The rat endozepine-like peptide gene is highly expressed in late haploid stages of male germ cell development

Nucleoside diphosphate kinases 1 and 2 regulate a protective liver response to a high-fat diet

The synthesis of fatty acids from acetyl-coenzyme A (AcCoA) is deregulated in diverse pathologies, including cancer. Here, we report that fatty acid accumulation is negatively regulated by nucleoside diphosphate kinases 1 and 2 (NME1/2), housekeeping enzymes involved in nucleotide homeostasis that were recently found to bind CoA. We show that NME1 additionally binds AcCoA and that ligand recognition involves a unique binding mode dependent on the CoA/AcCoA 3' phosphate. We report that Nme2 knockout mice fed a high-fat diet (HFD) exhibit excessive triglyceride synthesis and liver steatosis. In liver cells, NME2 mediates a gene transcriptional response to HFD leading to the repression of fatty acid accumulation and activation of a protective gene expression program via targeted histone acetylation. Our findings implicate NME1/2 in the epigenetic regulation of a protective liver response to HFD and suggest a potential role in controlling AcCoA usage between the competing paths of histone acetylation and fatty acid synthesis.

Roles of acyl-CoA-binding proteins in plant reproduction

Acyl-CoA-binding proteins (ACBPs) constitute a well-conserved family of proteins in eukaryotes that are important in stress responses and development. Past studies have shown that ACBPs are involved in maintaining, transporting and protecting acyl-CoA esters during lipid biosynthesis in plants, mammals, and yeast. ACBPs show differential expression and various binding affinities for acyl-CoA esters. Hence, ACBPs can play a crucial part in maintaining lipid homeostasis. This review summarizes the functions of ACBPs during the stages of reproduction in plants and other organisms. A comprehensive understanding on the roles of ACBPs during plant reproduction may lead to opportunities in crop improvement in agriculture.

Models of in vitro spermatogenesis

Understanding the mechanisms that lead to the differentiation of male germ cells from their spermatogonial stem cells through meiosis to give rise to mature haploid spermatozoa has been a major quest for many decades. Unlike most other cell types this differentiation process is more or less completely dependent upon the cells being located within the strongly structured niche provided by mature Sertoli cells within an intact seminiferous epithelium. While much new information is currently being obtained through the application and description of relevant gene mutations, there is still a considerable need for in vitro models with which to explore the mechanisms involved. Not only are systems of in vitro spermatogenesis important for understanding the basic science, they have marked pragmatic value in offering ex vivo systems for the artificial maturation of immature germ cells from male infertility patients, as well as providing opportunities for the transgenic manipulation of male germ cells. In this review, we have summarized literature relating to simplistic culturing of germ cells, co-cultures of germ cells with other cell types, especially with Sertoli cells, cultures of seminiferous tubule fragments, and briefly mention the opportunities of xenografting larger testicular pieces. The majority of methods are successful in allowing the differentiation of small steps in the progress of spermatogonia to spermatozoa; few tolerate the chromosomal reduction division through meiosis, and even fewer seem able to complete the complex morphogenesis which results in freely swimming spermatozoa. However, recent progress with complex culture environments, such as 3-d matrices, suggest that possibly success is now not too far away.

Connecting cis-elements and trans-factors with mechanisms of developmental regulation of mRNA translation in meiotic and haploid mammalian spermatogenic cells

mRNA-specific regulation of translational activity plays major roles in directing the development of meiotic and haploid spermatogenic cells in mammals. Although many RNA-binding proteins (RBPs) have been implicated in normal translational control and sperm development, little is known about the keystone of the mechanisms: the interactions of RBPs and microRNAs withcis-elements in mRNA targets. The problems in connecting factors and elements with translational control originate in the enormous complexity of post-transcriptional regulation in mammalian cells. This creates confusion as to whether factors have direct or indirect and large or small effects on the translation of specific mRNAs. This review argues that gene knockouts, heterologous systems, and overexpression of factors cannot provide convincing answers to these questions. As a result, the mechanisms involving well-studied mRNAs (Ddx4/Mvh,Prm1,Prm2, andSycp3) and factors (DICER1, CPEB1, DAZL, DDX4/MVH, DDX25/GRTH, translin, and ELAV1/HuR) are incompletely understood. By comparison, mutations in elements can be used to define the importance of specific pathways in regulating individual mRNAs. However, few elements have been studied, because the only reliable system to analyze mutations in elements, transgenic mice, is considered impractical. This review describes advances that may facilitate identification of the direct targets of RBPs and analysis of mutations incis-elements. The importance of upstream reading frames in the developmental regulation of mRNA translation in spermatogenic cells is also documented.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Seminiferous tubule transfection in vitro to define post-meiotic gene regulation

