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DNA binding and bending properties of the post-meiotically expressed Sry-related protein Sox-5.

Sox-5 is one of a family of genes which show homology to the HMG box region of the testis determining gene SRY. We have used indirect immunofluorescence to show that Sox-5 protein is localized to the nucleus of post-meiotic round spermatids in the mouse testis. In vitro footprinting and gel retardation assays demonstrate that Sox-5 binds specifically to the sequence AACAAT with moderately high affinity (Kd of approximately 10(-9) M). Moreover, interaction of Sox-5 with its target DNA induces a significant bend in the DNA, characteristic of HMG box proteins. Circular dichroism spectroscopy of the Sox-5 HMG box and its specific complex with DNA shows an alteration in the DNA spectrum, perhaps as a consequence of DNA bending, but none in the protein spectrum on complex formation. The dependence of the change in the CD spectrum with protein to DNA ratio demonstrates the formation of a 1:1 complex. Analysis of the structure of the Sox-5 HMG box by 2D NMR suggests that both the location of helical secondary structure as well as the tertiary structure is similar to that of HMG1 box 2.

Amino Acid Sequence↗

Proenkephalin gene expression in testicular interstitial cells is down-regulated coincident with the appearance of pachytene spermatocytes.

Two distinct forms of proenkephalin messenger RNA (mRNA) are present in the murine testis, a family of 1.7 kilobases (kb), germ cell-specific transcripts and a 1.45-kb form that is also found in somatic tissues. In situ hybridization and molecular analysis of purified spermatogenic cell types were used to characterize the cellular localization of these different transcripts during development of the mouse testis. Both forms of proenkephalin mRNA were observed in isolated germ cells by RNA gel-blot analysis, but in distinct developmental patterns; the 1.7-kb transcripts were present in cells undergoing meiosis and spermiogenesis, whereas the 1.45-kb mRNA was detected primarily in type B spermatogonia. In contrast, in situ hybridization analysis did not detect significant amounts of the 1.45-kb transcript in any spermatogenic cell type. Using transcript-specific probes, distinct patterns of developmental expression were evident for the two mRNAs. The 1.45-kb transcript was the only form detected in the prepubertal testis, where it was localized mainly in interstitial cells. In contrast, the 1.7-kb transcripts were the major mRNAs observed in the adult testis and were localized to spermatogenic cells. A transition from the prepubertal to the adult pattern occurred on or about postnatal day 21, when proenkephalin-expressing pachytene spermatocytes begin to populate the seminiferous tubules. In situ hybridization analysis further demonstrated that proenkephalin gene expression in mutant (at/at) mice, which lack germ cells, was identical to that observed in the early prepubertal testis. These results suggest that the 1.45-kb proenkephalin mRNA is developmentally down-regulated in mouse interstitial cells and that this process requires ongoing spermatogenesis.

Animals↗

Cloning and characterization of a cAMP-specific cyclic nucleotide phosphodiesterase.

Cyclic nucleotide phosphodiesterases (PDEs) regulate intracellular levels of cAMP and cGMP by hydrolyzing them to their corresponding 5' monophosphates. We report here the cloning and characterization of a novel cAMP-specific PDE from mouse testis. This unique phosphodiesterase contains a catalytic domain that overall shares <40% sequence identity to the catalytic domain of all other known PDEs. Based on this limited homology, this new PDE clearly represents a previously unknown PDE gene family designated as PDE8. The cDNA for PDE8 is 3,678 nucleotides in length and is predicted to encode an 823 amino acid enzyme. The cDNA includes a full ORF as it contains an in-frame stop codon before the start methionine. PDE8 is specific for the hydrolysis of cAMP and has a Km of 0.15 microM. Most common PDE inhibitors are ineffective antagonists of PDE8, including the nonspecific PDE inhibitor 3-isobutyl-1-methylxanthine. Dipyridamole, however, an inhibitor that is generally considered to be relatively specific for the cGMP selective PDEs, does inhibit PDE8 with an IC50 of 4.5 microM. Tissue distribution studies of 22 different mouse tissues indicates that PDE8 has highest expression in testis, followed by eye, liver, skeletal muscle, heart, 7-day embryo, kidney, ovary, and brain in decreasing order. In situ hybridizations in testis, the tissue of highest expression, shows that PDE8 is expressed in the seminiferous epithelium in a stage-specific manner. Highest levels of expression are seen in stages 7-12, with little or no expression in stages 1-6.

