Separation of mouse testis cells on a Celsep (TM) apparatus and their usefulness as a source of high molecular weight DNA or RNA

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

Genome-wide chromatin occupancy of BRDT and gene expression analysis suggest transcriptional partners and specific epigenetic landscapes that regulate gene expression during spermatogenesis

BRDT, a member of the BET family of double bromodomain-containing proteins, is essential for spermatogenesis in the mouse and has been postulated to be a key regulator of transcription in meiotic and post-meiotic cells. To understand the function of BRDT in these processes, we first characterized the genome-wide distribution of the BRDT binding sites, in particular within gene units, by ChIP-Seq analysis of enriched fractions of pachytene spermatocytes and round spermatids. In both cell types, BRDT binding sites were mainly located in promoters, first exons, and introns of genes. BRDT binding sites in promoters overlapped with several histone modifications and histone variants associated with active transcription, and were enriched for consensus sequences for specific transcription factors, including MYB, RFX, ETS, and ELF1 in pachytene spermatocytes, and JunD, c-Jun, CRE, and RFX in round spermatids. Subsequent integration of the ChIP-seq data with available transcriptome data revealed that stage-specific gene expression programs are associated with BRDT binding to their gene promoters, with most of the BDRT-bound genes being upregulated. Gene Ontology analysis further identified unique sets of genes enriched in diverse biological processes essential for meiosis and spermiogenesis between the two cell types, suggesting distinct developmentally stage-specific functions for BRDT. Taken together, our data suggest that BRDT cooperates with different transcription factors at distinctive chromatin regions within gene units to regulate diverse downstream target genes that function in male meiosis and spermiogenesis.

Meiotic failure in cyclin A1-deficient mouse spermatocytes triggers apoptosis through intrinsic and extrinsic signaling pathways and 14-3-3 proteins

Cyclin A1 (Ccna1), a member of the mammalian A type cyclins, is most abundantly expressed in spermatocytes and is essential for spermatogenesis in the mouse. Ccna1- deficient spermatocytes arrest at late meiotic prophase and undergo apoptosis. To further delineate the mechanisms and key factors involved in this process, we have examined changes in expression of genes involved in both intrinsic and extrinsic signaling pathways that trigger apoptosis in the mutant spermatocytes. Our results show that both pathways are involved, and that the factors involved in the intrinsic pathway were expressed earlier than those involved in the extrinsic pathway. We have also begun to identify in vivo Ccna1-interacting proteins, using an unbiased biochemical approach, and identified 14-3-3, a key regulator of apoptosis, as a Ccna1-interacting protein. Expression levels of 14-3-3 proteins remain unchanged between wild type and mutant testes but there were differences in the subcellular distribution. In wild type control, 14-3-3 is detected in both cytosolic and nuclear fractions whereas it is restricted to the cytoplasm in mutant testes. This differential distribution of 14-3-3 may contribute to the induction of apoptosis in Ccna1-deficient spermatocytes. These results provide insight into the apoptotic mechanisms and pathways that are triggered when progression through the meiotic cell cycle is defective in male gametogenesis.

BET Protein BRDT Complexes With HDAC1, PRMT5, and TRIM28 and Functions in Transcriptional Repression During Spermatogenesis

The expression of BRDT, a member of the BET sub-family of double bromodomain-containing proteins, is restricted to the male germ line, specifically to pachytene-diplotene spermatocytes and early spermatids. We previously showed that loss of the first bromodomain of BRDT by targeted mutagenesis (Brdt(ΔBD1) ) resulted in sterility and abnormalities in spermiogenesis, but little is known about BRDT's function at the molecular level. As part of studies designed to identify BRDT-interacting proteins we stably introduced a FLAG-tagged BRDT cDNA into 293T cells, which do not normally express BRDT. Affinity-purification of FLAG-tagged BRDT complexes indicated that BRDT has novel interactions with the histone deacetylase HDAC1, the arginine-specific histone methyltransferase 5 PRMT5, and the Tripartite motif-containing 28 protein TRIM28. Immunofluorescent microscopy revealed that BRDT co-localized with each of these proteins in round spermatids and co-immunoprecipitation of testicular extracts showed that these proteins interact with BRDT. Furthermore, they bind the promoter of H1t, a putative target of BRDT-containing complexes. This binding of H1t was lost in mice expressing the Brdt(ΔBD1) mutant protein and concomitantly, H1t expression was elevated in round spermatids. Our study reveals a role for BRDT-containing complexes in the repression of gene expression in vivo that correlates with dramatic effects on chromatin remodeling and the progression of spermiogenesis.

Mammalian E-type cyclins control chromosome pairing, telomere stability and CDK2 localization in male meiosis

Loss of function of cyclin E1 or E2, important regulators of the mitotic cell cycle, yields viable mice, but E2-deficient males display reduced fertility. To elucidate the role of E-type cyclins during spermatogenesis, we characterized their expression patterns and produced additional deletions of Ccne1 and Ccne2 alleles in the germline, revealing unexpected meiotic functions. While Ccne2 mRNA and protein are abundantly expressed in spermatocytes, Ccne1 mRNA is present but its protein is detected only at low levels. However, abundant levels of cyclin E1 protein are detected in spermatocytes deficient in cyclin E2 protein. Additional depletion of E-type cyclins in the germline resulted in increasingly enhanced spermatogenic abnormalities and corresponding decreased fertility and loss of germ cells by apoptosis. Profound meiotic defects were observed in spermatocytes, including abnormal pairing and synapsis of homologous chromosomes, heterologous chromosome associations, unrepaired double-strand DNA breaks, disruptions in telomeric structure and defects in cyclin-dependent-kinase 2 localization. These results highlight a new role for E-type cyclins as important regulators of male meiosis.

Understanding the control of meiosis is fundamental to deciphering the origin of male infertility. Although the mechanisms controlling meiosis are poorly understood, key regulators of mitosis, such as cyclins, appear to be critical. In this regard, male mice deficient for cyclin E2 exhibit subfertility and defects in spermatogenesis; however, neither the stages of germ cell differentiation affected nor the responsible mechanisms are known. We investigated how E-type cyclins control male meiosis by examining their expression in spermatogenesis and the consequences that multiple deletions of Ccne1 and Ccne2 alleles produce. Loss of Ccne2 expression increases cyclin E1 levels as a compensatory effect, but there are still meiotic defects and subfertility. Further, loss of one Ccne1 allele in the absence of cyclin E2 results in infertility as does loss of the remaining Ccne1 allele, but with even more severe meiotic abnormalities. We further found that cyclin E1 is involved in sex chromosome synapsis while E2 is involved with homologous pairing and chromosome and telomere integrity. These processes and structures were severely disrupted in absence of both cyclin E1 and E2, uncovering new roles for the E-type cyclins in regulating male meiosis.

