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

Spermatogenic cell-specific type 1 hexokinase (HK1S) is essential for capacitation-associated increase in tyrosine phosphorylation and male fertility in mice

Hexokinase (HK) catalyzes the first irreversible rate-limiting step in glycolysis that converts glucose to glucose-6-phosphate. HK1 is ubiquitously expressed in the brain, erythrocytes, and other tissues where glycolysis serves as the major source of ATP production. Spermatogenic cell-specific type 1 hexokinase (HK1S) is expressed in sperm but its physiological role in male mice is still unknown. In this study, we generate Hk1s knockout mice using the CRISPR/Cas9 system to study the gene function in vivo. Hk1s mRNA is exclusively expressed in testes starting from postnatal day 18 and continuing to adulthood. HK1S protein is specifically localized in the outer surface of the sperm fibrous sheath (FS). Depletion of Hk1s leads to infertility in male mice and reduces sperm glycolytic pathway activity, yet they have normal motile parameters and ATP levels. In addition, by using in vitro fertilization (IVF), Hk1s deficient sperms are unable to fertilize cumulus-intact or cumulus-free oocytes, but can normally fertilize zona pellucida-free oocytes. Moreover, Hk1s deficiency impairs sperm migration into the oviduct, reduces acrosome reaction, and prevents capacitation-associated increases in tyrosine phosphorylation, which are probable causes of infertility. Taken together, our results reveal that HK1S plays a critical role in sperm function and male fertility in mice.

Mass Spectrometry Reveals New Insights into the Production of Superoxide Anions and 4-Hydroxynonenal Adducted Proteins in Human Sperm

The free-radical theory of male infertility suggests that reactive oxygen species produced by the spermatozoa themselves are a leading cause of sperm dysfunction, including loss of sperm motility. However, the field is overshadowed on several fronts, primarily because: i) the probes used to measure reactive oxygen species (ROS) are imprecise; and ii) many reports suggesting that oxygen radicals are detrimental to sperm function add an exogenous source of ROS. Herein, a more reliable approach to measure superoxide anion production by human spermatozoa based on MS analysis is used. Furthermore, the formation of the lipid-peroxidation product 4-hydroxynonenal (4-HNE) during in vitro incubation using proteomics is also investigated. The data demonstrate that neither superoxide anion nor other free radicals that cause 4-HNE production are related to the loss of sperm motility during incubation. Interestingly, it appears that many of the 4-HNE adducted proteins, found within spermatozoa, originate from the prostate. A quantitative SWATH analysis demonstrate that these proteins transiently bind to sperm and are then shed during in vitro incubation. These proteomics-based findings propose a revised understanding of oxidative stress within the male reproductive tract.

The thermo-sensitive gene expression signatures of spermatogenesis

BACKGROUND

Spermatogenesis in most mammals (including human and rat) occurs at ~ 3 °C lower than body temperature in a scrotum and fails rapidly at 37 °C inside the abdomen. The present study investigates the heat-sensitive transcriptome and miRNAs in the most vulnerable germ cells (spermatocytes and round spermatids) that are primarily targeted at elevated temperature in a bid to identify novel targets for contraception and/or infertility treatment.

METHODS

Testes of adult male rats subjected to surgical cryptorchidism were obtained at 0, 24, 72 and 120 h post-surgery, followed by isolation of primary spermatocytes and round spermatids and purification to > 90% purity using a combination of trypsin digestion, centrifugal elutriation and density gradient centrifugation techniques. RNA isolated from these cells was sequenced by massive parallel sequencing technique to identify the most-heat sensitive mRNAs and miRNAs.

RESULTS

Heat stress altered the expression of a large number of genes by ≥2.0 fold, out of which 594 genes (286↑; 308↓) showed alterations in spermatocytes and 154 genes (105↑; 49↓) showed alterations in spermatids throughout the duration of experiment. 62 heat-sensitive genes were common to both cell types. Similarly, 66 and 60 heat-sensitive miRNAs in spermatocytes and spermatids, respectively, were affected by ≥1.5 fold, out of which 6 were common to both the cell types.

CONCLUSION

The study has identified Acly, selV, SLC16A7(MCT-2), Txnrd1 and Prkar2B as potential heat sensitive targets in germ cells, which may be tightly regulated by heat sensitive miRNAs rno-miR-22-3P, rno-miR-22-5P, rno-miR-129-5P, rno-miR-3560, rno-miR-3560 and rno-miR-466c-5P.

Multi-tissue computational modeling analyzes pathophysiology of type 2 diabetes in MKR mice

Computational models using metabolic reconstructions for in silico simulation of metabolic disorders such as type 2 diabetes mellitus (T2DM) can provide a better understanding of disease pathophysiology and avoid high experimentation costs. There is a limited amount of computational work, using metabolic reconstructions, performed in this field for the better understanding of T2DM. In this study, a new algorithm for generating tissue-specific metabolic models is presented, along with the resulting multi-confidence level (MCL) multi-tissue model. The effect of T2DM on liver, muscle, and fat in MKR mice was first studied by microarray analysis and subsequently the changes in gene expression of frank T2DM MKR mice versus healthy mice were applied to the multi-tissue model to test the effect. Using the first multi-tissue genome-scale model of all metabolic pathways in T2DM, we found out that branched-chain amino acids' degradation and fatty acids oxidation pathway is downregulated in T2DM MKR mice. Microarray data showed low expression of genes in MKR mice versus healthy mice in the degradation of branched-chain amino acids and fatty-acid oxidation pathways. In addition, the flux balance analysis using the MCL multi-tissue model showed that the degradation pathways of branched-chain amino acid and fatty acid oxidation were significantly downregulated in MKR mice versus healthy mice. Validation of the model was performed using data derived from the literature regarding T2DM. Microarray data was used in conjunction with the model to predict fluxes of various other metabolic pathways in the T2DM mouse model and alterations in a number of pathways were detected. The Type 2 Diabetes MCL multi-tissue model may explain the high level of branched-chain amino acids and free fatty acids in plasma of Type 2 Diabetic subjects from a metabolic fluxes perspective.

