Transformation: how do nematode sperm become activated and crawl?

A paternal protein facilitates sperm RNA delivery to regulate zygotic development

Sperm contributes essential paternal factors, including the paternal genome, centrosome, and oocyte-activation signals, to sexual reproduction. However, it remains unresolved how sperm contributes its RNA molecules to regulate early embryonic development. Here, we show that the Caenorhabditis elegans paternal protein SPE-11 assembles into granules during meiotic divisions of spermatogenesis and later matures into a perinuclear structure where sperm RNAs localize. We reconstitute an SPE-11 liquid-phase scaffold in vitro and find that SPE-11 condensates incorporate the nematode RNA, which, in turn, promotes SPE-11 phase separation. Loss of SPE-11 does not affect sperm motility or fertilization but causes pleiotropic development defects in early embryos, and spe-11 mutant males reduce mRNA levels of genes crucial for an oocyte-to-embryo transition or embryonic development. These results reveal that SPE-11 undergoes phase separation and associates with sperm RNAs that are delivered to oocytes during fertilization, providing insights into how a paternal protein regulates early embryonic development.

Adverse effects of microcystins on sperm: A systematic review

Eutrophication of water bodies can lead to cyanobacterial blooms, with the resultant release of microcystins (MCs), posing a threat to the ecosystem and human health. MCs are environmental toxins with male reproductive toxicity. However, there is a dearth of reviews focusing on sperm or spermatogenesis. In this paper, studies on sperm toxicity caused by MCs in recent 20 years were collected and summarized, aiming at revealing the toxic effects and potential mechanisms of MCs on sperm. Based on the previous findings, MCs can decline sperm quality and count, and cause malformation in vertebrates and invertebrates. The reason might be that MCs cause indirect damage to sperm through impairing the structure and function of the testis. The mechanisms of MCs-induced sperm toxicity mainly result from alterations in genetic material, abnormalities in the structure and function of sperm. The epigenetic modifications such as miRNA and piRNA were also involved in MC-LR-induced sperm damage. In conclusion, MCs exposure is harmful to sperm, but its direct effects and mechanisms on sperm are still not known, which remains a significant research direction. Our review will provide a basis for the protection of male reproductive health damage caused by microcystins.

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.

Sperm-specific glycogen synthase kinase 3 is required for sperm motility and the post-fertilization signal for female meiosis II in Caenorhabditis elegans

In most sexually reproducing animals, sperm entry provides the signal to initiate the final stages of female meiosis. In Caenorhabditis elegans, this signal is required for completion of female anaphase I and entry into meiosis II (MII). memi-1/2/3 (meiosis-to-mitosis) encode maternal components that facilitate this process; memi-1/2/3(RNAi) results in a skipped-MII phenotype. Previously, we used a gain-of-function mutation, memi-1(sb41), to identify genetic suppressors that represent candidates for the sperm-delivered signal. Herein, we characterize two suppressors of memi-1(sb41): gskl-1 and gskl-2. Both genes encode functionally redundant sperm glycogen synthase kinase, type 3 (GSK3) protein kinases. Loss of both genes causes defects in male spermatogenesis, sperm pseudopod treadmilling and paternal-effect embryonic lethality. The two kinases locate within the pseudopod of activated sperm, suggesting that they directly or indirectly regulate the sperm cytoskeletal polymer major sperm protein (MSP). The GSK3 genes genetically interact with another memi-1(sb41) suppressor, gsp-4, which encodes a sperm-specific PP1 phosphatase, previously proposed to regulate MSP dynamics. Moreover, gskl-2 gsp-4; gskl-1 triple mutants often skip female MII, similar to memi-1/2/3(RNAi). The GSK3 kinases and PP1 phosphatases perform similar sperm-related functions and work together for post-fertilization functions in the oocyte that involve MEMI.

Development of a water refractive index-matched microneedle integrated into a light sheet microscopy system for continuous embryonic cell imaging

In this study, microneedle-integrated light sheet microscopy (LSM) was developed for trapping and continuously imaging embryos of Caenorhabditis elegans with subcellular resolution. To reduce aberrations when the light sheet was propagated into the device, a microneedle was fabricated using a transparent, water refractive index-matched polymer. It was proven that when the light sheet emerged from the water-immersed objective and penetrated through the microneedle with a circular surface, even with a non-perpendicular incident angle, fewer aberrations were found. An embryo was injected into and trapped at the tip of the microneedle, which was positioned at the interrogation window of the LSM apparatus with the image plane perpendicular to the light sheet, and this setup was used to sequentially acquire embryo images. By applying the light sheet, higher-resolution, higher-contrast images were obtained. The system also showed low photobleaching and low phototoxicity to embryos of C. elegans. Furthermore, three-dimensional embryo images with a whole field of view of the microneedle could be achieved by stitching together images and reconstructing sequential two-dimensional embryo images.