BACKGROUND

Post-meiotically expressed genes in the testis are essential for the proper progression of spermatogenesis, and yet, aside from the construction of individual transgenic mice using specific promoters to drive reporter plasmids, there are only very limited possibilities for relevant and quantitative analysis of gene promoters. This is due to the special nature of post-meiotic haploid cells, which to date are not represented in any appropriate cell-lines. This article reports the development of novel methodology using isolated and cultured rat seminiferous tubules in a multiwell format, into which promoter-reporter constructs can be introduced by a combination of microinjection and electroporation.

METHODS

Culture conditions were developed which allowed the continued incubation of isolated rat seminiferous tubules for up to 48 h without obvious cell death and loss of post-meiotic cells. Transfection of intact seminiferous tubules by microinjection and electroporation was optimized to achieve high expression efficiencies of control plasmids, using either fluorescent protein or luciferase as reporters, thereby allowing both morphological as well as quantitative assessment.

RESULTS

Successful transfection was achieved into all cell types except for mature spermatozoa. However, there appeared to be only limited cell-type specificity for the promoters used, even though these had appeared to be specific when used in transgenic animals.

CONCLUSION

We have devised a methodology which allows relatively high throughput analysis of post-meiotic gene promoters into primary cells of intact seminiferous tubules. An apparent lack of cell-type specificity suggests that the gene fragments used do not contain sufficient targeting information, or that the transient episomal expression of the constructs does not encourage appropriate expression specificity. The results also highlight the doubtful interpretation of many studies using heterologous transfection systems to analyse post-meiotically expressed genes.

Acyl-CoA binding proteins; structural and functional conservation over 2000 MYA

Besides serving as essential substrates for beta-oxidation and synthesis of triacylglycerols and more complex lipids like sphingolipids and sterol esters, long-chain fatty acyl-CoA esters are increasingly being recognized as important regulators of enzyme activities and gene transcription. Acyl-CoA binding protein, ACBP, has been proposed to play a pivotal role in the intracellular trafficking and utilization of long-chain fatty acyl-CoA esters. Depletion of acyl-CoA binding protein in yeast results in aberrant organelle morphology incl. fragmented vacuoles, multi-layered plasma membranes and accumulation of vesicles of variable sizes. In contrast to synthesis and turn-over of glycerolipids, the levels of very-long-chain fatty acids, long-chain bases and ceramide are severely affected by Acb1p depletion, suggesting that Acb1p, rather than playing a general role, serves specific roles in cellular lipid metabolism.

Novel epididymis-specific mRNAs downregulated by HE6/Gpr64 receptor gene disruption

Targeted disruption of the epididymis-specific HE6/Gpr64 receptor gene in mice led to male infertility. In order to characterize the phenotype at a molecular level, we compared the gene expression patterns of wild type (wt) versus knockout (KO) caput epididymides. The caput region of KO males, although morphologically normal, nevertheless showed an aberrant expression pattern. Combining micro array analysis, differential library screening, Northern blot analysis and quantitative RT-PCR, we found that the knockout of the HE6/Gpr64 receptor was mainly associated with the downregulation of genes specific to the initial segment. The list of KO downregulated transcripts comprised Enpp2/autotaxin, the lipocalins 8 and 9, the beta-defensin Defb42, cystatins 8 and 12, as well as the membrane proteins Adam (A Disintegrin And Metalloprotease) 28, claudin-10, EAAC1, and the novel Me9. Clusterin/ApoJ and osteopontin/Spp1 mRNAs, on the other hand, were upregulated in the KO tissues. The Me9 transcript was studied in further detail, and we report here a cluster of related epididymis-specific genes. Me9 is specifically expressed in the initial segment and is representative of a novel and highly conserved mammalian gene family. The family consists of single-exon genes only; intron-containing paralogs have not yet been ascertained. The cloned cDNA sequences predicted hydrophobic polytopic membrane proteins containing the DUF716 motif. Protein expression was shown in the rodent caput epididymidis but remained uncertain in primates.

