The TE promoter element of the histone H1t gene is essential for transcription in transgenic mouse primary spermatocytes

Genetic contribution of HIST1H1T regulatory region alternations to human nonobstructive azoospermia

HIST1H1T encodes H1T, a testicular variant of histone H1, which is expressed during spermatogenesis especially in primary spermatocytes and facilitates histone to protamine exchanges during maturation of spermatozoa. The goal of the conducted research was to evaluate four genetic variations of HIST1H1T in men with nonobstructive azoospermia. This case-control study was conducted among a total number of 200 men, including 100 nonobstructive azoospermic (NOA) infertile men. In this study, three single-nucleotide polymorphisms, including c.-54C>T (rs72834678), c.-912A>C (rs707892) and c.-947A>G (rs74293938) in regulatory region as well as one SNP c.40G>C (rs198844) in coding region were identified using PCR sequencing. According to statistical analysis, none of those SNPs in regulatory regions showed significant differences in case and control groups. For SNP (c.40G>C), a significantly higher frequency of C allele in the case group was observed compared to the control group (p-value: .044). In conclusion, according to statistical analysis it seems that the polymorphism of c.40G>C is not associated with nonobstructive azoospermia.

Germline-specific H1 variants: the "sexy" linker histones

The eukaryotic genome is packed into chromatin, a nucleoprotein complex mainly formed by the interaction of DNA with the abundant basic histone proteins. The fundamental structural and functional subunit of chromatin is the nucleosome core particle, which is composed by 146 bp of DNA wrapped around an octameric protein complex formed by two copies of each core histone H2A, H2B, H3, and H4. In addition, although not an intrinsic component of the nucleosome core particle, linker histone H1 directly interacts with it in a monomeric form. Histone H1 binds nucleosomes near the exit/entry sites of linker DNA, determines nucleosome repeat length and stabilizes higher-order organization of nucleosomes into the ∼30 nm chromatin fiber. In comparison to core histones, histone H1 is less well conserved through evolution. Furthermore, histone H1 composition in metazoans is generally complex with most species containing multiple variants that play redundant as well as specific functions. In this regard, a characteristic feature is the presence of specific H1 variants that replace somatic H1s in the germline and during early embryogenesis. In this review, we summarize our current knowledge about their structural and functional properties.

The first bromodomain of Brdt, a testis-specific member of the BET sub-family of double-bromodomain-containing proteins, is essential for male germ cell differentiation

Brdt is a testis-specific member of the distinctive BET sub-family of bromodomain motif-containing proteins, a motif that binds acetylated lysines and is implicated in chromatin remodeling. Its expression is restricted to the germ line, specifically to pachytene and diplotene spermatocytes and early spermatids. Targeted mutagenesis was used to generate mice carrying a mutant allele of Brdt, Brdt(Delta)(BD1), which lacks only the first of the two bromodomains that uniquely characterize BET proteins. Homozygous Brdt(Delta)(BD1/)(Delta)(BD1) mice were viable but males were sterile, producing fewer and morphologically abnormal sperm. Aberrant morphogenesis was first detected in step 9 elongating spermatids, and those elongated spermatids that were formed lacked the distinctive foci of heterochromatin at the peri-nuclear envelope. Quantitative reverse transcription (RT)-PCR showed threefold increased levels of histone H1t (Hist1h1t) in Brdt(Delta)(BD1/)(Delta)(BD1) testes and chromatin immunoprecipitation revealed that Brdt protein, but not Brdt(DeltaBD1) protein, was associated with the promoter of H1t. Intracytoplasmic sperm injection suggested that the DNA in the Brdt(Delta)(BD1) mutant sperm could support early embryonic development and yield functional embryonic stem cells. This is the first demonstration that deletion of just one of the two bromodomains in members of the BET sub-family of bromodomain-containing proteins has profound effects on in vivo differentiation.

