Regulation of the synthesis of lactate dehydrogenase-X during spermatogenesis in the mouse

Specific cell-cell contact serves as the developmental signal to deactivate discoidin I gene expression in Dictyostelium discoideum

Specific cell-cell contact is a major regulatory signal controlling cell differentiation in Dictyostelium discoideum, causing dramatic changes in the developmental program of gene expression. In this report, we focus on the relationships between specific cell-cell contact and the activity of the genes for discoidin I, an endogenous lectin that has been implicated in the cell-cell cohesion process. By performing quantitative RNA dot-hybridization assays and RNA gel blot-hybridization analyses, using as a probe a recombinant plasmid containing a discoidin I cDNA insert, we have measured changes in discoiding I mRNA levels during normal development and in response to specific manipulations of the state of cellular aggregation. Our major findings are as follows. (i) During normal development on filters, there is a close temporal correspondence between the establishment of specific cell-cell contacts and the decline in discoidin I mRNA levels. By the tight-aggregate stage, discoidin I mRNA is barely detectable. (ii) When tight aggregates are disaggregated and the cells are maintained in the disaggregated state, there is a dramatic rise in discoidin I mRNA content. (iii) When cells are developed in suspension (conditions that interfere with the establishment of tight cell-cell contacts), discoidin I mRNA accumulates to abnormally high levels, and these persist well after the levels in filter-developed cells have declined. Taken together, these results strongly suggest that cell-cell contact is the normal developmental signal to deactivate discoidin I gene expression; thus, a contact-deactivated gene for which a recombinant DNA probe is available has now been identified. Furthermore, we demonstrate that exogenous cAMP almost completely blocks the disaggregation-induced reactivation of discoidin I gene expression. Possible mechanistic relationships between specific cell-cell contact, intracellular cAMP levels, and developmental gene expression are discussed.

Spermatogenic cell-specific type 1 hexokinase is the predominant hexokinase in sperm

Hexokinase is the first enzyme in the glycolytic pathway and utilizes ATP to convert glucose to glucose-6-phosphate (G6P). We previously identified three variant transcripts of Hk1 that are expressed specifically in spermatogenic cells, have different 5' untranslated regions, and encode a protein (HK1S, spermatogenic cell-specific type 1 hexokinase) in which the porin-binding domain (PBD) of HK1 is replaced by a novel N-terminal spermatogenic cell-specific region (SSR). However, the level of expression of the individual variant transcripts or of the other members of the hexokinase gene family (Hk2, Hk3, and Gck) in spermatogenic cells remains uncertain. We show that Hk1, Hk2, and Hk3 transcripts levels are quite low in spermatocytes and spermatids and Gck transcripts are relatively abundant in spermatids, but that glucokinase (GCK) is not detected in spermatozoa. Using real time RT-PCR (qPCR) with primers specific for each of the three variant forms and RNA from whole testis and isolated germ cells, we found that transcripts for Hk1_v2 and Hk1_v3, but not for Hk1_v1, are relatively high in spermatids. Similar results were seen using spermatogenic cells isolated by laser-capture microdissection (LCM). Immunoblotting studies found that HK1S is abundant in sperm, and immunostaining confirmed that HK1S is located mainly in the principal piece of the sperm flagellum, where other spermatogenic cell-specific glycolytic enzymes have been found. These results strongly suggest that HK1, HK2, HK3, and GCK are unlikely to have a role in glycolysis in sperm and that HK1S encoded by Hk1_v2 and Hk1_v3 serves this role.