3',5'-Cyclic-AMP Phosphodiesterases↗

Transcripts and CpG islands associated with the pro-opiomelanocortin gene and other neurally expressed genes.

DNA sequences of vertebrate genes which code for neural or neuroendocrine peptides were analysed in terms of CpG dinucleotide distribution and G+C content. The vast majority of the genes were found to contain a region with the sequence characteristics of a CpG island surrounding the 5' end. In mammalian species, the gene which codes for the neuroendocrine polypeptide pro-opiomelanocortin (POMC) was shown to be associated with two separate CpG islands: a 5' CpG island which surrounds the POMC transcription start site and a 3' CpG island which lies approximately 5 kb downstream, encompassing the third exon of POMC. Short POMC-related transcripts, known to be transcribed in the germline, were found to initiate from a promoter within the 3' CpG island. The start sites of the short POMC-related transcripts in mouse testis were mapped to the region coding for gamma MSH in exon 3, in a similar location to transcription start sites identified in other mammalian POMC genes. Similar short POMC-related transcripts were identified in both the mouse F9 embryonal carcinoma cell line and mouse embryonic stem cells, suggesting that transcription initiating within the third exon may occur very early in development. No short transcripts were detected by Northern blot hybridization in either Xenopus laevis testis or oocyte poly(A)+ RNA extracts. The Xenopus laevis POMC genes, A and B, were associated with neither a 5' nor a 3' CpG island. Hence, the presence of a 5' CpG island is not required for production of full-length transcripts from the Xenopus laevis POMC gene, but the presence of a 3' CpG island may be required for transcription to occur from the third exon.

Animals↗

The domain structure and the function of poly(ADP-ribose) synthetase.

Poly(ADP-ribose) synthetase is a chromatin-bound enzyme which synthesizes a protein-bound homopolymer of ADP-ribose utilizing NAD as a substrate. The characteristic nature of this enzyme is that it requires DNA for catalytic activity. The enzyme is rich in malignant tumor cells as well as in normal tissues where cell proliferation is very rapid. The enzyme has been purified to homogeneity from calf thymus, mouse testis and human placenta. The amino acid composition of these enzymes is very similar and a monoclonal antibody as well as antisera against the calf enzyme cross-reacts with mouse, chicken and human enzymes, suggesting that the antigenic structures of poly(ADP-ribose) synthetase are highly conserved in various animal cells. The native enzyme (Mr = 120K) is cleaved by limited proteolytic digestion into three different domains (Mr = 46K, 22K, 54K), the first containing the site for DNA binding, the second containing the site for automodification and the third containing the site for NAD binding. The DNA binding domain (Mr = 46K), like the native enzyme, has the ability to preferentially suppress nick induced random transcription initiation in a HeLa cell lysate, resulting in the production of run-off RNA initiated from the correct late promoter site on truncated DNA of adenovirus 2. The native enzyme poly(ADP-ribosyl)ates RNA polymerase and some other nuclear enzymes. These results, taken together, indicate that poly(ADP-ribose) synthetase plays a critical role in regulating gene expression in various eukaryotic cells.

Amino Acids↗

Localization of various secretory phospholipase A2 enzymes in male reproductive organs.

