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The role of the mesonephros in cell differentiation and morphogenesis of the mouse fetal testis.

In mouse fetal gonads, the adjacent mesonephros is required for seminiferous cord formation in vitro (Buehr et al., Development 117: 273-281, 1993). Here, we have investigated the role of mesonephric cells in seminiferous cord formation and in differentiation of Sertoli and Leydig cells. Undifferentiated male gonads with and without mesonephros at 11.5 dpc were cultured and immunocytochemical staining of Müllerian-inhibiting substance (MIS) was used as the criterion for Sertoli cell differentiation. For Leydig cells, testosterone (T) radioimmunoassay and cytochemical detection of delta 5-3 beta-hydroxysteroid-dehidrogenase (HSD) were undertaken. An ultrastructural study was also performed. In our culture conditions, the timing of differentiation of both Sertoli and Leydig cells was similar to that in the fetus. Although mesonephros is required for seminiferous cord formation, differentiation of Sertoli and Leydig cells proceeds in its absence at 11.5 dpc. Moreover, when 3H-thymidine labeled mesonephroi were grafted to unlabeled gonads, endothelial and peritubular myoid-like cells migrated into the gonad. We propose that these cells might be the mesonephric cells required for seminiferous cord formation.

Animals↗

Proteins homologous to the Xenopus germ cell-specific RNA-binding proteins p54/p56 are temporally expressed in mouse male germ cells.

Antibodies specific for the Xenopus oocyte cytoplasmic 6S mRNA-binding particle p54/p56 and antibodies against Xenopus germ cell DNA-binding protein FRG Y2 recognize two RNA-binding proteins of the mouse testis. The mouse testis proteins, estimated by SDS-PAGE to be about 48 and 52 kDa, form RNA-protein complexes with either translationally regulated or control RNAs, suggesting that they are sequence-independent RNA-binding proteins. The binding of the 48/52-kDa proteins to RNA is reduced by heparin. The expression of the 48/52-kDa mouse proteins is germ cell-specific and developmentally regulated in the testis with a maximal amount of the two proteins being detected in early postmeiotic cells (round spermatids), a cell type where many mRNAs are stored. The 48/52-kDa proteins are detected solely in the nonpolysomal fractions of postmitochondrial adult testis extracts and are not detected in extracts of brain, liver, or prepuberal testes from 12-day-old mice. We conclude that two RNA-binding proteins that appear to be immunological and functional homologues of the Xenopus germ cell-specific RNA/DNA-binding proteins p54/p56/FRG Y2 are present in male germ cells and form complexes with stored mRNAs.

Animals↗

Identification and characterization of cDNAs encoding four novel proteins that interact with translin associated factor-X.

Translin-associated factor X (TRAX) is the predominantly cytoplasmic binding partner of TB-RBP/translin in mouse testis. Four mouse testis cDNAs encoding specific TRAX-interacting proteins were isolated from a yeast two-hybrid library screen. One novel cDNA designated Tsnaxip1 (TRAX-interacting protein-1) encodes 709 amino acids. We isolated a cDNA encoding the 427 carboxy-terminal amino acids of MEA-2, a Golgi-associated, maleenhanced autoantigen; a cDNA encoding 429 amino acids with 73% homology to centrosomal Akap9; and a cDNA encoding 346 amino acids with 75% homology to SUN1, a predicted human protein that contains a SUN domain (which is present in some perinuclear proteins). Interactions were verified using in vitro synthesized fusion proteins. All four genes were expressed in the testis and enriched in germ cells. Confocal microscopy studies using green fluorescent protein fusion proteins determined that these TRAX-interacting proteins colocalize with TRAX. The data suggest that TRAX may have a function associated with perinuclear organelles during spermatogenesis.

A Kinase Anchor Proteins↗

Molecular cloning of a novel mouse testis-specific spermatogenic cell apoptosis inhibitor gene mTSARG7 as a candidate oncogene.

