Nuclear changes and acrosome formation during spermiogenesis in Euchistus heros (Hemiptera: Pentatomidae)

Ultrastructural and cytochemical studies were carried out on nuclear changes and acrosome formation during the spermiogenesis of the phytophagous bug Euchistus heros. The development of the nucleus involves changes in the shape and in degree of chromatin condensation: initially it is dispersed and with a low-electron density, then assumes a fibrillar arrangement and finally compacts in an electron-dense material. The acrosome is formed by the Golgi complex and presents unusual morphological features during its development. The reaction product of acid phosphatase, glucose-6-phosphatase and thiamine pyrophosphatase activities were detected during various stages of acrosome development. In contrast, residues of alpha-N-acetylgalactosamine and basic proteins were only reported in the intermediate and late stages of the differentiation process, respectively.

Stage and cell-specific expression of calmodulin-dependent phosphodiesterases in mouse testis

Calcium and cyclic nucleotides are second messengers that regulate the development and functional activity of spermatozoa. Calcium/calmodulin-dependent phosphodiesterases (CaM-PDEs) are abundant in testicular cells and in mature spermatozoa and provide one means by which calcium regulates cellular cyclic nucleotide content. We examined the spatial and temporal expression profiles of three knownCaM-PDE genes, PDE1A, PDE1B, and PDE1C, in the testis. In situ hybridization and immunofluorescent staining showed that both PDE1A and PDE1C are highly expressed but at different stages in developing germ cells. However, a very low hybridization signal of PDE1B exists uniformly throughout the seminiferous epithelium and the interstitium. More specifically, PDE1A mRNA is found in round to elongated spermatids, with protein expression in the tails of elongated and maturing spermatids. In contrast, PDE1C mRNA accumulates during early meiotic prophase and throughout meiotic and postmeiotic stages. Immunocytochemistry showed a diffuse, presumably cytosolic distribution of the expressed protein. The distinct spatial and temporal expression patterns of CaM-PDEs suggest important but different physiological roles for these CaM-PDEs in developing and mature spermatozoa.

Highly efficient base excision repair (BER) in human and rat male germ cells

The quality of germ cell DNA is critical for the fate of the offspring, yet there is limited knowledge of the DNA repair capabilities of such cells. One of the main DNA repair pathways is base excision repair (BER) which is initiated by DNA glycosylases that excise damaged bases, followed by incision of the generated abasic (AP) sites. We have studied human and rat methylpurine-DNA glycosylase (MPG), uracil-DNA glycosylase (UNG), and the major AP endonuclease (HAP1/APEX) in male germ cells. Enzymatic activities and western analyses indicate that these enzymes are present in human and rat male germ cells in amounts that are at least as high as in somatic cells. Minor differences were observed between different cellular stages of rat spermatogenesis and spermiogenesis. Repair of methylated DNA was also studied at the cellular level using the Comet assay. The repair was highly efficient in both human and rat male germ cells, in primary spermatocytes as well as round spermatids, compared to rat mononuclear blood cells or hepatocytes. This efficient BER removes frequently occurring DNA lesions that arise spontaneously or via environmental agents, thereby minimising the number of potential mutations transferred to the next generation.

Testis hormone-sensitive lipase expression in spermatids is governed by a short promoter in transgenic mice

A testicular form of hormone-sensitive lipase (HSL(tes)), a triacylglycerol lipase, and cholesterol esterase, is expressed in male germ cells. Northern blot analysis showed HSL(tes) mRNA expression in early spermatids. Immunolocalization of the protein in human and rodent seminiferous tubules indicated that the highest level of expression occurred in elongated spermatids. We have previously shown that 0.5 kilobase pairs of the human HSL(tes) promoter directs testis-specific expression of a chloramphenicol acetyltransferase reporter gene in transgenic mice and determined regions binding nuclear proteins expressed in testis but not in liver (Blaise, R., Grober, J., Rouet, P., Tavernier, G., Daegelen, D., and Langin, D. (1999) J. Biol. Chem. 274, 9327-9334). Mutation of a SRY/Sox-binding site in one of the regions did not impair in vivo testis-specific expression of the reporter gene. Further transgenic analyses established that 95 base pairs upstream of the transcription start site were sufficient for correct testis expression. In gel retardation assays using early spermatid nuclear extracts, a germ cell-specific DNA-protein interaction was mapped between -46 and -29 base pairs. The DNA binding nuclear protein showed properties of zinc finger transcription factors. Mutation of the region abolished reporter gene activity in transgenic mice, showing that it is necessary for testis expression of HSL(tes).