Identification of germ cell-specific genes in mammalian meiotic prophase

BACKGROUND

Mammalian germ cells undergo meiosis to produce sperm or eggs, haploid cells that are primed to meet and propagate life. Meiosis is initiated by retinoic acid and meiotic prophase is the first and most complex stage of meiosis when homologous chromosomes pair to exchange genetic information. Errors in meiosis can lead to infertility and birth defects. However, despite the importance of this process, germ cell-specific gene expression patterns during meiosis remain undefined due to difficulty in obtaining pure germ cell samples, especially in females, where prophase occurs in the embryonic ovary. Indeed, mixed signals from both germ cells and somatic cells complicate gonadal transcriptome studies.

RESULTS

We developed a machine-learning method for identifying germ cell-specific patterns of gene expression in microarray data from mammalian gonads, specifically during meiotic initiation and prophase. At 10% recall, the method detected spermatocyte genes and oocyte genes with 90% and 94% precision, respectively. Our method outperformed gonadal expression levels and gonadal expression correlations in predicting germ cell-specific expression. Top-predicted spermatocyte and oocyte genes were both preferentially localized to the X chromosome and significantly enriched for essential genes. Also identified were transcription factors and microRNAs that might regulate germ cell-specific expression. Finally, we experimentally validated Rps6ka3, a top-predicted X-linked spermatocyte gene. Protein localization studies in the mouse testis revealed germ cell-specific expression of RPS6KA3, mainly detected in the cytoplasm of spermatogonia and prophase spermatocytes.

CONCLUSIONS

We have demonstrated that, through the use of machine-learning methods, it is possible to detect germ cell-specific expression from gonadal microarray data. Results from this study improve our understanding of the transition from germ cells to meiocytes in the mammalian gonad. Further, this approach is applicable to other tissues for which isolating cell populations remains difficult.

Sp1 transcription factor and GATA1 cis-acting elements modulate testis-specific expression of mouse cyclin A1

Cyclin A1 is a male germ cell-specific cell cycle regulator that is essential for spermatogenesis. It is unique among the cyclins by virtue of its highly restricted expression in vivo, being present in pachytene and diplotene spermatocytes and not in earlier or later stages of spermatogenesis. To begin to understand the molecular mechanisms responsible for this narrow window of expression of the mouse cyclin A1 (Ccna1) gene, we carried out a detailed analysis of its promoter. We defined a 170-bp region within the promoter and showed that it is involved in repression of Ccna1 in cultured cells. Within this region we identified known cis-acting transcription factor binding sequences, including an Sp1-binding site and two GATA1-binding sites. Neither Sp1 nor GATA1 is expressed in pachytene spermatocytes and later stages of germ cell differentiation. Sp1 is readily detected at earlier stages of spermatogenesis. Site-directed mutagenesis demonstrated that neither factor alone was sufficient to significantly repress expression driven by the Ccna1 promoter, while concurrent binding of Sp1, and most likely GATA1 and possibly additional factors was inhibitory. Occupancy of Sp1 on the Ccna1 promoter and influence of GATA1-dependent cis-acting elements was confirmed by ChIP analysis in cell lines and most importantly, in spermatogonia. In contrast with many other testis-specific genes, the CpG island methylation status of the Ccna1 promoter was similar among various tissues examined, irrespective of whether Ccna1 was transcriptionally active, suggesting that this regulatory mechanism is not involved in the restricted expression of Ccna1.

The testis-specific double bromodomain-containing protein BRDT forms a complex with multiple spliceosome components and is required for mRNA splicing and 3'-UTR truncation in round spermatids

Members of the BET (bromodomain and extra terminal motif) family of proteins have been shown to be chromatin-interacting regulators of transcription. We previously generated a mutation in the testis-specific mammalian BET gene Brdt (bromodomain, testis-specific) that yields protein lacking the first bromodomain (BRDT(ΔBD1)) and observed disrupted spermiogenesis and male sterility. To determine whether BRDT(ΔBD1) protein results in altered transcription, we analyzed the transcriptomes of control versus Brdt(ΔBD1/ΔBD1) round spermatids. Over 400 genes showed statistically significant differential expression, and among the up-regulated genes, there was an enrichment of RNA splicing genes. Over 60% of these splicing genes had transcripts that lacked truncation of their 3'-untranslated region (UTR) typical of round spermatids. We selected four of these genes to characterize: Srsf2, Ddx5, Hnrnpk and Tardbp. The 3'-UTRs of Srsf2, Ddx5 and Hnrnpk mRNAs were longer in mutant round spermatids and resulted in reduced protein levels. Tardbp was transcriptionally up-regulated and a splicing shift toward the longer variant was observed. All four splicing proteins were found to complex with BRDT in control and mutant testes. We thus suggest that, along with modulating transcription, BRDT modulates gene expression as part of the splicing machinery. These modulations alter 3'-UTR processing in round spermatids; importantly, the BD1 is essential for these functions.

Expression of retinoic acid receptor alpha in the germline is essential for proper cellular association and spermiogenesis during spermatogenesis

Signaling through vitamin A metabolites is indispensable for spermatogenesis, and disruption of retinoic acid receptor alpha (RARalpha) function resulted in male sterility and aberrant spermatogenesis, which resembled vitamin A deficiency. Here we investigated the lineage- and cell-specific role of RARalpha-mediated signaling during spermatogenesis using germ-cell transplantation and genetically manipulated mouse models. We demonstrated that RARalpha-deficient germ-cell stem cells were able to repopulate germ-cell-depleted wild-type testes and initiate spermatogenesis; however, improper cellular associations and abnormal sperm formation were observed. We further generated RARalpha-deficient mice that expressed RARalpha-EGFP fusion protein uniquely in haploid germ cells. Strikingly, spermatid orientation, alignment and release, as well as sperm morphology, were normal and there was a partial rescue of sterility. These data provide the first direct evidence for a distinct requirement of RARalpha-mediated retinoid signaling specifically in germ cells.

Isolation and viability of presumptive spermatids collected from bull testes by Percoll density gradient