Transcription factor RFX2 is abundant in rat testis and enriched in nuclei of primary spermatocytes where it appears to be required for transcription of the testis-specific histone H1t gene

Previous work in our laboratory revealed upregulated transcription of the testis-specific linker histone H1t gene in pachytene primary spermatocytes during spermatogenesis. Using the H1t X-box as an affinity chromatography probe, we identified Regulatory Factor X2 (RFX2), a member of the RFX family of transcription factors, as a nuclear protein that binds the probe. We also showed that RFX2 activated the H1t promoter in transient expression assays. However, other RFX family members have the same DNA-binding domain and they also may regulate H1t gene expression. Therefore, in this study we examined the distribution of RFX2 and other RFX family members in rat testis germinal cells and in several tissues. Among tissues examined, RFX2 is most abundant in testis. Testis RFX2 is most abundant in spermatocytes where transcription of the H1t gene is upregulated and the steady-state H1t mRNA level is high. RFX2 levels decrease but RFX1 levels increase in early spermatids where H1t gene transcription is downregulated. Antibodies against RFX2 generate a shifted band in electrophoretic mobility shift assays (EMSA) using H1t or testisin X-box DNA probes with nuclear proteins from spermatocytes. These data support the hypothesis that RFX2 expression is upregulated in spermatocytes where it participates in activating transcription of the H1t gene and other testis genes. These data also support the possibility that other RFX family members may bind to the H1t promoter in other testis germinal cell types and in nongerminal cells to downregulate H1t gene transcription.

cis-requirement for the maintenance of round spermatid-specific transcription

Maintenance of strict developmental stage- and cell type-specific gene expression is critical for the progression of spermatogenesis. However, the mechanisms which sustain the spatiotemporal order of gene transcription within the seminiferous epithelium are poorly understood. Previous work has established that the proximal promoter of the mouse SP-10 gene was sufficient to maintain round spermatid-specific expression (Reddi, P.P., Shore, A.N., Shapiro, J.A., Anderson, A., Stoler, M.H., Acharya, K.K., 2003b. Spermatid-specific promoter of the SP-10 gene functions as an insulator in somatic cells. Dev. Biol. 262, 173-182). The present study addressed the cis-requirement for this regulation and sought to identify the cognate transcription factor(s). We found that mutation of two 5'-ACACAC motifs (at -172 and -160) within the -186/+28 SP-10 promoter led to premature and indiscriminate expression of a reporter gene in the seminiferous epithelium of transgenic mice, whereas the wild-type -186/+28 promoter retained spermatid specificity. Neither promoter showed ectopic expression in the somatic tissues. Expression cloning using the -186/-148 portion of the promoter yielded transcriptional repressors TDP-43 and Puralpha of which TDP-43 required the complementary 5'-GTGTGT elements located on the opposite strand for binding in vitro. Further, Northern analysis and immunohistochemistry of mouse testis showed the presence of TDP-43 in cell-types where the SP-10 gene remains repressed. Taken together, our results demonstrate that 5'-GTGTGT motifs on the complementary strand are required to prevent premature expression of SP-10 during spermatogenesis and implicate TDP-43 as the putative regulatory factor. The study also implied that additional level(s) of regulation keep the SP-10 gene silent in the somatic tissues.

Transcriptional activation of the testis-specific histone H1t gene by RFX2 may require both proximal promoter X-box elements

The rat testis-specific linker histone H1t gene is transcribed in pachytene primary spermatocytes during spermatogenesis. Our previous work using transgenic mice demonstrated that spermatocyte-specific transcription of the H1t gene is dependent upon a proximal promoter element designated the TE element. TE is composed of two adjacent and inverted imperfect repeat sequences designated TE1 and TE2 and both of these palindromic elements are similar in sequence to the X-box, a DNA consensus sequence that binds regulatory factor X (RFX). RFX2 is the major enriched protein derived from rat testis nuclear extracts when using the TE1 element as an affinity chromatography probe. Co-expression of RFX2 together with an H1t promoted reporter vector in transient expression assays activates the H1t promoter in the GC-2spd germinal cell line, and mutation of either X-box significantly represses activity. However, RFX2 partially reactivates the promoter when either of the X-box elements is independently mutated. In order to totally block reactivation by RFX2, it is necessary to mutate both X-boxes simultaneously. Therefore, RFX2 appears to be able to bind to either X-box independently to partially activate the promoter of the testis-specific histone H1t gene, but simultaneous binding of RFX2 to both X-box elements may be required for maximal promoter activation.

