FER-1 regulates Ca2+ -mediated membrane fusion during C. elegans spermatogenesis

Small RNA-mediated genetic switches coordinate ALG-3/4 small RNA pathway function

Coordination of gene regulatory networks is necessary for proper execution of cellular programs throughout development. RNA interference (RNAi) is an essential regulatory mechanism in all metazoans. Proper RNAi-mediated gene regulation requires coordination of several RNAi branches to ensure homeostasis. For example, in Caenorhabditis elegans, the Argonautes, ALG-3 and ALG-4, are expressed specifically during spermatogenesis (L4 stage) and bind small interfering RNAs (siRNAs) complementary to sperm-enriched genes. We find that alg-3 and alg-4 are regulated by siRNAs. Our work shows that gene switches are operated via these siRNAs to regulate the Argonautes' expression in a temporal manner. This RNAi-to-RNAi regulatory cascade is essential for coordinating ALG-3/4 pathway function, particularly during heat stress, to provide thermotolerant sperm-based fertility. This work provides insight into one regulatory motif used to maintain RNAi homeostasis, across developmental stages, despite environmental stressors. As RNAi pathways are evolutionarily conserved, other species likely use similar regulatory architectures to maintain RNAi homeostasis.

RNA-binding protein complex AMG-1/SLRP-1 mediates germline development and spermatogenesis by maintaining mitochondrial homeostasis in Caenorhabditis elegans

The mechanisms of RNA-binding proteins (RBPs)-mediated post-transcriptional regulation of pre-existing mRNAs, which is essential for spermatogenesis, remain poorly understood. In this study, we identify that a germline-specific mitochondrial RBP AMG-1(abnormal mitochondria in germline 1), a homolog of mammalian leucine-rich PPR motif-containing protein (LRPPRC), is required for spermatogenesis in Caenorhabditis elegans. The amg-1 mutation hinders germline development without affecting somatic development and leads to the aberrant mitochondrial morphology and structure associated with mitochondrial dysfunctions specifically in the germline. We demonstrate that AMG-1 is most frequently bound to mtDNA-encoded 12S and 16S ribosomal RNA, the essential components of mitochondrial ribosomes, and that 12S rRNA expression mediated by AMG-1 is crucial for germline mitochondrial protein homeostasis. Furthermore, steroid receptor RNA activator (SRA) stem loop interacting RNA binding protein (SLRP-1), a homolog of mammalian SRA stem loop interacting RNA binding protein (SLIRP) in C. elegans, interacts with AMG-1 genetically to regulate germline development and reproductive success in C. elegans. Overall, these findings reveal the novel function of mtRBP, specifically in regulating germline development.

Spermiogenesis in Caenorhabditis elegans: An Excellent Model to Explore the Molecular Basis for Sperm Activation

C. elegans spermiogenesis converts non-motile spermatids into motile, fertilization-competent spermatozoa. Two major events include the building of a pseudopod required for motility and fusion of membranous organelles (MOs)-intracellular secretory vesicles-with the spermatid plasma membrane required for the proper distribution of sperm molecules in mature spermatozoa. The mouse sperm acrosome reaction-a sperm activation event occurring during capacitation-is similar to MO fusion in terms of cytological features and biological significance. Moreover, C. elegans fer-1 and mouse Fer1l5, both encoding members of the ferlin family, are indispensable for MO fusion and acrosome reaction, respectively. Genetics-based studies have identified many C. elegans genes involved in spermiogenesis pathways; however, it is unclear whether mouse orthologs of these genes are involved in the acrosome reaction. One significant advantage of using C. elegans for studying sperm activation is the availability of in vitro spermiogenesis, which enables combining pharmacology and genetics for the assay. If certain drugs can activate both C. elegans and mouse spermatozoa, these drugs would be useful probes to explore the mechanism underlying sperm activation in these two species. By analyzing C. elegans mutants whose spermatids are insensitive to the drugs, genes functionally relevant to the drugs' effects can be identified.

Testis-enriched ferlin, FER1L5, is required for Ca2+-activated acrosome reaction and male fertility

Spermatozoa need to undergo an exocytotic event called the acrosome reaction before fusing with eggs. Although calcium ion (Ca2+) is essential for the acrosome reaction, its molecular mechanism remains unknown. Ferlin is a single transmembrane protein with multiple Ca2+-binding C2 domains, and there are six ferlins, dysferlin (DYSF), otoferlin (OTOF), myoferlin (MYOF), fer-1-like 4 (FER1L4), FER1L5, and FER1L6, in mammals. Dysf, Otof, and Myof knockout mice have been generated, and each knockout mouse line exhibited membrane fusion disorders such as muscular dystrophy in Dysf, deafness in Otof, and abnormal myogenesis in Myof. Here, by generating mutant mice of Fer1l4, Fer1l5, and Fer1l6, we found that only Fer1l5 is required for male fertility. Fer1l5 mutant spermatozoa could migrate in the female reproductive tract and reach eggs, but no acrosome reaction took place. Even a Ca2+ ionophore cannot induce the acrosome reaction in Fer1l5 mutant spermatozoa. These results suggest that FER1L5 is the missing link between Ca2+ and the acrosome reaction.

GLH-1/Vasa represses neuropeptide expression and drives spermiogenesis in the C. elegans germline

Germ granules harbor processes that maintain germline integrity and germline stem cell capacity. Depleting core germ granule components in C. elegans leads to the reprogramming of germ cells, causing them to express markers of somatic differentiation in day-two adults. Somatic reprogramming is associated with complete sterility at this stage. The resulting germ cell atrophy and other pleiotropic defects complicate our understanding of the initiation of reprogramming and how processes within germ granules safeguard the totipotency and immortal potential of germline stem cells. To better understand the initial events of somatic reprogramming, we examined total mRNA (transcriptome) and polysome-associated mRNA (translatome) changes in a precision full-length deletion of glh-1, which encodes a homolog of the germline-specific Vasa/DDX4 DEAD-box RNA helicase. Fertile animals at a permissive temperature were analyzed as young adults, a stage that precedes by 24 ​h the previously determined onset of somatic reporter-gene expression in the germline. Two significant changes are observed at this early stage. First, the majority of neuropeptide-encoding transcripts increase in both the total and polysomal mRNA fractions, suggesting that GLH-1 or its effectors suppress this expression. Second, there is a significant decrease in Major Sperm Protein (MSP)-domain mRNAs when glh-1 is deleted. We find that the presence of GLH-1 helps repress spermatogenic expression during oogenesis, but boosts MSP expression to drive spermiogenesis and sperm motility. These insights define an early role for GLH-1 in repressing somatic reprogramming to maintain germline integrity.