The objective of the present study was to develop a procedure for isolating pure populations of round spermatid(s) (RS) by Percoll density gradient from bull testes. Bull testes were de-capsulated and testicular tissues were dissociated enzymatically to recover RS. After being filtered through a 20 microm nylon mesh, the cells were centrifuged at 650 x g for 25 min through the discontinuous Percoll density gradients (20, 35, 40, 45 and 90% Percoll solution). Isolated cells were analyzed by microscopic observation for survivability and apoptosis. In Experiment 1, both microscopic observation and DNA analysis by flow cytometry showed that approximately 40% of cells collected from 35% Percoll gradient were presumptive RS, whereas in 40% Percoll gradient, mostly primary spermatocytes were observed. Experiment 2 compared the effect of 35% Percoll density isolation on the incidence of apoptosis and necrosis in fresh and frozen-thawed cells to those of untreated cells. The percentage (mean+/-S.E.M.) of necrosis in cells collected from 35% Percoll gradient was less (P<0.05) than in untreated and frozen-thawed cells from 35% Percoll gradient (11.7+/-3.1% compared with 26.3+/-2.0% and 53.5+/-1.3%, respectively), but the rate of apoptosis did not differ (1.2+/-0.49% compared with 2.5+/-0.8% and 0.9+/-0.04%, respectively). The proportional data (mean+/-S.E.M.) of live cells in Percoll treated group were greater (P<0.05) than in untreated and frozen-thawed cells from the 35% Percoll gradient (86.7+/-3.26% compared with 70.8+/-2.73% and 41.9+/-1.69%, respectively). Experiment 3 compared the development rates of embryos injected with RS isolated from fresh and frozen-thawed cells collected with the 35% Percoll gradient to those of untreated cells, and parthenotes as control. There were no significant (P>0.05) differences in the rates of cleavage and blastocyst development between untreated fresh cells and fresh cells collected from the 35% Percoll gradient (75.4 and 10.5% compared with 82.4 and 12.8%). However, there were lesser (P<0.05) cleavage and blastocyst rates in frozen-thawed cells from the 35% Percoll gradient (51.6 and 6.3%) and parthenotes (60.7 and 4.1%) were observed. These results suggest that isolation of presumptive RS by 35% Percoll density gradient is effective in eliminating apoptotic and early necrotic cells. However, the use of RS in improving the developmental potential of embryos merits further studies.

Separation of spermatogenic cells from adult transgenic mouse testes using unit-gravity sedimentation

During the final stage of spermatogenesis (i.e., spermiogenesis), round spermatids differentiate into mature spermatozoa. This transformation is mediated by a suite of nuclear packaging proteins. These include the transition proteins and the protamines. The two human protamines PRM1 and PRM2, and transition protein TNP2, are encoded by a single chromatin domain bounded by two regions of matrix attachment. Previous transgenic studies in our laboratory have shown that mice harboring a 40-kb segment of human chromosome 16p13.13 containing the PRM1--> PRM2-->TNP2 domain express the transgene in a haploid-specific, copy number-dependent, and position-independent manner. While these results indicate that this segment of the genome is a complete structural and functional regulatory unit, the elements governing the haploid expression of this suite of genes remain to be clearly defined. The preparation of spermatogenic cells is required to begin to address this mechanism. The CELSEP (Wescor/Dupont Inc. Wilmington, DE) unit-gravity sedimentation apparatus provides a simple, efficient, and reproducible means to separate testicular germ cells at all stages along this differentiative pathway. The high quality and integrity of germ cells obtained by this means provides a valuable resource for characterizing the molecular mechanisms governing the regulation of the PRM1-->PRM2-->TNP2 domain during spermatogenesis. A discussion of the CELSEP apparatus and the application of this methodology in our laboratory are presented.

A small RNA in testis and brain: implications for male germ cell development

BC1 RNA, a small non-coding RNA polymerase III transcript, is selectively targeted to dendritic domains of a subset of neurons in the rodent nervous system. It has been implicated in the regulation of local protein synthesis in postsynaptic microdomains. The gene encoding BC1 RNA has been suggested to be a master gene for repetitive ID elements that are found interspersed throughout rodent genomes. A prerequisite for the generation of repetitive elements through retroposition and subsequent transmission in the germline is expression of the master gene RNA in germ cells. To test this hypothesis, we have investigated expression of BC1 RNA in murine male germ cells. We report that BC1 RNA is expressed at substantial levels in a subset of male germ cells. Results from cell fractionation experiments, developmental analysis,and northern and in situ hybridization showed that the RNA was expressed in pre-meiotic spermatogonia, with particularly high amounts in syncytial ensembles of cells that are primed for synchronous spermatogenic differentiation. BC1 RNA continued to be expressed in spermatocytes, but expression levels decreased during further spermatogenic development, and low or negligible amounts of BC1 RNA were identified in round and elongating spermatids. The combined data indicate that BC1 RNA operates in groups of interconnected germ cells, including spermatogonia, where it may function in the mediation of translational control. At the same time, the identification of BC1 RNA in germ cells provides essential support for the hypothesis that repetitive ID elements in rodent genomes arose from the BC1 RNA gene through retroposition.

Characterization of D1Pas1, a mouse autosomal homologue of the human AZFa region DBY, as a nuclear protein in spermatogenic cells

OBJECTIVE

To gain insight into the function of D1Pas1 in spermatogenesis.

DESIGN

The cellular and subcellular distribution of D1Pas1 protein were examined.

SETTING

Academic research laboratory.

ANIMALS

Swiss Webster and C57B1/6J mice.

INTERVENTION(S)

Antibodies were generated against a D1Pas1 fusion protein. Immunoblot analysis was performed on lysates of testicular cells separated into enriched populations of spermatogenic cells and fractionated into nuclear and cytoplasmic compartments. Immunohistochemistry was performed on histological sections of testis from adult and postnatal day 17 mice.

MAIN OUTCOME MEASURE(S)

D1Pas1 protein distribution.

RESULT(S)

D1Pas1 was expressed in germ cells, and its expression was developmentally regulated because it was detected specifically in the meiotic and postmeiotic haploid stages of spermatogenesis. D1Pas1 protein was predominantly localized in the nucleus, with weak cytoplasmic staining.

CONCLUSION(S)

Nuclear localization of D1Pas1 in the testis and its sequence homology to putative RNA helicases suggests a role of D1Pas1 in pre-mRNA processing during spermatogenesis. Germ cell expression of D1Pas1 and homology to the Y chromosome gene DBY, which is located in an area deleted in azoospermia, suggests a potential role for an autosomal gene in the regulation of spermatogenesis.

Role of class B scavenger receptor type I in phagocytosis of apoptotic rat spermatogenic cells by Sertoli cells

Rat Sertoli cells phagocytose apoptotic spermatogenic cells, which consist mostly of spermatocytes, in primary culture by recognizing phosphatidylserine (PS) exposed on the surface of degenerating spermatogenic cells. We compared the mode of phagocytosis using spermatogenic cells at different stages of spermatogenesis. Spermatogenic cells were separated into several groups based on their ploidy, with purities of 60-90%. When the fractionated spermatogenic cell populations were subjected to a phagocytosis assay, cells with ploidies of 1n, 2n, and 4n were almost equally phagocytosed by Sertoli cells. All the cell populations exposed PS on the cell surface, and phagocytosis of all cell populations was similarly inhibited by the addition of PS-containing liposomes. Class B scavenger receptor type I (SR-BI), a candidate for the PS receptor, was detected in Sertoli cells. Overexpression of the rat SR-BI cDNA increased the PS-mediated phagocytic activity of Sertoli cell-derived cell lines. Moreover, phagocytosis of spermatogenic cells by Sertoli cells was inhibited in the presence of an anti-SR-BI antibody. Finally, the addition of high density lipoprotein, a ligand specific for SR-BI, decreased both phagocytosis of spermatogenic cells and incorporation of PS-containing liposomes by Sertoli cells. In conclusion, SR-BI functions at least partly as a PS receptor, enabling Sertoli cells to recognize and phagocytose apoptotic spermatogenic cells at all stages of differentiation.