Patterns of translational regulation in the mammalian testis

The translational activity of more than 40 different mRNAs in rodent testes has been analyzed by determining the proportions of inactive free-mRNPs and active polysomal mRNAs in sucrose gradients. These mRNAs can be sorted into several groups comprising mRNAs with similar patterns of translational activity in particular cell types. mRNAs in testicular somatic cells sediment primarily with polysomes, indicating that they are translated efficiently, whereas the vast majority of mRNAs in late meiotic and haploid spermatogenic cells display high levels of free-mRNAPs, indicative of a block to the initiation of translation. Protamine mRNAs exemplify a group of mRNAs that is transcribed in round spermatids, stored as free-mRNPs for several days, and translated in elongated spermatids after the cessation of transcription. The extent to which the free-mRNPs in primary spermatocytes and round spermatids are due to developmental changes in translational activity is unclear. mRNAs at these stages can often be detected earlier than the corresponding protein, implicating either a delay in translational activation or difficulties in detecting the protein. In contrast, sucrose gradients consistently indicate little difference in the proportions of various mRNAs in free-mRNPs in primary spermatocytes and round spermatids, implying that the proportions of translationally active mRNAs remain essentially constant. Since the levels of some mRNAs appear to greatly exceed the amount that is translated, the biological significance of some free-mRNPs in meiotic and early haploid cells in unclear. There are numerous examples of controls over the translation of individual mRNAs in meiotic and haploid cells; the proportions of various mRNAs in free-mRNPs range from virtually none to virtually all, and individual mRNAs are activated at specific stages in elongated spermatids. Existing evidence is contradictory whether the mRNAs in the protamine/transition protein gene family are repressed by mRNP proteins of sequestration.

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.

Differences in regulation of testis specifc lactate dehydrogenase in rat and mouse occur at multiple levels

The testis specific form of lactate dehydrogenase (LDH-C4) is encoded by a single locus, Ldh-c, and is tightly regulated in a tissue specific manner. Here we show differences in expression of Ldh-c between rat and mouse, and describe the levels at which regulation of this gene differs in the two species. Our results demonstrate that the Ldh-c message level is nearly nine fold greater in mouse testis and remains high post-meiotically. In contrast, rat Ldh-c mRNA is highest in primary spermatocytes and reduced in spermatids. The results of nuclear run-on assays indicate that the transcription rate of Ldh-c is only moderately higher in mouse than rat, and cannot account for a significant portion of the observed differences. Similar decay rates for both rat and mouse Ldh-c mRNA in actinomycin-D clearance assays indicate comparable cytoplasmic stabilities for the two messages. From these results we infer that nuclear prostranscriptional events contribute to the differences in Ldh-c message levels.

Steroid hormone regulation of the Achlya ambisexualis 85-kilodalton heat shock protein, a component of the Achlya steroid receptor complex

The steroid hormone antheridiol regulates sexual development in the fungus Achlya ambisexualis. Analyses of in vivo-labeled proteins from hormone-treated cells revealed that one of the characteristic antheridiol-induced proteins appeared to be very similar to the Achyla 85-kilodalton (kDa) heat shock protein. Analysis of in vitro translation products of RNA isolated from control, heat-shocked, or hormone-treated cells demonstrated an increased accumulation of mRNA encoding a similar 85-kDa protein in both the heat-shocked and hormone-treated cells. Northern (RNA) blot analyses with a Drosophila melanogaster hsp83 probe indicated that a mRNA species of approximately 2.8 kilobases was substantially enriched in both heat-shocked and hormone-treated cells. The monoclonal antibody AC88, which recognizes the non-hormone-binding component of the Achyla steroid receptor, cross-reacted with Achlya hsp85 in cytosols from heat-shocked cells. This monoclonal antibody also recognized both the hormone-induced and heat shock-induced 85-kDa in vitro translation products. Taken together, these data suggest that similar or identical 85-kDa proteins are independently regulated by the steroid hormone antheridiol and by heat shock and that this protein is part of the Achyla steroid receptor complex. Our results demonstrate that the association of hsp90 family proteins with steroid receptors observed in mammals and birds extends also to the eucaryotic microbes and suggest that this association may have evolved early in steroid-responsive systems.

