Molecular cloning and characterization of oppo 1: a haploid germ cell-specific complementary DNA encoding sperm tail protein

The Ultrastructure and Composition of Bovine Spermatozoa

This chapter provides a cytological and compositional evaluation of the various compartments and sub-compartments making up the bull spermatozoon. The intention is to define the sperm head and tail compartments from an ultrastructural perspective and attribute to them their protein constituents gathered from both traditional and modern proteomic approaches. Common to both approaches, the compositional analysis is dependent on the fractionation and isolation of the sperm compartments combined with polyacrylamide gel electrophoresis (PAGE) and Western blotting to detect the identities of the proteins, and immunocytochemistry to confirm their residency. As will be appreciated, the identity of a particular sperm protein together with its residency provide valuable insights not only into its role, but also to the role of the specific sperm compartment it occupies, in development and/or fertilization. Attention is also given in this chapter to the consequences (on sperm structure and fertility) of inactivating genes that play key roles in sperm formation, especially if their phenotypes appear to match common bull sperm abnormalities. The keywords below cover the sperm head and tail compartments addressed in this chapter.

The association of ODF4 with AK1 and AK2 in mice is essential for fertility through its contribution to flagellar shape

Normal sperm flagellar shape and movement are essential for fertilization. The integral protein outer dense fiber 4 (ODF4) localizes to ODFs, but its function remains unclear. Adenylate kinase (AK) is a phosphotransferase that catalyzes the interconversion and controls the concentration equilibrium of adenine nucleotides. AK shuttles ATP to energy-consuming sites. Here, we report on the relationship of flagellar shape and movement with ODF4, AK1 and AK2 by using Odf4-deletion (Odf4^-/-) mice. Soluble ODF4 is coimmunoprecipitated with AK1 and AK2 in Odf4^+/+ spermatozoa. ODF4, AK1 and AK2 localize to whole flagella (plasmalemma, mitochondria, ODFs, and residual cytoplasmic droplets (CDs)), principal pieces, and midpieces, respectively. Odf4^-/- sperm flagella lose ODF4 and reduce AK1 and AK2 but produce ATP. The flagellum is bent (hairpin flagellum) with a large CD in the midpiece. There is no motility in the midpiece, but the principal piece is motile. Odf4^-/- spermatozoa progress backward and fail to ascend in the uterus. Thus, Odf4^-/- males are infertile owing to abnormal flagellar shape and movement caused mainly by the loss of ODF4 with AK1 and AK2. This study is supported by the rescue experiment; the abnormalities and male infertility caused by Odf4 deletion were reversed by Odf4 restoration.

Chromosome 17 translocation affects sperm morphology: Two case studies and literature review

We present two cases of infertile males with teratozoospermia stemming from chromosome 17 translocation. The patients present karyotypes that have not been previously reported. Genes located on breakpoints (17p11.2, 9q31, and 11p15) were analysed to find the probable mechanism affecting sperm morphology. Our results suggest that ALKBH5, TOP3A, and LLGL1 interactions may be an underlying cause of abnormal sperm head morphology. Translocation of chromosome 17 occurred in conjunction with chromosome 9 and chromosome 11 translocation in the two cases, resulting in oligozoospermia and asthenozoospermia, respectively. These abnormal phenotypes may involve meiosis- and motility-related genes such as LDHC, DNHD1, UBQLN3, and NUP98. Translocation is thus a risk factor for sperm morphological abnormalities and motility deficiency. The interaction network of 22 genes on breakpoints suggests that they contribute to spermatogenesis as a group. In conclusion, this study highlighted the importance of investigating genes linked to sperm morphology, together with chromosome 17 translocation and reproductive risks. For patients interested in screening before a future pregnancy, we recommend preimplantation genetic diagnosis to reduce the risk of karyotypically unbalanced foetuses and birth defects.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylation in Mouse Pachytene Spermatocytes and Round Spermatids

Spermatogenesis, an efficient and complex system in male germline development, requires a series of elaborately regulated genetic events in which diploid spermatogonia differentiate into haploid spermatozoa. N6-methyladenosine (m6A) is an important epigenetic RNA modification that occurs during spermatogenesis. ALKBH5 is an m6A eraser and knocking out Alkbh5 increases the level of total m6A methylation and causes male infertility. In this study, comprehensive analyses of MeRIP-seq and RNA-seq data revealed differences between wild-type (WT) and Alkbh5 knockout (KO) mice. In pachytene spermatocytes (PA), 8,151 m6A peaks associated with 9,959 genes were tested from WT and 10,856 m6A peaks associated with 10,016 genes were tested from KO mice. In the round spermatids (RO), 10,271 m6A peaks associated with 10,109 genes were tested from WT mice and 9,559 m6A peaks associated with 10,138 genes were tested from KO mice. The peaks were mainly concentrated in the coding region and the stop codon of the GGAC motif. In addition, enrichment analysis showed significant m6A methylation genes in related pathways in spermatogenesis. Furthermore, we conducted joint analyses of the m6A methylome and RNA transcription, suggesting an m6A regulatory mechanism of gene expression. Finally, seven differentially expressed mRNAs from RNA-seq data in both PA and RO were verified using qPCR. Overall, our study provides new information on m6A modification changes between WT and KO in PA and RO, and may provide new insights into the molecular mechanisms of m6A modification in germ cell development and spermatogenesis.