The testicular germ-cell protease PC4 is also expressed in macrophage-like cells of the ovary

PC4 is a serine protease primarily expressed in spermatids. We have produced PC4-deficient mice carrying an insertion of the bacterial gene for beta galactosidase under the PC4 gene promoter. Male mice lacking PC4 (-/-) exhibit severely reduced fertility. Surprisingly, the fertility of female mice is also significantly diminished in these mutants (Mbikay et al., 1997. Proc. Natl. Acad. Sci. USA 94, 6842-6846). The aim of this study was to determine the site of PC4 expression in mouse ovaries. Using a histoenzymatic assay for beta-galactosidase, we show that the PC4 promoter can drive strong expression of this enzyme in the theca-interstitium and in degenerating corpora lutea of +/- ovaries. We also demonstrate that PC4 transcripts can be detected by RT-PCR in the ovaries of +/- and +/+ mice, but not in those of -/- mice. The cells expressing PC4 were macrophage-like, since they expressed the macrophage markers CD11b and F4/80, as well as interleukin 1beta and tumor necrosis factor alpha (TNFalpha). Expression of PC4 was also detected in the mouse macrophage RAW264.7 cell line. Interestingly, TNFalpha transcripts were 3-fold more abundant in ovarian macrophage-like cells from -/- mice than in those from +/+ mice, suggesting a constitutive state of activation of the mutant cells. An inverse relationship between PC4 expression and macrophage activation was also observed in RAW264.7 cells. When these cells were activated using bacterial lipopolysaccharide, the level of PC4 transcripts decreased, while that of TNFalpha increased. These observations identify PC4 as an enzyme that could influence ovarian physiology by affecting macrophage functions.

Rat spermatogenic cell beta-D-galactosidase: characterization, biosynthesis, and immunolocalization

In this study we have demonstrated that the rat sperm acrosomal beta-d-galactosidase is expressed in late spermatocytes and spermatids (round, elongated/condensed) during spermatogenesis. The enzyme is an exoglycohydrolase which, along with other exoglycohydrolases and proteases, is thought to aid in penetration of the zona pellucida, the extracellular glycocalyx that surrounds the mammalian egg. The presence of the enzyme in spermatocytes was confirmed by multiple approaches using biochemical, biosynthetic, and immunohistochemical protocols. The germ cells (spermatocytes, round spermatids, and elongated/condensed spermatids), purified from rat testis, were found to contain beta-galactosidase and four other glycohydrolases (beta-d-glucuronidase, alpha-d-mannosidase, alpha-l-fucosidase, and beta-N-acetylglucosaminidase). With the exception of alpha-l-fucosidase, the other enzymes assayed demonstrated a two- to threefold higher activity per cell in spermatocytes than in round spermatids. Immunoblotting approaches of affinity-purified germ cell extracts demonstrated several molecular forms of beta-galactosidase in spermatocytes and round spermatids; one of these forms (62 kDa) was seen only in round spermatids. The biosynthetic approach demonstrated that the enzyme is synthesized in spermatocytes and round spermatids in culture in high-molecular-weight precursor forms (90/88 kDa) which undergo processing to lower molecular weight mature forms in a cell-specific manner. The net result is the formation of predominantly 64- and 62-kDa forms in spermatocytes and round spermatids, respectively. The conversion of precursor forms to mature forms in the diploid and haploid cells in culture is rapid with t(1/2) of 6.5 and 9.0 h, respectively. Immunohistochemical approaches revealed an immunopositive reaction in the Golgi membranes, Golgi-associated vesicles, and lysosome-like structures in the late spermatocytes and early round spermatids. The forming/formed acrosome in round and elongated spermatids was also immunoreactive.