Redefining the architecture of ferlin proteins: Insights into multi-domain protein structure and function

Ferlins are complex, multi-domain proteins, involved in membrane trafficking, membrane repair, and exocytosis. The large size of ferlin proteins and the lack of consensus regarding domain boundaries have slowed progress in understanding molecular-level details of ferlin protein structure and function. However, in silico protein folding techniques have significantly enhanced our understanding of the complex ferlin family domain structure. We used RoseTTAFold to assemble full-length models for the six human ferlin proteins (dysferlin, myoferlin, otoferlin, Fer1L4, Fer1L5, and Fer1L6). Our full-length ferlin models were used to obtain objective domain boundaries, and these boundaries were supported by AlphaFold2 predictions. Despite the differences in amino acid sequence between the ferlin proteins, the domain ranges and distinct subdomains in the ferlin domains are remarkably consistent. Further, the RoseTTAFold/AlphaFold2 in silico boundary predictions allowed us to describe and characterize a previously unknown C2 domain, ubiquitous in all human ferlins, which we refer to as C2-FerA. At present, the ferlin domain-domain interactions implied by the full-length in silico models are predicted to have a low accuracy; however, the use of RoseTTAFold and AlphaFold2 as a domain finder has proven to be a powerful research tool for understanding ferlin structure.

Analysis of the MCTP Amino Acid Sequence Reveals the Conservation of Putative Calcium- and Lipid-Binding Pockets Within the C2 Domains In Silico

MCTPs (Multiple C2 Domains and Transmembrane region Proteins) are evolutionarily and structurally related to other C2 proteins, which are central to exocytosis and membrane trafficking; however, their specific function has been little studied. MCTPs are associated with endosomes and the endoplasmic reticulum and possess three C2 domains (C2A-C2C) and two transmembrane regions (TMRs) well conserved in different species. Here, we generated structural models of the MCTP C2 domains of C. elegans and analyzed their putative function by docking, which revealed that these domains possess Ca²⁺- and lipid-binding pockets, suggesting that MCTPs play a significant, calcium-dependent role in membrane physiology.

Zinc is an intracellular signal during sperm activation in Caenorhabditis elegans

Sperm activation is a rapid and dramatic cell differentiation event that does not involve changes in transcription, and the signaling cascades that mediate this process have not been fully defined. zipt-7.1 encodes a zinc transporter, and zipt-7.1(lf) mutants display sperm-activation defects, leading to the hypothesis that zinc signaling mediates sperm activation in Caenorhabditis elegans. Here, we describe the development of a method for dynamic imaging of labile zinc during sperm activation using the zinc-specific fluorescence probe FluoZin-3 AM and time-lapse confocal imaging. Two phases of dynamic changes in labile zinc levels were observed during sperm activation. Forced zinc entry using the zinc ionophore pyrithione activated sperm in vitro, and it suppressed the defects of zipt-7.1(lf) mutants, indicating that high levels of cytosolic zinc are sufficient for sperm activation. We compared activation by zinc pyrithione to activation by extracellular zinc, the Na+/H+ antiporter monensin and the protease cocktail pronase in multiple mutant backgrounds. These results indicate that the protease pathway does not require zinc signaling, suggesting that zinc signaling is sufficient to activate sperm but is not always necessary.

SLC-30A9 is required for Zn2+ homeostasis, Zn2+ mobilization, and mitochondrial health

The trace element zinc is essential for many aspects of physiology. The mitochondrion is a major Zn²⁺ store, and excessive mitochondrial Zn²⁺ is linked to neurodegeneration. How mitochondria maintain their Zn²⁺ homeostasis is unknown. Here, we find that the SLC-30A9 transporter localizes on mitochondria and is required for export of Zn²⁺ from mitochondria in both Caenorhabditis elegans and human cells. Loss of slc-30a9 leads to elevated Zn²⁺ levels in mitochondria, a severely swollen mitochondrial matrix in many tissues, compromised mitochondrial metabolic function, reductive stress, and induction of the mitochondrial stress response. SLC-30A9 is also essential for organismal fertility and sperm activation in C. elegans, during which Zn²⁺ exits from mitochondria and acts as an activation signal. In slc-30a9-deficient neurons, misshapen mitochondria show reduced distribution in axons and dendrites, providing a potential mechanism for the Birk-Landau-Perez cerebrorenal syndrome where an SLC30A9 mutation was found.

Membrane contact site-dependent cholesterol transport regulates Na+/K+-ATPase polarization and spermiogenesis in Caenorhabditis elegans

Spermiogenesis in nematodes is a process whereby round and quiescent spermatids differentiate into asymmetric and crawling spermatozoa. The molecular mechanism underlying this symmetry breaking remains uncharacterized. In this study, we revealed that sperm-specific Na⁺/K⁺-ATPase (NKA) is evenly distributed on the plasma membrane (PM) of Caenorhabditis elegans spermatids but is translocated to and subsequently enters the invaginated membrane of the spermatozoa cell body during sperm activation. The polarization of NKA depends on the transport of cholesterol from the PM to membranous organelles (MOs) via membrane contact sites (MCSs). The inositol 5-phosphatase CIL-1 and the MO-localized PI4P phosphatase SAC-1 may mediate PI4P metabolism to drive cholesterol countertransport via sterol/lipid transport proteins through MCSs. Furthermore, the NKA function is required for C. elegans sperm motility and reproductive success. Our data imply that the lipid dynamics mediated by MCSs might play crucial roles in the establishment of cell polarity. eGraphical abstract.

An Emerging Therapeutic Approach by Targeting Myoferlin (MYOF) for Malignant Tumors

Myoferlin (MYOF), as a member of the ferlin family, is a type II transmembrane protein with a single transmembrane domain at the carbon terminus. Studies have shown that MYOF is involved in pivotal physiological functions related to numerous cell membranes, such as extracellular secretion, endocytosis cycle, vesicle trafficking, membrane repair, membrane receptor recycling, and secreted protein efflux. Recently, the studies have also revealed that MYOF is overexpressed in a variety of cancers such as colorectal cancer, pancreatic cancer, breast cancer, melanoma, gastric cancer, and non-small-cell lung cancer. High expression of MYOF is associated with the high invasion of tumors and poor clinical prognosis. MYOF medicates the expression, secretion, and distribution of proteins, which were closely related to cancers, as well as the energy utilization of cancer cells, lipid metabolism and other physiological activities by regulating the physiological processes of membrane transport. In this short article, we briefly summarize the latest progress related to MYOF, indicating that small molecule inhibitors targeting the MYOF-C2D domain can selectively inhibit the proliferation and migration of cancer cells, and MYOF may be a promising target for the treatment of malignant tumors.

Conserved sperm factors are no longer a bone of contention

Proteins related to a molecule involved in the formation of osteoclasts in bone are required for fertilization in worms, flies and mammals.