Flow cytometric method to isolate round spermatids from mouse testis

The purpose of this study was to isolate pure populations of round spermatids from mouse testis by flow cytometry followed by cell sorting. Cell suspensions from mouse testis were enriched in germ cells by centrifugation on a discontinuous Percoll gradient, then analysed using a FACScalibur flow cytometer measuring the cell size and density. A large and well-delimited population of cells (R1) expected to contain round spermatids was observed on the dot plot diagram. Sorted R1 cells were very homogeneous in size (approximately 11 microns) and displayed the characteristic cytological aspect of round spermatids. Spermatid-specific gene expression was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of R1 cells using primers for protamine 2 gene (PRM2) and SP-10. A positive signal for SP-10 was obtained with a single cell using nested primers. The 5.5 kb transcript of c-kit, which is not expressed in spermatids, was not detected by nested RT-PCR, excluding a contamination with spermatogonia. Our results clearly established that flow cytometry followed by cell sorting allows the isolation of a highly homogeneous population of round spermatids from the testis.

Developmental schedule of the postnatal rat testis determined by flow cytometry

Analysis of the biochemical events and the genes expressed at various postnatal developmental stages in the testis of mammals is of great importance for understanding spermatogenesis in general and meiosis in particular. A prerequisite for such an analysis is the characterization of a detailed developmental schedule of the postnatal testis. In this study we used four-parameter flow cytometry analysis to determine a detailed testicular developmental schedule in rats as compared to mice. A dot plot of forward-scatter/side-scatter of testicular cell suspensions from mature animals revealed 7 distinct subpopulations within the testis. These, when analyzed by fluorescence parameters, were divided into 4 levels of fluorescence: cells containing 4d DNA, 2d DNA, and 2 levels of haploid cells. Observing the acquisition pattern of these subpopulations during postnatal development, we were able to suggest the following developmental schedule for the rat. At postnatal Days 6-7, the testis contains somatic cells and spermatogonia cells only. By Days 13-14, leptotene spermatocytes appear; by Days 17-18, zygotene spermatocytes are present; by Days 19-20 and Days 22-23, early and late pachytene spermatocytes, respectively, are seen. Haploid round spermatids first appear at Days 24-25 and elongating spermatids by Days 30-31; by Day 36, elongated spermatozoa can be found.

Disruption of murine alpha-enolase by a retroviral gene trap results in early embryonic lethality

Gene trapping with the retroviral ROSA beta geo vector was used to generate lines of mice carrying disrupted genes. Both cDNA and genomic flanks have been cloned from a number of these lines. One mutation has been shown to disrupt the alpha-enolase gene by insertion of the splice-trap vector into the first intron. In adult mice, lacZ expression was detected only in testes. Embryonic expression was detected from 10.5-day postcoitum embryos and was seen as a diffuse staining pattern over much of the embryo, consistent with the housekeeping gene function of alpha-enolase. This mutation results in an early recessive embryonic lethality. Mice heterozygous for the mutation have no obvious phenotype. Mutations of this gene in humans are reported to be associated with rare autosomal-dominant, non-spherocytic haemolytic anaemia. This phenotype is not reproduced in mice heterozygous for this mutation.

Molecular cloning and tissue-specific expression of the mouse homologue of the rat brain 14-3-3 theta protein: characterization of its cellular and developmental pattern of expression in the male germ line

The highly conserved 14-3-3 family of proteins, originally reported as brain-specific and then found in various somatic cells and oocytes, interacts with several important signal transduction kinases so that actually the 14-3-3 protein are considered as modulators of multiple signal transduction pathways. Here we show that a 14-3-3 protein is also expressed in the male germ cells, thus extending the protein cellular distribution to a cell line never reported to express 14-3-3 proteins. Screening of a mouse spermatogenic cells lambda gt11 cDNA library with affinity-purified polyclonal antibodies to the tyrosine kinase SP42 allowed the isolation of several positive clones. Sequencing of a positive cDNA clone revealed a 735-nucleotide open reading frame encoding a protein of 245 amino acids (27,778 Da). The predicted protein was found to be identical to the most recently discovered 14-3-3 isoform, the theta subtype from a rat brain. Here we demonstrate that 14-3-3 theta mRNA is highly expressed in testis and brain only. Western immunoblot analyses confirm the Northern blot data. Developmental Northern and Western blot analyses are consistent with an expression and translation of the 14-3-3 theta gene throughout spermatogenesis. However, analysis of RNA from purified populations of spermatogenic cells at different developmental stages and immunohistochemistry on adult testis sections reveal that within the testis the 14-3-3 theta gene products are most abundant in meiotic prophase spermatocytes, and, above all, in differentiating spermatids. Both testicular and epididymal spermatozoa are negative. The present study is the first report on the presence and molecular characterization of the 14-3-3 theta gene product in the male germ line. Our observations suggest that this specific member of the 14-3-3 protein family could play distinct modulatory roles in the complex development of the mammalian male germ cell lineage.

The NIMA-related kinase 2, Nek2, is expressed in specific stages of the meiotic cell cycle and associates with meiotic chromosomes

The Aspergillus nimA gene encodes a Ser/Thr protein kinase which is required for mitosis, in addition to Cdc2, and which has been suggested to have a role in chromosomal condensation. In this study, we isolated a potential murine homologue of nimA, Nek2, which was shown to be expressed most abundantly in the testis of the adult tissues examined. Its expression in the testis was restricted to the germ cells, with highest levels detected in spermatocytes at pachytene and diplotene stages. Immunohistochemical analysis revealed that Nek2 localized to nuclei, exhibiting a non-uniform distribution within the nucleus. Nek2 appeared to be associated with meiotic chromosomes, an association that was better defined by immunolocalization to hypotonically dispersed meiotic chromosomes. This localization was more apparent in regions of dense chromatin, including the sex vesicle, and was also obvious at some of the chromosome ends. The presence of Nek2 protein was not unique to male germ cells, as it was found in meiotic pachytene stage oocytes as well. Furthermore, in an in vitro experimental setting in which meiotic chromosome condensation was induced with okadaic acid, a concomitant induction of Nek2 kinase activity was observed. The expression of Nek2 in meiotic prophase is consistent with the hypothesis that in vivo, Nek2 is involved in the G2/M phase transition of the cell cycle. Our results further provide evidence that in vivo, mouse Nek2 is involved in events of meiosis, including but not limited to chromosomal condensation.

