, E2F6 overexpression was capable of reducing their transcription. These findings indicate that E2F6 possesses a broad ability to bind to and regulate the meiosis-specific gene population.

Analysis of meiotic prophase I in live mouse spermatocytes

Events occurring during meiotic prophase I are critical for the successful production of haploid gametes. Many prophase I events are mediated by a meiosis-specific structure called the synaptonemal complex. To date, the limited knowledge we have about the dynamics of these prophase I events in mice comes from fixed, two-dimensional preparations of meiotic cells making it impossible to study the three-dimensional (3D) arrangement of meiotic chromosomes. The current study involves the development of an imaging system to view prophase I events in live mammalian spermatocytes by generating a transgenic mouse, Sycp3-Eyfp ( 21HC ), expressing a fluorescently tagged synaptonemal complex protein, SYCP3. Using this live imaging system, the 3D structural arrangement of chromosomes in the different prophase I substages has been characterized in live spermatocytes, and aspects of the 3D architecture of spermatocytes have been observed that would not be possible with existing techniques. Additionally, chromosome movement in prophase I spermatocytes and meiotic progression from pachynema to diplonema were observed following treatment with the phosphatase inhibitor, okadaic acid (OA), which accelerates the progression of cells through late prophase I. These studies demonstrate that the Sycp3-Eyfp ( 21HC ) live imaging system is a useful tool for the study of mammalian prophase I dynamics.

MSY2 and polypyrimidine tract binding protein 2 stabilize mRNAs in the mammalian testis

MSY2 is a highly conserved and abundant DNA/RNA-binding protein that functions as a global stabilizer/translational suppressor of mRNAs in male germ cells. The polypyrimidine tract binding protein, PTBP2, is an RNA-binding protein that splices nuclear transcripts and stabilizes specific mRNAs in the cytoplasm. The mechanisms whereby MSY2 selects and stabilizes a large group of male germ cell mRNAs and PTBP2 stabilizes specific mRNAs such as the phosphoglycerate kinase 2 mRNA in the testis and in transfected cells will be discussed.

The putative peroxisomal gene Pxt1 is exclusively expressed in the testis

Genes reported to be crucial for spermatogenesis are often exclusively expressed in the testis. We have identified a novel male germ cell-specific expressed gene named peroxisomal testis specific 1 (Pxt1) with expression starting at the spermatocyte stage during mouse spermatogenesis. The putative amino acid sequence encoded by the cDNA of the Pxt1 gene contains a conserved Asn-His-Leu (NHL)-motif at its C-terminal end, which is characteristic for peroxisomal proteins. Pxt1-EGFP fusion protein is co-localized with known peroxisomal marker proteins in transfected NIH3T3 cells. In addition, we could demonstrate that the peroxisomal targeting signal NHL is functional and responsible for the correct subcellular localization of the Pxt1-EGFP fusion protein. In male germ cells peroxisomes were reported only in spermatogonia. The Pxt1 gene is so far the first gene coding for a putative peroxisomal protein which is expressed in later steps of spermatogenesis, namely in pachytene spermatocytes.

In vivo analysis of developmentally and evolutionarily dynamic protein-DNA interactions regulating transcription of the Pgk2 gene during mammalian spermatogenesis

Transcription of the testis-specific Pgk2 gene is selectively activated in primary spermatocytes to provide a source of phosphoglycerate kinase that is critical to normal motility and fertility of mammalian spermatozoa. We examined dynamic changes in protein-DNA interactions at the Pgk2 gene promoter during murine spermatogenesis in vivo by performing genomic footprinting and chromatin immunoprecipitation assays with enriched populations of murine spermatogenic cells at stages prior to, during, and following transcription of this gene. We found that genes encoding the testis-specific homeodomain factor PBX4 and its coactivator, PREP1, are expressed in patterns that mirror expression of the Pgk2 gene and that these factors become bound to the Pgk2 enhancer in cells in which this gene is actively expressed. We therefore suggest that these factors, along with CREM and SP3, direct stage- and cell type-specific transcription of the Pgk2 gene during spermatogenesis. We propose that binding of PBX4, plus its coactivator PREP1, is a rate-limiting step leading to the initiation of tissue-specific transcription of the Pgk2 gene. This study provides insight into the developmentally dynamic establishment of tissue-specific protein-DNA interactions in vivo. It also allows us to speculate about the events that led to tissue-specific regulation of the Pgk2 gene during mammalian evolution.