Expression of the lipocalin-type prostaglandin D synthase gene in the reproductive tracts of Holstein bulls

The aim of this study was to localize expression of the prostaglandin D synthase gene in the reproductive tracts of Holstein bulls using northern blotting and in situ hybridization. For northern blotting, a digoxigenin-labelled prostaglandin D synthase cDNA probe was used to probe blots containing RNA isolated from the testes, epididymides, vas deferens, ampullae, seminal vesicles, prostate and bulbourethral glands of bulls. The digoxigenin-labelled cDNA for the bovine homologue of prostaglandin D synthase hybridized to a single band (approximately 0.9 kb) to RNA samples from the caput, corpus and cauda epididymides, as well as RNA samples from the vas deferens and the ampulla. The probe also detected a single band in testis samples, although the transcript size was slightly larger (approximately 1.0 kb) than the transcript found in the other tissues. The highest expression of prostaglandin D synthase was observed in the testes and caput epididymides. Prostaglandin D synthase transcripts were not found in the seminal vesicles or the prostate or bulbourethral glands using northern blotting. For in situ hybridization, antisense and sense riboprobes were synthesized and used to hybridize to cryosections obtained from the reproductive tissues of bulls. In situ hybridization of bull testes showed that prostaglandin D synthase transcripts were present within the germ cells in the adluminal compartment of the seminiferous tubules containing round and elongated spermatids, indicating that expression varied with stage of development of the seminiferous tubules. Prostaglandin D synthase expression was observed in the epithelial cells of the epididymides with greatest expression occurring in the caput epididymidis. Some expression was also observed in the epithelial cells of the vas deferens and a few cells of some lobules in the prostate and bulbourethral glands. Expression of the prostaglandin D synthase gene was not detected in ampullae or seminal vesicles by in situ hybridization.

Immunohistochemical localization of V-ATPases in rat spermatids

The sperm acrosome exhibits a low pH. However, the mechanism of acidification in the acrosome remains unclear. Vacuolar-type proton ATPase (V-ATPase) has been shown to play a principle role in generating and maintaining the acidity of organelles such as lysosomes and endosomes. In this study, we examined whether V-ATPase is localized in the acrosome membranes using immunohistochemical techniques. Sections of rat testis were immunostained using antibodies against V-ATPase. Under light microscopic observation, the perinuclear region in spermatids at an early stage of development was heavily immunostained. At the electron microscopic level, gold particles showing the presence of V-ATPase were localized to the acrosome membranes in the developing spermatids. V-ATPase was also localized to the membrane of vesicles locating between the trans-Golgi area and the acrosome. These observations suggest that V-ATPase may play a role in acrosome acidification.

Biosynthesis, processing, and subcellular localization of rat spermbeta-D-galactosidase

During spermatogenesis, spermatids synthesize constituent proteins present in mature spermatozoa; however, little information exists on the molecular processes involved. In previous studies, this laboratory reported the characterization of rat sperm beta-D-galactosidase. In this paper, we report the localization of this enzyme along with its biosynthesis and processing. An antibody against rat luminal fluid beta-D-galactosidase was used to immunolocalize the enzyme in the testis and in epididymal spermatozoa. We found that beta-D-galactosidase is localized within the acrosomal cap of spermatids and in the acrosome and cytoplasmic droplet of epididymal spermatozoa. A combination of germ cell radiolabeling, immunoprecipitation, SDS-PAGE, and autoradiography revealed that spermatids produce two forms of beta-D-galactosidase, 90 and 88 kDa. During pulse-chase analysis, a 56-kDa form appeared. Treatment of beta-D-galactosidase immunoprecipitates from testicular spermatozoa with N-glycanase or Endo H revealed that both the 90- and 88-kDa forms become a 70-kDa polypeptide on SDS-PAGE. Since Endo H or N-glycanase treatment provided similar results, the presence of extensive N-linked high mannose/hybrid-type glycans on these proteins is indicated. Treatment of the 56-kDa form of beta-D-galactosidase with Endo H or N-glycanase resulted in the appearance of 52- and 50-kDa forms, respectively. This result suggests that the 56-kDa form contains N-linked high mannose/hybrid as well as complex oligosaccharides. During epididymal maturation, the 90-kDa form of beta-D-galactosidase persists in caput epididymal spermatozoa and is gradually converted to a major 74-kDa form in cauda spermatozoa. In addition to the 90- to 74-kDa forms, cauda spermatozoa show a 56- to 52-kDa form on Western immunoblots. Since only the high-molecular weight forms of beta-D-galactosidase are present on immunoblots of isolated sperm heads, we suggest that they are acrosomal in origin and that the 56-kDa form, which is processed to 52 kDa in cauda spermatozoa, is associated with the cytoplasmic droplet.