Testis-specific transcriptional control

In the testis, tissue-specific transcription is essential for proper expression of the genes that are required for the reproduction of the organism. Many testis-specific genes are required for mitotic proliferation of spermatogonia, spermatocytes undergoing genetic recombination and meiotic divisions, and differentiation of haploid spermatids. In this article we describe some of the genes that are transcribed in male germinal cells and in non-germinal testis cells. Because significant progress has been made in examination of promoter elements and their cognate transcription factors that are involved in controlling transcription of the testis-specific linker histone H1t gene in primary spermatocytes, this work will be reviewed in greater detail. The gene is transcriptionally active in spermatocytes and repressed in all other germinal and non-germinal cell types and, therefore, it serves as a model for study of regulatory mechanisms involved in testis-specific transcription.

Regulatory factor X2 (RFX2) binds to the H1t/TE1 promoter element and activates transcription of the testis-specific histone H1t gene

Transcription of the mammalian testis-specific linker histone H1t gene occurs only in pachytene primary spermatocytes during spermatogenesis. Studies of the wild type (Wt) and mutant H1t promoters in transgenic mice show that transcription of the H1t gene is dependent upon the TE promoter element. We purified an 85 kDa protein from rat testis nuclear extracts using the TE1 subelement as an affinity chromatography probe and analysis revealed that the protein was RFX2. The TE1 element is essentially an X-box DNA consensus element and regulatory factor X (RFX) binds specifically to this element. Polyclonal antibodies directed against RFX2 supershift the low mobility testis nuclear protein complex formed in electrophoretic mobility shift assays (EMSA). RFX2 derived from primary spermatocytes, where the transcription factor is relatively abundant, binds with high affinity to the TE1 element. Coexpression of RFX2 together with an H1t promoter/reporter vector activates the H1t promoter in a cultured GC-2spd germinal cell line, but mutation of either the TE1 subelement or the TE2 subelements represses activity. These observations lead us to conclude that the TE1 and TE2 subelements of the testis-specific histone H1t promoter are targets of the transcription factor RFX2 and that this factor plays a key role in activating transcription of the H1t gene in primary spermatocytes. Published 2003 Wiley-Liss, Inc.

RFX2 is a potential transcriptional regulatory factor for histone H1t and other genes expressed during the meiotic phase of spermatogenesis

H1t is a novel linker histone variant synthesized in mid- to late pachytene spermatocytes. Its regulatory region is of interest because developmentally specific expression has been impressed on an otherwise ubiquitously expressed promoter. Using competitive band-shift assays and specific antisera, we have now shown that the H1t-60 CCTAGG palindrome motif region binds members of the RFX family of transcriptional regulators. The testis-specific binding complex contains RFX2, probably as a homodimer. Other DNA-protein complexes obtained from testis as well as somatic organs contain RFX1, primarily as a heterodimer. Western blots confirmed that RFX2 expression is greatly enhanced in adult testis and that RFX2 is equally prominent in highly enriched populations of late pachytene spermatocytes and round spermatids. Immunohistochemistry carried out on mouse testis showed that RFX2 is strongly expressed in pachytene spermatocytes, remains high in early round spermatids, and declines only in advance of nuclear condensation. Maximum expression correlates well with the appearance of H1t. In contrast, RFX1 immunoreactivity in germ cells was only detected in late round spermatids. RFX-specific band complexes were also identified for both the mouse lamin C2 and Sgy promoters, using either testis nuclear extracts or in vitro-synthesized RFX2. These results call attention to RFX2 as a transcription factor with obvious potential for the regulation of gene expression during meiosis and the early development of spermatids.

Specific binding of nuclear proteins to a bifunctional promoter element upstream of the H1/AC box of the testis-specific histone H1t gene

The testis-specific histone H1t gene is transcribed exclusively in primary spermatocytes during spermatogenesis. Studies with transgenic mice show that 141 base pairs (bp) of the H1t proximal promoter accompanied with 800 bp of downstream sequence are sufficient for tissue-specific transcription. Nuclear proteins from testis and pachytene spermatocytes produce footprints spanning the region covering the repressor element (RE) from 100 to 125 nucleotides upstream of the H1t transcriptional initiation site. Only testis nuclear proteins bind to the 5'-end of the element and produce a unique, low-mobility complex in electrophoretic mobility shift assays. This testis complex is distinct from the complex formed by a repressor protein derived from several cell lines that binds to the 3'-end of the element. The testis complex band is formed when using nuclear proteins from primary spermatocytes, where the H1t gene is transcribed, and band intensity drops 70%-80% when using nuclear proteins from early spermatids, where H1t gene transcription ceases. Protein-DNA cross-linking experiments using testis nuclear proteins produce electrophoretic bands of 59, 52, and 50 kDa on SDS/PAGE gels.