Localization of a long-chain acyl-CoA hydrolase in spermatogenic cells in mice

Brain acyl-CoA hydrolase (BACH) hydrolyzes long-chain acyl-CoAs to free fatty acids and CoA-SH. BACH is highly distributed in brain and is localized in neurons, but not glial cells. This suggests that BACH plays a specific role in neurons. BACH is also detected in testis, although the expression profile of BACH is unknown in testis. In this study, developmental changes and cellular distribution of BACH were examined in mouse testis. Before postnatal day (P) 10, BACH was detected at very low levels by Western blotting. Then, BACH content rapidly increased from P14 and reached maximum levels at P21, remaining high until at least P70. The increase in BACH content corresponded to the appearance of pachytene spermatocytes, which was confirmed by immunohistochemistry. BACH was also detectable in spermatids, but not in spermatogonia, mature spermatozoa. These results suggest that BACH is expressed in a cell-specific manner and plays a role in spermatogenesis.

Meiotic messenger RNA and noncoding RNA targets of the RNA-binding protein Translin (TSN) in mouse testis

In postmeiotic male germ cells, TSN, formerly known as testis brain-RNA binding protein, is found in the cytoplasm and functions as a posttranscriptional regulator of a group of genes transcribed by the transcription factor CREM-tau. In contrast, in pachytene spermatocytes, TSN is found predominantly in nuclei. Tsn-null males show a reduced sperm count and high levels of apoptosis in meiotic cells, suggesting a critical function for TSN during meiosis. To identify meiotic target RNAs that associate in vivo with TSN, we reversibly cross-linked TSN to RNA in testis extracts from 17-day-old and adult mice and immunoprecipitated the complexes with an affinity-purified TSN antibody. Extracts from Tsn-null mice were used as controls. Cloning and sequencing the immunoprecipitated RNAs, we identified four new TSN target mRNAs, encoding diazepam-binding inhibitor-like 5, arylsulfatase A, a tetratricopeptide repeat structure-containing protein, and ring finger protein 139. In contrast to the population of postmeiotic translationally delayed mRNAs that bind TSN, these four mRNAs are initially expressed in pachytene spermatocytes. In addition, anti-TSN also precipitated a nonprotein-coding RNA (ncRNA), which is abundant in nuclei of pachytene spermatocytes and has a putative polyadenylation signal, but no open reading frame. A second similar ncRNA is adjacent to a GGA repeat, a motif frequently associated with recombination hot spots. RNA gel-shift assays confirm that the four new target mRNAs and the ncRNA specifically bind to TSN in testis extracts. These studies have, for the first time, identified both mRNAs and a ncRNA as TSN targets expressed during meiosis.

Cloning and characterization of rat spermatid protein SSP411: a thioredoxin-like protein

In an attempt to identify new sperm-specific genes that are involved in sperm maturation, fertilization, and embryo development, such as the mammalian ortholog of the sperm-supplied protein gene, spe-11, in Caenorhabditis elegans, we cloned and characterized a new spermatid-specific protein gene, ssp411, from adult rat testes. The ssp411 cDNA shared >85% sequence identity with an unnamed human protein, FLJ21347, and an uncharacterized mouse testicular protein called transcript increased in spermiogenesis 78 (TISP78). A 2.8-kb ssp411 mRNA was expressed in a testis-specific and age-dependent manner; the mRNA was evident at 28 days and remained at high levels throughout adulthood. An SSP411 protein of molecular weight 88 000 was detected in testicular extracts by Western blot analysis. Ssp411 mRNA and SSP411 protein, as analyzed by in situ hybridization and immunohistochemistry, were both expressed in a stage-dependent fashion during the cycle of the seminiferous epithelium. The ssp411 mRNA was predominantly localized to round and elongated spermatids, with maximal expression at stages VII-XII. The SSP411 protein was mainly observed in elongated spermatids and reached its highest levels during stages V-VI. A conserved thioredoxin-like domain was detected in the N-terminal region of SSP411 and its orthologs. An analysis of the predicted 3-dimensional structural modeling and folding pattern further suggested that SSP411 is identifiable as a member of thioredoxin family. In summary, we have identified a new rat spermatid protein gene, ssp411, and its orthologs in human and mouse and demonstrated that SSP411 might belong to a testis-specific thioredoxin family. This suggests that SSP411 may play a role in sperm maturation, fertilization, and/or embryo development, as has been shown in thioredoxin family.