Disruption of a spermatogenic cell-specific mouse enolase 4 (eno4) gene causes sperm structural defects and male infertility

Sperm utilize glycolysis to generate ATP required for motility, and several spermatogenic cell-specific glycolytic isozymes are associated with the fibrous sheath (FS) in the principal piece of the sperm flagellum. We used proteomics and molecular biology approaches to confirm earlier reports that a novel enolase is present in mouse sperm. We then found that a pan-enolase antibody, but not antibodies to ENO2 and ENO3, recognized a protein in the principal piece of the mouse sperm flagellum. Database analyses identified two previously uncharacterized enolase family-like candidate genes, 64306537H0Rik and Gm5506. Northern analysis indicated that 64306537H0Rik (renamed Eno4) was transcribed in testes of mice by Postnatal Day 12. To determine the role of ENO4, we generated mice using embryonic stem cells in which an Eno4 allele was disrupted by a gene trap containing a beta galactosidase (beta-gal) reporter (Eno4(+/Gt)). Expression of beta-gal occurred in the testis, and male mice homozygous for the gene trap allele (Eno4(Gt/Gt)) were infertile. Epididymal sperm numbers were 2-fold lower and sperm motility was reduced substantially in Eno4(Gt/Gt) mice compared to wild-type mice. Sperm from Eno4(Gt/Gt) mice had a coiled flagellum and a disorganized FS. The Gm5506 gene encodes a protein identical to ENO1 and also is transcribed at a low level in testis. We conclude that ENO4 is required for normal assembly of the FS and provides most of the enolase activity in sperm and that Eno1 and/or Gm5506 may encode a minor portion of the enolase activity in sperm.

Metabolic substrates exhibit differential effects on functional parameters of mouse sperm capacitation

Although substantial evidence exists that sperm ATP production via glycolysis is required for mammalian sperm function and male fertility, conflicting reports involving multiple species have appeared regarding the ability of individual glycolytic or mitochondrial substrates to support the physiological changes that occur during capacitation. Several mouse models with defects in the signaling pathways required for capacitation exhibit reductions in sperm ATP levels, suggesting regulatory interactions between sperm metabolism and signal transduction cascades. To better understand these interactions, we conducted quantitative studies of mouse sperm throughout a 2-h in vitro capacitation period and compared the effects of single substrates assayed under identical conditions. Multiple glycolytic and nonglycolytic substrates maintained sperm ATP levels and comparable percentages of motility, but only glucose and mannose supported hyperactivation. These monosaccharides and fructose supported the full pattern of tyrosine phosphorylation, whereas nonglycolytic substrates supported at least partial tyrosine phosphorylation. Inhibition of glycolysis impaired motility in the presence of glucose, fructose, or pyruvate but not in the presence of hydroxybutyrate. Addition of an uncoupler of oxidative phosphorylation reduced motility with pyruvate or hydroxybutyrate as substrates but unexpectedly stimulated hyperactivation with fructose. Investigating differences between glucose and fructose in more detail, we demonstrated that hyperactivation results from the active metabolism of glucose. Differences between glucose and fructose appeared to be downstream of changes in intracellular pH, which rose to comparable levels during incubation with either substrate. Sperm redox pathways were differentially affected, with higher levels of associated metabolites and reactive oxygen species generated during incubations with fructose than during incubations with glucose.

LDHC: the ultimate testis-specific gene

Lactate dehydrogenase C (LDHC) was, to the best of our knowledge, the first testis-specific isozyme discovered in male germ cells. In fact, this was accomplished shortly before "isozymes or isoenzymes" became a field of study. LDHC was detected initially in human spermatozoa and spermatogenic cells of the testes by gel electrophoresis. Immunohistochemistry was used to localize LDHC first in early-pachytene primary spermatocytes, with an apparent increase in quantity after meiosis, to its final localization in and on the principal piece of the sperm tail. After several decades of biologic, biochemical, and genetic investigations, we now know that the lactate dehydrogenase isozymes are ubiquitous in vertebrates, developmentally regulated, tissue and cell specific, and multifunctional. Here, we will review the history of LDHC and the work that demonstrates clearly that it is required for sperm to accomplish their ultimate goal, fertilization.

Computational analyses of mammalian lactate dehydrogenases: human, mouse, opossum and platypus LDHs

Computational methods were used to predict the amino acid sequences and gene locations for mammalian lactate dehydrogenase (LDH) genes and proteins using genome sequence databanks. Human LDHA, LDHC and LDH6A genes were located in tandem on chromosome 11, while LDH6B and LDH6C genes were on chromosomes 15 and 12, respectively. Opossum LDHC and LDH6B genes were located in tandem with the opossum LDHA gene on chromosome 5 and contained 7 (LDHA and LDHC) or 8 (LDH6B) exons. An amino acid sequence prediction for the opossum LDH6B subunit gave an extended N-terminal sequence, similar to the human and mouse LDH6B sequences, which may support the export of this enzyme into mitochondria. The platypus genome contained at least 3 LDH genes encoding LDHA, LDHB and LDH6B subunits. Phylogenetic studies and sequence analyses indicated that LDHA, LDHB and LDH6B genes are present in all mammalian genomes examined, including a monotreme species (platypus), whereas the LDHC gene may have arisen more recently in marsupial mammals.

Male infertility caused by spermiogenic defects: lessons from gene knockouts

Spermiogenesis refers to the process by which postmeiotic spermatids differentiate into elongated spermatids and eventually spermatozoa. During spermiogenesis, round spermatids undergo dynamic morphologic changes, which include nuclear condensation and elongation, formation of flagella and acrosome, reorganization of organelles and elimination of cytoplasm upon spermiation. This cellular differentiation process is unique to male haploid germ cells, which may explain why approximately half of the testis-specific genes are exclusively expressed in spermiogenesis. The spermiogenesis-specific expression implies that these genes contribute to either structural or functional aspects of future sperm. Many such genes have been inactivated in mice and some of these gene knockout mice display male infertility due to nonfunctional sperm which display no or various degrees of structural abnormalities. Since the majority of these spermiogenesis-specific genes are highly conserved between mice and humans, findings from knockout mouse studies may be applicable to human infertility. Here, I briefly review some of these spermatid-specific gene knockouts. The mouse studies strongly suggest that sperm quality rather than quantity is a better indicator of male fertility and novel assays should be developed to determine sperm functionality.

Sperm surface antigens and the prospects for contraceptive vaccine development

It has been estimated that 500 million couples world-wide have no access to contraception and that approximately 20% of births between 1995 and 2000 will be unwanted. Such statistics have important implications for the rate of world population growth and the possibility of maintaining a sustainable population. Although political change and the empowerment of women across the world will help address these issues, it will also be important to increase the availability of contraceptives; not only the modalities that are in current use, but also novel methods that will satisfy needs that are presently unfulfilled. One such alternative could be a vaccine targeting the human spermatozoon.