TE2 and TE1 sub-elements of the testis-specific histone H1t promoter are functionally different

The testis-specific linker histone H1t gene is transcribed exclusively in pachytene primary spermatocytes. Tissue specific expression of the gene is mediated in part by transcriptional factors that bind elements located within the proximal and distal promoter. A 40 bp promoter element, designated H1t/TE, that is located within the proximal promoter between the CCAAT-box and AC-box, is known to be essential for H1t gene transcription in transgenic animals. In the present study, we show by SDS-PAGE analysis of UV crosslinked protein and DNA and by electrophoretic mobility shift assays (EMSA) of testis nuclear proteins separated on a non-denaturing glycerol gradient that the TE1 sub-element is bound by a protein complex. Mutation of TE1 leads to a drop in H1t promoter activity in germinal GC-2spd cells as well as in nongerminal Leydig, NIH3T3, and C127I cell lines. Although TE1 and TE2 sub-elements have similar sequences, mutation of the TE2 sub-element causes an increase in promoter activity in C127I and Leydig cells. The rat TE1 but not TE2 contains a CpG dinucleotide and this cytosine is methylated in liver but not in primary spermatocytes. Methylation of the cytosine at this site almost eliminates nuclear protein binding. Thus, there are significant functional differences in the TE2 and TE1 sub-elements of the H1t promoter with TE1 serving as a transcriptional activator binding site and TE2 serving as a repressor binding site in some cell lines.

Transcriptional repression of the testis-specific histone H1t gene mediated by an element upstream of the H1/AC box

The testis-specific histone H1t gene is transcribed exclusively in primary spermatocytes and may be important for chromatin structure, transcription, and DNA repair during this stage of spermatogenesis. Transcriptional repression of the gene in other cell types is mediated in part by specific proximal and distal promoter elements and in some cell types by methylation of CpG dinucleotides within the promoter. Our laboratory identified a distal promoter element located between 948 and 780 bp upstream from the transcription initiation site and another laboratory identified a GC-rich region between the TATA box and transcription initiation site that contribute to repression. In this article we address transcriptional repression of the histone H1t gene by an element within the proximal promoter. We report discovery of an element designated H1t promoter repressor element (RE) located between -130 and -106 bp that contributes to repression. The findings support the hypothesis that multiple mechanisms are involved in transcriptional repression of the H1t gene. Transcriptional repression mediated by the RE element in NIH 3T3 cells appears to differ significantly from the mechanism mediated by the GC-rich region. Furthermore, binding proteins that form the RE complex are not present in rat testis where the gene is actively transcribed. Our findings provide a molecular basis for histone H1t gene repression.

H1t/GC-box and H1t/TE1 element are essential for promoter activity of the testis-specific histone H1t gene

The testis-specific linker histone H1t gene is transcribed exclusively in mid to late pachytene primary spermatocytes. Tissue-specific expression of the gene is mediated primarily through elements located within the proximal promoter. Previous work in transgenic animals identified a unique 40-base pair promoter element designated H1t/TE that is essential for spermatocyte-specific expression. The H1t/TE element contains three subelements designated TE2, GC-box, and TE1 based on in vitro footprinting and electrophoretic mobility shift assays. Because GC-box is a consensus site for binding of Sp transcription-factor family members, experiments were performed demonstrating that two Sp family members, Sp1 and Sp3, were present in testis cells from 9-day-old and adult rats and in pachytene primary spermatocytes and early spermatids. A 95- to 105-kDa form of Sp1 is most abundant in the tissues and cell lines examined, but a 60-kDa form of Sp1 is the most abundant species in spermatocytes and early spermatids. Further examination of Sp1 and Sp3 from adult testis, primary spermatocytes, and early spermatids showed that they can bind to the H1t/TE element. In order to determine the contributions of the subelements to H1t transcription, we mutated each of them in H1t promoter luciferase reporter vectors. Mutation of the GC-box and TE1 subelement reduced expression 77% and 49%, respectively, compared with the wild-type H1t promoter in transient expression assays in a testis GC-2spd cell line that was derived from germinal cells. These studies suggest that Sp transcription factors may be involved in transcription of the H1t gene and the GC-box and the TE1 subelement are required for activation of the H1t promoter.

