For male Caenorhabditis elegans, sperm activation is a "just-in-time" event

Early-life long-term ibuprofen exposure reduces reproductive capacity involved in spermatogenesis impairment and associated with the transcription factor DAF-5 in Caenorhabditis elegans

Pharmaceuticals and personal care products (PPCPs) are emerging environmental contaminants and have raised significant concern due to their potential adverse impact on the environment. Ibuprofen is one of the most extensively used non-steroidal anti-inflammatory drugs (NSAIDs) and is also considered an environmental contaminant. The negative impact of ibuprofen on non-target organisms has been documented; however, the molecular mechanisms behind its reproductive toxicity remain unclear. We investigated the impact of early-life long-term ibuprofen exposure on reproductive capacity and its involvement of spermiogenesis in the non-target model organism Caenorhabditis elegans. Hermaphrodites were exposed to various ibuprofen concentrations (0.1, 1, 10, and 100 mg/L), resulting in a dose-dependent inhibition of reproduction. In addition, the lowest observed adverse effect concentration (LOAEC) for ibuprofen exposure on the total brood size of C. elegans was 0.1 mg/L, a concentration that falls within the environmentally relevant range for ibuprofen. Outcross progeny assays revealed a significant 47% reduction in total brood size for larval males (him-5) exposed to ibuprofen, while females (fog-2) exhibited only a minor effect. We found that early-life long-term ibuprofen exposure impairs spermatogenesis. The number of mitotic cells significantly reduced by 31%. The rate of sperm malformation in exposed males was 63%, much higher than in unexposed males (11%). Additionally, the percentage of sperm activation decreased from 89% to 39% in ibuprofen-exposed worms. Mechanistic insights indicated that ibuprofen downregulated mRNA levels of genes related to spermatogenesis and DAF-7/TGF-β signaling. RNAi assays provided evidence for the crucial role of the transcription factor DAF-5 in mediating the spermatogenesis impairment by ibuprofen. Our study provides insight into the environmental impacts of pharmaceutical contaminants, such as ibuprofen, on both male and female reproductive systems to safeguard environmental health.

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.

Effects of 10 T static magnetic field on the function of sperms and their offspring in Caenorhabditis elegans

With the wide application of static magnetic fields (SMFs), the risk of living organisms exposed to man-made magnetic fields that the intensity is much higher than geomagnetic field has gradually increased. Reproductive system is highly sensitive to environmental stress; however, the influence of high SMFs on reproduction system is still largely unknown. Here we explored the biological responses of SMFs exposure at an intensity of 10 T on the sperms and their offspring in him-5 male mutants of Caenorhabditis elegans (C. elegans). The size of unactivated sperms was deceased by 10 T SMF exposure, instead of the morphology. Exposure to 10 T SMF significantly altered the function of sperms in him-5 worms including the activation of sperms and the non-transferred ratio of sperms. In addition, the brood size assay revealed that 10 T SMF exposure eventually diminished the reproductive capacity of him-5 male worms. The lifespan of outcrossed offspring from exposed him-5 male mutants and unexposed fog-2 female mutants was decreased by 10 T SMF in a time dependent manner. Together, our findings provide novel information regarding the adverse effects of high SMFs on the sperms of C. elegans and their offspring, which can improve our understanding of the fundamental aspects of high SMFs on biological system.

Spatial expression pattern of serine proteases in the blood fluke Schistosoma mansoni determined by fluorescence RNA in situ hybridization

Background

The blood flukes of genus Schistosoma are the causative agent of schistosomiasis, a parasitic disease that infects more than 200 million people worldwide. Proteases of schistosomes are involved in critical steps of host–parasite interactions and are promising therapeutic targets. We recently identified and characterized a group of S1 family Schistosoma mansoni serine proteases, including SmSP1 to SmSP5. Expression levels of some SmSPs in S. mansoni are low, and by standard genome sequencing technologies they are marginally detectable at the method threshold levels. Here, we report their spatial gene expression patterns in adult S. mansoni by the high-sensitivity localization assay.

Methodology

Highly sensitive fluorescence in situ RNA hybridization (FISH) was modified and used for the localization of mRNAs encoding individual SmSP proteases (including low-expressed SmSPs) in tissues of adult worms. High sensitivity was obtained due to specifically prepared tissue and probes in combination with the employment of a signal amplification approach. The assay method was validated by detecting the expression patterns of a set of relevant reference genes including SmCB1, SmPOP, SmTSP-2, and Sm29 with localization formerly determined by other techniques.

Results

FISH analysis revealed interesting expression patterns of SmSPs distributed in multiple tissues of S. mansoni adults. The expression patterns of individual SmSPs were distinct but in part overlapping and were consistent with existing transcriptome sequencing data. The exception were genes with significantly low expression, which were also localized in tissues where they had not previously been detected by RNA sequencing methods. In general, SmSPs were found in various tissues including reproductive organs, parenchymal cells, esophagus, and the tegumental surface.

Conclusions

The FISH-based assay provided spatial information about the expression of five SmSPs in adult S. mansoni females and males. This highly sensitive method allowed visualization of low-abundantly expressed genes that are below the detection limits of standard in situ hybridization or by RNA sequencing. Thus, this technical approach turned out to be suitable for sensitive localization studies and may also be applicable for other trematodes. The results suggest that SmSPs may play roles in diverse processes of the parasite. Certain SmSPs expressed at the surface may be involved in host–parasite interactions.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04773-8.

Genome-wide tissue-specific gene expression, co-expression and regulation of co-expressed genes in adult nematode Ascaris suum

BACKGROUND

Caenorhabditis elegans has traditionally been used as a model for studying nematode biology, but its small size limits the ability for researchers to perform some experiments such as high-throughput tissue-specific gene expression studies. However, the dissection of individual tissues is possible in the parasitic nematode Ascaris suum due to its relatively large size. Here, we take advantage of the recent genome sequencing of Ascaris suum and the ability to physically dissect its separate tissues to produce a wide-scale tissue-specific nematode RNA-seq datasets, including data on three non-reproductive tissues (head, pharynx, and intestine) in both male and female worms, as well as four reproductive tissues (testis, seminal vesicle, ovary, and uterus). We obtained fundamental information about the biology of diverse cell types and potential interactions among tissues within this multicellular organism.

METHODOLOGY/PRINCIPAL FINDINGS

Overexpression and functional enrichment analyses identified many putative biological functions enriched in each tissue studied, including functions which have not been previously studied in detail in nematodes. Putative tissue-specific transcriptional factors and corresponding binding motifs that regulate expression in each tissue were identified, including the intestine-enriched ELT-2 motif/transcription factor previously described in nematode intestines. Constitutively expressed and novel genes were also characterized, with the largest number of novel genes found to be overexpressed in the testis. Finally, a putative acetylcholine-mediated transcriptional network connecting biological activity in the head to the male reproductive system is described using co-expression networks, along with a similar ecdysone-mediated system in the female.

CONCLUSIONS/SIGNIFICANCE

The expression profiles, co-expression networks and co-expression regulation of the 10 tissues studied and the tissue-specific analysis presented here are a valuable resource for studying tissue-specific biological functions in nematodes.

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.