Stage-specific signals in germ line differentiation: control of Sertoli cell phagocytic activity by spermatogenic cells

Differentiation of male germ cells requires a continuous cross-talk with their somatic support, the Sertoli cell. An in vitro model of Sertoli cells was recently provided by established cell lines which maintain Sertoli-specific characteristics, among which is a regulated phagocytic capacity. In vivo, Sertoli cells take up the residual cytoplasm expelled from the maturing sperm, a process restricted to a limited period of germinal maturation, and they also eliminate abnormally differentiated germ cells in case of hormonal deficiency. Cells of the Sertoli line efficiently take up latex beads, as well as dead cells in the cultures. A semiquantitative assay of phagocytosis was developed, based on the uptake of fluorescent latex beads. 15P-1 cultures were found to contain a minor fraction of active phagocytes. After addition of a defined fraction of germ cells, however, all the cells internalized beads as efficiently as macrophages. The inducing cell was identified as the pachytene spermatocyte, a cell type which, in vivo, is associated with Sertoli cells when they express their phagocytic potential. These inducing meiotic cells were not internalized themselves. Rather, they interacted with Sertoli cells via a surface signal that was resistant to formaldehyde fixation. The whole induction process does not involve changes in Sertoli gene expression, since it occurs even in the presence of high doses of cycloheximide. After the required initial contact, further maintenance of the activity was dependent on factor(s) secreted in the medium of the activated culture. Phagocytosis was, on the other hand, abrogated in the presence of factor(s) secreted by a distinct fraction of germ cells, enriched in the late stages (second division) of meiosis.

Molecular cloning of mouse somatic and testis-specific H2B histone genes containing a methylated CpG island

We have isolated a mouse testis-specific H2B histone gene based on the unusual methylation of the CpG island of rat testis-specific H2B gene in somatic tissues. After digestion of genomic DNA with the methylation-sensitive restriction enzyme Hha I, we found that, among 10-20 copies of mouse H2B histone genes, at least three copies are methylated in somatic tissues, but not in testis. Cloning and sequence analysis of two methylated H2B genes revealed that one gene, MTH2B, is strikingly similar to the testis-specific histone H2B (TH2B) gene of rat and the other, psH2B, is a pseudogene of the somatic-type H2B gene. Northern blot analysis revealed that the expression of the MTH2B gene is testis-specific. During spermatogenesis, the MTH2B gene is expressed predominantly in pachytene spermatocytes, as observed in the expression of rat TH2B gene. Interestingly, the MTH2B gene is largely unmethylated in embryonic stem cells, but methylated in F9 embryonal carcinoma cells. The psH2B pseudogene is methylated in somatic tissues and F9 cells, but only partially methylated in embryonic stem cells. Methylation of the psH2B pseudogene seems to be attributed to its location within the context of repetitive sequences including the B1 element. The unmethylation of both H2B histone genes in the testis explains how CpG islands of those histone genes can be maintained during evolution despite heavy methylation in somatic tissues.

sp42, the boar sperm tyrosine kinase, is a male germ cell-specific product with a highly conserved tissue expression extending to other mammalian species

sp42, a tyrosine kinase of 42 kDa originally found in ejaculated boar spermatozoa, is so far the only tyrosine protein kinase to have been purified from mature male germ cells. We have developed and characterized rabbit polyclonal antibodies specifically directed against the boar sperm enzyme, which has been here purified to homogeneity. Anti-sp42 serum and sp42 affinity-purified antibodies work very well in western blot, immunoprecipitation and immunocytochemistry, and do not inhibit sp42 catalytic activity. Immunoblotting analyses reveal the presence of sp42 both in maturing boar epididymal (caput, corpus and cauda segment) spermatozoa and in testicular spermatogenic cells, thus establishing that the protein is effectively expressed in the germ cells and is not a sperm-associated protein secreted by the epididymal epithelium or male accessory glands. This finding is further strengthened by the fact that sp42 is not glycosylated, since different lectins fail to bind to sp42 and treatment of sp42 with different deglycosylation enzymes does not result in a reduction of the molecular mass of sp42. When different boar tissues are immunoscreened in western blot analysis, the results are all sp42-negative. The extension of the study to other mammalian species (human, mouse and rat) demonstrates that proteins immunologically related to boar sp42, which share the same molecular mass and tyrosine kinase activity, are both expressed in spermatogenic cells and maintained in mature sperm cells. Intriguingly, when a wide spectrum of somatic mouse and rat tissues is probed with sp42-antiserum, no tissue presents anti-sp42 immunoreactivity. Immunocytochemistry shows that in boar spermatozoa sp42 is confined to the tail mid-piece, while by immunohistochemistry carried out on sections of adult rat testis the appearance time of the kinase appears to be consistent with a post-meiotic synthesis in haploid spermatids. Altogether, these results demonstrate that boar sp42 is a new male germ cell-specific gene product, with highly conserved tissue expression extended to other mammalian species, and suggest a possible role played by the cytoplasmic tyrosine kinase in the cell signalling network specific to haploid male germ cells.

Cdk family genes are expressed not only in dividing but also in terminally differentiated mouse germ cells, suggesting their possible function during both cell division and differentiation

The roles of the cyclin dependent kinase (Cdk) family in murine germ cell development have been examined by studying the expression of five Cdk family genes (Cdc2, Cdk2, Cdk4, Pctaire-1, and Pctaire-3) in mouse reproductive organs. Northern blot and in situ hybridization analyses revealed distinctive expression patterns of these genes with striking cellular, lineage, and developmental stage specificity. We observed Cdk expression in cell types with proliferative activity: Cdc2 and Cdk2 expression in premeiotic spermatocytes in the testis, and Cdc2, Cdk2, and Cdk4 expression in granulosa cells of ovarian follicles. Cdc2 transcripts were most abundant in late pachytene to diplotene spermatocytes, soon to undergo meiosis. Surprisingly, we also observed expression of Cdk family genes in non-proliferating cell types. All five Cdk family genes examined were expressed in Sertoli cells of the adult testis, which are no longer mitotically active. With regard to Pctaire-1 and Pctaire-3, the highest levels of expression were observed in postmeiotic spermatids. Immunoblot analysis also revealed the presence of high levels of Pctaire-1 in postmeiotic germ cells. These results suggest that Cdk family kinases may exhibit various functions in germinal and somatic cells during gametogenesis, not only in the cell cycle but also in other regulatory processes, including differentiation.