Generation of rat mutants using a coat color-tagged Sleeping Beauty transposon system

A significant barrier to exploiting the full potential of the rat as a biomedical model is the lack of tools to easily modify its germline. Here we show that a tyrosinase-tagged Sleeping Beauty transposon can be used as a simple, efficient method to generate rat mutants in vivo. By making two lines of transgenic rats, one carrying the transposon and another expressing the transposase in germ cells, we are able to obtain bigenic males in which transposition occurs in the germ cells. We show that transposition leads to the appearance of new coat colors in the offspring. Using such bigenic males, we obtained an average of 1.2 transpositions per gamete and identified 19 intragenic integration events among 96 transposition sites that were sequenced. In addition, gene trapping was confirmed and rats with evidence for transposon-induced dominant ocular anomalies were identified. These data suggest that the modified Sleeping Beauty transposon represents a powerful new tool for producing molecularly defined mutagenesis in the rat.

Polypyrimidine tract binding protein 2 stabilizes phosphoglycerate kinase 2 mRNA in murine male germ cells by binding to its 3'UTR

The mRNA that encodes the testis-specific protein phosphoglycerate kinase (PGK2) is a long-lived mRNA that is transcribed in meiotic and postmeiotic male germ cells. Pgk2 mRNA is present in germ cells for up to 2 wk before its protein product is detected. Using affinity chromatography with the 3'-UTR of the Pgk2 mRNA, several proteins, including the RNA-binding protein, polypyrimidine tract binding protein 2 (PTBP2), were identified in mouse testis extracts. Coimmunoprecipitation experiments confirmed that PTBP2 binds to Pgk2 mRNA in the testis and RNA gel shifts demonstrated that PTBP2, but not PTBP1, binds to a specific region of the Pgk2 3'-UTR. Recombinant PTBP2 increased the stability of reporter constructs that contained the 3'-UTR Pgk2 sequence element in both testis extracts and transfected HeLa cells. We propose that PTBP2 is a trans-acting factor that helps to stabilize Pgk2 mRNA in male mouse germ cells.

Epigenetic regulation of testis-specific gene expression

Cellular differentiation is mediated by differential gene expression. The cells of the testis are no exception. Indeed, recent studies based on microarray and expressed sequence tag analyses have revealed dynamic changes in gene expression during spermatogenesis. The autosomal phosphoglycerate kinase gene Pgk2 is an example of a gene that is tightly regulated during spermatogenesis, with transcription initiating in primary spermatocytes and ceasing in postmeiotic spermatids. Our studies show that this tissue-specific transcription is regulated at multiple levels, including binding of ubiquitous and testis-specific transcription factors, reconfiguration of nucleosomes, decondensation of chromatin, modifications of specific residues in histones, and demethylation of DNA. Our ability to isolate relatively pure populations of different spermatogenic cell types has allowed us to determine the order of these events that lead up to initiation of transcription of the Pgk2 gene. By examining similar parameters in transgenic mice carrying various portions of Pgk2 regulatory sequence, we have localized specific signals responsible for each of these regulatory events. Together these results demonstrate that activation of testis-specific transcription of the Pgk2 gene involves a multifaceted, ordered cascade of epigenetic events that potentiates this locus in preparation for the initiation of transcription.

LINEs, SINEs and processed pseudogenes: parasitic strategies for genome modeling

Two major classes of retrotransposons have invaded eukaryotic genomes: the LTR retrotransposons closely resembling the proviral integrated form of infectious retroviruses, and the non-LTR retrotransposons including the widespread, autonomous LINE elements. Here, we review the modeling effects of the latter class of elements, which are the most active in humans, and whose enzymatic machinery is subverted to generate a large series of "secondary" retroelements. These include the processed pseudogenes, naturally present in all eukaryotic genomes possessing non-LTR retroelements, and the very successful SINE elements such as the human Alu sequences which have evolved refined parasitic strategies to efficiently bypass the original "protectionist" cis-preference of LINEs for their own retrotransposition.