Current evidence suggests the presence of transcripts for several secretory phospholipase A(2) (sPLA(2)) enzymes in male genital organs. In this study, we examined by immunohistochemistry the localization of group IIA, IIC, IID, IIE, IIF, V and X sPLA(2)s in male genital organs. In sPLA(2)-IIA-deficient C57BL/6 mouse testis, sPLA(2)-IIC, -IID, -IIE, -IIF, -V and -X were diversely expressed in spermatogenic cells within the seminiferous tubules. Immunoblotting revealed the presence of these sPLA(2)s in mouse spermatozoa. In addition, sPLA(2)-IIF, -V and -X were localized in the interstitial Leydig cells. The same set of sPLA(2)s was detected in a mouse cultured Leydig cell line, and adenovirus-mediated transfer of these sPLA(2)s into Leydig cells resulted in increased prostaglandin production. sPLA(2)-IIC, -IID, -IIE, -IIF, -V and -X were also detected diversely in the epithelium of the epididymis, vas deferens, seminal vesicles, and prostate. In a sPLA(2)-IIA-positive FVB strain, weak expression of sPLA(2)-IIA was detected in Leydig cells. Notable differences in the sPLA(2) expression profiles were found in the seminal vesicles and prostate between mice and humans. Taken together, individual sPLA(2)s exhibit distinct or partially overlapping localizations in male reproductive organs, suggesting both specific and redundant functions.

Animals↗

Overexpression of follistatin-like 3 in gonads causes defects in gonadal development and function in transgenic mice.

Activin has numerous biological activities including regulation of follicular development, spermatogenesis, and steroidogenesis within the gonads. Activities of activin are regulated by follistatin (FST), an activin binding protein, and perhaps follistatin-like 3 (FSTL3; also known as FLRG and FSRP). FSTL3 is a recently described member of the FST family having an overall structure and activity profile similar to that of FST, including binding and neutralization of activin. FSTL3 is most highly expressed in the placenta and testis, whereas FST is highest in the ovary and kidney, suggesting that FSTL3 has biological actions that do not entirely overlap those of FST. To investigate the role of local FSTL3 as a potential regulator of activin action in gonad development and function, we examined FSTL3 expression in the mouse testis. FSTL3 protein was localized to Leydig cells, spermatagonia, and mature spermatids in normal male mice. We then created transgenic mice using a human FSTL3 cDNA driven by the mouse alpha-inhibin promoter. Three of five transgenic founders were fertile and were bred to establish lines. In the highest expressing line 3, transgene expression was largely restricted to gonads, with pituitary, adrenal, brain, and uterine expression being substantially lower. Gonad weights, sperm counts, and fertility were significantly reduced in transgenic males, and reduced litter size was evident in line 3 females. Within the testis, highest transgene expression was observed in Sertoli cells, and although most tubules showed evidence of normal spermatogenic development, degenerating tubules devoid of germ cells and Leydig cell hyperplasia were also evident in every line 3 animal examined. Ovaries from line 3 females contained fewer antral follicles and more apparent follicular atresia. Although circulating human FSTL3 levels were undetectable, FSH and LH levels in adult transgenic mice were not significantly different from wild-type animals. However, testosterone levels were significantly increased at d 21 and significantly reduced at d 60 compared with wild-type males. These results suggest that FSTL3 is likely to be a local regulator of activin action in gonadal development and gametogenesis and, further, that activin appears to have important actions in gonadal development and function that are critical for normal reproduction.

Animals↗

Identification of novel Prominin-1/CD133 splice variants with alternative C-termini and their expression in epididymis and testis.

Prominin-1/CD133 is a five-membrane-span glycoprotein that is thought to act as an organizer of plasma-membrane protrusions. Here, we report the molecular and cell-biological characterization of four novel prominin-1 splice variants isolated from a mouse testis cDNA library and referred to as prominin-1.s3 to prominin-1.s6. Compared with kidney-derived prominin-1.s1, the s3, s4 and s5 variants contain a distinct cytoplasmic C-terminal domain. The s4 and s5 variants bear, in addition, two and one inframe deletion(s), respectively, in the extracellular domains. The s6 variant displays a truncated C-terminal domain caused by a premature termination resulting from intron retention. Upon their ectopic expression in Chinese hamster ovary cells, the s3 and s6 variants were found to be concentrated in plasma-membrane protrusions, whereas the s4 and s5 variants did not reach the cell surface. Biochemical analyses suggest that most of the prominin-1 in the adult male reproductive system is expressed as the s6 variant. Immunohistological and electron microscopic analyses show that prominin-1 is: (1) confined to the apical surface of the epithelium all along the epididymal duct, with the exception of the initial segment; (2) concentrated in stereocilia of the epididymal duct epithelium; and (3) found on the tail of developing spermatozoa in seminiferous tubules. Our data suggest that prominin-1 is involved in the formation and/or stabilization of epididymal stereocilia and the tail of spermatozoa, and hence might play a dual role in the biogenesis of spermatozoa.