CEP128 is involved in spermatogenesis in humans and mice

Centrosomal proteins are necessary components of the centrosome, a conserved eukaryotic organelle essential to the reproductive process. However, few centrosomal proteins have been genetically linked to fertility. Herein we identify a homozygous missense variant of CEP128 (c.665 G > A [p.R222Q]) in two infertile males. Remarkably, male homozygous knock-in mice harboring the orthologous CEP128^R222Q variant show anomalies in sperm morphology, count, and motility. Moreover, Cep128 knock-out mice manifest male infertility associated with disrupted sperm quality. We observe defective sperm flagella in both homozygous Cep128 KO and KI mice; the cilia development in other organs is normal—suggesting that CEP128 variants predominantly affected the ciliogenesis in the testes. Mechanistically, CEP128 is involved in male reproduction via regulating the expression of genes and/or the phosphorylation of TGF-β/BMP-signalling members during spermatogenesis. Altogether, our findings unveil a crucial role for CEP128 in male fertility and provide important insights into the functions of centrosomal proteins in reproductive biology.

CEP128 is a centrosomal protein important for the organization of centriolar microtubules. Here, the authors show that a CEP128 variant observed in human male siblings causes reduced sperm counts and morphologically abnormal sperm when modeled in mice, suggesting a role for CEP128 in male fertility.

Molecular basis of the morphogenesis of sperm head and tail in mice

Background

The spermatozoon has a complex molecular apparatus necessary for fertilization in its head and flagellum. Recently, numerous genes that are needed to construct the molecular apparatus of spermatozoa have been identified through the analysis of genetically modified mice.

Methods

Based on the literature information, the molecular basis of the morphogenesis of sperm heads and flagella in mice was summarized.

Main findings (Results)

The molecular mechanisms of vesicular trafficking and intraflagellar transport in acrosome and flagellum formation were listed. With the development of cryo‐electron tomography and mass spectrometry techniques, the details of the axonemal structure are becoming clearer. The fine structure and the proteins needed to form the central apparatus, outer and inner dynein arms, nexin‐dynein regulatory complex, and radial spokes were described. The important components of the formation of the mitochondrial sheath, fibrous sheath, outer dense fiber, and the annulus were also described. The similarities and differences between sperm flagella and Chlamydomonas flagella/somatic cell cilia were also discussed.

Conclusion

The molecular mechanism of formation of the sperm head and flagellum has been clarified using the mouse as a model. These studies will help to better understand the diversity of sperm morphology and the causes of male infertility.

Outer dense fibers stabilize the axoneme to maintain sperm motility

Outer dense fibers (ODFs), as unique accessory structures in mammalian sperm, are considered to play a role in the protection of the sperm tail against shear forces. However, the role and relevant mechanisms of ODFs in modulating sperm motility and its pathological involvement in asthenozoospermia were unknown. Here, we found that the percentage of ODF defects was higher in asthenozoospermic samples than that in control samples and was significantly correlated with the percentage of axoneme defects and non-motile sperm. Furthermore, the expression levels of ODF major components (Odf1, 2, 3, 4) were frequently down-regulated in asthenozoospermic samples. Intriguingly, the positive relationship between ODF size and sperm motility existed across species. The conditional disruption of Odf2 expression in mice led to reduced sperm motility and the characteristics of asthenozoospermia. Meanwhile, the expression of acetylated α-tubulin was decreased in sperm from both Odf2 conditional knockout (cKO) mice and asthenozoospermic men. Immunofluorescence and biochemistry analyses showed that Odf2 could bind to acetylated α-tubulin and protect the acetylation level of α-tubulin in HEK293T cells in a cold environment. Finally, we found that lithium elevated the expression levels of Odf family proteins and acetylated α-tubulin, elongated the midpiece length and increased the percentage of rapidly moving sperm in mice. Our results demonstrate that ODFs are beneficial for sperm motility via stabilization of the axoneme and that hypo-expression of Odf family proteins is involved in the pathogenesis of asthenozoospermia. The lithium administration assay will provide valuable insights into the development of new treatments for asthenozoospermia.