D- and L-lactate dehydrogenases during invertebrate evolution

BACKGROUND

The L-lactate and D-lactate dehydrogenases, which are involved in the reduction of pyruvate to L(-)-lactate and D(+)-lactate, belong to evolutionarily unrelated enzyme families. The genes encoding L-LDH have been used as a model for gene duplication due to the multiple paralogs found in eubacteria, archaebacteria, and eukaryotes. Phylogenetic studies have suggested that several gene duplication events led to the main isozymes of this gene family in chordates, but little is known about the evolution of L-Ldh in invertebrates. While most invertebrates preferentially oxidize L-lactic acid, several species of mollusks, a few arthropods and polychaetes were found to have exclusively D-LDH enzymatic activity. Therefore, it has been suggested that L-LDH and D-LDH are mutually exclusive. However, recent characterization of putative mammalian D-LDH with significant similarity to yeast proteins showing D-LDH activity suggests that at least mammals have the two naturally occurring forms of LDH specific to L- and D-lactate. This study describes the phylogenetic relationships of invertebrate L-LDH and D-LDH with special emphasis on crustaceans, and discusses gene duplication events during the evolution of L-Ldh.

RESULTS

Our phylogenetic analyses of L-LDH in vertebrates are consistent with the general view that the main isozymes (LDH-A, LDH-B and LDH-C) evolved through a series of gene duplications after the vertebrates diverged from tunicates. We report several gene duplication events in the crustacean, Daphnia pulex, and the leech, Helobdella robusta. Several amino acid sequences with strong similarity to putative mammalian D-LDH and to yeast DLD1 with D-LDH activity were found in both vertebrates and invertebrates.

CONCLUSION

The presence of both L-Ldh and D-Ldh genes in several chordates and invertebrates suggests that the two enzymatic forms are not necessarily mutually exclusive. Although, the evolution of L-Ldh has been punctuated by multiple events of gene duplication in both vertebrates and invertebrates, a shared evolutionary history of this gene in the two groups is apparent. Moreover, the high degree of sequence similarity among D-LDH amino acid sequences suggests that they share a common evolutionary history.

X-ray analysis of phosphoglycerate kinase 2, a sperm-specific isoform from Mus musculus

Phosphoglycerate kinase 2 (PGK2) is an isozyme of the glycolytic pathway that provides ATP required for sperm motility. It is encoded by an autosomal retrogene that is expressed only during spermatogenesis, concomitant with the inactivation of the X-linked Pgk1 gene. PGK2 from the mouse, Mus musculus, has been overexpressed from a plasmid in bacteria and purified. It was crystallized in three forms: as the apoenzyme, as a complex with 3-phosphoglycerate (3PG), and as a complex with 3PG and ATP. The crystal structures were solved to 2.7, 2.0, and 2.7 A resolutions, respectively. The overall fold is nearly identical with previously solved mammalian PGK1 molecules. The apoenzyme is in the "open" form; that is the N-terminal domain that can bind 3PG and the C-terminal domain that binds ATP are too far apart for the substrates to interact. Binding 3PG causes a 13 degree rotation that partially closes the structure and causes helix 13, which is disordered in the unliganded structure, to stabilize. Binding ATP leaves the protein in the open configuration but also causes helix 13 to be ordered. Sequence alignment suggests that the active site of PGK2 is essentially identical to that of the cytoplasmic PGK1, but significant differences accumulate on a side of the C-terminal domain away from the active site. These changes may mediate the binding of this isoform to other proteins within the sperm flagellum, while still allowing the hinging action between the domains that is essential to catalytic activity.

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.

Biomarkers of semen in the vagina: applications in clinical trials of contraception and prevention of sexually transmitted pathogens including HIV

Biomarkers of vaginal exposure to semen, long used in forensic medicine, are now becoming important in the development of vaginal microbicides to prevent HIV/STIs and the development of contraceptives. Semen biomarkers could help evaluate the safety of a new physical or chemical barrier, give preliminary indication of the effectiveness of physical barriers such as diaphragms or condoms, and provide information on unprotected intercourse among participants in a clinical trial who have been advised to use condoms. Candidate biomarkers of semen exposure fall into two broad categories: (1) biomarkers of seminal plasma, among which prostate-specific antigen (PSA) is the best characterized; and (2) biomarkers of spermatozoa and other cells present in semen. This paper, authored by a working group of investigators performing research in the field of semen biomarkers, summarizes the characteristics of an ideal semen biomarker, reviews preclinical and clinical data on existing and potential biomarkers, and outlines the steps that should be carried out to develop an improved biomarker of semen exposure.

Systematic variation in mRNA 3'-processing signals during mouse spermatogenesis

Gene expression and processing during mouse male germ cell maturation (spermatogenesis) is highly specialized. Previous reports have suggested that there is a high incidence of alternative 3′-processing in male germ cell mRNAs, including reduced usage of the canonical polyadenylation signal, AAUAAA. We used EST libraries generated from mouse testicular cells to identify 3′-processing sites used at various stages of spermatogenesis (spermatogonia, spermatocytes and round spermatids) and testicular somatic Sertoli cells. We assessed differences in 3′-processing characteristics in the testicular samples, compared to control sets of widely used 3′-processing sites. Using a new method for comparison of degenerate regulatory elements between sequence samples, we identified significant changes in the use of putative 3′-processing regulatory sequence elements in all spermatogenic cell types. In addition, we observed a trend towards truncated 3′-untranslated regions (3′-UTRs), with the most significant differences apparent in round spermatids. In contrast, Sertoli cells displayed a much smaller trend towards 3′-UTR truncation and no significant difference in 3′-processing regulatory sequences. Finally, we identified a number of genes encoding mRNAs that were specifically subject to alternative 3′-processing during meiosis and postmeiotic development. Our results highlight developmental differences in polyadenylation site choice and in the elements that likely control them during spermatogenesis.