RNA interference during spermatogenesis in mice

Spermatogenesis consists of complex cellular and developmental processes, such as the mitotic proliferation of spermatogonial stem cells, meiotic division of spermatocytes, and morphogenesis of haploid spermatids. In this study, we show that RNA interference (RNAi) functions throughout spermatogenesis in mice. We first carried out in vivo DNA electroporation of the testis during the first wave of spermatogenesis to enable foreign gene expression in spermatogenic cells at different stages of differentiation. Using prepubertal testes at different ages and differentiation stage-specific promoters, reporter gene expression was predominantly observed in spermatogonia, spermatocytes, and round spermatids. This method was next applied to introduce DNA vectors that express small hairpin RNAs, and the sequence-specific reduction in the reporter gene products was confirmed at each stage of spermatogenesis. RNAi against endogenous Dmc1, which encodes a DNA recombinase that is expressed and functionally required in spermatocytes, led to the same phenotypes observed in null mutant mice. Thus, RNAi is effective in male germ cells during mitosis and meiosis as well as in haploid cells. This experimental system provides a novel tool for the rapid, first-pass assessment of the physiological functions of spermatogenic genes in vivo.

Ontogeny of a Demethylation Domain and Its Relationship to Activation of Tissue-Specific Transcription1

We examined DNA methylation throughout the endogenous murine testis-specific phosphoglycerate kinase (Pgk2) gene and in human PGK2 promoter/CAT reporter transgenes in mouse spermatogenic cells before, during, and following the period of active transcription of this gene. We observed the gradual development of a domain of demethylation beginning over the promoter and then expanding approximately 1 kilobase in each direction within the endogenous Pgk2 gene. This demethylation domain develops in the absence of DNA replication and precedes other molecular changes that potentiate tissue-specific activation of this gene. Studies with transgenes show that a signal residing in the Pgk2 core promoter directs this gene-, cell type-, and stage-specific demethylation process. These results are consistent with a model in which regulated, tissue- and gene-specific demethylation initiates a cascade of subsequent molecular events required for tissue-specific activation of transcription during spermatogenesis in vivo.

Deletion of the Parkin coregulated gene causes male sterility in the quaking(viable) mouse mutant

Quaking(viable) (qk(v)) is a recessive neurological mouse mutation with severe dysmyelination of the CNS and spermiogenesis failure. The molecular lesion in the qk(v) mutant is a deletion of approximately 1 Mb on mouse chromosome 17 that alters the expression of the qk gene in oligodendrocytes. Complementation analysis between the qk(v) mutation and qk mutant alleles generated through chemical mutagenesis showed that the male sterility is a distinctive feature of the qk(v) allele. This observation suggested that the sperm differentiation defect in qk(v) is due to the deletion of a gene(s) distinct from qk. Here, we demonstrate that the deletion of Pacrg is the cause of male sterility in the qk(v) mutant. Pacrg is the mouse homologue of the human PARKIN-coregulated gene (PACRG), which encodes for a protein whose biochemical function remains unclear. We show that Pacrg is highly expressed in the testes in both mice and humans. In addition, the expression pattern of Pacrg during spermiogenesis suggests that it plays a role in sperm differentiation. In support of this hypothesis, we show that transgenic expression of Pacrg in testes restores spermiogenesis and fertility in qk(v) males. This finding provides the first in vivo evidence, to our knowledge, for the function of Pacrg in a model organism. Immunolocalization experiments on isolated spermatozoa show that the Pacrg protein is present in mature sperm. Remarkably, the mammalian Pacrg protein shares significant sequence similarities with gene products from flagellated protozoans, suggesting that Pacrg may be necessary for proper flagellar formation in many organisms.

The murine testicular transcriptome: characterizing gene expression in the testis during the progression of spermatogenesis

One of the most promising applications of microarrays is the study of changes in gene expression associated with the growth and development of mammalian tissues. The testis provides an excellent model to determine the ability of microarrays to effectively characterize the changes in gene expression as an organ develops from birth to adulthood. To this end, a developmental testis gene expression time course profiling the expression patterns of approximately 36 000 transcripts on the Affymetrix MGU74v2 GeneChip platform at 11 distinct time points was created to gain a greater understanding of the molecular changes necessary for and elicited by the development of the testis. Additionally, gene expression profiles of isolated testicular cell types were created that can aid in the further characterization of the specific functional actions of each cell type in the testis. Statistical analysis of the data revealed 11 252 transcripts (9846 unique) expressed differentially in a significant manner. Subsequent cluster analysis produced five distinct expressional patterns within the time course. These patterns of expression are present at distinct chronological periods during testis development and often share similarities with cell-specific expression profiles. Analysis of cell-specific expression patterns produced unique and characteristic groups of transcripts that provide greater insight into the activities, biological and chronological, of testicular cell types during the progression of spermatogenesis. Further analysis of this time course can provide a distinct and more definitive view into the genes implicated, known and unknown, in the maturation, maintenance, and function of the testis and the integrated process of spermatogenesis.