A novel mouse gene, mTSARG7 (GenBank accession No. AY489184), with a full cDNA length of 2279 bp and containing 12 exons and 11 introns, was cloned from a mouse expressed sequence tag (GenBank accession No. BE644543) that was significantly up-regulated in cryptorchidism. The gene was located in mouse chromosome 8A1.3 and encoded a protein containing 403 amino acid residues that was a new member of the acyltransferase family because the sequence contained the highly conserved phosphate acyltransferase (PlsC) domain existing in all acyltransferase-like proteins. The mTSARG7 protein and AU041707 protein shared 83.9% identity in 402 amino acid residues. Expression of the mTSARG7 gene was restricted to the mouse testis. The results of the in situ hybridization analysis revealed that the mTSARG7 mRNA was expressed in mouse spermatogonia and spermatocytes. Subcellular localization studies showed that the EGFP-tagged mTSARG7 protein was localized in the cytoplasm of GC-1 spg cells. The mTSARG7 mRNA expression was initiated in the mouse testis in the second week after birth, and the expression level increased steadily with spermatogenesis and sexual maturation of the mouse. The results of the heat stress experiment showed that the mTSARG7 mRNA expression gradually decreased as the heating duration increased. The pcDNA3.1 Hygro(-)/mTSARG7 plasmid was constructed and introduced into GC-1 spg cells by liposome transfection. The mTSARG7 can accelerate GC-1 spg cells, causing them to traverse the S-phase and enter the G2-phase, compared with the control group where this did not occur as there was no transfection of mTSARG7. In conclusion, our results suggest that this gene may play an important role in spermatogenesis and the development of cryptorchid testes, and is a testis-specific apoptosis candidate oncogene.

Amino Acid Sequence↗

The site of aromatization in the mouse cryptorchid testis.

Using the mouse cryptorchid model, degenerations of germ cells were observed as well as a reduced size of seminiferous tubules, while the area of the interstitial tissue increased. Aromatase, the enzyme responsible for the conversion of androgens into oestrogens, was immunolocalized in Leydig cells and in germ cells from both scrotal and abdominal testes, and in Sertoli cells only in a control testis. In the cryptorchid testis, aromatase was strongly expressed in a few tubules, including those spermatids that were still present. Other cells inside the tubules were negative for aromatase. In both testes, oestrogen receptors alpha were expressed only in Leydig cells. Strong aromatase expression in germ cells indicates an additional source of oestrogens in the testis besides the interstitial tissue.

Animals↗

Mouse testicular Leydig cells express Klk21, a tissue kallikrein that cleaves fibronectin and IGF-binding protein-3.

We have cloned a type of cDNA for a functional glandular kallikrein, designated as mouse Klk21 (mKlk21), from the adult mouse testis cDNA library. mKlk21 was expressed in the kidney, submaxillary glands, and testis of the mouse. In the testis, mKlk21 mRNA was detectable at 4 wk of postnatal development and became more prominent thereafter. The mKlk21 gene was expressed exclusively in the Leydig cells of adult mice. When Leydig cells isolated from 2-wk-old mouse testis were cultured in the presence of T, mKlk21 expression was induced significantly. Active recombinant mKlk21 showed trypsin-like specificity, favorably cleaving Arg-X bonds of synthetic peptide substrates. The enzyme activity was strongly inhibited with typical serine protease inhibitors. mKlk21 hydrolyzed casein, gelatin, fibronectin, and IGF-binding protein-3 (IGFBP-3). As in mKlk21, IGF-I and IGFBP-3 were expressed in the Leydig cells of the adult mouse testis, although the transcript of IGFBP-3 was not detected in all of the observed cells. The culture medium of Leydig cells isolated from adult mouse testes contained an mKlk21-like enzyme activity capable of degrading IGFBP-3. These results suggest that mKlk21 plays a role in Leydig cell function in the adult mouse testis.

Amino Acid Sequence↗

Cbfa1, an essential transcription factor for bone formation, is expressed in testis from the same promoter used in bone.