Separation of round spermatids from the rat using an immunoselection panning technique

A method was devised for the isolation of round spermatids from the rat using a positive immunoselection technique (panning). A testis suspension was prepared from adult rats by enzymatic digestion of seminiferous tubules with collagenase. Specific mouse monoclonal antibody (97.25) was indirectly attached to Petri dishes and used in a panning protocol to purify spermatids from the testis cell suspension. The quantity and purity of cells isolated were determined by cell counts and histochemical (periodic acid-Schiff stain) or by immunostaining with acrosome-specific antibodies. A mean yield of 1.38 +/- 0.15 x 10(7) cells per dish was obtained with a purity of more than 90%. The viability of the cells was confirmed by epifluorescent microscopy with propidium iodide/carboxyfluorescein acetate probes. Northern blot analysis of RNA extracted directly from the dish indicated good integrity of a spermatid-specific transcript of glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

Characterization of the heat shock protein P70 in rat spermatogenic cells

A number of hsp70-like proteins are associated with developing male germ cells. One of these molecules, P70, is not sensitive to heat stress and is germ cell-specific, and its expression is developmentally regulated. We have characterized the association of the rat P70(rP70) with differentiating germ cells in the testis and with posttesticular sperm. An antibody originally raised against human sperm proacrosin (designated C3; Sigel et al., 1987: J Reprod Immunol 11:307-319) was found to immunostain rP70 by immunoblot analysis and was used in subsequent studies of the rP70 molecule. The C3 antibody reacted with P70 isoforms in rat, human, mouse, guinea pig, boar, and rooster testicular homogenates. In the developing rat testis, abundant rP70 protein levels were first detected on postnatal day 22, with upregulation to adult levels occurring after postnatal day 28. Purified populations of adult rat pachytene spermatocytes, round spermatids, and elongating spermatids, isolated by unit gravity velocity sedimentation, all expressed rP70. Posttesticular sperm exhibited a loss of the rP70 molecule; caput epididymal sperm were weakly immunoreactive for rP70, but no immunoreactivity was observed in either cauda epididymal sperm or epididymal fluid. In contrast to human ejaculated sperm, rat ejaculated sperm did not express rP70. The loss of P70 from rat posttesticular sperm may reflect species-specific differences in P70 functions, which are thought to include a role in the structural modifications that occur during germ cell differentiation.

Sequence and expression of a cDNA encoding the mouse homologue of the rat ribosomal protein L28

A cDNA encoding the mouse homologue of the rat ribosomal protein L28 was isolated from an adult mouse total testis cDNA library. The L28 cDNA contained a single long open reading frame and exhibited a high degree of conservation to rat L28 at both the nucleotide and amino-acid levels. Northern blot hybridization analysis detected a single transcript in embryo, placenta and adult tissues.

Transcriptional control of the heme oxygenase gene during mouse spermatogenesis

The activation of the heme oxygenase (HO) gene during development of mouse male germ cells was examined by nuclear run-off assay. Results showed that the HO gene was activated in male germ cells, especially in spermatogonia and that the mRNA was stored throughout meiosis. In contrast, Western blotting analysis revealed that HO was expressed during spermatogenesis to spermatocytes. As the mouse HO gene is known to have a 12-o-tetradecanoyl-phorbol 13-acetate(TPA)-responsive element (TRE) in its upstream region and is activated by TPA in mouse M1 cells, we also examined the activation of the nuclear proto-oncogenes fos and jun, which are activators of TRE. Both genes were found to be activated with expression of their protein products only in spermatogonia. Moreover activation of fos, jun and HO genes in spermatogonia was strongly inhibited by a c-kinase inhibitor. These results suggest that the HO gene is activated at the spermatogonia stage by a fos/jun heterodimer complex (AP1) through c-kinase activation.

Haploid specific activations of protamine 1 and hsc70t genes in mouse spermatogenesis

Protamine 1 and heat shock cognate 70 kDa protein (hsc70t) are known to be synthesized in haploid cells during spermatogenesis, and the mRNAs of these proteins have also been shown to accumulate in the haploid cells. However, it is unknown at which stage of spermatogenesis the genes for these proteins are actually activated. To examine this problem, we fractionated mouse adult testes cells at four different developmental stages, extracted their nuclei and carried out run-off assays with hsc70t and protamine 1 DNA probes. Results showed that both genes are mainly activated at the round spermatid stage. As the protein products of these genes accumulate at the later stage, it is interesting that these genes are regulated at the transcriptional and translational levels during spermatogenesis.

HSP86 and HSP84 exhibit cellular specificity of expression and co-precipitate with an HSP70 family member in the murine testis

This study extends to the protein level our previous observations, which had established the stage and cellular specificity of expression of hsp86 and hsp84 in the murine testis in the absence of exogenous stress. Immunoblot analysis was used to demonstrate that HSP86 protein was present throughout testicular development and that its levels increased with the appearance of differentiating germ cells. HSP86 was most abundant in the germ cell population and was present at significantly lower levels in the somatic cells. By contrast, the HSP84 protein was detected in the somatic cells of the testis rather than in germ cells. The steady-state levels of HSP86 and HSP84 paralleled the pattern of the expression of their respective mRNAs, suggesting that regulation at the level of translation was not a major mechanism controlling hsp90 gene expression in testicular cells. Immunoprecipitation analysis revealed that a 70-kDa protein coprecipitated with the HSP86/HSP84 proteins in testicular homogenates. This protein was identified as an HSP70 family member by immunoblot analysis, suggesting that HSP70 and HSP90 family members interact in testicular cells.

Identification of a mouse B-type cyclin which exhibits developmentally regulated expression in the germ line

To begin to examine the function of cyclins in mammalian germ cells, we have screened an adult mouse testis cDNA library for the presence of B-type cyclins. We have isolated cDNAs that encode a murine B-type cyclin, which has been designated cycB1. cycB1 was shown to be expressed in several adult tissues and in the midgestation mouse embryo. In the adult tissues, the highest levels of cycB1 transcripts were seen in the testis and ovary, which contain germ cells at various stages of differentiation. The major transcripts corresponding to cycB1 are 1.7 and 2.5 kb, with the 1.7 kb species being the predominant testicular transcript and the 2.5 kb species more abundant in the ovary. Examination of cDNAs corresponding to the 2.5 kb and 1.7 kb mRNAs revealed that these transcripts encode identical proteins, differing only in the polyadenylation signal used and therefore in the length of their 3' untranslated regions. Northern blot and in situ hybridization analyses revealed that the predominant sites of cycB1 expression in the testis and ovary were in the germinal compartment, particularly in early round spermatids in the testis and growing oocytes in the ovary. Thus cycB1 is expressed in both meiotic and postmeiotic cells. This pattern of cycB1 expression further suggests that cycB1 may have different functions in the two cell types, only one of which correlates with progression of the cell cycle.

Zfp-37, a new murine zinc finger encoding gene, is expressed in a developmentally regulated pattern in the male germ line

To begin to examine the function in the mouse testis of genes containing the zinc finger motif, we have screened an adult mouse total testis cDNA library with probes to a conserved region of zinc fingers. We have isolated cDNAs for a new murine zinc finger encoding gene that has been designated Zfp-37. Northern blot hybridization analysis revealed Zfp-37 transcripts at high levels in the testis, the only adult tissue in which Zfp-37 expression was observed. Zfp-37 was also expressed at lower levels in the mid-gestation embryo and placenta. The major testicular transcripts are 2.3 and 2.6 kb. A 4.0 kb transcript was detected at lower levels in the testis as well as in embryo and placenta. Northern blot and in situ hybridization analysis revealed that expression of Zfp-37 was most abundant in germ cells which have completed meiosis and are undergoing the complex morphogenetic changes of spermiogenesis. The pattern of expression of Zfp-37 and the presence of the zinc finger domain suggest that Zfp-37 may have a role in regulating spermiogenesis.