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.

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.

The Use of the Nematode Caenorhabditis elegans to Evaluate the Adverse Effects of Epoxiconazole Exposure on Spermatogenesis

There is increasing evidence that epoxiconazole exposure can affect reproductive function, but few studies have investigated adverse effects on spermatogenesis. The nematode Caenorhabditis elegans (C. elegans) was used in our study to assess effects of epoxiconazole on spermatogenesis in male nematodes after 48 h of exposure to concentrations of 0.1, 1.0, or 10.0 μg/L. The results demonstrated that epoxiconazole exposure affected spermatogenesis, decreasing the number of total germ cells, mitotic cells, meiotic cells and spermatids, spermatid diameter, and cross-sectional area, and inducing mitotic germ cell proliferation arrest, premature entry into meiosis, and sperm activation inhibition; however, sperm transfer showed no abnormal changes. In addition, the results showed that epoxiconazole activated the transforming growth factor-β (TGFβ) signaling pathway and increased the expression levels of gene daf-1, daf-3, daf-4, daf-5 and daf-7 in nematodes. We therefore propose that epoxiconazole acts by activating the TGFβ signaling pathway, leading to the impairment of spermatogenesis and the consequent decline in male fertility.

Insights into zinc and cadmium biology in the nematode Caenorhabditis elegans

Zinc is an essential metal that is involved in a wide range of biological processes, and aberrant zinc homeostasis is implicated in multiple human diseases. Cadmium is chemically similar to zinc, but it is a nonessential environmental pollutant. Because zinc deficiency and excess are deleterious, animals require homeostatic mechanisms to maintain zinc levels in response to dietary fluctuations. The nematode Caenorhabditis elegans is emerging as a powerful model system to investigate zinc trafficking and homeostasis as well as cadmium toxicity. Here we review genetic and molecular studies that have combined to generate a picture of zinc homeostasis based on the transcriptional control of zinc transporters in intestinal cells. Furthermore, we summarize studies of cadmium toxicity that reveal intriguing parallels with zinc biology.

Effects of Microcystin-LR Exposure on Spermiogenesis in Nematode Caenorhabditis elegans

Little is known about the effect on spermiogenesis induced by microcystin-leucine arginine (MC-LR), even though such data are very important to better elucidate reproductive health. In the current work, with the aid of nematode Caenorhabditis elegans (C. elegans) as an animal model, we investigated the defects on spermiogenesis induced by MC-LR. Our results showed that MC-LR exposure induced sperm morphology abnormality and caused severe defects of sperm activation, trans-activation, sperm behavior and competition. Additionally, the expression levels of spe-15 were significantly decreased in C. elegans exposed to MC-LR lower than 16.0 μg/L, while the expression levels of spe-10 and fer-1 could be significantly lowered in C. elegans even exposed to 1.0 μg/L of MC-LR. Therefore, the present study reveals that MC-LR can induce adverse effects on spermiogenesis, and those defects of sperm functions may be induced by the decreases of spe-10, spe-15 and fer-1 gene expressions in C. elegans.

Electron microscopic observation of the sagittal structure of Drosophila mature sperm

Observation of sperm development and determination of their morphological characteristics are very important to the understanding of phylogenetic relationships and the study of sperm function during fertilization. Although ultrastructural studies of sperm development in the testes of the fruit fly Drosophila have been performed, there are few reports describing electron microscopic morphology of mature sperm, that is, those released from the testes to the seminal vesicles. Here, we present the first report of the sagittal organization of Drosophila sperm head and neck regions by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The head and tail structures of a mature sperm, for example, the acrosome, nucleus, and flagellum, were easy to distinguish by the morphological characteristics of the sperm surface by SEM. The morphological relationships between the surface and internal structures of mature sperm were confirmed by observing longitudinal sections with TEM. Our approach overcame the technical difficulties involved in sample preparation for electron microscopic observation of the Drosophila mature sperm head, and therefore, this study serves as an important foundation for future genetic dissection of sperm ultrastructure and function in male sterile mutants.

Proteomic analysis of adult Ascaris suum fluid compartments and secretory products

Background

Strategies employed by parasites to establish infections are poorly understood. The host-parasite interface is maintained through a molecular dialog that, among other roles, protects parasites from host immune responses. Parasite excretory/secretory products (ESP) play major roles in this process. Understanding the biology of protein secretion by parasites and their associated functional processes will enhance our understanding of the roles of ESP in host-parasite interactions.