Sequence and developmental expression of the mRNA encoding the seleno-protein of the sperm mitochondrial capsule in the mouse

We have characterized cDNA clones encoding the selenium-containing polypeptide of the keratinous mitochondrial capsule in mouse sperm. The longest open reading frame encodes a polypeptide 143 amino acids long which contains 21% cysteine and 27% proline and closely resembles the size and amino acid composition of bull mitochondrial capsule seleno-protein (V. Pallini, B. Baccetti, and A. G. Burrini, 1979, in "The Spermatozoon," D. W. Fawcett and J. M. Bedford, Eds., pp. 141-151, Urban & Schwartzenberg, Baltimore/Munich). The reading frame encoding the mitochondrial capsule seleno-protein ends with an amber stop codon suggesting that selenium is not incorporated cotranslationally into the protein by an opal suppressor selenocysteyl-tRNA as has been found for several eukaryotic and bacterial proteins. Northern blots using RNA extracted from purified spermatogenic cells and staged prepuberal mice suggest that the mitochondrial capsule seleno-protein mRNA is first transcribed in late meiotic cells and that the levels of the mRNA increase after meiosis in early haploid cells. Southern blots demonstrate that there is one copy of the gene in the mouse genome. The identification of this cDNA clone, in combination with previous work (K. C. Kleene, 1989, Development 106, 367-373) demonstrates that the mRNA for the mitochondrial capsule seleno-protein is translationally repressed with long homogenous poly(A) tracts in round spermatids and translationally active with shortened heterogenous poly(A) tracts in elongating spermatids.

Steroid hormone regulation of the Achlya ambisexualis 85-kilodalton heat shock protein, a component of the Achlya steroid receptor complex

The steroid hormone antheridiol regulates sexual development in the fungus Achlya ambisexualis. Analyses of in vivo-labeled proteins from hormone-treated cells revealed that one of the characteristic antheridiol-induced proteins appeared to be very similar to the Achyla 85-kilodalton (kDa) heat shock protein. Analysis of in vitro translation products of RNA isolated from control, heat-shocked, or hormone-treated cells demonstrated an increased accumulation of mRNA encoding a similar 85-kDa protein in both the heat-shocked and hormone-treated cells. Northern (RNA) blot analyses with a Drosophila melanogaster hsp83 probe indicated that a mRNA species of approximately 2.8 kilobases was substantially enriched in both heat-shocked and hormone-treated cells. The monoclonal antibody AC88, which recognizes the non-hormone-binding component of the Achyla steroid receptor, cross-reacted with Achlya hsp85 in cytosols from heat-shocked cells. This monoclonal antibody also recognized both the hormone-induced and heat shock-induced 85-kDa in vitro translation products. Taken together, these data suggest that similar or identical 85-kDa proteins are independently regulated by the steroid hormone antheridiol and by heat shock and that this protein is part of the Achyla steroid receptor complex. Our results demonstrate that the association of hsp90 family proteins with steroid receptors observed in mammals and birds extends also to the eucaryotic microbes and suggest that this association may have evolved early in steroid-responsive systems.

Stage-specific expression of the lactate dehydrogenase-X gene in adult and developing mouse testes

Lactate dehydrogenase-X (LDH-X), a glycolytic enzyme found only in mammalian testes and spermatozoa, is encoded by a single gene (Ldh-x) in the mouse haploid genome. Several studies have demonstrated that LDH-X is associated with germ cells at specific stages of development. We have examined the expression of the Ldh-x gene during mouse spermatogenesis and testis maturation using in situ mRNA hybridization and immunocytochemistry. The results showed that transcription and translation of the Ldh-x gene are initiated at the pachytene stage of germ cell differentiation. However, although the amount of LDH-X protein increased as the germ cells progressed to maturation, its mRNA level was greatly decreased. These observations were confirmed by Northern analysis of total RNA derived from fractionated spermatogenic cells and developing testes. Furthermore, Northern studies also indicated two sizes of Ldh-x transcripts among different populations of spermatogenic cells in mature mouse testis.