Basic fibroblast growth factor (bFGF) in rodent testis. Presence of bFGF mRNA and of a 30 kDa bFGF protein in pachytene spermatocytes

We have previously described a 30 kDa basic fibroblast growth factor (bFGF)-like protein in rodent testicular homogenates and have shown that pachytene spermatocytes are the sites of predominant immunoreactivity for this bFGF-like protein (Mayerhofer, A., Russell, L.D., Grothe, C., Rudolf, M. and Gratzl, M. (1991) Endocrinology 129, 921-924). We have now addressed the question whether this 30 kDa bFGF-like protein is a large bFGF form and whether it is produced by pachytene spermatocytes. We detected bFGF mRNA in homogenates of isolated mouse spermatocytes (which consisted mainly of pachytene spermatocytes) using S1 nuclease protection assays. As shown by Western blot analyses, the bFGF mRNA in mouse spermatocytes is translated into bFGF of an approximate molecular weight of 30 kDa. Neither bFGF mRNA, nor bFGF itself, was observed in isolated mouse Leydig cells. These results indicate that the immunoreactive bFGF-like protein observed previously in germ cells of the murine testis is identical to bFGF. Thus, germ cells of the testis produce bFGF, which may exert regulatory function in the process of spermatogenesis.

Mouse proacrosin gene: nucleotide sequence, diploid expression, and chromosomal localization

Acrosin is a serine proteinase located in the acrosome of the sperm in a zymogen form, proacrosin. As deduced from the cDNA sequences of human, boar, and mouse proacrosin, the enzyme is synthesized as a preproenzyme, preproacrosin, which contains a hydrophobic leader sequence of 15 to 18 amino acid residues. We have isolated the gene coding for mouse proacrosin from a mouse cosmid library, using cDNA clones as probes. The gene comprises six exons, and one of the five introns is located in the 5'-untranslated region. The transcription initiation site of the preproacrosin mRNA could be assigned to the residue T, 581 nucleotides upstream of the translation initiation codon ATG, with primer extension analysis. TATA and CAAT boxes could be identified at positions -26 and -97, respectively. Similar to other serine proteases, the coding sequence encompasses five exons and the three active-site residues His, Asp, and Ser are encoded by three different exons (E2, E3, E5). The proline-rich domain, which is a characteristic feature of the proacrosin polypeptide, is encoded in exon 5 with the serine active-site residue. The gene is located on chromosome 15 of the mouse genome, bands E/F, and is a member of a syntenic group that was mapped on human chromosome 22, q13-qter. During spermatogenesis the proacrosin gene in the mouse is expressed diploid, in contrast to a haploid expression observed in bull, boar, and rat.

Stage and lineage-regulated expression of two hsp90 transcripts during mouse germ cell differentiation and embryogenesis

The expression of members of the heat shock protein 90 (hsp90) gene family during testicular and embryonic development was investigated. Two different hsp90 transcripts were detected in RNA from mouse testis, approximately 3.2 kb and 2.9 kb in size, and were shown to exhibit cellular and developmental stage specificity of expression. The larger, more abundant transcript was expressed at high levels in the germinal compartment of the testis, particularly in germ cells in meiotic prophase. The smaller hsp90 transcript was expressed predominantly in the somatic compartment of the testis. Expression of the two hsp90 transcripts was observed in testes of other species, suggesting an important role for hsp90 in mammalian testicular function. In addition, expression of both hsp90 transcripts was detected in the embryonic and extra-embryonic compartments of mid-gestation embryos.

Allele- and haploid-specific product generated by alternative splicing from a mouse t complex responder locus candidate

Mouse t haplotypes represent a variant form of chromosome 17 that has evolved the ability to propagate through natural populations by the phenomenon of 'transmission ratio distortion' (TRD), in which heterozygous +/t males transmit their t-carrying chromosome to 95% or more of their offspring. Although multiple t-associated loci have a role in expression of this phenotype, only one--the t complex responder (Tcr) locus--is responsible for determining which of the two homologues of chromosome 17 will be transmitted at a high ratio. A candidate gene (Tcp-10b) for Tcr that is expressed in both meiotic and post-meiotic male germ cells has been cloned. But for this candidate gene to function as the haploid effector of TRD, the t-allele of this gene (Tcp-10bt) must express a unique product in a haploid-specific manner. Here we show that a change in the splicing pattern of Tcp-10bt transcripts occurs during sperm differentiation. This change results in a unique allele-specific and haploid-specific transcript which could encode a variant polypeptide that would fulfil the conditions required of the Tcr effector of TRD.

Several testis-expressed genes in the mouse t-complex have expression differences between wild-type and t-mutant mice

The t-complex of the mouse occupies the proximal half of chromosome 17 and contains genes which have profound effects on spermatogenesis. Mutations of several loci in the t-complex appear to interact to cause male sterility or transmission ratio distortion (TRD). By cDNA screening or chromosomal walking we have identified seven genes, which are expressed in the germ cells of testis and map to various regions of the t-complex. These genes were named t-complex testis-expressed (Tctex) genes. An analysis of their expression patterns in testes from +/+, +/t, and t/t mice was done by in situ hybridization and by northern blotting. Six genes begin to be expressed at the pachytene stage: Three of them are more abundant at pachytene stage, while three others are more abundant at postmeiotic stages. One gene is expressed at all the stages of spermatogenesis. Interestingly, four Tctex genes show differences in the amount of transcript between wild-type and t-mutant testes. The chromosomal location and expression pattern imply that Tctex genes might be candidate genes for sterility or TRD.

Tissue-specific expression from a compound TATA-dependent and TATA-independent promoter

We have found that the mouse metallothionein-I (MT-I) gene promoter functions in an unusual, compound manner. It directs both TATA-dependent and TATA-independent modes of transcription in vivo. The TATA-dependent message is initiated at the previously characterized +1 transcription start site and is the predominant species in most tissues. In many cell types it is metal inducible. The TATA-independent initiation sites are distributed over the 160 bp upstream of the previously characterized +1 start site, and the RNA products are present in all tissues examined. Only in testis, however, do the TATA-independent transcripts predominate, accumulating to highest levels in pachytene-stage meiotic cells and early spermatids. Unlike the TATA-dependent +1 transcript, these RNAs are not induced by metal, even in cultured cells in which the +1 species is induced. Transfection studies of site-directed mutants show that destruction of the TATA element drastically alters the ratio of the two RNA classes in cells in which the +1 transcripts normally dominates. In TATA-minus mutants, the TATA-independent RNAs become the most prevalent, although they remain refractory to metal induction. Thus, the MT-I promoter utilizes two different types of core promoter function within a single cell population. The two different types of core promoter respond very differently to environmental stimuli, and the choice between them appears to be regulated in a tissue-specific fashion.