Sperm DNA methylation mediates the association of male age on reproductive outcomes among couples undergoing infertility treatment

Parental age at time of offspring conception is increasing in developed countries. Advanced male age is associated with decreased reproductive success and increased risk of adverse neurodevelopmental outcomes in offspring. Mechanisms for these male age effects remain unclear, but changes in sperm DNA methylation over time is one potential explanation. We assessed genome-wide methylation of sperm DNA from 47 semen samples collected from male participants of couples seeking infertility treatment. We report that higher male age was associated with lower likelihood of fertilization and live birth, and poor embryo development (p < 0.05). Furthermore, our multivariable linear models showed male age was associated with alterations in sperm methylation at 1698 CpGs and 1146 regions (q < 0.05), which were associated with > 750 genes enriched in embryonic development, behavior and neurodevelopment among others. High dimensional mediation analyses identified four genes (DEFB126, TPI1P3, PLCH2 and DLGAP2) with age-related sperm differential methylation that accounted for 64% (95% CI 0.42-0.86%; p < 0.05) of the effect of male age on lower fertilization rate. Our findings from this modest IVF population provide evidence for sperm methylation as a mechanism of age-induced poor reproductive outcomes and identifies possible candidate genes for mediating these effects.

Functionally non-redundant paralogs spe-47 and spe-50 encode FB-MO associated proteins and interact with him-8

The activation of C. elegans spermatids to crawling spermatozoa is affected by a number of genes including spe-47. Here, we investigate a paralog to spe-47: spe-50, which has a highly conserved sequence and expression, but which is not functionally redundant to spe-47. Phylogenetic analysis indicates that the duplication event that produced the paralogs occurred prior to the radiation of the Caenorhabditis species included in the analysis, allowing a long period for the paralogs to diverge in function. Furthermore, we observed that knockout mutations in both genes, either alone or together, have little effect on sperm function. However, hermaphrodites harboring both knockout mutations combined with a third mutation in the him-8 gene are nearly self-sterile due to a sperm defect, even though they have numerous apparently normal sperm within their spermathecae. We suggest that the sperm in these triple mutants are defective in fusing with oocytes, and that the effect of the him-8 mutation is unclear but likely due to its direct or indirect effect on local chromatin structure and function.

Depletion of gipc-1 and gipc-2 causes infertility in Caenorhabditis elegans by reducing sperm motility

The G-protein signaling pathway plays a key role in multiple cellular processes and is well conserved in eukaryotes. Although GIPC (G-protein α subunit interacting protein (GAIP)-interacting protein, C terminus) has been studied in several model organisms, little is known about its role in Caenorhabditis elegans. In the present study, we investigated the roles of gipc-1 and gipc-2 in C. elegans. We observed that they were exclusively expressed in sperm throughout the development and that gipc-1; gipc-2 double mutants were infertile. Further examination of sperm development in gipc-1; gipc-2 mutants revealed defective sperm activation and abnormal pseudopod extension that resulted in reduced sperm motility. Moreover, major sperm protein (MSP) was abnormally segregated between spermatids and residual bodies in gipc-1; gipc-2 mutants. Our findings indicate that gipc-1 and gipc-2 are required for the proper pseudopod extension of sperm during the terminal differentiation of spermatids. During this process, the segregation of MSP into spermatids is important for ensuring normal sperm motility during fertilization.

MCTP-1 modulates neurotransmitter release in C. elegans

Multiple C2 and Transmembrane Domain Proteins (MCTPs) are putative calcium sensors. Proteins that contain C2 domains play essential roles in membrane trafficking and exocytosis; however, MCTPs functions in neurotransmitter release are not known. Here we report that in C. elegans mctp-1 is under the control of two promoters - one active in the nervous system and the second in the spermatheca. We generated and characterized a loss of function amt1 mutant and compared it to a previously published loss of function mutant (av112). Loss of mctp-1 function causes defects in egg-laying, crawling velocity, and thrashing rates. Both amt1 and av112 mutants are hyposensitive to the acetylcholinesterase blocker aldicarb, suggesting that MCTP-1 may play a role in synaptic vesicle release.

Functions of Vertebrate Ferlins

Ferlins are multiple-C2-domain proteins involved in Ca²⁺-triggered membrane dynamics within the secretory, endocytic and lysosomal pathways. In bony vertebrates there are six ferlin genes encoding, in humans, dysferlin, otoferlin, myoferlin, Fer1L5 and 6 and the long noncoding RNA Fer1L4. Mutations in DYSF (dysferlin) can cause a range of muscle diseases with various clinical manifestations collectively known as dysferlinopathies, including limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. A mutation in MYOF (myoferlin) was linked to a muscular dystrophy accompanied by cardiomyopathy. Mutations in OTOF (otoferlin) can be the cause of nonsyndromic deafness DFNB9. Dysregulated expression of any human ferlin may be associated with development of cancer. This review provides a detailed description of functions of the vertebrate ferlins with a focus on muscle ferlins and discusses the mechanisms leading to disease development.

Selection for bull fertility: a review

Fertility is a critically important factor in cattle production because it directly relates to the ability to produce the offspring necessary to offset costs in production systems. Female fertility has received much attention and has been enhanced through assisted reproductive technologies, as well as genetic selection; however, improving bull fertility has been largely ignored. Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Selection and management to improve bull fertility not only have the potential to increase conception rates but also have the capacity to improve other economically relevant production traits. Bull fertility has reportedly been genetically correlated with traits such as average daily gain, heifer pregnancy, and calving interval. Published studies show that bull fertility traits are low to moderately heritable, indicating that improvements in bull fertility can be realized through selection. Although female fertility has continued to progress according to increasing conception rates, the reported correlation between male and female fertility is low, indicating that male fertility cannot be improved by selection for female fertility. Correlations between several bull fertility traits, such as concentration, number of spermatozoa, motility, and number of spermatozoa abnormalities, vary among studies. Using male fertility traits in selection indices would provide producers with more advanced selection tools. The objective of this review was to discuss current beef bull fertility measurements and to discuss the future of genetic evaluation of beef bull fertility and potential genetic improvement strategies.

Myoferlin, a Membrane Protein with Emerging Oncogenic Roles

Myoferlin (MYOF), initially identified in muscle cells, is a member of the Ferlin family involved in membrane fusion, membrane repair, and membrane trafficking. Dysfunction of this protein is associated with muscular dysfunction. Recently, a growing body of studies have identified MYOF as an oncogenic protein. It is overexpressed in a variety of human cancers and promotes tumorigenesis, tumor cell motility, proliferation, migration, epithelial to mesenchymal transition, angiogenesis as well as metastasis. Clinically, MYOF overexpression is associated with poor outcome in various cancers. It can serve as a prognostic marker of human malignant disease. MYOF drives the progression of cancer in various processes, including surface receptor transportation, endocytosis, exocytosis, intercellular communication, fit mitochondrial structure maintenance and cell metabolism. Depletion of MYOF demonstrates significant antitumor effects both in vitro and in vivo, suggesting that targeting MYOF may produce promising clinical benefits in the treatment of malignant disease. In the present article, we reviewed the physiological function of MYOF as well as its role in cancer, thus providing a general understanding for further exploration of this protein.