A preliminary account of the properties of recombinant human Glyoxylate reductase (GRHPR), LDHA and LDHB with glyoxylate, and their potential roles in its metabolism

Human lactate dehydrogenase (LDH) is thought to contribute to the oxidation of glyoxylate to oxalate and thus to the pathogenesis of disorders of endogenous oxalate overproduction. Glyoxylate reductase (GRHPR) has a potentially protective role metabolising glyoxylate to the less reactive glycolate. In this paper, the kinetic parameters of recombinant human LDHA, LDHB and GR have been compared with respect to their affinity for glyoxylate and related substrates. The Km values and specificity constants (Kcat/K(M)) of purified recombinant human LDHA, LDHB and GRHPR were determined for the reduction of glyoxylate and hydroxypyruvate. K(M) values with glyoxylate were 29.3 mM for LDHA, 9.9 mM for LDHB and 1.0 mM for GRHPR. For the oxidation of glyoxylate, K(M) values were 0.18 mM and 0.26 mM for LDHA and LDHB respectively with NAD+ as cofactor. Overall, under the same reaction conditions, the specificity constants suggest there is a fine balance between the reduction and oxidation reactions of these substrates, suggesting that control is most likely dictated by the ambient concentrations of the respective intracellular cofactors. Neither LDHA nor LDHB utilised glycolate as substrate and NADPH was a poor cofactor with a relative activity less than 3% that of NADH. GRHPR had a higher affinity for NADPH than NADH (K(M) 0.011 mM vs. 2.42 mM). The potential roles of LDH isoforms and GRHPR in oxalate synthesis are discussed.

Glyceraldehyde 3-phosphate dehydrogenase-S, a sperm-specific glycolytic enzyme, is required for sperm motility and male fertility

Although glycolysis is highly conserved, it is remarkable that several unique isozymes in this central metabolic pathway are found in mammalian sperm. Glyceraldehyde 3-phosphate dehydrogenase-S (GAPDS) is the product of a mouse gene expressed only during spermatogenesis and, like its human ortholog (GAPD2), is the sole GAPDH isozyme in sperm. It is tightly bound to the fibrous sheath, a cytoskeletal structure that extends most of the length of the sperm flagellum. We disrupted Gapds expression by gene targeting to selectively block sperm glycolysis and assess its relative importance for in vivo sperm function. Gapds(-/-) males were infertile and had profound defects in sperm motility, exhibiting sluggish movement without forward progression. Although mitochondrial oxygen consumption was unchanged, sperm from Gapds(-/-) mice had ATP levels that were only 10.4% of those in sperm from WT mice. These results imply that most of the energy required for sperm motility is generated by glycolysis rather than oxidative phosphorylation. Furthermore, the critical role of glycolysis in sperm and its dependence on this sperm-specific enzyme suggest that GAPDS is a potential contraceptive target, and that mutations or environmental agents that disrupt its activity could lead to male infertility.

Abundance of repetitive sequence elements in the mouse testis-specific lactate dehydrogenase-C gene

We have cloned and sequenced the entire mouse ldhc gene and mapped it physically in relation to the somatic ldha gene. The 2 genes were found to be oriented in head-to-tail fashion with about a 6-kilobase (kb) distance between the 3' end of ldha and the 5' end of ldhc. The ldhc gene is composed of 43% repetitive elements compared to only 16% in the ldha gene. Despite the close physical distance of mouse ldha and ldhc, the 2 genes have a very different content of repetitive elements, and this most likely reflects different levels of selective pressure.

Isolation and characterization of a human sperm antigen gene h-Sp-1

We isolated and characterized a human sperm antigen gene (h-Sp-1) from human testis complementary DNA using antiserum against the human sperm membrane. Northern blot analysis detected two transcripts (2.3 and 1.1 kb) of the h-Sp-1 gene. The 2.3-kb transcript is ubiquitous, whereas the 1.1-kb transcript is specific to the human testis with a high level of expression. Determination of the base sequence of h-Sp-1 showed a size of 2170 bp and 43.4% homology with human synaptophysin. The base sequence indicates a molecule consisting of 259 amino acids, with four hydrophilic and four hydrophobic regions. In order to further characterize the h-Sp-1 molecule, we synthesized the probable region of amino acids with high antigenicity based on the amino acid sequence (amino acid nos. 174-198) and immunized rabbits to prepare an antiserum. In our experimental model of fertilization between human sperm and zona pellucida-free hamster ova, partial inhibition of fertilization was observed. We were able to synthesize a large quantity of recombinant protein by inserting the h-Sp-1 gene into a baculovirus vector and infecting spodoptera frugiperda culture cells (sf9 insect cells). The synthesized protein had a molecular weight of 30 kDa. We then immunized Balb/c mice with this protein to prepare a monoclonal antibody (G3G9), which was used to localize the h-Sp-1 molecule in sperm and tissues (e.g. testis). The h-Sp-1 molecule was present in the cell membrane from the head to tail of human sperm. Staining of the testis and epididymis also showed h-Sp-1 to be present in spermatogonia, spermatocyte, sperm and epididymal duct epithelium. These findings suggest that the h-Sp-1 molecule is expressed in sperm and testes and plays a role in fertilization.

Immunization of female cynomolgus macaques with a synthetic epitope of sperm-specific lactate dehydrogenase results in high antibody titers but does not reduce fertility

Previous studies have reported reduced fertility in female baboons immunized with a synthetic peptide derived from the sperm-specific isozyme of lactate dehydrogenase (LDH-C). In this study, a similar approach was used to immunize female cynomolgus macaques with the same peptide sequence (bC5-19) conjugated to a T-cell epitope from tetanus toxin (TT). Twelve female monkeys were immunized with bC5-19:TT delivered with Ribi MPL adjuvant vehicle, and 10 control female monkeys were injected with the adjuvant vehicle only. All 12 females in the treatment group developed LDH-C-specific serum antibodies as measured by ELISA, but anti-LDH-C antibodies were not detected in vaginal fluids of the immunized animals. After 4 months of timed mating immediately following the immunizations, five of the ten immunized females became pregnant, as did six of the ten control females. Anti-sera from both pregnant and nonpregnant bC5-19:TT-immunized females recognize a single band at 35 kDa on Western blots of whole sperm extracts, and purified Igs from the same sera localize along the principle piece of the flagellum of permeabilized sperm.

