Parallel Evolution of Sperm Hyper-Activation Ca2+ Channels

Overdrive is essential for targeted sperm elimination by Segregation Distorter

Intra-genomic conflict driven by selfish chromosomes is a powerful force that shapes the evolution of genomes and species. In the male germline, many selfish chromosomes bias transmission in their own favor by eliminating spermatids bearing the competing homologous chromosomes. However, the mechanisms of targeted gamete elimination remain mysterious. Here, we show that Overdrive (Ovd), a gene required for both segregation distortion and male sterility in Drosophila pseudoobscura hybrids, is broadly conserved in Dipteran insects but dispensable for viability and fertility. In D. melanogaster, Ovd is required for targeted Responder spermatid elimination after the histone-to-protamine transition in the classical Segregation Distorter system. We propose that Ovd functions as a general spermatid quality checkpoint that is hijacked by independent selfish chromosomes to eliminate competing gametes.

Involvement of CATSPER 2 mutation in a familial context of unexplained infertility and fertilization failure associated with hearing loss: a case report

Objective

To explore the functional implications of a homozygous CATSPER 2 (cation channel for sperm) deletion within the acrosome reaction pathway during fertilization in 2 brothers, who have unexplained infertility and hearing loss.

Design

Case report.

Patients

Two twin brothers aged 30 years with hearing loss and unexplained infertility.

Exposure or Intervention

Molecular genetic diagnosis of deafness. Evaluation of the acrosome reaction and calcium mobilization assays after induction by progesterone and ionomycin on spermatozoa of the CATSPER 2-mutated patient and on fertile controls.

Main Outcome Measures

Fertilization rate during conventional in vitro fertilization. Molecular genetic test. Percentage of acrosome-reacted spermatozoa with peanut agglutinin lectin staining. Recording of progesterone and ionomycin-induced intracellular calcium signals with a fluorescent probe.

Results

Mr. S and his brother have normal, conventional sperm parameters. Both brothers have had repeated intrauterine insemination failures and one fertilization failure after conventional in vitro fertilization. Mr. S obtained 2 healthy babies after intracytoplasmic sperm injection. Genetic analysis found a homozygote deletion of the STRC (stereocilin) gene (NM 153700: c.1-? 5328+?del) that removes the CATSPER 2 gene. Mutation of the STRC gene is known to be associated with hearing loss. Sperm functional tests revealed an inability of progesterone to activate intracellular calcium signaling and to induce acrosome reaction.

Conclusion

We demonstrate the absence of a calcium signal and acrosome reaction after progesterone in our patient with a CATSPER 2 mutation. We emphasize the importance of the male medical interview and of the genetic investigation of hearing loss. We show that in vitro fertilization-intracytoplasmic sperm injection is necessary, even where normal sperm parameters are present.

Sperm plasma membrane ion transporters and male fertility potential: A perspective under the prism of cryopreservation

Intracellular calcium homeostasis plays a crucial role in spermatozoa by regulating physiological functions associated with sperm quality and male fertility potential. Intracellular calcium fine balance in the sperm cytoplasm is strictly dependent on sperm surface channels including the CatSper channel. CatSpers' role is to ensure the influx of extracellular calcium, while intracellular pH alkalinization serves as a stimulus for the activation of several channels, including CatSper. Overall, the generation of intracellular calcium spikes through CatSper is essential for fertilization-related processes, such as sperm hyperactivation, acrosome reaction, egg chemotaxis, and zona pellucida penetration. Multiple lines of evidence suggest that disruption in the close interaction among ions, pH, and CatSper could impair male fertility potential. In contemporary times, the growing reliance on Medically Assisted Reproduction procedures underscores the impact of cryopreservation on gametes. In fact, a large body of literature raises concerns about the cryo-damages provoked by the freeze-thawing processes, that can affect the plasma membrane integrity, thus the structure of pivotal ion channels, and the fine regulation of both intracellular calcium and pH. This review aims to provide an overview of the importance of the CatSper channel in sperm quality and further fertilization potential. Additionally, it addresses the emerging issue of cryopreservation's impact on the functionality of this sperm channel.

Convergent rates of protein evolution identify novel targets of sexual selection in primates

Sexual selection is the differential reproductive success of individuals, resulting from competition for mates, mate choice, or success in fertilization. In primates, this selective pressure often leads to the development of exaggerated traits which play a role in sexual competition and successful reproduction. In order to gain insight into the mechanisms driving the development of sexually selected traits, we used an unbiased genome-wide approach across 21 primate species to correlate individual rates of protein evolution to relative testes size and sexual dimorphism in body size, 2 anatomical hallmarks of sexual selection in mammals. Among species with presumed high levels of sperm competition, we detected strong conservation of testes-specific proteins responsible for spermatogenesis and ciliary form and function. In contrast, we identified accelerated evolution of female reproductive proteins expressed in the vagina, cervix, and fallopian tubes in these same species. Additionally, we found accelerated protein evolution in lymphoid tissue, indicating that adaptive immune functions may also be influenced by sexual selection. This study demonstrates the distinct complexity of sexual selection in primates revealing contrasting patterns of protein evolution between male and female reproductive tissues.

