The mouse t-complex gene, Tcp-11, is under translational control

Mouse t-complex protein 11 is important for progressive motility in sperm†

The t-complex is defined as naturally occurring variants of the proximal third of mouse chromosome 17 and has been studied by mouse geneticists for decades. This region contains many genes involved in processes from embryogenesis to sperm function. One such gene, t-complex protein 11 (Tcp11), was identified as a testis-specific gene whose protein is present in elongating spermatids. Later work on Tcp11 localized TCP11 to the sperm surface and acrosome cap and implicated TCP11 as important for sperm capacitation through the cyclic AMP/Protein Kinase A pathway. Here, we show that TCP11 is cytoplasmically localized to elongating spermatids and absent from sperm. In the absence of Tcp11, male mice have severely reduced fertility due to a significant decrease in progressively motile sperm; however, Tcp11-null sperm continues to undergo tyrosine phosphorylation, a hallmark of capacitation. Interestingly, null sperm displays reduced PKA activity, consistent with previous reports. Our work demonstrates that TCP11 functions in elongated spermatids to confer proper motility in mature sperm.

Comparative expression profiling of testis-enriched genes regulated during the development of spermatogonial cells

The testis has been identified as the organ in which a large number of tissue-enriched genes are present. However, a large portion of transcripts related to each stage or cell type in the testis still remains unknown. In this study, databases combined with confirmatory measurements were used to investigate testis-enriched genes, localization in the testis, developmental regulation, gene expression profiles of testicular disease, and signaling pathways. Our comparative analysis of GEO DataSets showed that 24 genes are predominantly expressed in testis. Cellular locations of 15 testis-enriched proteins in human testis have been identified and most of them were located in spermatocytes and round spermatids. Real-time PCR revealed that expressions of these 15 genes are significantly increased during testis development. Also, an analysis of GEO DataSets indicated that expressions of these 15 genes were significantly decreased in teratozoospermic patients and polyubiquitin knockout mice, suggesting their involvement in normal testis development. Pathway analysis revealed that most of those 15 genes are implicated in various sperm-related cell processes and disease conditions. This approach provides effective strategies for discovering novel testis-enriched genes and their expression patterns, paving the way for future characterization of their functions regarding infertility and providing new biomarkers for specific stages of spematogenesis.

PABP interacting protein 2A (PAIP2A) regulates specific key proteins during spermiogenesis in the mouse

During spermiogenesis, expression of the specific proteins needed for proper differentiation of male germ cells is under translational control. We have shown that PAIP2A is a major translational regulator involved in the maturation of male germ cells and male fertility. To identify the proteins controlled by PAIP2A during spermiogenesis, we characterized the proteomic profiles of elongated spermatids from wild-type (WT) mice and mice that were Paip2a/Paip2b double-null mutants (DKO). Elongated spermatid populations were obtained and proteins were extracted and separated on gradient polyacrylamide gels. The gels were digested with trypsin and peptides were identified by mass spectrometry. We identified 632 proteins with at least two unique peptides and a confidence level of 95%. Only 209 proteins were consistently detected in WT or DKO replicates with more than five spectra. Twenty-nine proteins were differentially expressed with at least a 1.5-fold change; 10 and 19 proteins were down- and up-regulated, respectively, in DKO compared to WT mice. We confirmed the significantly different expression levels of three proteins, EIF4G1, AKAP4, and HK1, by Western blot analysis. We have characterized novel proteins that have their expression controlled by PAIP2A; of these, 50% are involved in flagellar structure and sperm motility. Although several proteins affected by abrogation of Paip2a have established roles in reproduction, the roles of many others remain to be determined.

Fertilisation Promoting Peptide: a key player in male fertility/subfertility?

'Male factor' problems contribute to subfertility in a significant proportion of couples. In some instances, defective sperm production has qualitative and/or quantitative effects on the semen profile; in others, no obvious defects can be detected, yet spermatozoa are non-fertilising. Recent studies have revealed that fertilisation promoting peptide (FPP), which is structurally related to thyrotrophin releasing hormone (TRH) and found in the prostate gland and seminal plasma of many mammals, has important biologically relevant effects on both mouse and human spermatozoa. In the presence of physiological concentrations of FPP, spermatozoa become fertile more quickly and are then inhibited from undergoing spontaneous acrosome loss, a step that would render them non-fertilising. In vivo, these responses could be extremely important in maximising fertilising potential of the few spermatozoa that reach the site of fertilisation. Prostatic dysfunction results in decreased production of FPP and increased production of less bioactive FPP-related peptides. A putative receptor (TCP-11) for FPP has been identified in the mouse; the gene (with a human homologue) which codes for TCP-11 resides within a complex known to contain genes affecting male fertility. These results strongly suggest that FPP plays an important role in normal fertility and that it might therefore provide both new therapeutic approaches for some cases of unexplained infertility and new approaches for male contraception.