Novel testis-expressed profilin IV associated with acrosome biogenesis and spermatid elongation

A novel profilin, named profilin IV, was cloned and characterized as a testicular isoform, distinct from the previously described testis-specific profilin III. Profilin IV showed only 30% amino acid identity with the other mammalian profilins; nevertheless, database searches produced significant alignments with the conserved profilin domain. Northern blot analysis and in situ transcript hybridization suggested that profilin IV, like profilin III, is transcribed in the germ cells. However, the timing of their expression during post-natal development of rat testis and in the rat spermatogenetic cycle was distinct. In the human testis, profilin IV mRNA expression correlates with the presence of germ cells suggesting that it may be a suitable molecular diagnostic parameter to supplement conventional histopathological diagnostics in the assessment of testicular biopsies. The predicted profilin IV protein was verified employing an anti-oligopeptide antibody. Western blot analysis detected an immunorelated testicular protein of approximately 14 kDa. Immunohistochemistry revealed an intracellular protein of the rat, the mouse and the human testis accumulating asymmetrically in the cytoplasm of round and elongating spermatids with its perinuclear location coinciding with the position of the developing acrosome-acroplaxome and the manchette. Profilin IV thus may regulate testicular actin cytoskeleton dynamics and play a role in acrosome generation and spermatid nuclear shaping.

Post-meiotic gene products as targets for male contraception

Post-meiotic stages of male germ cell maturation represent an interesting target system for the development of novel male contraceptive agents. In the human, these stages represent a period of only about 16 days differentiation, and thus targeting these cells would represent a contraceptive approach with a relatively rapid onset and equivalent recovery. Results from the Human Genome Project suggest that these cells also express a high number of very specific transcripts, though whether all of these are functional and/or essential for sperm differentiation and function requires more research. Until recently, however, these haploid stages were relatively inaccessible to molecular research because of the lack of appropriate model systems and methods. This situation has recently improved, with several new techniques involving manipulation of primary cells and seminiferous tubules, germ cell transplantation and the development of new immortalized cell-lines. Also, new biochemical approaches are yielding more information about haploid-specific transcription factors, such as GCNF. It is therefore to be expected that soon several new targets for a potential post-meiotic male contraceptive will become available for pharmaceutical development.

Organization of seminiferous epithelium in primates: relationship to spermatogenic efficiency, phylogeny, and mating system

The succession in time and space of specific germ cell associations, denoted as spermatogenic stages, is a typical feature of mammalian spermatogenesis. The arrangement of these stages is either single stage (one spermatogenic stage per tubular cross-section) or multistage (more than one spermatogenic stage per tubular cross-section). It has been proposed that the single-stage versus multistage arrangement is related to spermatogenic efficiency and that the multistage arrangement is typical for hominids. In the present work, the arrangement of spermatogenic stages and the spermatogenic efficiency of 17 primate species, comprising Strepsirrhini (Prosimians: Lemuriformes, Lorisiformes), Platyrrhini (New World primates), Catarrhini (Old World primates), and Hominoidea (great apes and humans), were analyzed comparatively by quantitative histological and flow cytometric means. We found a predominant single-stage tubular organization in the Strepsirrhini, indicating that the single-stage form represents the ancestral state. The highest degree of multistage complexity was found in Hominoidea (except orangutan) and in Platyrrhini, but not in Catarrhini. Hence, no direct relationship between single-stage/multistage tubular topography and phylogeny could be established across primates. In fact, the tubule arrangement seen in Platyrrhini and Catarrhini primates is the reverse of what might be expected from phylogeny. Interestingly, spermatogenic efficiency was similar in all species. We found no correlation between single-stage/multistage arrangement and spermatogenic efficiency or mating system. We speculate that the presence of a single-stage/multistage organization might simply reflect germ cell clonal size. Our findings further indicate that sperm competition in primates is not reflected at the level of testicular function.