Progesterone interacts with the mutational hot-spot of TRPV4 and acts as a ligand relevant for fast Ca2+-signalling

Steroids are also known to induce immediate physiological and cellular response which occurs within minutes to seconds, or even faster. Such non-genomic actions of steroids are rapid and are proposed to be mediated by different ion channels. Transient receptor potential vanilloid sub-type 4 (TRPV4), is a non-specific polymodal ion channel which is involved in several physiological and cellular processes. In this work, we explored the possibilities of Progesterone (P4) as an endogenous ligand for TRPV4. We demonstrate that P4 docks as well as physically interacts with the TM4-loop-TM5 region of TRPV4, a region which is a mutational hotspot for different diseases. Live cell imaging experiments with a genetically encoded Ca2+-sensor suggests that P4 causes quick influx of Ca2+ specifically in the TRPV4 expressing cells, which can be partially blocked by TRPV4-specific inhibitor, suggesting that P4 can act as a ligand for TRPV4. Such P4-mediated Ca2+-influx is altered in cells expressing disease causing TRPV4 mutants, namely in L596P, R616Q, and also in embryonic lethal mutant L618P. P4 dampens, both in terms of "extent" as well as the "pattern" of the Ca2+-influx by other stimulus too in cells expressing TRPV4-Wt, suggesting that P4 crosstalk with the TRPV4-mediated Ca2+-signalling, both in quick and long-term manner. We propose that P4 crosstalk with TRPV4 might be relevant for both acute and chronic pain as well as for other health-related functions.

Recurrent Duplication and Diversification of Acrosomal Fertilization Proteins in Abalone

Reproductive proteins mediating fertilization commonly exhibit rapid sequence diversification driven by positive selection. This pattern has been observed among nearly all taxonomic groups, including mammals, invertebrates, and plants, and is remarkable given the essential nature of the molecular interactions mediating fertilization. Gene duplication is another important mechanism that facilitates the generation of molecular novelty through functional divergence. Following duplication, paralogs may partition ancestral gene function (subfunctionalization) or acquire new roles (neofunctionalization). However, the contributions of duplication followed by sequence diversification to the molecular diversity of gamete recognition genes has been understudied in many models of fertilization. The marine gastropod mollusk abalone is a classic model for fertilization. Its two acrosomal proteins (lysin and sp18) are ancient gene duplicates with unique gamete recognition functions. Through detailed genomic and bioinformatic analyses we show how duplication events followed by sequence diversification has played an ongoing role in the evolution of abalone acrosomal proteins. The common ancestor of abalone had four members of its acrosomal protein family in a tandem gene array that repeatedly experienced positive selection. We find that both sp18 paralogs contain positively selected sites located in different regions of the paralogs, suggestive of functional divergence where selection acted upon distinct binding interfaces in each paralog. Further, a more recent species-specific duplication of both lysin and sp18 in the European abalone H. tuberculata is described. Despite clade-specific acrosomal protein paralogs, there are no concomitant duplications of egg coat proteins in H. tuberculata, indicating that duplication of egg proteins per se is not responsible for retention of duplicated acrosomal proteins. We hypothesize that, in a manner analogous to host/pathogen evolution, sperm proteins are selected for increased diversity through extensive sequence divergence and recurrent duplication driven by conflict mechanisms.

Unconventional conservation reveals structure-function relationships in the synaptonemal complex

Functional requirements constrain protein evolution, commonly manifesting in a conserved amino acid sequence. Here, we extend this idea to secondary structural features by tracking their conservation in essential meiotic proteins with highly diverged sequences. The synaptonemal complex (SC) is a ~100-nm-wide ladder-like meiotic structure present in all eukaryotic clades, where it aligns parental chromosomes and regulates exchanges between them. Despite the conserved ultrastructure and functions of the SC, SC proteins are highly divergent within Caenorhabditis. However, SC proteins have highly conserved length and coiled-coil domain structure. We found the same unconventional conservation signature in Drosophila and mammals, and used it to identify a novel SC protein in Pristionchus pacificus, Ppa-SYP-1. Our work suggests that coiled-coils play wide-ranging roles in the structure and function of the SC, and more broadly, that expanding sequence analysis beyond measures of per-site similarity can enhance our understanding of protein evolution and function.