DNA polymerase lambda (Pol lambda), a novel eukaryotic DNA polymerase with a potential role in meiosis

A new gene (POLL) encoding a novel DNA polymerase (Pol lambda) has been identified at mouse chromosome 19. Murine Pol lambda, consisting of 573 amino acid residues, has a 32% identity to Pol beta, involved in nuclear DNA repair in eukaryotic cells. It is interesting that Pol lambda contains all the critical residues involved in DNA binding, nucleotide binding and selection, and catalysis of DNA polymerization, that are conserved in Pol beta and other DNA polymerases belonging to family X. Murine Pol lambda, overproduced in Escherichia coli, displayed intrinsic DNA polymerase activity when assessed by in situ gel analysis. Pol lambda also conserves the critical residues of Pol beta required for its intrinsic deoxyribose phosphate lyase (dRPase) activity. The first 230 amino acid residues of Pol lambda, that have no counterpart in Pol beta, contain a BRCT domain, present in a variety of cell-cycle check-point control proteins responsive to DNA damage and proteins involved in DNA repair. Northern blotting, in situ hybridization analysis and immunostaining showed high levels of Pol lambda specifically expressed in testis, being developmentally regulated and mainly associated to pachytene spermatocytes. These first evidences, although indirect, suggest a potential role of Pol lambda in DNA repair synthesis associated with meiosis.

Telomere length in male germ cells is inversely correlated with telomerase activity

Telomeres, the noncoding sequences at the ends of chromosomes, progressively shorten with each cellular division. Spermatozoa have very long telomeres but they lack telomerase enzymatic activity that is necessary for de novo synthesis and addition of telomeres. We performed a telomere restriction fragment analysis to compare the telomere lengths in immature rat testis (containing type A spermatogonia) with adult rat testis (containing more differentiated germ cells). Mean telomere length in the immature testis was significantly shorter in comparison to adult testis, suggesting that type A spermatogonia probably have shorter telomeres than more differentiated germ cells. Then, we isolated type A spermatogonia from immature testis, and pachytene spermatocytes and round spermatids from adult testis. Pachytene spermatocytes exhibited longer telomeres compared to type A spermatogonia. Surprisingly, although statistically not significant, round spermatids showed a decrease in telomere length. Epididymal spermatozoa exhibited the longest mean telomere length. In marked contrast, telomerase activity, measured by the telomeric repeat amplification protocol was very high in type A spermatogonia, decreased in pachytene spermatocytes and round spermatids, and was totally absent in epididymal spermatozoa. In summary, these results indicate that telomere length increases during the development of male germ cells from spermatogonia to spermatozoa and is inversely correlated with the expression of telomerase activity.

Lanosterol 14alpha-demethylase (CYP51), NADPH-cytochrome P450 reductase and squalene synthase in spermatogenesis: late spermatids of the rat express proteins needed to synthesize follicular fluid meiosis activating sterol

Lanosterol 14alpha-demethylase (CYP51) is a cytochrome P450 enzyme involved primarily in cholesterol biosynthesis. CYP51 in the presence of NADPH-cytochrome P450 reductase converts lanosterol to follicular fluid meiosis activating sterol (FF-MAS), an intermediate of cholesterol biosynthesis which accumulates in gonads and has an additional function as oocyte meiosis-activating substance. This work shows for the first time that cholesterogenic enzymes are highly expressed only in distinct stages of spermatogenesis. CYP51, NADPH-P450 reductase (the electron transferring enzyme needed for CYP51 activity) and squalene synthase (an enzyme preceding CYP51 in the pathway) proteins have been studied. CYP51 was detected in step 3-19 spermatids, with large amounts in the cytoplasm/residual bodies of step 19 spermatids, where P450 reductase was also observed. Squalene synthase was immunodetected in step 2-15 spermatids of the rat, indicating that squalene synthase and CYP51 proteins are not equally expressed in same stages of spermatogenesis. Discordant expression of cholesterogenic genes may be a more general mechanism leading to transient accumulation of pathway intermediates in spermatogenesis. This study provides the first evidence that step 19 spermatids and residual bodies of the rat testis have the capacity to produce MAS sterols in situ.