Ferlin Overview: From Membrane to Cancer Biology

In mammal myocytes, endothelial cells and inner ear cells, ferlins are proteins involved in membrane processes such as fusion, recycling, endo- and exocytosis. They harbour several C2 domains allowing their interaction with phospholipids. The expression of several Ferlin genes was described as altered in several tumoural tissues. Intriguingly, beyond a simple alteration, myoferlin, otoferlin and Fer1L4 expressions were negatively correlated with patient survival in some cancer types. Therefore, it can be assumed that membrane biology is of extreme importance for cell survival and signalling, making Ferlin proteins core machinery indispensable for cancer cell adaptation to hostile environments. The evidences suggest that myoferlin, when overexpressed, enhances cancer cell proliferation, migration and metabolism by affecting various aspects of membrane biology. Targeting myoferlin using pharmacological compounds, gene transfer technology, or interfering RNA is now considered as an emerging therapeutic strategy.

Caenorhabditis elegans sperm membrane protein interactome

The interaction and organization of proteins in the sperm membrane are important for all aspects of sperm function. We have determined the interactions between 12 known mutationally defined and cloned sperm membrane proteins in a model system for reproduction, the nematode Caenorhabditis elegans. Identification of the interactions between sperm membrane proteins will improve our understanding of and ability to characterize defects in sperm function. To identify interacting proteins, we conducted a split-ubiquitin membrane yeast two-hybrid analysis of gene products identified through genetic screens that are necessary for sperm function and predicted to encode transmembrane proteins. Our analysis revealed novel interactions between sperm membrane proteins known to have roles in spermatogenesis, spermiogenesis, and fertilization. For example, we found that a protein known to play a role in sperm function during fertilization, SPE-38 (a predicted four pass transmembrane protein), interacts with proteins necessary for spermiogenesis and spermatogenesis and could serve as a central organizing protein in the plasma membrane. These novel interaction pairings will provide the foundation for investigating previously unrealized membrane protein interactions during spermatogenesis, spermiogenesis, and sperm function during fertilization.

Autophagy in C. elegans development

Autophagy involves the sequestration of cytoplasmic contents in a double-membrane structure referred to as the autophagosome and the degradation of its contents upon delivery to lysosomes. Autophagy activity has a role in multiple biological processes during the development of the nematode Caenorhabditis elegans. Basal levels of autophagy are required to remove aggregate prone proteins, paternal mitochondria, and spermatid-specific membranous organelles. During larval development, autophagy is required for the remodeling that occurs during dauer development, and autophagy can selectively degrade components of the miRNA-induced silencing complex, and modulate miRNA-mediated silencing. Basal levels of autophagy are important in synapse formation and in the germ line, to promote the proliferation of proliferating stem cells. Autophagy activity is also required for the efficient removal of apoptotic cell corpses by promoting phagosome maturation. Finally, autophagy is also involved in lipid homeostasis and in the aging process. In this review, we first describe the molecular complexes involved in the process of autophagy, its regulation, and mechanisms for cargo recognition. In the second section, we discuss the developmental contexts where autophagy has been shown to be important. Studies in C. elegans provide valuable insights into the physiological relevance of this process during metazoan development.

Proteinase K is an activator for the male-dependent spermiogenesis pathway in Caenorhabditis elegans: Its application to pharmacological dissection of spermiogenesis

Caenorhabditis elegans spermiogenesis involves spermatid activation into spermatozoa. Activation occurs through either SPE-8 class-dependent or class-independent pathways. Pronase (Pron) activates the SPE-8 class-dependent pathway, whereas no in vitro tools are available to stimulate the SPE-8 class-independent pathway. Thus, whether there is a functional relationship between these two pathways is currently unclear. In this study, we found that proteinase K (ProK) can activate the SPE-8 class-independent pathway. In vitro spermiogenesis assays using Pron and ProK suggested that SPE-8 class proteins act in the hermaphrodite- and male-dependent spermiogenesis pathways and that some spermatid proteins presumably working downstream of spermiogenesis pathways, including MAP kinases, are preferentially involved in the SPE-8 class-dependent pathway. We screened a library of chemicals, and a compound that we named DDI-1 inhibited both Pron- and ProK-induced spermiogenesis. To our surprise, several DDI-1 analogues that are structurally similar to DDI-1 blocked Pron, but not ProK, induced spermiogenesis. Although the mechanism by which DDI-1 blocks spermiogenesis is yet unknown, we have begun to address this issue by selecting two DDI-1-resistant mutants. Collectively, our data support a model in which C. elegans male and hermaphrodite spermiogenesis each has its own distinct, parallel pathway.

Transmission of the malaria parasite requires ferlin for gamete egress from the red blood cell

Ferlins mediate calcium-dependent vesicular fusion. Although conserved throughout eukaryotic evolution, their function in unicellular organisms including apicomplexan parasites is largely unknown. Here, we define a crucial role for a ferlin-like protein (FLP) in host-to-vector transmission of the rodent malaria parasite Plasmodium berghei. Infection of the mosquito vectors requires the formation of free gametes and their fertilisation in the mosquito midgut. Mature gametes will only emerge upon secretion of factors that stimulate the disruption of the red blood cell membrane and the parasitophorous vacuole membrane. Genetic depletion of FLP in sexual stages leads to a complete life cycle arrest in the mosquito. Although mature gametes form normally, mutants lacking FLP remain trapped in the red blood cell. The egress defect is rescued by detergent-mediated membrane lysis. In agreement with ferlin vesicular localisation, HA-tagged FLP labels intracellular speckles, which relocalise to the cell periphery during gamete maturation. Our data define FLP as a novel critical factor for Plasmodium fertilisation and transmission and suggest an evolutionarily conserved example of ferlin-mediated exocytosis.

Fer1l6 is essential for the development of vertebrate muscle tissue in zebrafish

The precise spatial and temporal expression of genes is essential for proper organismal development. Despite their importance, however, many developmental genes have yet to be identified. We have determined that Fer1l6, a member of the ferlin family of genes, is a novel factor in zebrafish development. We find that Fer1l6 is expressed broadly in the trunk and head of zebrafish larvae and is more restricted to gills and female gonads in adult zebrafish. Using both genetic mutant and morpholino knockdown models, we found that loss of Fer1l6 led to deformation of striated muscle tissues, delayed development of the heart, and high morbidity. Further, expression of genes associated with muscle cell proliferation and differentiation were affected. Fer1l6 was also detected in the C2C12 cell line, and unlike other ferlin homologues, we found Fer1l6 expression was independent of the myoblast-to-myotube transition. Finally, analysis of cell and recombinant protein-based assays indicate that Fer1l6 colocalizes with syntaxin 4 and vinculin, and that the putative C2 domains interact with lipid membranes. We conclude that Fer1l6 has diverged from other vertebrate ferlins to play an essential role in zebrafish skeletal and cardiac muscle development.

Myoferlin-Mediated Lysosomal Exocytosis Regulates Cytotoxicity by Phagocytes

During inflammation, phagocytes release digestive enzymes from lysosomes to degrade harmful cells such as pathogens and tumor cells. However, the molecular mechanisms regulating this process are poorly understood. In this study, we identified myoferlin as a critical regulator of lysosomal exocytosis by mouse phagocytes. Myoferlin is a type II transmembrane protein with seven C2 domains in the cytoplasmic region. It localizes to lysosomes and mediates their fusion with the plasma membrane upon calcium stimulation. Myoferlin promotes the release of lysosomal contents, including hydrolytic enzymes, which increase cytotoxicity. These data demonstrate myoferlin's critical role in lysosomal exocytosis by phagocytes, providing novel insights into the mechanisms of inflammation-related cellular injuries.