Identification of a short PIASx gene promoter that directs male germ cell-specific transcription in vivo

PIASx gene encodes two SUMO E3 ligases that are highly expressed in the testis. We have isolated and analyzed the promoter of the murine PIASx gene. Electrophoretic mobility shift assays with testicular nuclear extracts showed that the proximal promoter forms a major DNA-protein complex containing Sp1, Sp2, and Sp3 transcription factors. Reporter gene assays in cultured cells indicated that a fragment comprising nucleotides from -168 to +76 relative to transcription start site is sufficient for basal promoter activity in cultured cells, but these in vitro assays failed to reveal clear differences in promoter activity between testis- and non-testis-derived cell lines. Interestingly, however, the proximal promoter encompasses the elements necessary for a testis-specific transcription in vivo, as it directed beta-galactosidase expression exclusively to male germ cells in transgenic mice. In conclusion, we have characterized the minimal PIASx promoter that can be used for highly specific targeting of transgene expression to male germ cells.

Usp9y (ubiquitin-specific protease 9 gene on the Y) is associated with a functional promoter and encodes an intact open reading frame homologous to Usp9x that is under selective constraint

Sequences complementary to the X-linked ubiquitin-specific protease gene Usp9x (Dffrx) have been shown to map to the Sxr(b) interval of the mouse Y Chromosome (chr) and to be expressed in a testis-specific manner. In humans, ubiquitously expressed functional homologues (USP9Y and USP9X DFFRY/DFFRX) are present on both sex chromosomes, whereas in mouse it remains to be demonstrated that the Y-linked sequences encode a functional protein. In this paper, it is shown that the Usp9y gene encodes a potentially functional ubiquitin-specific protease possessing a core promoter region that shares several features characteristic of other testis-specific genes. Analysis of synonymous and nonsynonymous nucleotide changes suggests that there is constraint on the amino acid sequence of both the mouse Usp9x and Usp9y genes, a finding that mirrors similar analysis of the human orthologs. Thus, in both mouse and human, selection is acting to maintain the amino acid sequence of the X and Y-linked genes. This indicates that in both species the genes on each sex chromosome continue to encode an important function.

A 3-kilobase region derived from the rat cathepsin L gene directs in vivo expression of a reporter gene in sertoli cells in a manner comparable to that of the endogenous gene

During mammalian spermatogenesis, the transcription of several genes in Sertoli cells is turned on and off as the adjacent male germ cells progress through the stages of the cycle of the seminiferous epithelium. A requirement for defining how germ cells regulate this process is the identification of a promoter that confers, in vivo, accurate, stage-specific gene expression in Sertoli cells. To date, such a promoter has not been identified. Using transgenic mice, we show that the 3-kilobase genomic fragment immediately upstream of the rat cathepsin L translation start site directs expression of the reporter gene, beta-galactosidase, only in Sertoli cells. The expression pattern of the reporter gene recapitulated that of the endogenous gene in Sertoli cells as 75% of the seminiferous tubules that contained X-gal positive Sertoli cells were at stages VI-VIII and beta-galactosidase enzymatic activity was 4-fold higher in mature testes compared with immature testes. This is, to our knowledge, the first identification of a promoter region that contains all of the regulatory elements required for accurate, stage-specific gene expression in Sertoli cells.