TFIIAalpha/beta-like factor is encoded by a germ cell-specific gene whose expression is up-regulated with other general transcription factors during spermatogenesis in the mouse

TFIIAalpha/beta-like factor (ALF) is a testis-specific counterpart of the large subunit of human general transcription factor TFIIA. Northern analysis shows that ALF mRNA first appears in mouse testis at Postnatal Day 14. Similarly, expression of the general transcription factors TBP, TRF2, TFIIAalpha/beta, TFIIAgamma, and TFIIIB(90) is also increased beginning at Postnatal Day 14, suggesting that there is a coordinated induction of many general transcription factors during male germ cell differentiation. Analysis of male germ cells separated by Staput sedimentation shows that ALF is present in pachytene spermatocytes and haploid spermatids. In addition, in situ hybridization experiments with adult mouse testis shows that ALF is present in haploid spermatids. Searches of the human genome sequence database using the basic local alignment search tool reveal that the ALF and TFIIAalpha/beta(GTF2A1) genes are both composed of nine exons, whereas the TFIIAgamma (GTF2A2) gene is composed of five exons. Furthermore, nucleotide and amino acid comparisons among human and mouse ALF, TFIIAalpha/beta, and TFIIAgamma cDNA sequences show that ALF has diverged more rapidly than either TFIIAalpha/beta or TFIIAgamma. Finally, the ALF and SBLF (Stoned B-Like Factor) sequences present in the chimeric SALF cDNA are both present on human chromosome 2, and an analysis of the corresponding genes suggests a model for the formation of SALF.

Human leucocyte antigen I expression in spermatozoa from infertile men

The expression of class I human leucocyte antigen (HLA) has been investigated by reverse transcription polymerase chain reaction (RT-PCR) and flow cytometry on human purified ejaculated spermatozoa from an infertile population. Similar investigation in a control fertile population has been performed. Among 22 fertile and 20 infertile men, 17 were selected for the study because they showed no contamination with non-sperm cells. HLA I molecules were expressed in four of nine fertile subjects (44.4%) and three of eight infertile subjects (37.5%), with no significant difference between groups. These data demonstrate for the first time the presence of class I HLA antigens on spermatozoa of infertile subjects. In addition, considering that similar results have been obtained in both fertile and infertile populations, the hypothesis that the fertilizing capacity of the spermatozoon is independent of class I HLA-antigen expression on their surface may be advanced.

Human leukocyte antigen II expression in sperm cells: comparison between fertile and infertile men

Human leukocyte antigens (HLA) class II transcripts in mature spermatozoa of healthy volunteers have recently been demonstrated using reverse transcription polymerase chain reaction (RT-PCR). HLA II expression was investigated on ejaculated sperm cells in fertile and infertile men by RT-PCR and flow cytometry. Among 22 fertile and 20 infertile men, 18 were selected for the study because they showed no contamination with non-sperm cells. HLA II mRNA transcripts were expressed in all but 1 of 8 infertile subjects and in only 2 of 10 fertile ones. The cytofluorometric analysis on three RT-PCR positive samples confirmed the presence of class II antigens on cell surfaces. These data clearly confirm the presence of both HLA II mRNA and surface molecules on human sperm cells. In addition, an interesting nonrandom distribution of positivity among fertile and infertile samples regarding HLA II expression (p < .025) suggests a possible correlation with infertility.

Molecular cloning and characterization of functional domains of a human testis-specific isoform of calpastatin

Human serum containing sperm-agglutinating antibodies was used to screen a testis cDNA expression library to identify the cognate antigens that may be responsible for this biological effect. The longest positive phage clone (1.9 kb) was sequenced and found to be a testis-specific isoform of calpastatin (tCAST). The testis-specific segment of tCAST is encoded by a single exon within intron 14 of the calpastatin gene. A unique protein isoform is produced that differs in domain structure from the somatic calpastatins (sCAST). Human sCAST most commonly has an N-terminal domain L plus the four functional calpain inhibitory domains. Human tCAST consists of a 40-amino-acid N-terminal T domain plus a part of domain II and all of domains III and IV from the somatic isoform. Our data show that the T domain can target cytosolic localization and membrane association of tCAST, whereas domain I of sCAST exhibits a nuclear localization function. Calpastatin is the endogenous inhibitor of calpain. The calpain/calpastatin system is involved in membrane fusion events for several cell types, and calpain has been localized to the sperm acrosome. We detected tCAST in human sperm and testes extracts by Western blotting with specific antisera. These observations suggest that tCAST may modulate calpain in the calcium-mediated acrosome reaction that is required for fertilization.

IMP-L3, A 20-hydroxyecdysone-responsive gene encodes Drosophila lactate dehydrogenase: structural characterization and developmental studies

IMP-L3, a gene isolated as a potential mediator of imaginal disc morphogenesis in Drosophila melanogaster, encodes lactate dehydrogenase (LDH). The predicted amino acid sequence of IMP-L3 is 58-61% identical to those of human LDHs. In cultured imaginal discs, IMP-L3 transcript levels and LDH enzyme activity increase in response to the steroid hormone, 20-hydroxyecdysone. In embryos, IMP-L3 transcript and LDH activity appear in developing somatic muscles by late stage 13, well before the onset of muscular contraction. High levels of transcript and LDH activity persist throughout embryogenesis and throughout larval development. The gene has been localized by in situ hybridization and deficiency mapping to 65A7-65B2 on the third chromosome. LDH activity is reduced to approximately 50% of wild type in animals heterozygous for a deficiency that removes the 65A-B region. Embryos deficient for the 65A-b region lack LDH activity. We conclude that IMP-L3 is the only gene that encodes LDH in Drosophila.

Aggregation of hsp70 and hsc70 in vivo is distinct and temperature-dependent and their chaperone function is directly related to non-aggregated forms

We used non-denaturing gradient analysis of cell extracts before and after heat treatment of the cells and showed that hsp70 and hsc70 aggregate in vivo in a temperature-dependent fashion. Their aggregation profiles were found to be clearly distinguishable and sensitive to ATP depletion. Pore exclusion limit electrophoresis showed that these two proteins are mainly found in autoaggregated forms including dimers, trimers and oligomers. The addition of denatured luciferase to the cell extracts reversed the aggregation of both proteins towards their non-aggregated forms. Immunoprecipitation and Western-blot analysis showed that the non-aggregated form is the only one bound to denatured luciferase. Our results suggest that aggregated hsp70 and hsc70 represent predominantly self-associated molecules unable to exert chaperone activity. The cochaperone hsp40 was also found to be aggregated and, on addition of denatured luciferase, its aggregation was reversed to a non-aggregated state. Immunoprecipitation analysis indicated that hsp40 forms a complex with the non-aggregated form of hsc70 and denatured luciferase. These results confirm previous in vitro studies and support the suggestion that in vivo cytosolic hsp70 and hsc70 exist mainly in an oligomer-monomer equilibrium which is dependent on the environmental temperature, the levels of ATP and the presence of denatured proteins.