New mutation causing sterility in the mouse

A new murine mutation, skeletal fusions with sterility, sks, has been identified. This mutation causes arrest during the pachytene stage of virtually all spermatogenic cells. Defects in chromosome pairing and appearance of the synaptonemal complex during meiosis in the male are apparent, but defective pairing is probably not the cause of sterility. Affected females are functionally infertile. Oocytes are capable of undergoing meiotic maturation in vitro but cannot be fertilized in vitro. Affected individuals of both sexes are characterized by fusions of vertebrae and of ribs. The sks gene has been mapped to Chromosome 4, 16.6 cM distal to the brown locus.

Changes in polyadenylation of lactate dehydrogenase-X mRNA during spermatogenesis in mice

The expression of the mRNA for mouse testicular lactate dehydrogenase (LDH-X) was examined by RNA:cDNA hybridization in situ in the testis and by Northern analyses of meiotic and postmeiotic spermatogenic cell populations. Silver grains accumulated in cells inside the second layer from the periphery of the seminiferous tubule, confirming previous findings that LDH-X mRNA first appears in the spermatocyte and continues to accumulate until the late spermatid stage. Northern analyses showed that meiotic and postmeiotic cells contained 1.2 and 1.3 kb classes of hybridizing mRNA, respectively. RNase H digestion of oligo (dT)-hybridized RNA and poly(U)-Sepharose column chromatography with differential elution by formamide revealed that the difference in size of the two classes of mRNAs was due to the poly(A) tail length of the LDH-X mRNA. When the distribution of the LDH-X mRNA was examined across polysome gradients, both mRNAs were partially associated with polysomes. These results suggest that the changes in the polyadenylation of LDH-X mRNA were associated with the meiotic division during spermatogenesis in the mouse. They raise the possibility that the stable accumulation of the LDH-X mRNAs in the postmeiotic cells is enhanced by poly(A) tails of increased length.

Molecular isolation and sequence determination of the cDNA for the mouse sperm-specific lactate dehydrogenase-X gene

Several cDNA clones for the mouse lactate dehydrogenase-X (LDH-X), a sperm-specific glycolytic enzyme, were isolated from mouse testicular cDNA libraries constructed in the bacteriophage vectors, lambda gt11 and gt10. The largest cDNA clone contains an insert of 1135 base pairs in length and an open reading frame that encodes a 332 amino acid polypeptide with a molecular weight of 35.89 kD. The deduced amino acid sequence of this protein is in close agreement with the published sequence of mouse LDH-X obtained by direct protein sequencing. Northern analysis of RNA isolated from different tissues detected a single size mRNA of 1.5 kilobases in mouse testis but not in brain or liver. The Ldh-x structural gene was estimated to be about 12 kb in size as demonstrated by Southern hybridization analysis of mouse genomic DNA using the full-length cDNA as a probe.

Epitopes of human testis-specific lactate dehydrogenase deduced from a cDNA sequence

The sequence and structure of human testis-specific L-lactate dehydrogenase [LDHC4, LDHX; (L)-lactate: NAD+ oxidoreductase, EC 1.1.1.27] has been derived from analysis of a complementary DNA (cDNA) clone comprising the complete protein coding region of the enzyme. From the deduced amino acid sequence, human LDHC4 is as different from rodent LDHC4 (73% homology) as it is from human LDHA4 (76% homology) and porcine LDHB4 (68% homology). Subunit homologies are consistent with the conclusion that the LDHC gene arose by at least two independent duplication events. Furthermore, the lower degree of homology between mouse and human LDHC4 and the appearance of this isozyme late in evolution suggests a higher rate of mutation in the mammalian LDHC genes than in the LDHA and -B genes. Comparison of exposed amino acid residues of discrete antigenic determinants of mouse and human LDHC4 reveals significant differences. Knowledge of the human LDHC4 sequence will help design human-specific peptides useful in the development of a contraceptive vaccine.