Germ cell specific promoter drives ectopic transgene expression during embryogenesis

In this study, we used the male germ cell-specific phosphoglycerate kinase 2 (Pgk2) promoter to generate Pgk2Cre transgenic mice to allow investigation of genes critically involved in meiosis. The Pgk2 promoter had been used previously to target transgene expression to spermatocytes and spermatids in several laboratories including ours. In several Cre targeting experiments using other promoters, ectopic Cre expression had been observed, but the timing and extent of this expression was not analyzed. We demonstrate that in adult mice the Pgk2Cre transgene is expressed specifically in spermatocytes and spermatids, as expected. However, in offspring from matings of Pgk2Cre mice and an H19loxP indicator strain, we discovered that recombination events had occurred in several, but not all, tissues to varying extents. The lacZ-loxP transgenic indicator strain was next used to uncover ectopic Cre expression even in single cells, which indicated that the Pgk2Cre transgene is expressed between days 11 and 15 during embryogenesis in several tissues and organs. Using an RT PCR assay we were unable to detect endogenous Pgk2 mRNA during embryogenesis or in adult tissues other than testis. In conclusion, the Pgk2 promoter is a valid choice for targeting gene expression to meiotic male germ cells, since transient ectopic expression is unlikely to have a discernable effect in most studies, but it may be inappropriate for utilization with Cre recombinase.

Organization and chromosomal localization of the murine Testisin gene encoding a serine protease temporally expressed during spermatogenesis

The recently characterized human serine protease, Testisin, is expressed on premeiotic testicular germ cells and is a candidate type II tumor suppressor for testicular cancer. Here we report the cloning, characterization and expression of the gene encoding mouse Testisin, Prss21. The murine Testisin gene comprises six exons and five introns and spans approximately 5 kb of genomic DNA with an almost identical structure to the human Testisin gene, PRSS21. The gene was localized to murine chromosome 17 A3.3-B; a region syntenic with the location of PRSS21 on human chromosome 16p13.3. Northern blot analyses of RNA from a range of adult murine tissues demonstrated a 1.3 kb mRNA transcript present only in testis. The murine Testisin cDNA shares 65% identity with human Testisin cDNA and encodes a putative pre-pro-protein of 324 amino acids with 80% similarity to human Testisin. The predicted amino-acid sequence includes an N-terminal signal sequence of 27 amino acids, a 27 amino-acid pro-region, a 251 amino-acid catalytic domain typical of a serine protease with trypsin-like specificity, and a C-terminal hydrophobic extension which is predicted to function as a membrane anchor. Immunostaining for murine Testisin in mouse testis demonstrated specific staining in the cytoplasm and on the plasma membrane of round and elongating spermatids. Examination of murine Testisin mRNA expression in developing sperm confirmed that the onset of murine Testisin mRNA expression occurred at approximately day 18 after birth, corresponding to the appearance of spermatids in the testis, in contrast to the expression of human Testisin in spermatocytes. These data identify the murine ortholog to human Testisin and demonstrate that the murine Testisin gene is temporally regulated during murine spermatogenesis.

Immortalization of murine male germ cells at a discrete stage of differentiation by a novel directed promoter-based selection strategy

We developed a novel promoter-based selection strategy that could be used to produce cell lines representing sequential stages of spermatogenesis. The method is based on immortalization and subsequent targeted selection by using differentiation-specific promoter regions. As an example for this approach, a new murine germ cell line (GC-4spc) was established using a vector construct that contains the SV40 large T antigen and the neomycin phosphotransferase II gene under the control of the SV40 early promoter and a spermatocyte-specific promoter for human phosphoglycerate kinase 2, respectively. The GC-4spc was characterized as a cell line at the stage between preleptotene and early pachytene spermatocytes. Transcription of three germ cell-specific expressed genes, Pgk2, proacrosin, and the A-myb proto-oncogene, were detected in the GC-4spc cell line using reverse transcription-polymerase chain reaction. Furthermore, TSPY (human testis-specific protein, Y-encoded) and PGK2 (human phosphoglycerate kinase 2) promoter regions showed different transcriptional activities in the GC-4spc cell line compared with the spermatogonia-derived cell line GC-1spg. Thus, our strategy could be used for immortalization of cells at specific stages of differentiation, allowing production of a series of cultured cell lines representing sequential stages of differentiation in given cell lineages.

Lessons from knockout and transgenic mice for infertility in men

This review concentrates on the clear cases where knocking out a gene in mice has caused male infertility and thus comes near to proving that the gene plays a role in the development of sperm. Knockout mice have been created with primary defects at every stage of spermatogenesis thus creating a framework for decoding the genetic hierarchy that causes male germ cell differentiation. As well as defining essential genes in vivo experiments have defined promoter and untranslated sequences responsible for the expression of proteins at all the spermatogenic stages. In conclusion knockout mice remain the ultimate test of spermatogenic hypotheses as well as providing detailed information about this complex process.