Specific localization of RBM1a in the nuclei of all cell types except elongated spermatids within seminiferous tubules of the human

Recent studies have indicated that at least three regions (AZF a-c) on the long arm of the Y-chromosome code for factors are involved in spermatogenesis. One of the candidate genes in the AZFb region is RBM1a, coding for a protein with an RNA binding motif. In this study, poly clonal antibodies raised against a 15 amino acid peptide, corresponding to residues 263-304 of the deduced amino acid sequence of RBM1a, has been used to localize the RBM1a protein in the human testis. Immunohistochemistry on normal human testis using this RBM1a antibody, localized the antigen to the nuclei of spermatogonia, primary spermatocytes, and round spermatids but not to the nuclei of elongated spermatids. The antibody also specifically identified the nuclei of Sertoli cells, although the fluorescence was not as strong as in the germ cell nuclei it identified. No specific fluorescence was seen in the nuclei of either peritubular, endothelial or Leydig cells. Western blot of normal human testicular tissue using the anti-RBM1a antibody gave rise to a single specific band of approximately 55 kDa, corresponding to the expected size of RBM1a. In view of its expression in germ cells, and because RBM1a has an RNA binding domain, RBM1a may be involved in RNA processing, such as RNA splicing or RNA export which are events necessary for normal spermatogenesis.

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.

Fertilization promoting peptide — A possible regulator of sperm function in vivo

Fertilization promoting peptide (FPP), a tripeptide related to thyrotrophin releasing hormone (TRH), is found in seminal plasma. Recent evidence obtained in vitro suggests that FPP may play an important role in regulating sperm fertility in vivo. Specifically, FPP initially stimulates nonfertilizing (uncapacitated) spermatozoa to "switch on" and become fertile more quickly, but then arrests capacitation so that spermatozoa do not undergo spontaneous acrosome loss and therefore do not lose fertilizing potential. These responses are mimicked, and indeed augmented, by adenosine, known to regulate the adenylyl cyclase (AC)/cAMP signal transduction pathway. Both FPP and adenosine have been shown to stimulate cAMP production in uncapacitated cells but inhibit it in capacitated cells, with FPP receptors somehow interacting with adenosine receptors and G proteins to achieve regulation of AC. These events affect the tyrosine phosphorylation state of various proteins, some being important in the initial "switching on," others possibly being involved in the acrosome reaction itself. Calcitonin and angiotensin II, also found in seminal plasma, have similar effects in vitro on uncapacitated spermatozoa and can augment responses to FPP, suggesting that all four molecules may be involved in regulating availability of cAMP. It is plausible that these molecules have similar effects in vivo, affecting fertility by stimulating and then maintaining fertilizing potential. Either reductions in the availability of FPP, adenosine, calcitonin, and angiotensin II or defects in their receptors could contribute to male infertility. These exciting results may provide new approaches for diagnostic tests and treatments of certain categories of male infertility.

New insights into the t-complex and control of sperm function

The mouse t-complex, located on chromosome 17, contains genes known to influence male, but not female, fertility. Although some t-complex genes are recessive lethals, t-chromosomes are maintained in the population by transmission ratio distortion. When male mice heterozygous for the t-chromosome mate with wild-type females, most offspring will possess the t-chromosome, indicating a link between t-complex genes and sperm function. Several proteins coded for by t-complex genes have been localised in the sperm flagellum, suggesting roles relating to motility. Another t-complex protein appears able to regulate the adenylyl cyclase/cAMP signal transduction pathway, known to play an important role in capacitation. Defective motility and/or failure to capacitate ("switch on") would result in poorly fertile or infertile spermatozoa. Given the existence of human homologues for many genes in the t-complex and the prevalence of "male factor" infertility, information obtained about the t-complex not only will provide insight into basic biological mechanisms but may be of future clinical relevance as well.

Modulation of mammalian sperm function by fertilization promoting peptide (FPP)

Fertilization promoting peptide (FPP; pGlu-Glu-ProNH2) is produced by the prostate gland and secreted into seminal plasma. When added to uncapacitated mouse and human sperm suspensions, it stimulates capacitation as demonstrated by both cytological changes and increased fertilizing ability in vitro. When added to capacitated suspensions, FPP inhibits spontaneous acrosome loss but cells retain high fertility in vitro. Adenosine elicits similar responses to FPP in both uncapacitated and capacitated cells and FPP + adenosine has a greater effect on uncapacitated cells than either used individually. We have proposed that these two molecules modulate the same pathway (adenylate cyclase/cAMP) but act via different receptors. The structure of FPP is crucial for bioactivity: loss of the terminal amide group abolishes activity and substitution of the central glutamic acid can markedly alter activity. Most recently we have found that stimulation of TCP-11, the product of the mouse t-complex gene Tcp-11, elicits responses indistinguishable from those obtained with FPP and we have hypothesized that the protein TCP-11 is the receptor for FPP. The existence of a human homologue for Tcp-11 suggests that the gene product, in conjunction with FPP, could play an important role in human fertility.