Locus determining the human sperm-specific lactate dehydrogenase, LDHC, is syntenic with LDHA

From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldh1, Ldh2, and Ldh3, respectively.

A postmeiotically expressed clone encodes lactate dehydrogenase isozyme X

We have analysed by the DNA sequencing one of the cDNA clones, pPM459, to mRNA abundant in spermatids of mice. This clone contained 535 base pair nucleotides with a coding region for 139 amino acids and a 3' untranslated region including a single polyadenylation signal. Screening of the protein database revealed that the deduced amino acid sequence highly matched the carboxyl terminal residues 192-330 of mouse lactate dehydrogenase isozyme X (LDH-X). Taken together with our previous report which showed transcription of the message hybridizing to pPM459 after meiosis, it was demonstrated that LDH-X mRNA synthesis continued during the postmeiotic phase in spermatogenesis.

Genetic analysis of mammalian spermatogenesis: use of the t complex in the mouse in studies of spermatogenesis and sperm function

Our observations suggest that sperm populations from the caudae epididymides of tw32/+ mice undergo hyperactivation in vitro sooner and to a much greater extent than do sperm populations from congenic +/+ mice: (1) epididymal tw32/+ sperm populations become significantly less progressive in vitro than do +/+ sperm populations; (2) low (0.1 mM) levels of Ca2+ prevent this loss of progressiveness; (3) epididymal tw32/+ sperm populations have trajectories and progressiveness values similar to both +/+ and tw32/+ oviductal sperm populations; (4) an inhibitor of capacitation inhibits the loss of progressiveness. This divergence from normal motility may be the result of expression of one of the factors involved in transmission distortion of the t complex.

Haploid accumulation and translational control of phosphoglycerate kinase-2 messenger RNA during mouse spermatogenesis

The intracellular location of the mRNA for the testis-specific isozyme of phosphoglycerate kinase-2 (PGK-2) has been determined for two spermatogenic cell types. The mRNA activity for PGK-2 from the polysomal and nonpolysomal fractions of pachytene primary spermatocytes or round spermatids has been assayed by cell-free translation with the polypeptide products monitored by immunoprecipitation, followed by one-dimensional or two-dimensional electrophoresis and fluorography. The results reveal that the majority of PGK-2 mRNA activity of round spermatids was present in the polysomal fraction while the relatively less abundant PGK-2 mRNA of pachytene primary spermatocytes was present in the nonpolysomal fraction. No PGK-2 mRNA activity was observed in the cytoplasmic RNA from primitive type A spermatogonia or prepubertal Sertoli cells. These data indicate that mature PGK-2 mRNA first appears in the cytoplasm of spermatogenic cells during the prophase of meiosis and increases in amount after meiosis. Although mature PGK-2 mRNA is present in meiotic cells it is not actively translated until after meiosis has been completed. Thus, mRNA accumulation and translational mechanisms are involved in the control of phosphoglycerate kinase-2 synthesis during spermatogenesis.

U1 small nuclear ribonucleoprotein studied by in vitro assembly

The small nuclear RNAs are known to be complexed with proteins in the cell (snRNP). To learn more about these proteins, we developed an in vitro system for studying their interactions with individual small nuclear RNA species. Translation of HeLa cell poly(A)+ mRNA in an exogenous message-dependent reticulocyte lysate results in the synthesis of snRNP proteins. Addition of human small nuclear RNA U1 to the translation products leads to the formation of a U1 RNA-protein complex that is recognized by a human autoimmune antibody specific for U1 snRNP. This antibody does not react with free U1 RNA. Moreover, addition of a 10- to 20-fold molar excess of transfer RNA instead of U1 RNA does not lead to the formation of an antibody-recognized RNP. The proteins forming the specific complex with U1 RNA correspond to the A, B1, and B2 species (32,000, 27,000, and 26,000 mol wt, respectively) observed in previous studies with U1 snRNP obtained by antibody-precipitation of nuclear extracts. The availability of this in vitro system now permits, for the first time, direct analysis of snRNA-protein binding interactions and, in addition, provides useful information on the mRNAs for snRNP proteins.