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.

Ectopic activation of the transcription promoter for the testis-specific mouse Pgk-2 gene on elimination of a cis-acting upstream DNA region

Transgenic mice carrying the coding sequence of beta-galactosidase, for which expression was driven by various upstream regions including the transcription promoter of the testis-specific mouse Pgk-2 gene, were generated. Expression of beta-galactosidase mRNA driven by the region between nucleotide positions -1404 and +61, with respect to the transcription initiation site numbered +1, was examined by reverse transcription-mediated polymerase chain reaction, blot hybridization and in situ hybridization, and compared with that of endogenous Pgk-2 mRNA. The results revealed that the 1.4kb DNA region is sufficient for determining the organ-specific, developmental stage-specific and spermatogenic stage-specific transcription of the mouse Pgk-2 gene. When the region between -684 and +61 was used to generate transgenic mice, beta-galactosidase mRNA was detectable not only in the testis, but also in other organs such as brain and lung. However, the timing and cell-type specificity of testicular expression of beta-galactosidase mRNA were retained in these mice. Because the region between -1404 and -685 repressed the Pgk-2 promoter in somatic cell-derived cell lines, it is suggested that the organ specificity of Pgk-2 transcription is achieved at least partly by negative regulation.

Localization, expression and genomic structure of the gene encoding the human serine protease testisin

Testisin is a recently identified human serine protease expressed by premeiotic testicular germ cells and is a candidate tumor suppressor for testicular cancer. Here, we report the characterization of the gene encoding testisin, designated PRSS21, and its localization on the short arm of human chromosome 16 (16p13.3) between the microsatellite marker D16S246 and the radiation hybrid breakpoint CY23HA. We have further refined the localization to cosmid 406D6 in this interval and have established that the gene is approximately 4. 5 kb in length, and contains six exons and five intervening introns. The structure of PRSS21 is very similar to the human prostasin gene (PRSS8) which maps nearby on 16p11.2, suggesting that these genes may have evolved through gene duplication. Sequence analysis showed that the two known isoforms of testisin are generated by alternative pre-mRNA splicing. A major transcription initiation site was identified 97 nucleotides upstream of the testisin translation start and conforms to a consensus initiator element. The region surrounding the transcription initiation site lacks a TATA consensus sequence, but contains a CCAAT sequence and includes a CpG island. The 5'-flanking region contains several consensus response elements including Sp1, AP1 and several testis-specific elements. Analysis of testisin gene expression in tumor cell lines shows that testisin is not expressed in testicular tumor cells but is aberrantly expressed in some tumor cell lines of non-testis origin. These data provide the basis for identifying potential genetic alterations of PRSS21 that may underlie both testicular abnormalities and tumorigenesis.

Round spermatid-specific transcription of the mouse SP-10 gene is mediated by a 294-base pair proximal promoter

Spermiogenesis is the terminal phase of male germ cell differentiation during which haploid spermatids engage in coordinate expression of a number of testis-specific genes, including those specifying acrosomal proteins. To begin to understand the transcriptional regulation during acrosomal biogenesis, we initiated promoter analysis of the gene encoding the acrosomal protein SP-10. SP-10 was previously shown to be transcribed within Golgi-phase round spermatids in the human. The present study characterizes SP-10 gene expression during spermiogenesis in the mouse and identifies regions of the mouse SP-10 (mSP-10) promoter that are capable of driving round spermatid-specific transcription in vivo. Expression of mSP-10 mRNA was initiated in early round spermatids coincident with acrosomal biogenesis and was terminated prior to nuclear elongation. The core promoter of mSP-10 lacked a TATA box but contained a canonical initiator (Inr) element surrounding the transcription start site. Using transgenic mice, we showed that the -408 to +28-base pair (bp) or the -266 to +28-bp mSP-10 5' flanking region is sufficient to direct round spermatid-specific expression of a green fluorescent protein reporter gene. On the other hand, the -91 to +28-bp mSP-10 gene fragment lacked promoter activity in vivo. This is the first functional characterization of a testis-specific gene promoter active in early round spermatids.