SPEER--a new family of testis-specific genes from the mouse

Differential cloning revealed a partial mRNA sequence expressed in the mouse testis, which on further molecular characterization proved to be a member of a new family of 14 transcribed genes. Six of the genes appear to be expressed pseudogenes. The remainder indicate an open reading frame of approximately 200-220 amino acids encoding proteins with a very high proportion of alpha helical secondary structure, comprising approximately 15% glutamate residues. Because of this property, the family has been named SPErm-associated glutamate (E)-Rich protein (SPEER). Three members were chosen for more detailed characterization: SPEER-1 (pseudogene), SPEER-2, and SPEER-4D. All three are expressed tissue specifically in the testis of mice, with only very weak expression evident in the rat testis but in no other species tested. Using reverse transcription-polymerase chain reaction (RT-PCR), all three transcripts can be detected also in the epididymis, presumably due to the presence of spermatozoa. All three transcripts are expressed to high levels in haploid germ cells at the spermatocyte-spermatid transition. SPEER-1 mRNA is present in the cytoplasm as a sense transcript, SPEER-2 appears to be made mostly as an antisense transcript, whereas SPEER-4D appears to be localized within a subcellular compartment as a conventional sense transcript. Codon usage analysis suggests that all but the pseudogenes can be expressed as protein, confirmed for SPEER-2 and SPEER-4D by in vitro transcription/translation. An antibody raised against a peptide region of SPEER-4D, which probably cross-reacts with other SPEER members, immunohistochemically stains the nuclei of early round spermatids. While there are no true homologies to other proteins in the genome databases, some motifs are present that suggest a relationship to nuclear matrix proteins, implying that the SPEER family is a new group of haploid sperm-specific nuclear factors.

Testis-specific expression of rat mitochondrial glycerol-3-phosphate dehydrogenase in haploid male germ cells

Mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) is regulated by multiple promoters in a tissue-specific manner. We characterized the testis-specific promoter C of the mGPDH gene and investigated the cellular localization of mGPDH within the testis. Electrophoretic mobility shift experiments identified a cAMP-response element (CRE) site at -57 that was active in the testis. An in vitro-translated CRE modulator (CREM) protein was able to bind this CRE site, and an anti-CREM antibody interfered with this complex. Ectopic expression of the testis-specific transcriptional activator CREMtau and protein kinase A in human hepatocarcinoma HepG2 cells activated a promoter C-driven luciferase construct in transient transfection experiments. Furthermore, mGPDH expression was undetectable in testis of CREM-deficient mice. The cellular localization of mGPDH expression and translation in adult rat testis was determined by in situ hybridization and immunohistochemistry techniques. The mGPDH transcripts were detected solely in postmeiotic germ cells. Expression of mGPDH was restricted from round spermatids to early elongating spermatids. The mGPDH protein was delayed in postmeiotic germ cells, restricted from late elongating spermatids to mature spermatids. Our results indicate that rat mGPDH is expressed by a testis-specific promoter from haploid male germ cells in a stage-specific manner.

The evolution of the endozepine-like peptide (ELP) in the mammalian testis

The endozepine-like peptide (ELP) is a testis-specific isoform of the acyl-CoA binding protein (ACBP) and shares the latter's peptide motif for binding mid-long chain acyl-CoA groups. ELP is expressed both as mRNA and protein at high levels in the testes of a wide range of mammals, including rodents, carnivores and ruminants. However, the ELP gene is progressively inactivated through primate evolution, with no protein detectable in a range of primates studied, including human. In nonprimate species, ELP is expressed in very late postmeiotic germ cell stages only, such that its function in these species is probably associated with the metabolism of the mature spermatozoon. Current research is looking at both the function of the ELP protein and the haploid regulation of the gene.

A possible meiotic function of the peculiar patterns of gene expression in mammalian spermatogenic cells

This review focuses on the striking differences in the patterns of transcription and translation in somatic and spermatogenic cells in mammals. In early haploid cells, mRNA translation evidently functions to restrict the synthesis of certain proteins, notably protamines, to transcriptionally inert late haploid cells. However, this does not explain why a substantial proportion of virtually all mRNA species are sequestered in translationally inactive free-messenger ribonucleoprotein particles (free-mRNPs) in meiotic cells, since most mRNAs undergo little or no increase in translational activity in transcriptionally active early haploid cells. In addition, most mRNAs in meiotic cells appear to be overexpressed because they are never fully loaded on polysomes and the levels of the corresponding protein are often much lower than the mRNA and are sometimes undetectable. A large number of genes are expressed at grossly higher levels in meiotic and/or early haploid spermatogenic cells than in somatic cells, yet they too are translated inefficiently. Many genes utilize alternative promoters in somatic and spermatogenic cells. Some of the resulting spermatogenic cell-altered transcripts (SCATs) encode proteins with novel functions, while others contain features in their 5'-UTRs, secondary structure or upstream reading frames, that are predicted to inhibit translation. This review proposes that the transcriptional machinery is modified to provide access to specific DNA sequences during meiosis, which leads to mRNA overexpression and creates a need for translational fine-tuning to prevent deleterious consequences of overproducing proteins.