Genetic dissection of bull fertility in US Jersey dairy cattle

The service sire has been recognized as an important factor affecting herd fertility in dairy cattle. Recent studies suggest that genetic factors explain part of the difference in fertility among Holstein sires. The main objective of this study was to dissect the genetic architecture of sire fertility in US Jersey cattle. The dataset included 1.5 K Jersey bulls with sire conception rate (SCR) records and 96 K single nucleotide polymorphism (SNP) markers spanning the whole genome. The analysis included whole‐genome scans for both additive and non‐additive effects and subsequent functional enrichment analyses using KEGG Pathway, Gene Ontology (GO) and Medical Subject Headings (MeSH) databases. Ten genomic regions located on eight different chromosomes explained more than 0.5% of the additive genetic variance for SCR. These regions harbor genes, such as PKDREJ,EPB41L2,PDGFD,STX2,SLC25A20 and IP6K1, that are directly implicated in testis development and spermatogenesis, sperm motility and the acrosome reaction. In addition, the genomic scan for non‐additive effects identified two regions on BTA11 and BTA25 with marked recessive effects. These regions harbor three genes—FER1L5,CNNM4 and DNAH3—with known roles in sperm biology. Moreover, the gene‐set analysis revealed terms associated with calcium regulation and signaling, membrane fusion, sperm cell energy metabolism, GTPase activity and MAPK signaling. These gene sets are directly implicated in sperm physiology and male fertility. Overall, this integrative genomic study unravels genetic variants and pathways affecting Jersey bull fertility. These findings may contribute to the development of novel genomic strategies for improving sire fertility in Jersey cattle.

Proteomic and evolutionary analyses of sperm activation identify uncharacterized genes in Caenorhabditis nematodes

BACKGROUND

Nematode sperm have unique and highly diverged morphology and molecular biology. In particular, nematode sperm contain subcellular vesicles known as membranous organelles that are necessary for male fertility, yet play a still unknown role in overall sperm function. Here we take a novel proteomic approach to characterize the functional protein complement of membranous organelles in two Caenorhabditis species: C. elegans and C. remanei.

RESULTS

We identify distinct protein compositions between membranous organelles and the activated sperm body. Two particularly interesting and undescribed gene families-the Nematode-Specific Peptide family, group D and the here designated Nematode-Specific Peptide family, group F-localize to the membranous organelle. Both multigene families are nematode-specific and exhibit patterns of conserved evolution specific to the Caenorhabditis clade. These data suggest gene family dynamics may be a more prevalent mode of evolution than sequence divergence within sperm. Using a CRISPR-based knock-out of the NSPF gene family, we find no evidence of a male fertility effect of these genes, despite their high protein abundance within the membranous organelles.

CONCLUSIONS

Our study identifies key components of this unique subcellular sperm component and establishes a path toward revealing their underlying role in reproduction.

FerA is a Membrane-Associating Four-Helix Bundle Domain in the Ferlin Family of Membrane-Fusion Proteins

Ferlin proteins participate in such diverse biological events as vesicle fusion in C. elegans, fusion of myoblast membranes to form myotubes, Ca²⁺-sensing during exocytosis in the hair cells of the inner ear, and Ca²⁺-dependent membrane repair in skeletal muscle cells. Ferlins are Ca²⁺-dependent, phospholipid-binding, multi-C2 domain-containing proteins with a single transmembrane helix that spans a vesicle membrane. The overall domain composition of the ferlins resembles the proteins involved in exocytosis; therefore, it is thought that they participate in membrane fusion at some level. But if ferlins do fuse membranes, then they are distinct from other known fusion proteins. Here we show that the central FerA domain from dysferlin, myoferlin, and otoferlin is a novel four-helix bundle fold with its own Ca²⁺-dependent phospholipid-binding activity. Small-angle X-ray scattering (SAXS), spectroscopic, and thermodynamic analysis of the dysferlin, myoferlin, and otoferlin FerA domains, in addition to clinically-defined dysferlin FerA mutations, suggests that the FerA domain interacts with the membrane and that this interaction is enhanced by the presence of Ca²⁺.

MIB-1 Is Required for Spermatogenesis and Facilitates LIN-12 and GLP-1 Activity in Caenorhabditis elegans

Covalent attachment of ubiquitin to substrate proteins changes their function or marks them for proteolysis, and the specificity of ubiquitin attachment is mediated by the numerous E3 ligases encoded by animals. Mind Bomb is an essential E3 ligase during Notch pathway signaling in insects and vertebrates. While Caenorhabditis elegans encodes a Mind Bomb homolog (mib-1), it has never been recovered in the extensive Notch suppressor/enhancer screens that have identified numerous pathway components. Here, we show that C. elegans mib-1 null mutants have a spermatogenesis-defective phenotype that results in a heterogeneous mixture of arrested spermatocytes, defective spermatids, and motility-impaired spermatozoa. mib-1 mutants also have chromosome segregation defects during meiosis, molecular null mutants are intrinsically temperature-sensitive, and many mib-1 spermatids contain large amounts of tubulin. These phenotypic features are similar to the endogenous RNA intereference (RNAi) mutants, but mib-1 mutants do not affect RNAi. MIB-1 protein is expressed throughout the germ line with peak expression in spermatocytes followed by segregation into the residual body during spermatid formation. C. elegans mib-1 expression, while upregulated during spermatogenesis, also occurs somatically, including in vulva precursor cells. Here, we show that mib-1 mutants suppress both lin-12 and glp-1 (C. elegans Notch) gain-of-function mutants, restoring anchor cell formation and a functional vulva to the former and partly restoring oocyte production to the latter. However, suppressed hermaphrodites are only observed when grown at 25°, and they are self-sterile. This probably explains why mib-1 was not previously recovered as a Notch pathway component in suppressor/enhancer selection experiments.

Emerging Functional Differences between the Synaptotagmin and Ferlin Calcium Sensor Families

The ferlin family proteins have emerged as multi-C2 domain regulators of calcium-triggered membrane fusion and fission events. While initially determined to share many of the features of members of the synaptotagmin family of calcium sensors, ferlins in more recent studies have been found to interact directly with non-neuronal voltage-gated calcium channels and nucleate the assembly of membrane-trafficking protein complexes, functions that distinguish them from the more well studied members of the synaptotagmin family. Here we highlight some of the recent findings that have advanced our understanding of ferlins and their functional differences with the synaptotagmin family.