Neprilysin II: A putative novel metalloprotease and its isoforms in CNS and testis

Metalloproteases of the M13 subfamily, comprising namely neprylisin (NEP) and endothelin-converting enzyme (ECE), are involved in the metabolism of various neuronal and hormonal peptides, and inhibitors thereof have already led to therapeutically useful agents. Using homology cloning, we have identified a new member of this family in rat tissues. It is a glycosylated, type II integral membrane protein of 774 amino acids, containing a zinc-binding consensus motif, highly homologous to NEP and, therefore, designated NEPII. We have characterized multiple splice variants of NEPII mRNA with distinct expression patterns in brain regions, pituitary and testis. In situ hybridization of testis, where levels of the NEPII gene transcript are the highest, reveals a localization within round spermatids. In brain, NEPII is expressed heterogeneously among several neuronal populations and according to a pattern grossly complementary to that of NEP.

Induction of metallothionein synthesis with preservation of testicular function in rats following long term renal transplantation

Metallothionein (MT), as an acute phase or stress-response protein and free radical scavenger, is related to inflammation and cellular protection from oxidative damage. In order to evaluate long-term testicular damage and the role of MT following renal transplant, nine allogenic (Fisher 344 --> Lewis) and seven isogenic (Lewis --> Lewis) renal transplants were performed and the recipient rats were followed for 140 days when allografts develop chronic transplant rejection. Testicular weight, light microscopic morphology, and lactate dehydrogenase-X enzyme activity were assessed. Testicular MT was determined by Cd-heme assay, and was localized immunocytochemically using a polyclonal rabbit antibody. No differences in testis weight, morphology, or LDH-X enzyme activity were found between allograft and isograft recipients. Testicular MT level was significantly increased in the testis of allograft recipients. Testicular zinc (Zn) and copper (Cu) levels, but not iron (Fe) level, were significantly higher in testis with allograft kidney than that with isograft kidney. In addition, Cu/Zn ratio was also significantly high in the allograft group. However, the MT level did not show any significant correlation either with Cu and Zn alone or with Cu/Zn and Fe/Zn ratios. These data suggest that allogenic stimuli may induce MT synthesis in the recipient testis. The increased MT level in an allograft may offer a protective action from oxidative damage in the testis.

Ca(2+)/calmodulin-dependent protein kinase IV is expressed in spermatids and targeted to chromatin and the nuclear matrix

Ca(2+)/calmodulin-dependent protein kinase IV and calspermin are two proteins encoded by the Camk4 gene. Both are highly expressed in the testis, where in situ hybridization studies in rat testes have demonstrated that CaMKIV mRNA is localized to pachytene spermatocytes, while calspermin mRNA is restricted to spermatids. We have examined the expression patterns of both CaMKIV and calspermin in mouse testis and unexpectedly find that CaMKIV is expressed in spermatogonia and spermatids but excluded from spermatocytes, while calspermin is found only in spermatids. CaMKIV and calspermin expression in the testis are stage-dependent and appear to be coordinately regulated. In germ cells, we find that CaMKIV is associated with the chromatin. We further demonstrate that a fraction of CaMKIV in spermatids is hyperphosphorylated and specifically localized to the nuclear matrix. These novel findings may implicate CaMKIV in chromatin remodeling during nuclear condensation of spermatids.

Chromatin condensation during Scrobicularia plana spermiogenesis: a controlled and comparative enzymatic ultracytochemical study

In Scrobicularia plana testis, a nuclear acid phosphatase (ACPase) activity was detected in mid and late spermatids with the improved Gomori-chloride procedure. Lead deposits were first observed in mid spermatids at focal points over condensed chromatin strands, increasing in density as chromatin further condensated. In late spermiogenesis, lead deposits became concentrated between chromatin aggregates, and after total DNA compaction were transfered to the nuclear periphery and then shed into the cytoplasm. The specificity of the nuclear ACPase was tested against different pH values (3.9, 7.2, 7.8, 9.0), substrates (TPP, IDP, TMP, p-NCS, ATP, GTP, AMP, ADP, AMP-PNP) and inhibitors (NaF, levamisole, Zn, vanadate, theophylline). To further specify the nature of this nuclear ACPase, other enzymes were comparatively studied at their optimal pH values and at pH 5.0: nucleoside-diphosphatase, thiamin-pyrophosphatase, inorganic trimetaphosphatase, lysosomal arylsulfatases A and B, ATPase, GTPase, 5'-nucleotidase, adenylate kinase, and adenylate cyclase. Several other controls were introduced to exclude artefactual deposits induced by lead ions and tissue molecules. The results showed that the enzyme has an optimal pH at 5.0, a high specific affinity for beta-GP, and is inhibited by NaF, which suggests that it behaves as a type B-ACPase, and all controls demonstrated the specificity of the enzymic activity. Because lead deposits were specifically and temporally associated with spermatid chromatin condensation, when DNA and RNA synthesis, histones, phosphoproteins and RNA molecules strongly decrease, it is possible to suggest that the nuclear ACPase could be associated with DNA processing during chromatin compaction or involved in the hydrolysis of 2' and 3' nucleotides resulting from nuclear RNase action during RNA degradation.