Cbfa1 is an essential transcription factor for bone formation, but its transcripts have also been detected in thymus and testis. To elucidate the expression of Cbfa1 in testis, we isolated Cbfa1 cDNA from mouse testis. First we examined the length of the transcripts expressed in mouse testis by Northern hybridization. Using a cDNA probe that can detect both Type-I and Type-II Cbfa1 (Type-I: originally reported as Pebp2alphaA by Ogawa et al.; Type-II: originally reported as til-1 by Stewart et al.), 1.8-kb transcripts were detected in testis, and larger transcripts (6.3 kb and 7.4 kb) in T-cell lines, thymus and bone. Using a Type-II specific probe (bone isoform-specific probe), surprisingly, 1.8-kb testis transcript(s) were detected as well as those (6.3 kb) found in bone. In addition, the transcription start site in mouse testis coincides with one of three start sites identified in bone. These results suggest that the testis transcript is generated from the same promoter of Type-II Cbfa1, which is thought to be active only in osteoblasts and some chondrocytes. Next, to define the difference in length of transcripts, we isolated the Cbfa1 cDNA from mouse testis. Sequence analysis of the cDNA showed that alternative splicing around exon 2 and poly-adenylation within exon 8 occurred in the testis isoform, which produce the smaller transcripts. These data revealed that testis Cbfa1 mRNA is transcribed from same promoter used in bones, but the post-transcriptional regulation is different between testis and skeletal tissues.

Animals↗

Cell-to-cell electrical coupling in seminiferous cords of mouse fetal testis.

Experiments performed on mouse fetal testes in vitro using electrophysiological techniques and intracellular injections of the fluorescent tracer disodium fluorescein showed that junctional transfer occurs between cells inside the seminiferous cords. This suggests a possible metabolic cooperation between testis cells at an early stage of gonad development.

Animals↗

Deoxyribonucleic acid-protein interactions associated with transcriptional initiation of the mouse testis-specific cytochrome c gene.

Transcriptional regulation of the mouse testis-specific cytochrome c (cyt. cT) gene was studied by examining DNA-protein interactions in its proximal promoter. Testicular and liver nuclear proteins bound to the cyt. cT gene at sites -105 to -81, +87 to +113, and +146 to +169, suggesting interactions with ubiquitous nuclear proteins. Protein present in liver nuclear extracts bound to a fourth site at -176 to -125, whereas protein present in testicular nuclear extracts bound to a subregion of this site at -176 to -140. The sequence from -136 to -127, bound by liver but not testicular nuclear proteins, is similar to that of the binding site of a somatic c-mos repressor protein. Lastly, different nuclear proteins from mouse liver and testis bound to a region from -18 to +31 that contains a putative Y box at -13 to -2. Mobility shift assays, Southwestern blots, and immunoprecipitation studies have established that this putative Y box binds a 52-kDa mouse testicular homologue of the Xenopus germ cell-specific Y-box protein and a competing 50-kDa protein present in both liver and testis nuclear extracts. These data suggest that the testis-specific expression of the mouse cyt. cT gene during spermatogenesis may be regulated by the differential binding of tissue-specific nuclear proteins to its proximal promoter region.

Animals↗

Cloning and characterization of mouse klk27, a novel tissue kallikrein expressed in testicular Leydig cells and exhibiting chymotrypsin-like specificity.

A cDNA clone of a new mouse tissue kallikrein, designated mKlk27, was isolated from an adult mouse testis cDNA library. mKlk27 was expressed in the submaxillary glands and testis of the mouse. In testis, mKlk27 gene was expressed exclusively in the Leydig cells of the adult mouse. Active recombinant mKlk27 exhibited chymotrypsin-like cleavage specificity. A single amino-acid substitution of Gly for Asp at position 209 in mKlk27 resulted in complete loss of its chymotryptic activity but acquisition of tryptic activity. mKlk27 effectively hydrolyzed casein, gelatin and fibronectin. Insulin-like growth factor binding protein-3 was also hydrolyzed by recombinant mKlk27. These results suggest that mKlk27 plays an important role in association with the function of the adult mouse testis.

Amino Acid Sequence↗

The cDNA and protein sequences of mouse lactate dehydrogenase B. Molecular evolution of vertebrate lactate dehydrogenase genes A (muscle), B (heart) and C (testis).