Expression of testis-specific genes, TEX101 and ODF4, in chronic myeloid leukemia and evaluation of TEX101 immunogenicity

BACKGROUND AND OBJECTIVES

Cancer-testis (CT) antigens are a group of antigens with a restricted expression in normal tissues, except testis, and they have aberrant expression in different tumors. This pattern of expression has made them promising targets for immunotherapy and cancer detection. Our aim was to find new members of this group that might be useful as markers in the detection of cancer and immunotherapy.

DESIGN AND SETTING

A descriptive study conducted in referral centers of Tehran University of Medical Science from January 2008 to January 2009.

PATIENTS AND METHODS

We analyzed the expression of two testis-specific genes named ODF4 (outer dense fiber of sperm tails 4) and TEX101 (testis expressed 101) in 20 chronic myeloid leukemia (CML) and 20 normal samples by reverse transcription-polymerase chain reaction and sequencing. Immunogenicity of TEX101 was evaluated by means of enzyme-linked immunosorbent assay.

RESULTS

These two genes were expressed in 30% of CML patients but not in any of the healthy donors. Humoral response against TEX101 was not detected in any samples.

CONCLUSIONS

TEX101 and ODF4 are CT genes useful for detection of CML. Unlike many CT genes, overexpression of TEX101 was not shown to induce immunologic responses in these samples. According to the previous studies, overexpression of TEX101 leads to suppression of cancer invasion and metastasis; thus, the induction of the expression of TEX101 in cancer by epigenetic mechanisms may be a treatment strategy.

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.

Radial spoke protein 44 (human meichroacidin) is an axonemal alloantigen of sperm and cilia

To identify novel sperm alloantigens relevant to immune infertility, sera from infertile men containing antisperm antibodies (ASA) were employed on 2-D immunoblots of human sperm proteins. An immunoreactive protein spot (MW: 44 kDa, pI: 4.5) was microsequenced and the related cDNA was cloned yielding a 309 amino acid sequence corresponding to a gene currently annotated in Genbank as TSGA2 homolog (mouse) to signify 'testis specific gene A2'. In Genbank the protein deduced from this gene is currently named human meichroacidin, an orthologue of meichroacidin previously identified in mouse spermatocytes. Human TSGA2 mapped to chromosome 21q22.3. Human meichroacidin (hMCA) contained a single potential tyrosine phosphorylation site and five casein kinase phosporylation motifs. The N-terminus contained a Membrane Occupation Recognition Nexus (MORN) motif found in the lipid kinase-phosphatidylinositol 4-phosphate 5-kinase (PIP5K) family and junctophilins. However hMCA lacked the characteristic kinase homology domain of PIP5K. Northern blot analysis revealed 1.5 kb hMCA transcripts in testis and trachea with lower levels in thyroid and spinal cord. A semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis demonstrated occurrence of the mRNA messages in all the ciliated tissues tested with highest levels of messages in testis and trachea. Western blot analysis showed the presence of hMCA protein in brain, thyroid and trachea at the identical mass, 44 kDa, as in human testis. However, this immunoreactive pattern differed from that of sperm in which a 38 kDa form was also evident suggesting that hMCA undergoes proteolytic processing. In human testis, hMCA localized to the tails of developing spermatids and did not localize to the nucleus of either spermatocytes or spermatids. EM immunocytochemistry localized hMCA within the radial spokes of the axonemal complex of the sperm flagellum, and immunofluorescence studies revealed h-meichroacidin in the cilia of epithelial cells in the trachea and ependyma. Bioinformatic identification of orthologues of meichroacidin in several lower organisms including ciliates and flagellates suggest the protein plays a role in flagellar motility across phyla. We propose the term radial spoke protein 44 as an accurate designation, preferable to human meichroacidin because it denotes the restricted localization of the protein to the radial spokes of the axonemes of both sperm and cilia. Further, since the human gene is expressed in brain, thyroid, trachea and lung in addition to testis, we suggest that the gene name be changed from TSGA2 [testis specific gene A2] to radial spoke protein 44 [RSP44].

Characterization of a novel postacrosomal perinuclear theca-specific protein, CYPT1

The perinuclear theca (PT) is a unique cytoskeletal structure that surrounds the nucleus of the sperm. The posterior acrosome segment of the PT (postacrosomal PT) is thought to play roles in shaping the nucleus during differentiation of the spermatid and in activating the oocyte during fertilization. We isolated a cDNA clone that encoded a novel haploid germ cell-specific cysteine-rich perinuclear theca protein, CYPT1. The transcripts were expressed exclusively in testicular germ cells after meiotic division. Sequence analysis revealed that CYPT1 comprised 168 amino acids and that the N-terminal was rich in basic amino acids, including cysteine clusters. Immunohistochemical and biochemical analyses localized CYPT1 to the postacrosomal PT of elongated spermatids and mature sperm. The cypt1 had three paralogs that were expressed in adult testis. A comparison of genomic structure suggested that two of the three cypt1 paralogs were generated by gene triplication on the X chromosome, while one paralog was retrotransposed to an autosome. Interestingly, the 5'-flanking regions of these genes were highly homologous with the promoter region of the spermatid-specific gene Zfy-2. CYPT1 and the proteins of the paralogous genes constitute a novel, basic cysteine-rich sperm protein family that may contribute to the function of the postacrosomal PT during nuclear shaping.