AC133 Antigen↗

Cell-cell interaction between rat Sertoli cells and mouse germ cells in vitro.

An antiserum against rat germ cell membranes was prepared, and after absorption with protein extracts of rat liver and kidney and mouse testis, this antiserum reacted only with rat germ cell membranes and juxtanuclear vesicles in rat Sertoli cells. Germ cell-free rat Sertoli cell monolayers were cultured in vitro. Freshly isolated mouse germ cells adhered to these monolayers within 1 h. After a minimum of 3 days of such a co-culture, immunofluorescence and immunoblotting revealed that the mouse germ cells had obtained rat-antigenic determinants in their membranes. Our results indicate that this appearance of rat-specific antigens on mouse germ cells is specific and inducible.

Animals↗

Molecular cloning and characterization of phosphatidylcholine transfer protein-like protein gene expressed in murine haploid germ cells.

We have isolated a cDNA clone specifically expressed in spermiogenesis from a subtracted cDNA library of mouse testis. The cDNA consisted of 1392 nucleotides and had an open reading frame of 873 nucleotides encoding a protein of 291 amino acid residues. Computer-mediated homology search revealed that the nucleotide sequence was unique but the deduced amino acid sequence had similarity to mouse phosphatidylcholine transfer protein (PCTP). We named this newly isolated gene PCTP-like protein. Northern blot analysis revealed a 1.4-kilobase mRNA expressed in the testis, kidney, liver, and intestine with the highest level in the testis. Messenger RNA expression in the testis was detected first on Day 23 in postnatal development and then increased up to adulthood. The protein, having a molecular weight of approximately 40 000, was encoded by the mRNA and was detected at the tail of the elongated spermatids and sperm by immunohistochemical staining.

Aging↗

DNA damage caused by etoposide and gamma-irradiation induces gene conversion of the MHC in a mouse non-germline testis cell line.

We have explored the effects of gamma-irradiation and etoposide on the gene conversion frequency between the endogenous major histocompatibility complex class II genes Abk and Ebd in a mouse testis cell line of non-germline origin with a polymerase chain reaction assay. Both gamma-rays and etoposide were shown to increase the gene conversion frequency with up to 15-fold compared to untreated cells. Etoposide, which is an agent that stabilise a cleavable complex between DNA and DNA topoisomerase II, shows an increased induction of gene conversion events with increased dose of etoposide. Cells treated with gamma-rays, which induce strand breaks, had an increased gene conversion frequency when they were subjected to low doses of irradiation, but increasing doses of irradiation did not lead to an increase of gene conversion events, which might reflect differences in the repair process depending on the extent and nature of the DNA damage. These results where DNA damage was shown to be able to induce gene conversion of endogenous genes in mouse testis cells suggests that the DNA repair system could be involved in the molecular genetic mechanism that results in gene conversion in higher eukaryotes like mammals.

Amino Acid Sequence↗

Molecular cloning and characteristics of a novel zinc finger protein and its splice variant whose transcripts are expressed during spermatogenesis.

Testicular zinc finger protein (TZF) has a zinc finger motif of the Cys2-His2 type and its transcript is expressed predominantly in mouse spermatogenic cells. Using the fragment of TZF as a probe, we isolated the alternative splice variant form (TZF-L) from mouse testis cDNA library. Analysis of the open reading frame of each cDNA indicated that TZF and TZF-L were polypeptides of 942 and 2025 amino acid residues, respectively, and the N-terminal 902 amino acids of TZF-L were identical to those of TZF. The C-terminal region of TZF-L had more a zinc finger motif of the Cys2-His2 type and poly-Glu and poly-Pro regions. The mouse TZF/TZF-L gene spanned >20 kb and consisted of 11 exons. RT-PCR analysis of the expression level of mRNAs for mouse TZF and TZF-L showed that both transcripts are highly expressed in testis and moderately in kidney and ovary. Elevated expression of both transcripts during testicular development in mice was restricted to spermatocytes at the pachytene stage of meiotic prophase. Fusion proteins with GFP also demonstrated the nuclear localization of TZF and TZF-L. These experiments suggest that TZF and TZF-L may act to control the gene activity during spermatogenesis.