Postmeiotic modifications of spermatogenic cells are accompanied by inhibition of telomerase activity

We investigated whether testicular telomerase activity is due to telomerase expression in all cells or expression in a limited number of cells. Telomerase activity was assayed in highly purified fractions of spermatogonia cells plus primary spermatocytes, secondary spermatocytes plus round spermatids, secondary spermatocytes plus spermatids plus spermatozoa, round spermatids, or spermatozoa prepared from healthy or cryptorchid animals. Telomerase activity was additionally assayed in testicular tissue of prepubertal animals and animals with Sertoli cell only pathophysiology. Telomerase activity was detected in fractions containing primary spermatocytes and/or secondary spermatocytes and/or spermatids. Fractions enriched in round spermatids were positive for telomerase activity. In contrast, spermatozoa or Sertoli cell fractions were negative for telomerase activity. Using the relative telomerase activity assay and the sensitive quantitative telomerase assay to quantify telomerase activity, we showed that induction of cryptorchidism does not result in quantitative alterations in testicular tissue telomerase activity. In addition, elimination of round spermatids does not lead to significant alterations in testicular tissue telomerase activity. The present results suggest that the male gamete telomerase activity is inhibited during spermiogenesis. Furthermore, it appears that spermatogonia/primary spermatocytes are the main sources of telomerase activity in the testis.

Dual function of the selenoprotein PHGPx during sperm maturation

The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) changes its physical characteristics and biological functions during sperm maturation. PHGPx exists as a soluble peroxidase in spermatids but persists in mature spermatozoa as an enzymatically inactive, oxidatively cross-linked, insoluble protein. In the midpiece of mature spermatozoa, PHGPx protein represents at least 50 percent of the capsule material that embeds the helix of mitochondria. The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency.

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.

Alpha-mannosidases involved in N-glycan processing show cell specificity and distinct subcompartmentalization within the Golgi apparatus of cells in the testis and epididymis

The Golgi apparatus is enriched in specific enzymes involved in the maturation of carbohydrates of glycoproteins. Among them, alpha-mannosidases IA, IB and II are type II transmembrane Golgi-resident enzymes that remove mannose residues at different stages of N-glycan maturation. alpha-Mannosidases IA and IB trim Man9GlcNAc2 to Man5GlcNAc2, while alpha-mannosidase II acts after GlcNAc transferase I to remove two mannose residues from GlcNAcMan5GlcNAc2 to form GlcNAcMan3GlcNAc2 prior to extension into complex N-glycans by Golgi glycosyltransferases. The objective of this study is to examine the expression as well as the subcellular localization of these Golgi enzymes in the various cells of the male rat reproductive system. Our results show distinct cell-and region-specific expression of the three mannosidases examined. In the testis, only alpha-mannosidase IA and II were detectable in the Golgi apparatus of Sertoli and Leydig cells, and while alpha-mannosidase IB was present in the Golgi apparatus of all germ cells, only the Golgi apparatus of steps 1-7 spermatids was reactive for alpha-mannosidase IA. In the epididymis, principal cells were unreactive for alpha-mannosidase II, but they expressed alpha-mannosidase IB in the initial segment and caput regions, and alpha-mannosidase IA in the corpus and cauda regions. Clear cells expressed alpha-mannosidase II in all epididymal regions, and alpha-mannosidase IB only in the caput and corpus regions. Ultrastructurally, alpha-mannosidase IB was localized mainly over cis saccules, alpha-mannosidase IA was distributed mainly over trans saccules, and alpha-mannosidase II was localized mainly over medial saccules of the Golgi stack. Thus, the cell-specific expression and distinct Golgi subcompartmental localization suggest that these three alpha-mannosidases play different roles during N-glycan maturation.