Activity-Dependent Phosphorylation by CaMKIIδ Alters the Ca2+ Affinity of the Multi-C2-Domain Protein Otoferlin

Otoferlin is essential for fast Ca²⁺-triggered transmitter release from auditory inner hair cells (IHCs), playing key roles in synaptic vesicle release, replenishment and retrieval. Dysfunction of otoferlin results in profound prelingual deafness. Despite its crucial role in cochlear synaptic processes, mechanisms regulating otoferlin activity have not been studied to date. Here, we identified Ca²⁺/calmodulin-dependent serine/threonine kinase II delta (CaMKIIδ) as an otoferlin binding partner by pull-downs from chicken utricles and reassured interaction by a co-immunoprecipitation with heterologously expressed proteins in HEK cells. We confirmed the expression of CaMKIIδ in rodent IHCs by immunohistochemistry and real-time PCR. A proximity ligation assay indicates close proximity of the two proteins in rat IHCs, suggesting that otoferlin and CaMKIIδ also interact in mammalian IHCs. In vitro phosphorylation of otoferlin by CaMKIIδ revealed ten phosphorylation sites, five of which are located within C₂-domains. Exchange of serines/threonines at phosphorylated sites into phosphomimetic aspartates reduces the Ca²⁺ affinity of the recombinant C₂F domain 10-fold, and increases the Ca²⁺ affinity of the C₂C domain. Concordantly, we show that phosphorylation of otoferlin and/or its interaction partners are enhanced upon hair cell depolarization and blocked by pharmacological CaMKII inhibition. We therefore propose that otoferlin activity is regulated by CaMKIIδ in IHCs.

The Extended-Synaptotagmins

The extended-synaptotagmins (tricalbins in yeast) derive their name from their partial domain structure similarity to the synaptotagmins, which are characterized by an N-terminal membrane anchor and cytosolically exposed C2 domains. However, they differ from the synaptotagmins in localization and function. The synaptotagmins tether secretory vesicles, including synaptic vesicles, to the plasma membrane (PM) via their C2 domains and regulate their Ca²⁺ triggered exocytosis. In contrast, the extended-synaptotagmins are resident proteins of the endoplasmic reticulum (ER), which tether this organelle to the plasma membrane via their C2 domains, but not as a premise to fusion of the two membranes. They transport glycerolipids between the two bilayers via their lipid-harboring SMP domains and Ca²⁺ regulates their membrane tethering and lipid transport function. Additionally, the extended-synaptotagmins are more widely expressed in different organisms, as they are present not only in animal cells, but also in fungi and plants, which do not express the synaptotagmins. Thus, they have a more general function than the synaptotagmins, whose appearance in animal species correlated with the occurrence of Ca²⁺ triggered exocytosis. This article is part of a Special Issue entitled: Membrane Contact Sites edited by Christian Ungermann and Benoit Kornmann.

Dysferlin function in skeletal muscle: Possible pathological mechanisms and therapeutical targets in dysferlinopathies

Mutations in the dysferlin gene are linked to a group of muscular dystrophies known as dysferlinopathies. These myopathies are characterized by progressive atrophy. Studies in muscle tissue from dysferlinopathy patients or dysferlin-deficient mice point out its importance in membrane repair. However, expression of dysferlin homologous proteins that restore sarcolemma repair function in dysferlinopathy animal models fail to arrest muscle wasting, therefore suggesting that dysferlin plays other critical roles in muscle function. In the present review, we discuss dysferlin functions in the skeletal muscle, as well as pathological mechanisms related to dysferlin mutations. Particular focus is presented related the effect of dysferlin on cell membrane related function, which affect its repair, vesicle trafficking, as well as Ca(2+) homeostasis. Such mechanisms could provide accessible targets for pharmacological therapies.

A Role of TMEM16E Carrying a Scrambling Domain in Sperm Motility

Transmembrane protein 16E (TMEM16E) belongs to the TMEM16 family of proteins that have 10 transmembrane regions and appears to localize intracellularly. Although TMEM16E mutations cause bone fragility and muscular dystrophy in humans, its biochemical function is unknown. In the TMEM16 family, TMEM16A and -16B serve as Ca(2+)-dependent Cl(-) channels, while TMEM16C, -16D, -16F, -16G, and -16J support Ca(2+)-dependent phospholipid scrambling. Here, we show that TMEM16E carries a segment composed of 35 amino acids homologous to the scrambling domain in TMEM16F. When the corresponding segment of TMEM16A was replaced by this 35-amino-acid segment of TMEM16E, the chimeric molecule localized to the plasma membrane and supported Ca(2+)-dependent scrambling. We next established TMEM16E-deficient mice, which appeared to have normal skeletal muscle. However, fertility was decreased in the males. We found that TMEM16E was expressed in germ cells in early spermatogenesis and thereafter and localized to sperm tail. TMEM16E(-/-) sperm showed no apparent defect in morphology, beating, mitochondrial function, capacitation, or binding to zona pellucida. However, they showed reduced motility and inefficient fertilization of cumulus-free but zona-intact eggs in vitro. Our results suggest that TMEM16E may function as a phospholipid scramblase at inner membranes and that its defect affects sperm motility.

A New Player in the Spermiogenesis Pathway of Caenorhabditis elegans

Precise timing of sperm activation ensures the greatest likelihood of fertilization. Precision in Caenorhabditis elegans sperm activation is ensured by external signaling, which induces the spherical spermatid to reorganize and extend a pseudopod for motility. Spermatid activation, also called spermiogenesis, is prevented from occurring prematurely by the activity of SPE-6 and perhaps other proteins, termed "the brake model." Here, we identify the spe-47 gene from the hc198 mutation that causes premature spermiogenesis. The mutation was isolated in a suppressor screen of spe-27(it132ts), which normally renders worms sterile, due to defective transduction of the activation signal. In a spe-27(+) background, spe-47(hc198) causes a temperature-sensitive reduction of fertility, and in addition to premature spermiogenesis, many mutant sperm fail to activate altogether. The hc198 mutation is semidominant, inducing a more severe loss of fertility than do null alleles generated by CRISPR-associated protein 9 (Cas9) technology. The hc198 mutation affects an major sperm protein (MSP) domain, altering a conserved amino acid residue in a β-strand that mediates MSP-MSP dimerization. Both N- and C-terminal SPE-47 reporters associate with the forming fibrous body (FB)-membranous organelle, a specialized sperm organelle that packages MSP and other components during spermatogenesis. Once the FB is fully formed, the SPE-47 reporters dissociate and disappear. SPE-47 reporter localization is not altered by either the hc198 mutation or a C-terminal truncation deleting the MSP domain. The disappearance of SPE-47 reporters prior to the formation of spermatids requires a reevaluation of the brake model for prevention of premature spermatid activation.