Cloning, sequencing, and characterization of LDH-C4 from a fox testis cDNA library

A full-length cDNA encoding the sperm-specific enzyme lactate dehydrogenase-C4 was isolated from a fox testis cDNA expression library and sequenced. The deduced translated protein sequence was shown to be 86% identical to that of human LDH-C4. In the fox testis, mRNA encoding LDH-C4 was first detected in pachytene spermatocytes. The LDH-C4 protein monomer was identified in Western blots of sperm membrane extracts as having a molecular weight of approximately 35,000, consistent with the monomeric size of this subunit previously identified in sperm from other species. The LDH-C4 protein is localized on the sperm plasma membrane overlying the principal piece of the tail. Based on the available sequence data, we were able to identify an epitope within the N-terminal region of the LDH-C4 amino-acid sequence which when administered to female foxes is antigenic and produces antibodies capable of recognizing the native protein.

Testis-specific expression of mRNAs for a unique human type 1 hexokinase lacking the porin-binding domain

Several enzymes in the glycolytic pathway are reported to have spermatogenic cell-specific isozymes. We reported recently the cloning of cDNAs representing three unique type 1 hexokinase mRNAs (mHk1-sa, mHk1-sb, and mHk1-sc) present only in mouse spermatogenic cells and the patterns of expression of these mRNAs (Mori et al., 1993: Biol Reprod 49:191-203). The mRNAs contain a spermatogenic cell-specific sequence, but lack the sequence for the porin-binding domain that somatic cell hexokinases use to bind to a pore-forming protein in the outer mitochondrial membrane. We now report the cloning of cDNAs representing three unique human type 1 hexokinase mRNAs (hHK1-ta, hHK1-tb, and hHK1-tc) expressed in testis, but not detected by Northern analysis in other human tissues. These mRNAs also contain a testis-specific sequence not present in somatic cell type 1 hexokinase, but lack the sequence for the porin-binding domain. The hHK1-tb and hHK1-tc mRNAs each contain an additional unique sequence. The testis-specific sequence of the human mRNAs is similar to the spermatogenic cell-specific sequence of the mouse mRNAs. Furthermore, Northern analysis of RNA from mouse, hamster, guinea pig, rabbit, ram, human, and rat demonstrated expression of type 1 hexokinase mRNAs lacking the porin-binding domain in the testes of these mammals. These results suggest that hexokinase may have unique structural or functional features in spermatogenic cells and support a model proposed by others for hexokinase gene evolution in mammals.

A strategy for identifying candidate sperm antigens for immunocontraception: isolation of human testis cDNA clones using polyclonal antisera directed against hamster acrosomal membrane preparation

Components of the mammalian sperm acrosome that have been conserved during evolution are probably essential for fertilization and are therefore potential antigens for the development of an immunocontraceptive vaccine. In order to identify such protein components, a series of specific polyclonal antisera were generated by immunizing rabbits with purified acrosomal membrane fractions from hamster epididymal spermatozoa. Antisera were finally selected using immunological and in-vitro fertilization assays, and used to then screen a human testis lambda gt11 cDNA library. As a result of this screening over 70 clones were identified, selected and purified. The cDNAs were amplified by polymerase chain reaction (PCR) and the inserts characterized by restriction enzyme digestion and oligonucleotide probing techniques. The functional activity beta-galactosidase fusion proteins expressed by these clones (HA5-2, HA6-2 and HB4-1) inhibited significantly fertilization and reduced spermatozoa binding compared to controls. To date, sequence data has been obtained from HB4-1 (1.75 kb). The first 1132 nucleotides displayed > 96% homology to human testis-specific lactate dehydrogenase (LDH-C4) gene, the product of which is a known candidate antigen for a contraceptive vaccine. This finding suggests that a strategy involving the screening across species for conserved moieties of the mammalian acrosome may be useful for identifying candidate antigens for immunocontraception.

Genomic organization of a mouse glyceraldehyde 3-phosphate dehydrogenase gene (Gapd-s) expressed in post-meiotic spermatogenic cells

The Gapd-s gene encodes an isoform of the glyceraldehyde 3-phosphate dehydrogenase enzyme expressed only in post-meiotic spermatogenic cells. Two clones containing the Gapd-s gene were isolated from a mouse genomic library. Sequencing and restriction enzyme analysis demonstrated that this single-copy gene contains 11 exons and spans 9596 base pairs. The locations of Gapd-s exons and introns are conserved when compared to the corresponding portions of the chicken and human somatic Gapd genes. The promoter region contains no TATA box, although there is a potential SP1 recognition site within exon 1. Like other TATA-less genes, primer extension analysis reveals some heterogeneity in the site of transcription initiation with Gapd-s transcripts initiating from three discrete sites. Northern analysis demonstrated that a 1.5-kb Gapd-s mRNA is expressed in the testis in at least three mammalian orders, indicating that the Gapd-s gene appeared early in mammalian evolution. Using GAPD-deficient bacteria, mouse GAPD-S was shown to be capable of functioning as a glycolytic enzyme. Since GAPD has been proposed to be a key enzyme regulating glycolysis in spermatogenic cells, GAPD-S may represent a potential target for toxicological or contraceptive agents affecting fertility by interfering with glycolysis.

Evolutionary relationships of lactate dehydrogenases (LDHs) from mammals, birds, an amphibian, fish, barley, and bacteria: LDH cDNA sequences from Xenopus, pig, and rat

The nucleotide sequences of the cDNAs encoding LDH (EC 1.1.1.27) subunits LDH-A (muscle), LDH-B (liver), and LDH-C (oocyte) from Xenopus laevis, LDH-A (muscle) and LDH-B (heart) from pig, and LDH-B (heart) and LDH-C (testis) from rat were determined. These seven newly deduced amino acid sequences and 22 other published LDH sequences, and three unpublished fish LDH-A sequences kindly provided by G. N. Somero and D. A. Powers, were used to construct the most parsimonious phylogenetic tree of these 32 LDH subunits from mammals, birds, an amphibian, fish, barley, and bacteria. There have been at least six LDH gene duplications among the vertebrates. The Xenopus LDH-A, LDH-B, and LDH-C subunits are most closely related to each other and then are more closely related to vertebrate LDH-B than LDH-A. Three fish LDH-As, as well as a single LDH of lamprey, also seem to be more related to vertebrate LDH-B than to land vertebrate LDH-A. The mammalian LDH-C (testis) subunit appears to have diverged very early, prior to the divergence of vertebrate LDH-A and LDH-B subunits, as reported previously.