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 set of highly conserved RNA-binding proteins, alphaCP-1 and alphaCP-2, implicated in mRNA stabilization, are coexpressed from an intronless gene and its intron-containing paralog

Gene families normally expand by segmental genomic duplication and subsequent sequence divergence. Although copies of partially or fully processed mRNA transcripts are occasionally retrotransposed into the genome, they are usually nonfunctional ("processed pseudogenes"). The two major cytoplasmic poly(C)-binding proteins in mammalian cells, alphaCP-1 and alphaCP-2, are implicated in a spectrum of post-transcriptional controls. These proteins are highly similar in structure and are encoded by closely related mRNAs. Based on this close relationship, we were surprised to find that one of these proteins, alphaCP-2, was encoded by a multiexon gene, whereas the second gene, alphaCP-1, was identical to and colinear with its mRNA. The alphaCP-1 and alphaCP-2 genes were shown to be single copy and were mapped to separate chromosomes. The linkage groups encompassing each of the two loci were concordant between mice and humans. These data suggested that the alphaCP-1 gene was generated by retrotransposition of a fully processed alphaCP-2 mRNA and that this event occurred well before the mammalian radiation. The stringent structural conservation of alphaCP-1 and its ubiquitous tissue distribution suggested that the retrotransposed alphaCP-1 gene was rapidly recruited to a function critical to the cell and distinct from that of its alphaCP-2 progenitor.

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.

Antisense transgenics in animals

Antisense transgenesis provides a methodology for ablating gene expression in targeted tissues through the use of tissue-specific or controllable promoters. The two major features to be considered in the design of a construct for injection are (1) the target sequence and (2) the promoter to be used. Information is provided to help the investigator make decisions in these regards. The standard methodology of making transgenics is not replicated but some hints as how best to use a transgenic facility are provided. An overview of methods for studying transgene expression and target gene suppression is given. In summary, antisense transgenesis may provide a more readily achievable method for tissue-specific ablation of a gene's function than controllable knockouts provide.

Multiple elements influence transcriptional regulation from the human testis-specific PGK2 promoter in transgenic mice

The PGK2 gene is expressed in a strictly tissue-specific manner in meiotic spermatocytes and postmeiotic spermatids during spermatogenesis in eutherian mammals. Previous results indicate that this is regulated at the transcriptional level by core promoter sequences that bind ubiquitous transcription factors and by sequences in a 40-base pair (bp) upstream enhancer region (E1/E4) that bind tissue-specific transcription factors. Transgenic mice carrying different PGK2 promoter sequences linked to the chloramphenicol acetyltransferase (CAT) reporter gene, one containing only the 40-bp E1/E4 enhancer sequence plus the core promoter and two containing 515 bp of PGK2 promoter but with either the E1/E4 enhancer region or the Sp1-binding site in the core promoter disrupted by in vitro mutagenesis, all showed levels of expression reduced to less than half that of the wild-type 515 PGK2/CAT transgene. These results indicate that multiple factor-binding regions normally regulate initiation of transcription from the PGK2 promoter. The single disruption of any one of these binding activities reduced, but did not abolish, transgene expression. This is consistent with an "enhanceosome"-like function in this promoter involving multiple bound activator proteins that interact in a combinatorial manner to synergistically promote testis-specific transcription.

In vivo gene transfer to mouse spermatogenic cells by deoxyribonucleic acid injection into seminiferous tubules and subsequent electroporation

An in vivo gene transfer technique for living mouse testes was used to develop a novel transient expression assay system for transcriptional regulatory elements of spermatogenic specific genes. The combination of DNA injection into seminiferous tubules and subsequent in vivo electroporation resulted in an efficient and convenient assay system for gene expression during spermatogenesis. The transfer of the firefly luciferase reporting gene driven by the Protamine-1 (Prm-1) enhancer region revealed a significant increase in the activity of the reporter enzyme. Histochemical studies of the transfer of the lacZ gene driven by the Prm-1 enhancer showed specific lacZ expression only in haploid spermatid cells in adult testes, corresponding with the expression pattern of endogenous Prm-1. We were able to detect long-lasting transgene expression in the transfected spermatogenic cells. A group of spermatogenic differentiating cells maintained the transfected lacZ expression after more than 2 mo of transfection, suggesting that spermatogenic stem cells and/or spermatogonia could also incorporate foreign DNA and that the transgene could be transmitted to the progenitor cells derived from a transfected proliferating germ cell.