Methodology/Principal Findings

ESP was collected after culturing 10 adult female Ascaris suum. Perienteric fluid (PE) and uterine fluid (UF) were collected directly from adult females by dissection. Using SDS-PAGE coupled with LC-MS/MS, we identified 175, 308 and 274 proteins in ESP, PE and UF, respectively. Although many proteins were shared among the samples, the protein composition of ESP was distinct from PE and UF, whereas PE and UF were highly similar. The distribution of gene ontology (GO) terms for proteins in ESP, PE and UF supports this claim. Comparison of ESP composition in A. suum, Brugia malayi and Heligmosoides polygyrus showed that proteins found in UF were also secreted by males and by larval stages of other species, suggesting that multiple routes of secretion may be used for homologous proteins. ESP composition of nematodes is both phylogeny- and niche-dependent.

Conclusions/Significance

Analysis of the protein composition of A. suum ESP and UF leads to the conclusion that the excretory-secretory apparatus and uterus are separate routes for protein release. Proteins detected in ESP have distinct patterns of biological functions compared to those in UF. PE is likely to serve as the source of the majority of proteins in UF. This analysis expands our knowledge of the biology of protein secretion from nematodes and will inform new studies on the function of secreted proteins in the orchestration of host-parasite interactions.

Ascaris lumbricoides, the most prevalent metazoan parasite of humans, is a public health concern in resource-limited countries. Survival of this parasite in its host is mediated at least in part by parasite materials secreted into the host. Little is known about the composition of these secretions; defining their contents and functions will illuminate host-parasite interactions that lead to parasite establishment. Ascaris suum, a parasite of pigs, was used as a model organism because its genome has been sequenced and it is very closely related to A. lumbricoides. Excretory/secretory products (ESP), uterine fluid (UF) and perienteric fluid (PE) were collected from adult A. suum. Proteins were subjected to LC-MS/MS. ESP proteins (the ‘secretome’) included many also present in UF. Proteins in ESP but not in UF had considerably different characteristics than those in PE or UF, which were similar to each other. We conclude that proteins released from the secretory apparatus have distinct patterns of biological function and that UF proteins are likely derived from PE. Comparing the protein composition of A. suum ESP to ESP from B. malayi and H. polygyrus suggests that the secretome is conserved at the level of both phylogeny and host predilection site.

Role of posttranslational modifications in C. elegans and ascaris spermatogenesis and sperm function

Generally, spermatogenesis and sperm function involve widespread posttranslational modification of regulatory proteins in many different species. Nematode spermatogenesis has been studied in detail, mostly by genetic/molecular genetic techniques in the free-living Caenorhabditis elegans and by biochemistry/cell biology in the pig parasite Ascaris suum. Like other nematodes, both of these species produce sperm that use a form of amoeboid motility termed crawling, and many aspects of spermatogenesis are likely to be similar in both species. Consequently, work in these two nematode species has been largely complementary. Work in C. elegans has identified a number of spermatogenesis-defective genes and, so far, 12 encode enzymes that are implicated as catalysts of posttranslational protein modification. Crawling motility involves extension of a single pseudopod and this process is powered by a unique cytoskeleton composed of Major Sperm Protein (MSP) and accessory proteins, instead of the more widely observed actin. In Ascaris, pseudopod extension and crawling motility can be reconstituted in vitro, and biochemical studies have begun to reveal how posttranslational protein modifications, including phosphorylation, dephosphorylation and proteolysis, participate in these processes.

Cytosolic Ca(2+) as a multifunctional modulator is required for spermiogenesis in Ascaris suum

The dynamic polar polymers actin filaments and microtubules are usually employed to provide the structural basis for establishing cell polarity in most eukaryotic cells. Radially round and immotile spermatids from nematodes contain almost no actin or tubulin, but still have the ability to break symmetry to extend a pseudopod and initiate the acquisition of motility powered by the dynamics of cytoskeleton composed of major sperm protein (MSP) during spermiogenesis (sperm activation). However, the signal transduction mechanism of nematode sperm activation and motility acquisition remains poorly understood. Here we show that Ca(2+) oscillations induced by the Ca(2+) release from intracellular Ca(2+) store through inositol (1,4,5)-trisphosphate receptor are required for Ascaris suum sperm activation. The chelation of cytosolic Ca(2+) suppresses the generation of a functional pseudopod, and this suppression can be relieved by introducing exogenous Ca(2+) into sperm cells. Ca(2+) promotes MSP-based sperm motility by increasing mitochondrial membrane potential and thus the energy supply required for MSP cytoskeleton assembly. On the other hand, Ca(2+) promotes MSP disassembly by activating Ca(2+)/calmodulin-dependent serine/threonine protein phosphatase calcineurin. In addition, Ca(2+)/camodulin activity is required for the fusion of sperm-specifi c membranous organelle with the plasma membrane, a regulated exocytosis required for sperm motility. Thus, Ca(2+) plays multifunctional roles during sperm activation in Ascaris suum.