Membrane Repair: Mechanisms and Pathophysiology

Eukaryotic cells have been confronted throughout their evolution with potentially lethal plasma membrane injuries, including those caused by osmotic stress, by infection from bacterial toxins and parasites, and by mechanical and ischemic stress. The wounded cell can survive if a rapid repair response is mounted that restores boundary integrity. Calcium has been identified as the key trigger to activate an effective membrane repair response that utilizes exocytosis and endocytosis to repair a membrane tear, or remove a membrane pore. We here review what is known about the cellular and molecular mechanisms of membrane repair, with particular emphasis on the relevance of repair as it relates to disease pathologies. Collective evidence reveals membrane repair employs primitive yet robust molecular machinery, such as vesicle fusion and contractile rings, processes evolutionarily honed for simplicity and success. Yet to be fully understood is whether core membrane repair machinery exists in all cells, or whether evolutionary adaptation has resulted in multiple compensatory repair pathways that specialize in different tissues and cells within our body.

SNF-10 connects male-derived signals to the onset of sperm motility in C. elegans

Sperm from the nematode C. elegans gain motility during a process termed activation, which they initiate in response to specific environmental signals. During this process, a number of subcellular rearrangements occur, culminating in an altered morphology that allows the cell to crawl toward and fertilize oocytes. Both hermaphrodites and males produce sperm, and redundant, sex-biased pathways regulate the sperm's activation. The male-derived signal for sperm activation involves TRY-5, a trypsin-like serine protease in seminal fluid, but until recently it was unknown what factors were active downstream of TRY-5. In our recent paper, we reported the discovery of SNF-10, a solute carrier 6 (SLC6) family protein that is expressed by sperm and connects the activation signal to changes in sperm morphology and, ultimately, the onset of motility. Here, we review our recent results, focusing on potential models for SNF-10's function in C. elegans, and additionally discuss the role SLC6 transporters may play in male reproductive biology from invertebrates to mammals.

A genome-wide identification and classification of basic helix-loop-helix genes in the jewel wasp, Nasonia vitripennis (Hymenoptera: Pteromalidae)

Basic helix-loop-helix (bHLH) proteins are highly conserved DNA-binding transcription factors of a large superfamily. Animal bHLH proteins play important regulatory roles in various developmental processes such as neurogenesis, myogenesis, heart development, and hematopoiesis. The jewel wasp (Nasonia vitripennis) is a good model organism of hymenoptera insects for studies of developmental and evolutionary genetics. In this study, we identified 48 bHLH genes in the genome of N. vitripennis. According to phylogenetic analysis, based on N. vitripennis bHLH (NvbHLH) motif sequences and structural domain distribution in their full-length protein sequences, the identified NvbHLH genes were classified into 36 bHLH families with 19, 12, 9, 1, 6, and 1 member(s) in groups A, B, C, D, E, and F, respectively. Our classification to the identified NvbHLH family members confirms GenBank annotations for 21 of the 48 NvbHLH proteins and provides useful information for further characterization and annotation of the remaining 27 NvbHLH proteins. Compared to other insect species, N. vitripennis has the lowest number of bHLH family members. No NvbHLH members have been found in the families Net, MyoRa, and PTFa, while all other insect species have at least one member in each of the families. These data constitute a solid basis for further investigations into the functions of bHLH proteins in developmental regulation of N. vitripennis.

Quantitation of the calcium and membrane binding properties of the C2 domains of dysferlin

Dysferlin is a large membrane protein involved in calcium-triggered resealing of the sarcolemma after injury. Although it is generally accepted that dysferlin is Ca(2+) sensitive, the Ca(2+) binding properties of dysferlin have not been characterized. In this study, we report an analysis of the Ca(2+) and membrane binding properties of all seven C2 domains of dysferlin as well as a multi-C2 domain construct. Isothermal titration calorimetry measurements indicate that all seven dysferlin C2 domains interact with Ca(2+) with a wide range of binding affinities. The C2A and C2C domains were determined to be the most sensitive, with Kd values in the tens of micromolar, whereas the C2D domain was least sensitive, with a near millimolar Kd value. Mutagenesis of C2A demonstrates the requirement for negatively charged residues in the loop regions for divalent ion binding. Furthermore, dysferlin displayed significantly lower binding affinity for the divalent cations magnesium and strontium. Measurement of a multidomain construct indicates that the solution binding affinity does not change when C2 domains are linked. Finally, sedimentation assays suggest all seven C2 domains bind lipid membranes, and that Ca(2+) enhances but is not required for interaction. This report reveals for the first time, to our knowledge, that all dysferlin domains bind Ca(2+) albeit with varying affinity and stoichiometry.

Calpain cleavage within dysferlin exon 40a releases a synaptotagmin-like module for membrane repair

The muscular dystrophy protein dysferlin plays a key role in the calcium-activated vesicle fusion of membrane repair. This study establishes calpains as upstream regulators of dysferlin in the membrane repair cascade and further demonstrates that similar C-terminal modules are enzymatically released from other ferlin family members.

Dysferlin and calpain are important mediators of the emergency response to repair plasma membrane injury. Our previous research revealed that membrane injury induces cleavage of dysferlin to release a synaptotagmin-like C-terminal module we termed mini-dysferlin_C72. Here we show that injury-activated cleavage of dysferlin is mediated by the ubiquitous calpains via a cleavage motif encoded by alternately spliced exon 40a. An exon 40a–specific antibody recognizing cleaved mini-dysferlin_C72 intensely labels the circumference of injury sites, supporting a key role for dysferlin_Exon40a isoforms in membrane repair and consistent with our evidence suggesting that the calpain-cleaved C-terminal module is the form specifically recruited to injury sites. Calpain cleavage of dysferlin is a ubiquitous response to membrane injury in multiple cell lineages and occurs independently of the membrane repair protein MG53. Our study links calpain and dysferlin in the calcium-activated vesicle fusion of membrane repair, placing calpains as upstream mediators of a membrane repair cascade that elicits cleaved dysferlin as an effector. Of importance, we reveal that myoferlin and otoferlin are also cleaved enzymatically to release similar C-terminal modules, bearing two C2 domains and a transmembrane domain. Evolutionary preservation of this feature highlights its functional importance and suggests that this highly conserved C-terminal region of ferlins represents a functionally specialized vesicle fusion module.

SLC6 family transporter SNF-10 is required for protease-mediated activation of sperm motility in C. elegans

Motility of sperm is crucial for their directed migration to the egg. The acquisition and modulation of motility are regulated to ensure that sperm move when and where needed, thereby promoting reproductive success. One specific example of this phenomenon occurs during differentiation of the ameboid sperm of Caenorhabditis elegans as they activate from a round spermatid to a mature, crawling spermatozoon. Sperm activation is regulated by redundant pathways to occur at a specific time and place for each sex. Here, we report the identification of the solute carrier 6 (SLC6) transporter protein SNF-10 as a key regulator of C. elegans sperm activation in response to male protease activation signals. We find that SNF-10 is present in sperm and is required for activation by the male but not by the hermaphrodite. Loss of both snf-10 and a hermaphrodite activation factor render sperm completely insensitive to activation. Using in vitro assays, we find that snf-10 mutant sperm show a specific deficit in response to protease treatment but not to other activators. Prior to activation, SNF-10 is present in the plasma membrane, where it represents a strong candidate to receive signals that lead to subcellular morphogenesis. After activation, it shows polarized localization to the cell body region that is dependent on membrane fusions mediated by the dysferlin FER-1. Our discovery of snf-10 offers insight into the mechanisms differentially employed by the two sexes to accomplish the common goal of producing functional sperm, as well as how the physiology of nematode sperm may be regulated to control motility as it is in mammals.