Progressive inactivation of the haploid expressed gene for the sperm-specific endozepine-like peptide (ELP) through primate evolution

The endozepine-like peptide (ELP) is a novel intracellular molecule which is expressed in high amounts at both mRNA and protein levels very specifically in late haploid male germ cells. It is closely related to the ubiquitous acyl-CoA binding protein, is highly conserved, shares a similar ability to bind mid-long chain acyl-CoA, and is thus likely to be involved in mature sperm metabolism. While it has been characterized from diverse mammals, it has so far not been possible to identify an equivalent molecule in the primate testis. Using a PCR approach, combined with cDNA cloning and Northern hybridization, testicular transcripts and/or genomic DNA were analysed for different primate species, including human. In the marmoset and cynomolgus macaque normally structured transcripts appear to be expressed, though at a low level. In the human testis, two rare transcripts were characterized, hELP1 and hELP2, the products of independent duplicated genes. Both transcripts were longer than in non-mammalian species, included frame-shift mutations and substantial sequence insertions, preventing the translation of a sensible protein. Genomic PCR analysis of three anthropoid species, chimpanzee, gorilla and orangutan, showed the presence of a similarly mutated hELP1 gene. Only in the gorilla was a hELP2 gene identified, apparently lacking the frame-shift mutation, and thus potentially able to give rise to a functional ELP protein. Taken together, these results show that during primate evolution there has been a progressive inactivation of the ELP gene, initially with a down-regulation in lower primates, and subsequently with inactivating mutations in the open reading frame. At some time during simian evolution prior to these mutations there has been a gene duplication, though this second gene has also become inactivated in humans. In its pattern of evolution the ELP gene shows similarities with the MDC/fertilin family, whose members are also considered essential components of haploid sperm in non-primates, but which are progressively inactivated in anthropoids and humans. We should like to speculate that the established subfertility of the human male may not be a recent event, but the consequence of a longer evolutionary process whereby primates have traded off absolute fertility against social or sexual advantages.

Structure and expression of the mouse gene encoding the endozepine-like peptide from haploid male germ cells

The endozepine-like peptide (ELP) represents a testis-specific isoform of the ubiquitous acyl-CoA binding protein (ACBP) and is highly expressed in late haploid stages of male germ cell development. The genomic sequence of the functional ELP gene as well as that of a pseudogene were analysed from independent bacteriophage clones of a 129sv mouse genomic library. Unlike the ACBP gene, which comprises four exons, the ELP gene has only a single intron within the region of the 5' untranslated region, suggesting that, like some other haploid expressed genes, the ELP gene might have evolved by retroposon-mediated gene duplication. Primer extension analysis was used to define the start site for transcription and hence the 5' promoter region. Electrophoretic mobility shift analysis was carried out on this region comparing nuclear extracts from adult mouse testis with those from mouse liver. Several testis-specific DNA-protein complexes were observed throughout 700 bp upstream of the transcription start site. One of these could be identified as corresponding to a steroidogenic factor-1 (SF-1) binding element. Further analysis using pure transcription factors showed that this element at position -340 was able to bind specifically to both SF-1 and to the germ cell nuclear factor (GCNF). Immunohistochemical analysis using an ELP-specific antibody showed that expression was very restricted within the testis to the postmeiotic germ cells, and in the ovary to interstitial/luteal cells, cell-types known to express GCNF and SF-1, respectively. Testes of CREM-tau knockout mice, lacking all spermatogenic stages later than round spermatids, were devoid of ELP immunoreactivity, whereas in RAD6 knockout mice the few remaining elongated spermatids were clearly defined by this excellent late haploid marker product. The ELP gene and its product thus offer an ideal system with which to investigate the differentiation of late haploid stages of spermatogenesis.