Mouse lactate dehydrogenase-B cDNAs were isolated from cDNA libraries of macrophage (ICR strain) and thymus (F1 hybrid of C57BL/6 and CBA strains), and their nucleotide sequences determined. The lactate dehydrogenase-B cDNA insert of thymus clone mB188 consists of the protein-coding sequence (1002 nucleotides), the 5' (46 nucleotides) and 3' (190 nucleotides) non-coding regions, and poly(A) tail (19 nucleotides), while macrophage clone mB168 contains a partial lactate dehydrogenase cDNA insert from codon no. 55 to the poly(A) tail. Seven silent nucleotide substitutions at codon no. 142, 143, 186, 187, 241, 285 and 292, as well as a single nucleotide change in the 3' non-coding region, were found between these different strains of mice. The predicted sequence of 333 amino acids, excluding initiation methionine, was confirmed by sequencing and/or compositional analyses of a total of 103 (31%) amino acids from tryptic peptides of mouse lactate dehydrogenase-B protein. The nucleotide sequence of the mouse coding region for lactate dehydrogenase B shows 86% identity with that of the human isoenzyme, and only eight of the 139 nucleotide differences resulted in amino acid substitutions at residues 10, 13, 14, 17, 52, 132, 236 and 317. The rates of nucleotide substitutions at synonymous and nonsynonymous sites in the mammalian lactate dehydrogenase genes are calculated. The rates of synonymous substitutions for lactate dehydrogenase genes A (muscle) and B (heart) are considerably higher than the average rate computed from human and rodent genes. The rates of nonsynonymous substitutions for lactate dehydrogenase genes A (muscle) and B (heart), particularly the latter, are highly conservative. The rates of synonymous and nonsynonymous substitutions for the lactate dehydrogenase-C gene are about the same as the average rates for mammalian genes. A phylogenetic tree of vertebrate lactate dehydrogenase protein sequences is constructed. In agreement with the previous results, this analysis further indicates that lactate dehydrogenase-C gene branched off earlier than did lactate dehydrogenase-A and lactate dehydrogenase-B genes.

Amino Acid Sequence↗

Distribution of type I interleukin-1 receptor messenger RNA in testis: an in situ histochemical study in the mouse.

The cytokine interleukin-1 (IL-1) has been reported to inhibit the hypothalamic-pituitary-gonadal axis, both through actions in brain and at the gonadal level. Recently, high affinity binding sites for 125I-recombinant human IL-1 alpha have been identified in the mouse testis with characteristics similar to those of type I IL-1 receptors on T lymphocytes and fibroblasts. The present study employed in situ hybridization histochemistry with 35S-labeled antisense cRNA probes derived from a murine type I IL-1 receptor cDNA to identify type I IL-1 receptor mRNA in the mouse testis. An intense signal was observed over interstitial cells, and over the cytoplasm of the epithelium of epididymal ducts, most prominently in the head region. The signal over seminiferous tubules, and over sperm cells within tubules and epididymal ducts, was comparable to background. This distribution of type I IL-1 receptor mRNA was similar to that recently reported for 125(I)I-IL-1-alpha binding sites, and supports evidence implicating IL-1 as a direct regulator of gonadal function.

Animals↗

A novel N-terminal domain directs membrane localization of mouse testis-specific calpastatin.

Multiple isoforms of calpastatin have been identified with unique N-terminal regions followed by identical calpain inhibitory domains (II-IV). In many instances the isoforms are cell-type specific, although the precise functional differences among these N-terminal regions are largely unknown. Here we report a germ cell-specific isoform of calpastatin (tCAST) that consists of a novel N-terminal peptide of 40 amino acids (domain T) followed by domains II to IV of somatic calpastatin (sCAST). Domain T is responsible for membrane association of tCAST through a protein modification by myristylation. Mutation of the myristylation site eliminates membrane targeting. Unlike most of the isoforms of calpastatin that are generated through alternative RNA splicing or post-translational proteolysis, the testis-specific isoform is transcribed from an intronic promoter in haploid germ cells of the testis. The intronic promoter directs specific expression of a reporter transgene in developing germ cells of the mouse testis.

Animals↗

Distinct patterns of expression of the beta-1,4-galactosyltransferases during testicular development in the mouse.