Sp1 and Sp3 activate the testis-specific histone H1t promoter through the H1t/GC-box

The testis-specific linker histone H1t gene is transcribed exclusively in mid to late pachytene primary spermatocytes. Tissue specific expression of the gene is mediated in large part through elements located within the proximal promoter. Previous work in transgenic animals showed that a unique 40 bp promoter element designated H1t/TE is essential for spermatocyte-specific expression. The H1t/TE element contains a GC-box, which is a perfect consensus binding site for members of the Sp family of transcription factors. We have shown that Sp1 and Sp3 are present in testis cells from 9-day-old and adult rats and in pachytene primary spermatocytes and early spermatids and that they can bind to the H1t/GC-box. Mutagenesis of the GC-box reduced H1t promoter activity. Furthermore, a CpG dinucleotide within the GC-box was totally unmethylated in rat testis primary spermatocytes where the gene is transcribed but it was methylated in liver where the gene is silenced. These previous studies supported the importance of the GC-box and suggested that Sp transcription factors contribute to expression of the H1t gene. In this study, we show that co-transfection of Sp1 and Sp3 expression vectors leads to an upregulation of histone H1t promoter activity in several cell lines including testis GC-2spd cells. However, very low H1t promoter activity is seen in GC-2spd cells grown at 39 degrees C, which correlates with lower levels of Sp1 and Sp3 in these cells grown at this elevated temperature. Upregulation of the H1t promoter by Sp1 and Sp3 was also seen in cotransfected NIH3T3 and C127I cell lines. On the other hand, co-transfection of the Sp1 and Sp3 expression vectors does not lead to upregulation of activity of the cell-cycle dependent histone H1d promoter.

HMGA1 and HMGA2 protein expression in mouse spermatogenesis

The high-mobility group A (HMGA) nonhistone chromosomal proteins HMGA1 and HMGA2 play a role in determining chromatin structure and in regulating the transcription of several genes. High levels of these proteins are characteristic of rapidly dividing cells in embryonic tissue and in tumors. The aim of this study was to determine the role of HMGA1 and HMGA2 throughout mouse spermatogenesis. Northern blot analysis and immunocytochemistry showed HMGA1 and HMGA2 expression during the progression from spermatocyte to spermatid. Interestingly, Western blot analysis with antibodies against the HMGA1 gene product revealed only the HMG1c isoform (27 kDa) in the testis; HMGA1a and HMGA1b were undetectable. These three isoforms are encoded by the HMGA1 gene through alternative splicing. Finally, few spermatids and complete absence of spermatozoa were observed in the testes of HMGA2-null mice, which suggests that the HMGA2 gene plays a critical role in male fertility.

Structure of the 5' region of the Hst70 gene transcription unit: presence of an intron and multiple transcription initiation sites

The rat Hst70 gene and its mouse counterpart Hsp70.2 belong to the family of Hsp70 heat shock genes and are specifically expressed in male germ cells. Previous studies regarding the structure of the 5' region of the transcription unit of these genes as well as localization of the 'cis' elements conferring their testis-specific expression gave contradictory results [Widlak, Markkula, Krawczyk, Kananen and Huhtaniemi (1995) Biochim. Biophys. Acta 1264, 191-200; Dix, Rosario-Herrle, Gotoh, Mori, Goulding, Barret and Eddy (1996) Dev. Biol. 174, 310-321]. In the present paper we solve these controversies and show that the 5' untranslated region (UTR) of the Hst70 gene contains an intron which is localized similar to that of the mouse Hsp70.2 gene. Reverse transcriptase-mediated PCR, Northern blotting and RNase protection analysis revealed that the transcription initiation of both genes starts at two main distant sites, and one of them is localized within the intron. As a result two populations of Hst70 gene transcripts with similar sizes but different 5' UTR structures can be detected in total testicular RNA. Functional analysis of the Hst70 gene promoter in transgenic mice and transient transfection assays proved that the DNA fragment of approx. 360 bp localized upstream of the ATG transcription start codon is the minimal promoter required for testis-specific expression of the HST70/chloramphenicol acetyltransferase transgene. These experiments also suggest that the expression of the gene may depend on 'cis' regulatory elements localized within exon 1 and the intron sequences.