Tissue-specific expression from a compound TATA-dependent and TATA-independent promoter

We have found that the mouse metallothionein-I (MT-I) gene promoter functions in an unusual, compound manner. It directs both TATA-dependent and TATA-independent modes of transcription in vivo. The TATA-dependent message is initiated at the previously characterized +1 transcription start site and is the predominant species in most tissues. In many cell types it is metal inducible. The TATA-independent initiation sites are distributed over the 160 bp upstream of the previously characterized +1 start site, and the RNA products are present in all tissues examined. Only in testis, however, do the TATA-independent transcripts predominate, accumulating to highest levels in pachytene-stage meiotic cells and early spermatids. Unlike the TATA-dependent +1 transcript, these RNAs are not induced by metal, even in cultured cells in which the +1 species is induced. Transfection studies of site-directed mutants show that destruction of the TATA element drastically alters the ratio of the two RNA classes in cells in which the +1 transcripts normally dominates. In TATA-minus mutants, the TATA-independent RNAs become the most prevalent, although they remain refractory to metal induction. Thus, the MT-I promoter utilizes two different types of core promoter function within a single cell population. The two different types of core promoter respond very differently to environmental stimuli, and the choice between them appears to be regulated in a tissue-specific fashion.

Characterization and inducibility of hsp 70 proteins in the male mouse germ line

The properties and inducibility of the heat shock protein 70 (hsp 70) gene products were examined during differentiation of mouse testicular cells by one and two-dimensional gel electrophoresis and immunoblotting. Low levels of the 72- and 73-kD heat shock proteins normally found in mouse cell lines were detected in the mouse testis. A novel isoform with a relative molecular mass of 73 kD (called 73T) was also observed, in the presence or absence of heat shock. 73T was shown to be produced by germ cells since it was not detected in testes from mutant mice devoid of germ cells. Furthermore, 73T was found only in adult mouse testicular cells, not in testes from animals that lack meiotic germ cells. 73T was synthesized in enriched cell populations of both meiotic prophase and postmeiotic cells, but was not inducible by in vitro heat shock. In the adult testis, low levels of the bona fide 72-kD heat-inducible (hsp72) were induced in response to elevated temperatures. In contrast, in testes from animals in which only somatic cells and premeiotic germ cells were present, there was a substantial induction of hsp 72. It is suggested that hsp 72 is inducible in the somatic compartment and possibly in the premeiotic germ cells, but not in germ cells which have entered meiosis and which are expressing members of the hsp 70 gene family in a developmentally regulated fashion.

Expression of three t-complex genes, Tcp-1, D17Leh117c3, and D17Leh66, in purified murine spermatogenic cell populations

Transmission ratio distortion (TRD) is a property of the complete t-haplotype which results in the preferential transmission of the t-haplotype chromosome from heterozygous t/+ males to the majority of the progeny. Available data suggest that in t/+ males, a dysfunction of the wild-type sperm within the female reproductive tract is responsible for the observed deviation from Mendelian segregation ratios. Genetically, Lyon has shown that multiple loci within the t-complex are required for maximum levels of TRD. These loci include multiple t-complex distorters (Tcds) which act upon a single t-complex responder (Tcr). Testis-expressed genes have been cloned which map to the same subregions of the t-complex as the Tcds and Tcr and are thus considered candidate genes for the products of these loci. To begin to understand how the products of these loci biochemically control TRD, the expression of three TRD-candidate genes (Tcp-1, D17Leh117c3, and D17Leh66) has been determined in populations of spermatocytes and differentiated spermatids purified to near homogeneity by unit gravity sedimentation. Fractions covering the entire gradient were analysed resulting in a more accurate picture of the precise timing of expression than previously reported. Transcription of all three genes was up-regulated in pachytene primary spermatocytes and persisted at stable levels through the haploid spermatid stages. Significantly, only levels of mRNA encoded by D17Leh66, the candidate gene for Tcr, increased from early round to elongating-stage spermatids. If this pattern of expression does, in fact, represent Tcr, these data provide the first direct evidence that wild-type and t-haplotype Tcr elements could be differentially expressed in haploid spermatids.

The protein encoded by a murine male germ cell-specific transcript is a putative ATP-dependent RNA helicase

The murine PL10 cDNA corresponds to a transcript expressed only in the male germ line. Its expression is developmentally regulated, with high levels of transcripts being present during the meiotic and haploid stages of spermatogenesis. The deduced protein is shown to be highly homologous to the murine translation initiation factor eIF-4A and to other proteins that are also homologous to eIF-4A, including the Drosophila protein vasa. By consensus sequence conservation and comparison of secondary structure predictions, putative mononucleotide binding and DNA/RNA binding domains are proposed to be shared by all these proteins. Taken together, these results suggest a helicase function for PL10 protein similar to that of eIF-4A and suggests its possible role in a key step of the spermatogenic process. The possible significance of the similarity between the PL10 protein and the protein product of the maternal effect gene vasa is also discussed.

Expression of a testis-specific hsp70 gene-related RNA in defined stages of rat seminiferous epithelium

Changes in the level of a testis-specific hsp70 gene-related transcript (hst70 RNA) and its cellular localization during the cycle of rat seminiferous epithelium have been investigated. Segments of seminiferous tubules at defined stages of the cycle were isolated in living condition by transillumination-assisted microdissection and the exact stages identified by phase-contrast microscopy of live cell squashes. The levels of the hst70 RNA were determined by Northern and slot blotting of whole cell lysates. High levels were found in stages XII-XIV and I to early VII of the cycle, and low levels were found in other stages, i.e., late VII (VIId) through VIII-XI of the cycle. The in situ hybridization revealed that the hst70 gene was activated in late pachytene primary spermatocytes during stage XII of the cycle, and that mRNA was then present in cells during differentiation through diakinesis, meiotic divisions, and early spermiogenesis (steps 1 through early 7). The activation of the gene coding for hst70 RNA shortly before meiotic divisions may indicate that the gene product is needed either during differentiation of late spermatocytes into spermatids or later during spermiogenesis, and that the mRNA may be stored in early spermatids.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Meiotic expression of human ornithine transcarbamylase in the testes of transgenic mice

In an attempt to use mouse metallothionein-I (mMT-I) regulatory sequences to direct expression of human ornithine transcarbamylase in the liver of transgenic animals, fusion genes joining either 1.6 kilobases or 185 base pairs of the mMT-I regulatory region to the human ornithine transcarbamylase protein-coding sequence were used to produce transgenic mice. In mice carrying the fusion gene with 1.6 kilobases of the mMT-I 5'-flanking sequences, transgene expression was observed in a wide range of tissues, but, unexpectedly, expression in liver was never observed. Surprisingly, in mice carrying the fusion gene regulated by only 185 base pairs of the mMT-I 5'-flanking sequences, the transgene was expressed exclusively in male germ cells during the tetraploid, pachytene stage of meiosis.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.