The role of female reproductive fluid in sperm competition

The role of non-gametic components of the ejaculate (seminal fluid) in fertility and sperm competitiveness is now well established. Surprisingly, however, we know far less about female reproductive fluid (FRF) in the context of sexual selection, and insights into male-FRF interactions in the context of sperm competition have only recently emerged. Despite this limited knowledge, evidence from taxonomically diverse species has revealed insights into the effects of FRF on sperm traits that have previously been implicated in studies of sperm competition. Specifically, through the differential effects of FRF on a range of sperm traits, including chemoattraction and alterations in sperm velocity, FRF has been shown to exert positive phenotypic effects on the sperm of males that are preferred as mating partners, or those from the most compatible or genetically diverse males. Despite these tantalizing insights into the putative sexually selected functions of FRF, we largely lack a mechanistic understanding of these processes. Taken together, the evidence presented here highlights the likely ubiquity of FRF-regulated biases in fertilization success across a diverse range of taxa, thus potentially elevating the importance of FRF to other non-gametic components that have so far been studied largely in males. This article is part of the theme issue 'Fifty years of sperm competition'.

Recurrent Losses and Rapid Evolution of the Condensin II Complex in Insects

Condensins play a crucial role in the organization of genetic material by compacting and disentangling chromosomes. Based on studies in a few model organisms, the condensins I and II complexes are considered to have distinct functions, with the condensin II complex playing a role in meiosis and somatic pairing of homologous chromosomes in Drosophila. Intriguingly, the Cap-G2 subunit of condensin II is absent in Drosophila melanogaster, and this loss may be related to the high levels of chromosome pairing seen in flies. Here, we find that all three non-SMC subunits of condensin II (Cap-G2, Cap-D3, and Cap-H2) have been repeatedly and independently lost in taxa representing multiple insect orders, with some taxa lacking all three. We also find that all non-Dipteran insects display near-uniform low-pairing levels regardless of their condensin II complex composition, suggesting that some key aspects of genome organization are robust to condensin II subunit losses. Finally, we observe consistent signatures of positive selection in condensin subunits across flies and mammals. These findings suggest that these ancient complexes are far more evolutionarily labile than previously suspected, and are at the crossroads of several forms of genomic conflicts. Our results raise fundamental questions about the specific functions of the two condensin complexes in taxa that have experienced subunit losses, and open the door to further investigations to elucidate the diversity of molecular mechanisms that underlie genome organization across various life forms.

The CatSper channel is present and plays a key role in sperm motility of the Atlantic salmon (Salmo salar)

Among all the Ca²⁺ channels, CatSper channels have been one of the most studied in sperm of different species due to their demonstrated role in the fertilization process. In fish sperm, the calcium channel plays a key role in sperm activation. However, the functionality of the CatSper channels has not been studied in any of the fish species. For the first time, we studied the relationship of the CatSper channel with sperm motility in a fish, using Atlantic salmon (Salmo salar) as the model. The results of our study showed that the CatSper channel in Salmo salar has chemical-physical characteristics similar to those reported for mammalian CatSper channels. In this work, it was shown that Salmo salar CatSper 3 protein has a molecular weight of approximately 55-kDa similar to Homo sapiens CatSper 3. In silico analyses suggest that this channel forms a heterotetramer sensitive to the specific inhibitor HC-056456, with a binding site in the center of the pore of the CatSper channel, hindering or preventing the influx of Ca²⁺ ions. The in vitro assay of the sperm motility inhibition of Salmo salar with the inhibitor HC-056456 showed that sperm treated with this inhibitor significantly reduced the total and progressive motility (p < .0001), demonstrating the importance of this ionic channel for this cell. The complementation of the in silico and in vitro analyses of the present work demonstrates that the CatSper channel plays a key role in the regulation of sperm motility in Atlantic salmon.

Comparative genomic analysis suggests that the sperm-specific sodium/proton exchanger and soluble adenylyl cyclase are key regulators of CatSper among the Metazoa

BACKGROUND

CatSper is a sperm-specific calcium ion (Ca2+) channel, which regulates sperm flagellar beating by tuning cytoplasmic Ca2+ concentrations. Although this Ca2+ channel is essential for mammalian fertilization, recent bioinformatics analyses have revealed that genes encoding CatSper are heterogeneously distributed throughout the eukaryotes, including vertebrates. As this channel is activated by cytoplasmic alkalization in mammals and sea urchins, it has been proposed that the sperm-specific Na+/H+ exchanger (sNHE, a product of the SLC9C gene family) positively regulates its activity. In mouse, sNHE is functionally coupled to soluble adenylyl cyclase (sAC). CatSper, sNHE, and sAC have thus been considered functionally interconnected in the control of sperm motility, at least in mouse and sea urchin.