Identification and characterization of a haploid germ cell-specific nuclear protein kinase (Haspin) in spermatid nuclei and its effects on somatic cells

We have cloned the entire coding region of a mouse germ cell-specific cDNA encoding a unique protein kinase whose catalytic domain contains only three consensus subdomains (I-III) instead of the normal 12. The protein possesses intrinsic Ser/Thr kinase activity and is exclusively expressed in haploid germ cells, localizing only in their nuclei, and was thus named Haspin (for haploid germ cell-specific nuclear protein kinase). Western blot analysis showed that specific antibodies recognized a protein of Mr 83,000 in the testis. Ectopically expressed Haspin was detected exclusively in the nuclei of cultured somatic cells. Even in the absence of kinase activity, however, Haspin caused cell cycle arrest at G1, resulting in growth arrest of the transfected somatic cells. In a DNA binding experiment, approximately one-half of wild-type Haspin was able to bind to a DNA-cellulose column, whereas the other half was not. In contrast, all of the deletion mutant Haspin that lacked autophosphorylation bound to the DNA column. Thus, the DNA-binding activity of Haspin may, in some way, be associated with its kinase activity. These observations suggest that Haspin has some critical roles in cell cycle cessation and differentiation of haploid germ cells.

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.

Transition protein 4 from boar late spermatid nuclei is a topological factor that stimulates DNA-relaxing activity of topoisomerase I

Transition protein 4 (TP4) from boar late spermatid nuclei, having higher affinity for double-stranded DNA and a local melting activity of DNA, stimulated SV40 DNA-relaxing activity of eukaryotic topoisomerase I at TP4/DNA molar ratios of 6.6-11. A TP4-spermidine mixture stimulated the activity of topoisomerase I much more than spermidine alone, but no more than TP4 alone, and poly-L-arginine did not. These results suggest that TP4 contributes to the chromatin reorganization in the late spermatid nuclei from nucleosomal-type structure with negatively supercoiled DNA to nucleoprotamine structure with no supercoiled DNA.

Cloning of two isoforms of mouse DNA helicase Q1/RecQL cDNA; alpha form is expressed ubiquitously and beta form specifically in the testis

We cloned cDNAs encoding mouse homologues for the human DNA helicase Q1/RecQL (human helicase Q1) which has homology with the Escherichia coli RecQ protein and found that they encode two isoforms. The two isoforms are identical over the entire sequence except for the carboxyl terminal sequence spanning less than 30 amino acids. One of the two isoforms, alpha, contains a sequence, KKRK, in the carboxyl terminus, which is also contained in human helicase Q1 and was confirmed to function as the nuclear localization signal. The other form, beta, does not contain such a sequence. Expression of mouse helicase Q1 mRNA is extremely and relatively high in the testis and the thymus, respectively. RT-PCR analysis revealed that helicase Q1alpha was expressed in all tissues tested and the beta form was expressed only in the testis. A survey of expression of Q1alpha and Q1beta mRNA in the testis after birth revealed that Q1alpha mRNA is expressed in all testes of mice aged from 7 days to 8 weeks, and the expression of Q1beta mRNA begins 14 days after birth, corresponding to the appearance of cells in the pachytene stage.

Lipid metabolising enzymes in isolated rat testicular germ cells and changes associated with meiosis

To assess the lipid metabolising potential of testicular germ cells undergoing meiosis, spermatocytes and spermatids were isolated from adult rat testis and purified by centrifugal elutriation followed by density gradient centrifugation. Seven key enzymes of lipid metabolism (namely beta-hydroxybutyrate dehydrogenase, carnitine acetyl transferase, ATP citrate lyase, hydroxyacyl-CoA dehydrogenase, glycerol 3-phosphate dehydrogenase, acetyl-CoA carboxylase and long chain acyl-CoA synthetase) were assayed in cell homogenates. The results indicated that germ cells possess the key enzymes for de novo synthesis and oxidation of fatty acids. The significant increase in activities of anabolic enzymes and decrease in activities of catabolic enzymes in post-meiotic germ cells indicated a shift in lipid metabolism towards fatty acid synthesis during meiosis. Long chain acyl-CoA synthetase activity was not detected in the two cell types. The study indicates a major reorganization of fatty acid turnover during meiosis with equilibrium shifting in favour of synthesis.