Alternative Splicing↗

The poly(ADP-ribose) polymerase 1 interacts with Sry and modulates its biological functions.

Sry encodes a putative transcription factor that switches on testis differentiation during embryogenesis. Currently, the mechanism(s) by which Sry mediates such developmental process is still uncertain. To understand its gene regulation mechanism, we have utilized an in vitro affinity chromatography and proteomic strategy to identify and characterize Sry binding proteins from the mouse testis potentially involved in the formation of an Sry transcriptional complex(es). Our study has consistently identified the poly(ADP-ribose) polymerase 1 (PARP-1) as an Sry interactive protein. PARP-1 is expressed in mouse fetal gonads at the time of sex determination and co-localized with Sry in the nuclei of pre-Sertoli cells. PARP-1 could be co-immunoprecipitated with Sry in cultured cells. The interactive domains have been mapped to the HMG box of Sry and the zinc fingers of the PARP-1 protein, respectively. The Sry-PARP-1 interaction is evolutionarily conserved and it interferes with the ability of Sry in binding to its consensus sequence. In the presence of its substrate, PARP-1 poly(ADP-ribosyl)ates Sry and minimizes severely its DNA-binding activities. PARP-1 represses Sry-mediated transactivation of a reporter gene in cultured cells. Hence, PARP-1 could modulate the regulatory function(s) of Sry on its target genes in this developmental pathway.

Animals↗

Expression cloning, developmental expression and chromosomal localization of fibroblast growth factor-8.

A mouse testis cDNA library in lambda pCEV27 eukaryotic expression vector was transfected in NIH3T3 fibroblasts and several transformed foci were identified. A plasmid with high-titered focus forming activity was rescued from one of these transformants. Structural analysis of this cDNA predicted a protein identical to androgen induced growth factor (AIGF), recently identified as the eighth member of the fibroblast growth factor (FGF) family. A 1.6 kilobasepair transcript of the FGF-8 gene was detected in testis but not in other adult tissues analysed. During development, expression of FGF-8 was restricted to embryonic days 9 through 13 suggesting that the growth factor plays a role during a discrete stage of mouse embryogenesis. An exon-containing genomic clone of human FGF-8 was isolated and structural comparisons indicated that the gene structure of this region is highly conserved among the FGF genes. Using a panel of human-rodent somatic cell hybrids, the FGF-8 gene was localized to human chromosome 10.

3T3 Cells↗

Molecular cloning and sequencing of calnexin-t. An abundant male germ cell-specific calcium-binding protein of the endoplasmic reticulum.

A mouse testis cDNA expression library was screened using a monoclonal antibody (1C9) that recognized an abundant testis-specific 101-kDa endoplasmic reticulum-associated protein. The screening resulted in the isolation of a 2.3-kilobase cDNA clone (A2/6). The sequence encoded 611 amino acids with a calculated mass of 69,454 Da, that was 60% similar to mouse calnexin. A high affinity calcium binding domain, present in both calnexin and calreticulin, and one transmembrane domain similar to that of calnexin were found in the A2/6 protein domain. Northern blot analysis of total RNA from seven different tissues showed hybridization only to testis RNA. Southern blot analysis indicated that A2/6 was a single copy gene. The calculated molecular mass for A2/6 was unexpectedly lower than the 101-kDa protein recognized by 1C9 on Western blot analysis of total testis protein. However, Escherichia coli and in vitro translation products of A2/6 cDNA yielded a similar 100-kDa protein. Finally, using the recombinant protein, calcium binding activity was detected by a 45Ca2+ overlay assay. These results suggest that spermatogenic cell endoplasmic reticulum has a unique calcium binding protein, calnexin-t, which appears to be a calnexin variant.