Protein binding sites are conserved in U1 small nuclear RNA from insects and mammals

To gain insight into the ribonucleoprotein (RNP) structure of small nuclear RNAs, HeLa cell poly(A)+ mRNA was translated in a reticulocyte lysate, and the in vitro binding of 35S-labeled proteins to individual small nuclear RNA species was examined by using human autoimmune antibodies. A Mr 32,000 protein binds to U1 RNA but not to U2, U4, U5, or U6. The resulting U1 RNP complex is recognized both by Sm and RNP antibodies. U2 RNA also forms a complex with protein, which is recognized by Sm antibody. Thus, the lack of binding of the Mr 32,000 protein to U2 RNA is not due to a failure of U2 to bind specific proteins in the in vitro system. Similar translation-assembly experiments with Drosophila poly(A)+ mRNA reveal that a Mr 26,000 protein identified previously in Drosophila U1 RNP [Wieben, E. D. & Pederson, T. (1982) Mol. Cell. Biol. 2, 914-920] also binds to U1 RNA in vitro. When the translation products of HeLa or Drosophila mRNA are presented with U1 RNA of the other species, the Mrs 32,000 and 26,000 proteins recognize binding sites on the heterologous U1 and, in both cases, form complexes recognized by RNP antibody. These results establish that a Mr 32,000 protein is unique to U1 RNA in human cells and that the U1 RNA binding sites for this and a Mr 26,000 homologue have been highly conserved in evolution. These sites may be the identical 13 nucleotides at the 5' ends of human and Drosophila U1 RNA or a highly conserved aspect of U1 secondary structure.

Gene expression during mammalian spermatogenesis. II. Evidence for stage-specific differences in mRNA populations

Gene expression during murine spermatogenesis has been studied using highly enriched populations of cells obtained by velocity sedimentation at unit gravity and further purified by density gradient centrifugation through Percoll. Polypeptides whose synthesis was directed by total cytoplasmic RNA from round spermatids, pachytene spermatocytes, primitive type A spermatogonia, and Sertoli cells in cell-free translation systems have been compared by two-dimensional polyacrylamide gel electrophoresis, followed by fluorography. At the level of detection provided by the electrophoretic methods used, each population of cells contained mRNAs encoding over 200 polypeptides, many of which were present in high abundance in all four cell types. However, for each cell type examined, a minimum of 5-10% of these polypeptides appear to be either specific to or greatly enriched within a particular cell type. Analysis of the polysomal and nonpolysomal cell fractions from pachytene spermatocytes and round spermatids revealed that the two compartments share many identical mRNAs but specific mRNAs are selectively compartmentalized between the cell fractions and between the two cell types. Movement between compartments was seen; e.g., some polypeptides encoded by mRNA found primarily in the nonpolysomal fraction of pachytene cells were later seen in the polysomal fraction from round spermatids. Virtually every other combination was also observed. These results suggest that the control of gene expression at the level of selective production of mRNA and selective utilization of mRNA are among the mechanisms involved in regulation of spermatogenic cell differentiation.

Identification of lactate dehydrogenase-X translated in vitro from mouse testicular poly A-containing mRNA

1. The LDH-X polypeptide was specifically immunoprecipitated from the cell-free translation products of poly A-containing mRNA from mouse testes, and it represents 1-2% of the total proteins synethesized in vitro. 2. The in-vitro synthesized LDH-X polypeptide appears to have the same mol. wt of 36,000 as mouse authentic LDH-X and, thus, any presequence of LDH-X must be very short, if present at all. 3. The LDH-X was not found in the mouse liver mRNA translation products immunoprecipitated by anti-LDH-X antibodies.