Sequence homology among sperm antigens involved in mammalian fertilization: search for a common epitope for immunocontraception

Sequence homology was searched among the nine cDNAs/deduced amino acid sequences encoding for the eight fertilization-related sperm antigens: namely, lactate dehydrogenase (LDH-C4), galactosyltransferase (GT), SP-10, rabbit sperm autoantigen (RSA), guinea pig (g)PH-20, cleavage signal protein (CS-1), HSA-63, human (h)PH-20, and AgX-1, respectively. Most significant identity (> 50%) was found between HSA-63 and SP-10 (59.8%), and between gPH-20 and hPH-20 (61.1%); followed by identity between SP-10 and GT (34.7%); and then between AgX-1 and hPH-20 (39.4%). All others had identity < 25%. The significance of these sequence homologies among the sperm antigens in the development of an antisperm contraceptive vaccine is discussed.

Human testis vitamin D binding protein involved in infertility

Immunoglobulin G (IgG) fraction was prepared from a serum obtained from an infertile woman containing antisperm antibodies that induced head-to-head agglutination of human sperm. The antibodies in the IgG fraction interacted with a 60-kD protein found in human testes determined by Western blot. The 60-kD protein was purified from human testis by isoelectric focusing (IEF), affinity chromatography on blue sepharose column, and preparative electrophoresis with electroelution. The purified 60-kD protein migrated as a single homogeneous band when analyzed by SDS-PAGE. The amino acid sequence of the N-terminus was determined. The initial 10 amino acid residues were identical to the human serum vitamin D binding protein (VDBP). Polyclonal antibodies were raised against the 60-kD protein. The polyclonal anti-60-kD antibodies and the anti-VDBP antibodies obtained from a commercial source immobilized human sperm in vitro. The interacting antigens were located on the postacrosomal region and midpiece of human sperm, as determined by an immunofluorescence method. The IgG fraction prepared from the serum of an infertile woman interacted with the human testis 60-kD protein but failed to stain serum VDBP. The results suggest that the 60-kD and VDBP are related proteins but not identical entities and that the 60-kD protein contains a unique structural group lacking in serum VDBP. Production of antibodies against the unique structure of the 60-kD protein may be the cause of the infertility.

Antisperm antibodies: origin, regulation, and sperm reactivity in human infertility

OBJECTIVE

To follow-up and expand discussion on the action mechanisms of antisperm antibodies in human infertility, the etiology and control of antisperm antibody induction, sperm antigens involved in immunoinfertility, and strategies for therapy.

DESIGN

A review of the recent literature with an emphasis on female immunoinfertility.

RESULTS

The role of antisperm antibodies in clinical infertility continues to be defined. Through assisted reproductive technologies, antisperm antibodies were shown to exert detrimental effects on different prefertilization and possibly postfertilization events. The female reproductive tract is part of the common mucosal immune system and is able to mount effective immune responses against infectious agents, foreign antigens, and, occasionally, sperm cells. Sperm membranes and constituents contain numerous antigenic components foreign to the human body, and yet antisperm antibodies become problematic in few women exposed to semen. Semen and sperm cells contain immunosuppressive factors capable of inhibiting different immune cells. Fertile women apparently produce antisperm antibodies but also possess neutralizing serum anti-idiotypic antibodies that are lacking in virgin and immunoinfertile women.

CONCLUSIONS

Antisperm antibodies can affect adversely human fertility but normally may be controlled by anti-idiotypic antibodies, which along with immunosuppressor factors in semen prevent their induction to a significant degree. This balance between detrimental and "beneficial" immune response to sperm may be shifted toward an antisperm antibody response by stimulatory factors such as infection. Therapies may be devised to stimulate the anti-idiotypic antibody system, to induce immune tolerance to sperm antigens, and to use antigens to adsorb antisperm antibodies from spermatozoa.

Fertility studies with antisperm antibodies

Serum obtained from an infertile subject possessed antibodies that interacted with a human sperm glycoprotein with an estimated M(r) of 17,550 and pI of 5.65 containing 17.7% neutral hexoses and designated as the BS-17 component. Polyclonal antibodies raised against the BS-17 antigen blocked the capacity of human sperm to fertilize zona-free hamster ova in vitro; however, the antibodies did not influence the binding of human sperm to zone-free ova or alter the motility of human sperm. The antibodies inhibited the capacity of mouse sperm to fertilize ova upon in vivo insemination. The BS-17 antigen was detected in human, rat, mouse, rabbit, and hamster sperm by an immunocytochemical method, using polyclonal anti-BS-17 antibodies. Intense staining occurred over the surface of the acrosomal region of all mammalian sperm. The results suggest that the production of anti-BS-17 antibodies contribute to infertility by preventing the capacitation of sperm and/or by blocking the ability of capacitated sperm to fertilize the egg.

Testis-specific expression of a metallothionein I-driven transgene correlates with undermethylation of the locus in testicular DNA

Mice carrying a chimeric transgene of the human testis-specific lactate dehydrogenase cDNA driven by mouse metallothionein I promoter have been reported to express the transgene in a testis-specific manner in six founder lines. To study the mechanism by which this testis-specific expression is mediated, we have examined genomic placement, expression pattern, and methylation status of the transgene. Our results indicate that transgene expression is repressed in all somatic tissues examined even when heavy metals are administered. Nuclear run-on assays indicate that failure of expression in the liver (in which the metallothionein I promoter is highly active) occurs at the transcriptional level. In contrast, the transgene mRNA is transcribed in male germ cells and is developmentally regulated during spermatogenesis. Examination of the transgene methylation status reveals that expression is inversely correlated with hypermethylation of the locus; all CpG dinucleotides examined in the promoter region were found to be fully methylated in kidney and liver but were undermethylated in testis. Since methylation of the murine metallothionein I promoter is sufficient to inhibit its activity, it is likely that suppression of the transgene in somatic tissues is mediated by methylation.