RESULTS

We carried out a comparative genomic analysis to explore phylogenetic relationships among CatSper, sNHE and sAC in eukaryotes. We found that sNHE occurs only in Metazoa, although sAC occurs widely across eukaryotes. In animals, we found correlated and restricted distribution patterns of the three proteins, suggesting coevolution among them in the Metazoa. Namely, nearly all species in which CatSper is conserved also preserve sNHE and sAC. In contrast, in species without sAC, neither CatSper nor sNHE is conserved. On the other hand, the distribution of another testis-specific NHE (NHA, a product of the SLC9B gene family) does not show any apparent association with that of CatSper.

CONCLUSIONS

Our results suggest that CatSper, sNHE and sAC form prototypical machinery that functions in regulating sperm flagellar beating in Metazoa. In non-metazoan species, CatSper may be regulated by other H+ transporters, or its activity might be independent of cytoplasmic pH.

Exploration of miRNA and mRNA Profiles in Fresh and Frozen-Thawed Boar Sperm by Transcriptome and Small RNA Sequencing

Due to lower farrowing rate and reduced litter size with frozen-thawed semen, over 90% of artificial insemination (AI) is conducted using liquid stored boar semen. Although substantial progress has been made towards optimizing the cryopreservation protocols for boar sperm, the influencing factors and underlying mechanisms related to cryoinjury and freeze tolerance of boar sperm remain largely unknown. In this study, we report the differential expression of mRNAs and miRNAs between fresh and frozen-thawed boar sperm using high-throughput RNA sequencing. Our results showed that 567 mRNAs and 135 miRNAs were differentially expressed (DE) in fresh and frozen-thawed boar sperm. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the majority of DE mRNAs were enriched in environmental information processing such as cytokine-cytokine receptor interactions, PI3K-Akt signaling, cell adhesion, MAPK, and calcium signaling pathways. Moreover, the targets of DE miRNAs were enriched in significant GO terms such as cell process, protein binding, and response to stimuli. In conclusion, we speculate that DE mRNAs and miRNAs are heavily involved in boar sperm response to environment stimuli, apoptosis, and metabolic activities. The differences in expression also reflect the various structural and functional changes in sperm during cryopreservation.

Evolution of maternal and zygotic mRNA complements in the early Drosophila embryo

The earliest stages of animal development are controlled by maternally deposited mRNA transcripts and proteins. Once the zygote is able to transcribe its own genome, maternal transcripts are degraded, in a tightly regulated process known as the maternal to zygotic transition (MZT). While this process has been well-studied within model species, we have little knowledge of how the pools of maternal and zygotic transcripts evolve. To characterize the evolutionary dynamics and functional constraints on early embryonic expression, we created a transcriptomic dataset for 14 Drosophila species spanning over 50 million years of evolution, at developmental stages before and after the MZT, and compared our results with a previously published Aedes aegypti developmental time course. We found deep conservation over 250 million years of a core set of genes transcribed only by the zygote. This select group is highly enriched in transcription factors that play critical roles in early development. However, we also identify a surprisingly high level of change in the transcripts represented at both stages over the phylogeny. While mRNA levels of genes with maternally deposited transcripts are more highly conserved than zygotic genes, those maternal transcripts that are completely degraded at the MZT vary dramatically between species. We also show that hundreds of genes have different isoform usage between the maternal and zygotic genomes. Our work suggests that maternal transcript deposition and early zygotic transcription are remarkably dynamic over evolutionary time, despite the widespread conservation of early developmental processes.

CatSper: A Unique Calcium Channel of the Sperm Flagellum

To overcome egg protective vestments and ensure successful fertilization, mammalian spermatozoa switch symmetrical progressive motility to a powerful, whip-like flagellar motion, known as hyperactivation. The latter is triggered by a calcium influx through the sperm-specific, voltage-dependent, and alkalization-activated calcium channel of sperm - CatSper. The channel comprises nine subunits which together form a heteromeric complex. CatSper-deficient male mice and men with mutations in CatSper genes are infertile. This calcium channel is regulated by various endogenous compounds, such as steroids, prostaglandins, endocannabinoids, and intracellular pH. Being a sperm-specific ion channel that is not expressed anywhere else in the body, CatSper represents an ideal target for the development of female and even male contraceptives. In this review, we discuss the recent advances in studying CatSper functional properties and discuss future steps that are required to take in order to achieve a deep understanding of the molecular basis of CatSper function.