Isolation and expression analysis of the testis-specific gene, human OPPO1

PURPOSE

To investigate human spermatogenesis, we isolated human testis-specific genes.

METHODS

Using mouse amino acid sequences, we found the region including homology in amino acid level in the human genome sequences. The primers encompassing introns were made and RT-PCR and RACE were carried out. The resultant PCR products were sequenced.

RESULTS

The full-length cDNA of human OPPO1 was isolated. It encodes 257 amino acid residues. The expression of the human OPPO1 was predominantly in the testis. On the other hand, partial cDNAs of ZNF8, GR194, GR219, GR093, GR046, GR163, and GR200 were expressed in the various tissues.

CONCLUSIONS

Our data suggests that the human OPPO1 may play important roles in human spermatogenesis.

Transcription in haploid male germ cells

Major modifications in chromatin organization occur in spermatid nuclei, resulting in a high degree of DNA packaging within the spermatozoon head. However, before arrest of transcription during midspermiogenesis, high levels of mRNA are found in round spermatids. Some transcripts are the product of genes expressed ubiquitously, whereas some are generated from male germ cell-specific gene homologs of somatic cell genes. Others are transcript variants derived from genes with expression regulated in a testis-specific fashion. The haploid genome of spermatids also initiates the transcription of testis-specific genes. Various general transcription factors, distinct promoter elements, and specific transcription factors are involved in transcriptional regulation. After meiosis, spermatids are genetically but not phenotypically different, because of transcript and protein sharing through cytoplasmic bridges connecting spermatids of the same generation. Interestingly, different types of mRNAs accumulate in the sperm cell nucleus, raising the question of their origin and of a possible role after fertilization.

Cloning and developmental analysis of murid spermatid-specific thioredoxin-2 (SPTRX-2), a novel sperm fibrous sheath protein and autoantigen

Thioredoxins compose a growing family of proteins that participate in different cellular processes via redox-mediated reactions. We report here the cloning, developmental expression, and location of murid Sptrx-2. Mouse and rat SPTRX-2 proteins display a high homology to their human ortholog in the thioredoxin and NDP kinase domains, and the coding genes are located at syntenic positions. Northern blotting and in situ hybridization confirmed the testis-specific expression of murine Sptrx-2 mRNA, mostly in round spermatids. Immunohistochemical analysis of the 19 steps of rat spermiogenesis showed that SPTRX-2 expression becomes prominent in the cytoplasmic lobe of step 15-18 spermatids and diminishes in step 19 just before spermiation. However, in the spermatid tail, SPTRX-2 immunoreactivity increased from step 15 to 19 and was confined to the principal piece. By immunogold electron microscopy, SPTRX-2 was first detected scattered throughout the cytoplasm of the axoneme in step 14-15 spermatids, but began to be incorporated by step 16 into the fibrous sheath (FS). During steps 17-18, the labeling increased over the ribs and columns of the assembled FS. It peaked in step 19 and remained in the FS of epididymal spermatozoa. Immunoblots of isolated FS obtained from spermatozoa confirmed that SPTRX-2 is an integral component of the FS and a post-obstruction autoantigen in vasectomized rats. Our data indicate that SPTRX-2 incorporation into the FS lags well behind FS assembly, suggesting it is required during the final stages of sperm tail maturation in the testis and/or epididymis, where extensive disulfide bonding of FS proteins occurs.

Haprin, a novel haploid germ cell-specific RING finger protein involved in the acrosome reaction

The acrosome reaction (i.e. the exocytosis of the sperm vesicle) is a prerequisite for fertilization, but its molecular mechanism is largely unknown. We have identified a cDNA clone for a gene named haprin, which encodes a haploid germ cell-specific RING finger protein. This protein is a novel member of the RBCC (RING finger, B-box type zinc finger, and coiled-coil domain) motif family that has roles in several cellular processes, such as exocytosis. It is transcribed exclusively in testicular germ cells after meiotic division. Western blot and immunohistochemical analyses showed the molecular weight of Haprin protein to be Mr approximately 82,000. It was localized in the acrosomal region of elongated spermatids and mature sperm and was not present in acrosome-reacted sperm. The specific antibody against the RING finger domain of Haprin inhibited the acrosome reaction in permeabilized sperm. These results indicated that the novel RBCC protein Haprin plays a key role in the acrosome reaction and fertilization.