The regulation of spermatogenesis and sperm function in nematodes

In the nematode C. elegans, both males and self-fertile hermaphrodites produce sperm. As a result, researchers have been able to use a broad range of genetic and genomic techniques to dissect all aspects of sperm development and function. Their results show that the early stages of spermatogenesis are controlled by transcriptional and translational processes, but later stages are dominated by protein kinases and phosphatases. Once spermatids are produced, they participate in many interactions with other cells - signals from the somatic gonad determine when sperm activate and begin to crawl, signals from the female reproductive tissues guide the sperm, and signals from sperm stimulate oocytes to mature and be ovulated. The sperm also show strong competitive interactions with other sperm and oocytes. Some of the molecules that mediate these processes have conserved functions in animal sperm, others are conserved proteins that have been adapted for new roles in nematode sperm, and some are novel proteins that provide insights into evolutionary change. The advent of new techniques should keep this system on the cutting edge of research in cellular and reproductive biology.

Characterisation of Caenorhabditis elegans sperm transcriptome and proteome

BACKGROUND

Although sperm is transcriptionally and translationally quiescent, complex populations of RNAs, including mRNAs and non-coding RNAs, exist in sperm. Previous microarray analysis of germ cell mutants identified hundreds of sperm genes in Caenorhabditis elegans. To take a more comprehensive view on C. elegans sperm genes, here, we isolate highly pure sperm cells and employ high-throughput technologies to obtain sperm transcriptome and proteome.

RESULTS

First, sperm transcriptome consists of considerable amounts of non-coding RNAs, many of which have not been annotated and may play functional roles during spermatogenesis. Second, apart from kinases/phosphatases as previously reported, ion binding proteins are also enriched in sperm, underlying the crucial roles of intracellular ions in post-translational regulation in sperm. Third, while the majority of sperm genes/proteins have low abundance, a small number of sperm genes/proteins are hugely enriched in sperm, implying that sperm only rely on a small set of proteins for post-translational regulation. Lastly, by extensive RNAi screening of sperm enriched genes, we identified a few genes that control fertility. Our further analysis reveals a tight correlation between sperm transcriptome and sperm small RNAome, suggesting that the endogenous siRNAs strongly repress sperm genes. This leads to an idea that the inefficient RNAi screening of sperm genes, a phenomenon currently with unknown causes, might result from the competition between the endogenous RNAi pathway and the exogenous RNAi pathway.

CONCLUSIONS

Together, the obtained sperm transcriptome and proteome serve as valuable resources to systematically study spermatogenesis in C. elegans.

Argonautes promote male fertility and provide a paternal memory of germline gene expression in C. elegans

During each life cycle, germ cells preserve and pass on both genetic and epigenetic information. In C. elegans, the ALG-3/4 Argonaute proteins are expressed during male gametogenesis and promote male fertility. Here, we show that the CSR-1 Argonaute functions with ALG-3/4 to positively regulate target genes required for spermiogenesis. Our findings suggest that ALG-3/4 functions during spermatogenesis to amplify a small RNA signal that represents an epigenetic memory of male-specific gene expression. CSR-1, which is abundant in mature sperm, appears to transmit this memory to offspring. Surprisingly, in addition to small RNAs targeting male-specific genes, we show that males also harbor an extensive repertoire of CSR-1 small RNAs targeting oogenesis-specific mRNAs. Together, these findings suggest that C. elegans sperm transmit not only the genome but also epigenetic binary signals in the form of Argonaute/small RNA complexes that constitute a memory of gene expression in preceding generations.

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.

Trophoblast cell fusion and differentiation are mediated by both the protein kinase C and a pathways

The syncytiotrophoblast of the human placenta is an epithelial barrier that interacts with maternal blood and is a key for the transfer of nutrients and other solutes to the developing fetus. The syncytiotrophoblast is a true syncytium and fusion of progenitor cytotrophoblasts is the cardinal event leading to the formation of this layer. BeWo cells are often used as a surrogate for cytotrophoblasts, since they can be induced to fuse, and then express certain differentiation markers associated with trophoblast syncytialization. Dysferlin, a syncytiotrophoblast membrane repair protein, is up-regulated in BeWo cells induced to fuse by treatment with forskolin; this fusion is thought to occur through cAMP/protein kinase A-dependent mechanisms. We hypothesized that dysferlin may also be up-regulated in response to fusion through other pathways. Here, we show that BeWo cells can also be induced to fuse by treatment with an activator of protein kinase C, and that this fusion is accompanied by increased expression of dysferlin. Moreover, a dramatic synergistic increase in dysferlin expression is observed when both the protein kinase A and protein kinase C pathways are activated in BeWo cells. This synergy in fusion is also accompanied by dramatic increases in mRNA for the placental fusion proteins syncytin 1, syncytin 2, as well as dysferlin. Dysferlin, however, was shown to be dispensable for stimulus-induced BeWo cell syncytialization, since dysferlin knockdown lines fused to the same extent as control cells. The classical trophoblast differentiation marker human chorionic gonadotropin was also monitored and changes in the expression closely parallel that of dysferlin in all of the experimental conditions employed. Thus different biochemical markers of trophoblast fusion behave in concert supporting the hypothesis that activation of both protein kinase C and A pathways lead to trophoblastic differentiation.

Calcium signaling and the MAPK cascade are required for sperm activation in Caenorhabditis elegans

In nematode, sperm activation (or spermiogenesis), a process in which the symmetric and non-motile spermatids transform into polarized and crawling spermatozoa, is critical for sperm cells to acquire fertilizing competence. SPE-8 dependent and SPE-8 independent pathways function redundantly during sperm activation in both males and hermaphrodites of Caenorhabditis elegans. However, the downstream signaling for both pathways remains unclear. Here we show that calcium signaling and the MAPK cascade are required for both SPE-8 dependent and SPE-8 independent sperm activation, implying that both pathways share common downstream signaling components during sperm activation. We demonstrate that activation of the MAPK cascade is sufficient to activate spermatids derived from either wild-type or spe-8 group mutant males and that activation of the MAPK cascade bypasses the requirement of calcium signal to induce sperm activation, indicating that the MAPK cascade functions downstream of or parallel with the calcium signaling during sperm activation. Interestingly, the persistent activation of MAPK in activated spermatozoa inhibits Major Sperm Protein (MSP)-based cytoskeleton dynamics. We demonstrate that MAPK plays dual roles in promoting pseudopod extension during sperm activation but also blocking the MSP-based, amoeboid motility of the spermatozoa. Thus, though nematode sperm are crawling cells, morphologically distinct from flagellated sperm, and the molecular machinery for motility of amoeboid and flagellated sperm is different, both types of sperm might utilize conserved signaling pathways to modulate sperm maturation.