TCP-11, the product of a mouse t-complex gene, plays a role in stimulation of capacitation and inhibition of the spontaneous acrosome reaction

Tcp-11 is a candidate for a distorter gene within the t-complex on mouse chromosome 17; although t-complex genes appear to affect sperm function, relatively little is known about mechanisms whereby these genes might play a specific physiological role. We present evidence that the protein TCP-11 is found on the surface of mature epididymal spermatozoa. Although detected on both the acrosomal cap region of the head and the flagellum of acrosome-intact cells, it is absent from the heads of acrosome-reacted cells. When epididymal spermatozoa were incubated in the presence of anti-TCP-11 IgG Fab fragments for a total of 120 min and assessed using chlortetracycline fluorescence, we observed a stimulation of capacitation and an inhibition of spontaneous acrosome loss, suggestive of enhanced fertility compared with untreated suspensions. In vitro fertilization experiments confirmed that Fab-treated suspensions became fertile more quickly and then maintained high fertility. Because these responses were remarkably similar to those obtained using the TRH-related peptide FPP (fertilization promoting peptide; pGlu-Glu-ProNH2) and adenosine, we investigated responses to Fab fragments, FPP, and adenosine. Results indicated that the Fab fragments appear to work at the same extracellular site as FPP, one that is distinct from the adenosine site of action. Further evidence for this conclusion was obtained using pGlu-Gln-ProNH2, an FPP-related tripeptide known to competitively inhibit responses to FPP; as with FPP, pGlu-Glu-ProNH2 inhibited the stimulatory effect of Fab fragments in a concentration-dependent manner. From these results we suggest that TCP-11 may be the receptor for FPP and that the adenylate clyclase/cyclic AMP pathway may be the signal transduction pathway activated by interactions between extracellular effector molecules (e.g., Fab fragments or FPP acting as an agonist) and TCP-11. A mechanism such as this that promotes capacitation but inhibits spontaneous acrosome loss in vivo would play a very important role by helping to maximize the fertilizing potential of the few spermatozoa that reach the site of fertilization. The fact that there is a human homolog of Tcp-11 suggests that this gene could play an important role in regulation of human, as well as mouse, sperm function.

The molecular genetics of male infertility

Spermatogenesis is an elaborate process involving both cell division and differentiation, and cell-cell interactions. Defects in any of these processes can result in infertility, and in some cases these can be genetic in cause. Mapping experiments have defined at least three regions of the human Y chromosome that are required for normal spermatogenesis. Two of these contain the genes encoding the RNA binding proteins RBM and DAZ, suggesting that the control of RNA metabolism is likely to be an important control point for human spermatogenesis. A similar analysis in mice has shown that at least two regions of the mouse Y chromosome are essential for spermatogenesis. Both genetic and reverse genetic approaches have been used to identify mouse autosomal genes required for spermatogenesis. These studies have shown that genes in a number of different pathways are essential for normal spermatogenesis, and also provide putative models of human infertility.

Degeneracy in human multicopy RBM (YRRM), a candidate spermatogenesis gene

In order to search for mutations in the multicopy RBM genes that might be associated with male infertility, we have used sequence data from the reported cDNA clone to determine the intron exon boundaries of the YRRM 1 gene. This gene has 12 exons, three of which encode the putative RNA binding domain of the protein. Different copies of the gene contain sequence variations and, additionally, give rise to transcripts with different numbers of copies of the repeated SRGY motif. Since mutations in the RNA binding domain would seem likely to have an effect on the activity of the protein, we have scanned these exons for mutations by SSCP on DNA from normal and infertile men. Sequence differences in the exon encoding the N-terminal part of the RNA binding domain account for at least four different classes of the gene and give rise to different SSCP conformers. Sequence analysis shows that one of these classes is a pseudogene and that the members of another class are nonfunctional. RT-PCR shows that all classes are transcribed and that the A class is most abundant. We have found a point mutation that alters the highly conserved RNP2 motif in one infertile patient. This mutation is also found in his father. We have used PCR followed by SSCP analysis to map RBM on a Y Chromosome (Chr) YAC contig and have demonstrated a distribution that spans a major part of this chromosome's euchromatin.