Characterization of the H1t promoter: role of conserved histone 1 AC and TG elements and dominance of the cap-proximal silencer

H1t is a testis-specific variant histone 1 gene transcribed in pachytene spermatocytes. As part of a program to understand its transcriptional control, we have investigated the effect of the cap-proximal, GC-rich silencer element in the context of various lengths of upstream sequence. By transient transfection of NIH 3T3 cells, we showed that a targeted mutation in the silencer has a large (>10-fold) effect on reporter gene expression, regardless of the length of upstream sequence present. No other discrete silencing activity was observed in the upstream region extending to nucleotide -1842. Similarly, when the silencer mutation was introduced into the natural gene, H1t expression was readily detected in permanently transfected cells by both RNase protection and Western blot analysis, regardless of the extent of 5' or 3' flanking genomic DNA. In constructs with the mutated silencer, we showed interdependence of the characteristic H1 AC and TG box regulatory elements. Promoter up-regulation occurred only when both were intact, and possibly identical binding factors were demonstrated for each by electrophoretic mobility shift assays. In view of its precisely regulated but limited expression, it is interesting that H1t retains all the promoter elements known to activate standard H1 genes, including the TG/AC unit, SP1 site, and CCAAT element. Their presence emphasizes the apparent dominance of the silencer element in most cells.

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.

Testis-specific histone H1t gene is hypermethylated in nongerminal cells in the mouse

The testis-specific histone H1t gene is expressed only in pachytene primary spermatocytes during spermatogenesis. There is a correlation between the specific binding of testis nuclear proteins to a rat histone H1t promoter sequence, designated the H1t/TE element, and the onset of transcription in primary spermatocytes. Our laboratory has shown that mice bearing the rat gene with a deletion of the TE promoter element and replacement with a heterologous stuffer DNA fragment fail to express the rat H1t transgene in any tissue. In this study we report that five CpGs located within the H1t proximal promoter, including two CpGs located within the essential TE promoter element, contain unmethylated cytosines in vivo in genomic DNA derived from primary spermatocytes where the H1t gene is expressed. All seven CpGs are hypermethylated in vivo in genomic DNA derived from liver cells where gene expression is repressed. Further, in vitro methylation of an H1t promoter-driven reporter plasmid markedly reduced expression in a transient transfection assay system. These results suggest that cytosine methylation may contribute to the transcriptional silencing of the testis-specific histone H1t gene in nonexpressing tissues such as liver.

Elimination of male germ cells in transgenic mice by the diphtheria toxin A chain gene directed by the histone H1t promoter

Expression of the diphtheria toxin A-chain gene was directed to the male germ line by fusion to 1 kilobase of the 5'-flanking DNA of the rat histone H1t gene. Two independent lines of mice were established that expressed the toxic transgene. Female carriers were fertile; males were sterile although otherwise apparently normal. Adult transgenic males had very small testes that were virtually devoid of germ cells. A developmental study showed that germ cells survived until late fetal life but that testes of 3-day-old transgenic mice were severely depleted of prospermatogonia. During postnatal development of transgenic animals, remaining germ cells progressed to the pachytene stage of meiosis in 10% to 30% of tubular cross sections but degenerated before the completion of meiosis. By 3 mo of age the residual germ cells had almost completely disappeared. These transgenic lines demonstrate the complete tissue specificity of the H1t promoter and reveal a period of its activity just prior to formation of the definitive adult spermatogonial stem cell population. Whereas full expression of H1t occurs only in mid to late pachytene spermatocytes, one or more of the factors that impart tissue specificity to its expression must be transiently activated in the neonatal germ line. This report discusses the possibility that this genetic technique for eliminating germ cells may have practical application in making recipients for spermatogonial stem cell transplantation.

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 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.