Amino Acid Sequence↗

Characterization and comparative genomic analysis of intronless Adams with testicular gene expression.

ADAM (a disintegrin and metalloprotease) family members with testis-specific or -predominant gene expression are divided phylogenically into two groups: ADAMs 2, 3, 5, 27, and 32 (the first group) and ADAMs 4, 6, 20, 21, 24, 25, 26, 29, 30, and 34 (the second group). We cloned and sequenced cDNAs for previously unidentified mouse Adams that belong to the second group. We found that all the Adam genes in the second phylogenic group are transcribed by both somatic and germ cells in mouse testis, representing a unique expression pattern different from that of the first-group Adams. Genomic analyses revealed that all the second-group Adam genes lack introns interrupting protein-coding sequences and many of them are present as multicopy genes, resulting in total of 14 functional mouse genes in this phylogenic group. Comparing the mouse and human ADAM genes, we found that a number of these mouse Adam genes do not have human orthologues and, even if they exist, some orthologues are pseudogenes in human. These results suggest the differential expansion of the second-group Adam genes in the mouse genome during evolution and a relationship between these Adams and male reproduction unique to mouse.

Amino Acid Sequence↗

Translational regulation of a novel testis-specific RNF4 transcript.

The RING-finger protein SNURF/RNF4, a modulator of both steroid receptor dependent and basal transcription, is expressed at very high levels in testis and at much lower levels in several other tissues. In somatic tissues, the RNF4 gene is expressed as a 3-kb transcript while an additional shorter sized transcript (1.6 kb) was found in mouse testis. In murine germ cells, RNF4 protein expression is strongly modulated during progression of spermatogonia to spermatids, with a peak in spermatocytes. The expression of 3-kb transcript correlated with protein levels in the different germ cell populations. Conversely, the 1.6-kb transcript was abundantly and specifically expressed in spermatids, in which RNF4 protein was detected at very low levels. We have then examined possible mechanisms underlying this discrepancy. Primer extension and RNase protection analyses demonstrated that the 1.6- and 3.0-kb transcripts originate from the same promoter, encode for the same protein and differ in the 3' UTR. In vitro assays showed that protein degradation is not involved in the regulation of RNF4 protein level. Finally, polysome analysis revealed that only a slight fraction of the testis-specific transcript is engaged in translation, thus providing a feasible mechanism for the quantitative differences of RNF4 mRNA and protein levels. Present results demonstrate that RNF4 short transcript is poorly translated suggesting that this mechanism could be essential for normal spermatogenesis.

Alternative Splicing↗

Regulation of ALF gene expression in somatic and male germ line tissues involves partial and site-specific patterns of methylation.

ALF (TFIIAalpha/beta-like factor) is a germ cell-specific counterpart of the large (alpha/beta) subunit of general transcription factor TFIIA. Here we isolated homologous GC-rich promoters from the mouse and human ALF genes and used promoter deletion analysis to identify sequences active in COS-7 and 293 cells. Further, bisulfite sequence analysis of the mouse ALF promoter showed that all 21 CpG dinucleotides between -179 and +207 were partially methylated in five somatic tissues, brain, heart, liver, lung, and muscle, and in epididymal spermatozoa from adult mice. In contrast, DNA from prepubertal mouse testis and from purified spermatocytes were unmethylated except at C(+19)G and C(+170)G. We also found that ALF expression correlates with a strong promoter-proximal DNase I-hypersensitive site present in nuclei from testis but not from liver. Finally we show that in vitro methylation of the ALF promoter inhibits activity and that 5-aza-2'-deoxycytidine treatment reactivates the endogenous ALF gene in a panel of seven different mouse and human somatic cell lines. Overall the results show that silencing in somatic cells is methylation-dependent and reversible and that a unique CpG-specific methylation pattern at the ALF promoter precedes expression in pachytene spermatocytes. This pattern is transient as remethylation of the ALF promoter in haploid germ cell DNA has occurred by the time spermatozoa are present in the epididymis.

3T3 Cells↗