Cloning and sequencing of baboon and cynomolgus monkey intra-acrosomal protein SP-10: homology with human SP-10 and a mouse sperm antigen (MSA-63)

In this study, cDNAs encoding the intraacrosomal protein SP-10 were cloned and sequenced from baboon (Papio papio) and macaque (Macaca fascicularis) testis libraries and the sequence compared to that of human SP-10. Two alternatively spliced SP-10 cDNAs were obtained from both baboon and macaque testis libraries. The two cDNAs in each species contained open reading frames encoding proteins of exactly 285 and 251 amino acids. A 98% homology between baboon and macaque SP-10 was found at the protein and DNA levels. An 85% and 89% homology between baboon and macaque SP-10 and human SP-10 was present at the protein and DNA level, respectively. A mouse intraacrosomal protein, MSA-63, considered to be an SP-10 homologue, exhibited an overall 53% homology to nonhuman primate SP-10 and a 60% homology to human SP-10 at the protein level. Polymerase chain reaction analysis of testis mRNA confirmed the existence of two alternatively spliced SP-10 mRNAs in both nonhuman primates. Primer extension analysis indicated a common major transcriptional start site in baboon, macaque, and human SP-10 67 nucleotides 5' to the ATG codon. The amino acid sequence data for nonhuman primate SP-10s suggest that antibodies generated by vaccinating baboons and macaques with human SP-10 will likely recognize nonhuman primate SP-10, supporting the testing of an SP-10 contraceptive vaccine based on human SP-10 in these nonhuman primate models.

Sequence analysis of teleost retina-specific lactate dehydrogenase C: evolutionary implications for the vertebrate lactate dehydrogenase gene family

At least two gene duplication events have led to the three lactate dehydrogenase (LDH; EC 1.1.1.27) isozymes (LDH-A, LDH-B, and LDH-C) of chordates. The prevailing model for the evolution of the LDH loci involves duplication of a primordial LDH locus near the origin of vertebrates, giving rise to Ldh-A and Ldh-B. A third locus, designated Ldh-C, is expressed in the spermatocytes of mammals and a single family of birds and in the eye or liver tissues of teleost fishes. Ldh-C might have arisen independently in these taxa as duplications of either Ldh-A or Ldh-B. Several authors have challenged this traditional hypothesis on the basis of amino acid sequence and immunological similarity of the three LDH isozymes. They suggest that the primordial LDH gene was duplicated to form Ldh-C and a locus that later gave rise to Ldh-A and Ldh-B. We have differentiated between these hypotheses by determining the cDNA sequence of the retina-specific LDH-C from a teleost, Fundulus heteroclitus. On the basis of amino acid sequence similarity, we conclude that the LDH-C isozymes in fish and mammals are not orthologous but derive from independent gene duplications. Furthermore, our phylogenetic analyses support previous hypotheses that teleost Ldh-C is derived from a duplication of the Ldh-B locus.

In situ localization of male germ cell-associated kinase (mak) mRNA in adult mouse testis: specific expression in germ cells at stages around meiotic cell division

Biochemical analysis of the male germ cell-associated kinase (mak) gene, which was isolated recently by using weak cross-hybridization with the v-ros tyrosine kinase gene, revealed that the gene was highly expressed in mammalian testicular germ cells, but not in ovarian cells. In order to identify the cells which express the mak gene in more detail, we localized mak mRNA in frozen sections of mouse testis by non-radioactive in situ hybridization. In this study, we utilized thymine-thymine (T-T) dimerized mak cDNA as a haptenic, non-radioactive probe, and the signal was detected enzyme-immunohistochemically by using an anti-T-T antibody. As a result, mak mRNA was localized intensely in late pachytene (stage X) and diplotene (stage XI) spermatocytes, and faintly in dividing spermatocytes (stage XII) and early round spermatids (stage I-II), suggesting that the gene may play an important role in the phase around meiotic cell division, but not throughout the entire meiosis.

Alternative forms of Max as enhancers or suppressors of Myc-ras cotransformation

Max is a basic-helix-loop-helix-leucine zipper protein capable of forming sequence-specific DNA binding complexes with Myc proteins. An alternatively spliced messenger RNA has been identified that encodes a form of Max truncated at the COOH-terminus. This delta Max protein retained the ability to bind to the CACGTG motif in a complex with c-Myc but lacks the nuclear localization signal and the putative regulatory domain of Max. When tested in a myc-ras cotransformation assay in rat embryo fibroblasts, Max suppressed, whereas delta Max enhanced, transformation. Thus, the max gene may encode both a negative and a positive regulator of c-Myc function.

Evolutionary implications of the cDNA sequence of the single lactate dehydrogenase of a lamprey

All vertebrates other than lampreys exhibit multiple loci encoding lactate dehydrogenase +ADL-LDH; (S)-lactate:NAD+ oxidoreductase, EC 1.1.1.27+BD. Of these loci, Ldh-A is expressed predominantly in muscle, Ldh-B is expressed predominantly in heart, and Ldh-C (where present) exhibits different tissue-restricted patterns of expression depending on the taxon. To examine the relationship of the single LDH of lampreys to other vertebrate LDHs, we have determined the cDNA sequence of the LDH of the sea lamprey Petromyzon marinus and compared it to previously published sequences from bacteria, plants, and vertebrates. The lamprey sequence exhibits a mixture of features of both LDH-A and LDH-B at the amino acid level that may account for its intermediate kinetic properties. Both distance and maximum parsimony analyses strongly reject a relationship of lamprey LDH with mammalian LDH-C but do not significantly distinguish among remaining alternative phylogenetic hypotheses. Evolutionary parsimony analyses suggest that the lamprey LDH is related to Ldh-A and that the single locus condition has arisen as a result of the loss of Ldh-B (prior to the appearance of Ldh-C). The collection of LDH sequences for further studies of the evolution of the vertebrate LDH gene family will be facilitated by the PCR approach that we have used to obtain the lamprey sequence.

Methylation patterns of testis-specific genes

The methylation patterns of genes expressed in the mouse male germ line have been examined. Int-1, Hox-2.1, and Prm-1, all of which contain 5' CpG islands, were found to be completely unmethylated at many sites in these domains, both in somatic tissues and in sperm DNA. Many other testis-specific genes have a similar structure and are probably also constitutively unmethylated. Pgk-2, a non-CpG-island gene, is similar to somatic tissue-specific genes in that it is highly methylated in nonexpressing cell types but undermethylated in pachytene spermatocytes and round spermatids, where it is actively transcribed. At later stages of spermatogenesis, however, the gene becomes remethylated and thus acquires the full modification pattern in sperm DNA. In all these cases, the sperm DNA that emerges from the testis does not contain any germ-line-specific unmethylated sites and thus carries the methylation pattern typical of that in somatic tissues.