Glycosylation is one of the most important post-translational modifications and it is clear that the single step of beta-1,4-galactosylation is performed by a family of beta-1,4-galactosyltransferases (beta4-GalTs) and that each member of this family may play a distinct role in different tissues and cells. In this study, we characterized the gene expression of six beta4-GalTs in mouse testis and analyzed the changes of galactosylation of testis glycoproteins during postnatal development. Northern blot analysis revealed that beta4-GalT-I and beta4-GalT-IV were expressed mainly in newborn mouse testis and that the expression of beta4-GalT-II increased markedly and persisted at the highest levels in adult mouse testis. The expression of beta4-GalT-III and beta4-GalT-V, however, remained relatively at low levels during mouse testicular development. In contrast, the expression of beta4-GalT-VI was undetectable in mouse testis. The gene expression of beta4-GalT-II in mouse testis was further analyzed by in situ hybridization due to its unique expression pattern. Strong hybridization signals were detected in the seminiferous tubules and the expression varied among the different stages of spermatogenic differentiation. The distinct gene expression patterns of beta4-GalTs in mouse testis could affect the differential galactosylation of testis glycoproteins, as revealed by lectin histochemistry analysis.

Animals↗

Analysis of the expression of a large number of novel genes isolated from mouse prepubertal testis.

The analysis of genes expressed in a restricted temporal and spatial manner during spermatogenesis has given insights into different gene-regulatory mechanisms active in germ cells. However, very few genes have so far been described that are predominantly active in spermatogonia and the early meiotic cell types of testis. To isolate a battery of such genes, more than 100 different mRNA molecules were isolated from a mouse prepubertal testicular cDNA library, and their expression patterns in different tissues analyzed. Thirty mRNAs, 26 of them previously not described in the literature, were found to be predominantly expressed in mouse testis. A detailed analysis of their expression patterns identified a number of mRNA molecules differentially expressed in testicular cell types, including both germ cells and somatic cell types. Characterization of these mRNAs also revealed five distinct temporal phases of gene expression during prepubertal germ cell development. Three different genes, mainly active in the spermatogonial and the early meiotic cell types of testis, were isolated and will be used to characterize further stage-specific gene expression during germ cell differentiation.

Animals↗

Immunohistochemical localization of mouse testis-specific phosphoglycerate kinase (PGK-2) by monoclonal antibodies.

Monoclonal antibodies against mouse testis-specific phosphoglycerate kinase (PGK-2) were produced in order to determine immunohistochemically the onset of PGK-2 synthesis in the germinal epithelium of the mouse. PGK-2 was detected in testis sections in spermatids as early as stage 12 and in spermatozoa, but not in earlier stages of spermatogenesis nor in any somatic cells of the testis. During ontogeny, PGK-2 appears within the testis at day 30 post-partum, concomitant with spermatids entering the maturation phase. All three allelic isozymes PGK-2A, -2B, and -2C were detected equally by the monoclonal antibody in testis sections of several inbred mouse strains, each of which expresses a specific PGK-2 variant. Moreover, the monoclonal antibody against mouse PGK-2 reacted with heterologous sperm-specific PGK from rat, rabbit, and bull and, therefore, may serve as a useful immunochemical marker for mammalian spermatogenesis.

Aging↗

Effect of 5-bromodeoxyuridine on the synthesis of LDH-X in the postnatal testis of mouse.

The significance of normal DNA synthesis in the postnatal testis of mouse has been tested by using 5-bromodeoxyuridine (BUdR) on various days of development. Treatments with the drug were given for 48 h to the pups of different age groups starting immediately after birth up to day 8 post partum (PP). The appearance of the testis specific X-isozyme of lactate dehydrogenase (LDH-X) on day 17 PP has been used as a marker of spermatocyte differentiation. Autoradiographic studies on the testes of 4 to 5-day-old mice indicated that the highest percentage of prespermatogonia were labelled with 3H-BUdR. While a significant decline was noted in LDH-X synthesis on day 17 PP in the pups treated with BUdR on day 4-5 PP, other experimental animals subjected to similar treatments with BUdR on days 0-1, 2-3 and 6-7 PP showed no such decline. These results indicate that the prespermatogonia in day 4-5 PP testis are particularly susceptible to BUdR which blocks further differentiation. The possible reasons for this effect are discussed.

Animals↗