Mechanisms of Sperm–Egg Interactions: What Ascidian Fertilization Research Has Taught Us

Sast1-mediated manifold effects inhibit Plutella xylostella fertility

BACKGROUND

Plutella xylostella (Linnaeus) is a destructive pest of cruciferous crops due to its strong reproductive capacity and extensive resistance to pesticides. Seminal fluid proteins (SFPs) are the main effective factors that determine the reproductive physiology and behaviour of both sexes. Although an increasing number of SFPs have been identified, the effects of astacins in SFPs on agricultural pests have not yet been reported. Here, we elucidated the mechanisms by which Sast1 (seminal astacin 1) regulates the fertility of Plutella xylostella (L.).

RESULTS

PxSast1 was specifically expressed in the testis and accesssory gland. CRISPR/Cas9-induced PxSast1 knockout successfully constructed two homozygous mutant strains. Sast1 impaired the fertility of P. xylostella by separately regulating the reproductive capacity of males and females. Loss of PxSast1, on the one hand, significantly decreased the ability of males to mate and fertilize, mainly manifested as shortened mating duration, reduced mating competitiveness and decreased eupyrene sperm production; on the other hand, it significantly inhibited the expression of chorion genes in females, resulting in oogenesis deficits. Simultaneously, for mated females, the differentially expressed genes in signalling pathways related to oogenesis and chorion formation were significantly enriched after PxSast1 knockout.

CONCLUSION

These analyses of the functions of PxSast1 as the regulator of spermatogenesis and oogenesis establish its importance in the fertility process of P. xylostella, as well as its potential as a promising target for genetic regulation-based pest control. © 2024 Society of Chemical Industry.

Plant reproduction: Fertilization SALvaged by the central cell

Flowering plants evolved glandular synergid cells assisting female gametes to attract pollen tubes carrying sperm cells. A recent study shows how central cells serve as a back-up to ensure pollen tube attraction and reproductive success in the absence of the assistants.

Extraction, Isolation, Characterization, and Biological Activity of Sulfated Polysaccharides Present in Ascidian Viscera Microcosmus exasperatus

Ascidians are marine invertebrates that synthesize sulfated glycosaminoglycans (GAGs) within their viscera. Ascidian GAGs are considered analogues of mammalian GAGs and possess great potential as bioactive compounds, presenting antitumoral and anticoagulant activity. Due to its worldwide occurrence and, therefore, being a suitable organism for large-scale mariculture in many marine environments, our main objectives are to study Microcosmus exasperatus GAGs regarding composition, structure, and biological activity. We also aim to develop efficient protocols for sulfated polysaccharides extraction and purification for large-scale production and clinical applications. GAGs derived from M. exasperatus viscera were extracted by proteolytic digestion, purified by ion-exchange liquid chromatography, and characterized by agarose gel electrophoresis and enzymatic treatments. Anticoagulant activity was evaluated by APTT assays. Antitumoral activity was assessed in an in vitro model of tumor cell culture using MTT, clonogenic, and wound healing assays, respectively. Our results show that M. exasperatus presents three distinct polysaccharides; among them, two were identified: a dermatan sulfate and a fucosylated dermatan sulfate. Antitumoral activity was confirmed for the total polysaccharides (TP). While short-term incubation does not affect tumor cell viability at low concentrations, long-term TP incubation decreases LLC tumor cell growth/proliferation at different concentrations. In addition, TP decreased tumor cell migration at different concentrations. In conclusion, we state that M. exasperatus presents great potential as an alternative GAG source, producing compounds with antitumoral properties at low concentrations that do not possess anticoagulant activity and do not enhance other aspects of malignancy, such as tumor cell migration. Our perspectives are to apply these molecules in future preclinical studies for cancer treatment as antitumoral agents to be combined with current treatments to potentiate therapeutic efficacy.

Proteasome-Associated Proteins, PA200 and ECPAS, Are Essential for Murine Spermatogenesis

Proteasomes are highly sophisticated protease complexes that degrade non-lysosomal proteins, and their proper regulation ensures various biological functions such as spermatogenesis. The proteasome-associated proteins, PA200 and ECPAS, are predicted to function during spermatogenesis; however, male mice lacking each of these genes sustain fertility, raising the possibility that these proteins complement each other. To address this issue, we explored these possible roles during spermatogenesis by producing mice lacking these genes (double-knockout mice; dKO mice). Expression patterns and quantities were similar throughout spermatogenesis in the testes. In epididymal sperm, PA200 and ECPAS were expressed but were differentially localized to the midpiece and acrosome, respectively. Proteasome activity was considerably reduced in both the testes and epididymides of dKO male mice, resulting in infertility. Mass spectrometric analysis revealed LPIN1 as a target protein for PA200 and ECPAS, which was confirmed via immunoblotting and immunostaining. Furthermore, ultrastructural and microscopic analyses demonstrated that the dKO sperm displayed disorganization of the mitochondrial sheath. Our results indicate that PA200 and ECPAS work cooperatively during spermatogenesis and are essential for male fertility.

TMT-based proteomics analysis of growth advantage of triploid Apostichopus japonicus

Polyploid breeding can produce new species with a faster growth rate, higher disease resistance, and higher survival rate, and has achieved significant economic benefits. This study investigated the protein differences in the body wall of triploid Apostichopus japonicus and diploid A. japonicus using isotope-labeled relative and absolute quantitative Tandem Mass Tag technology. A total of 21,096 independent peptides and 4621 proteins were identified. Among them, there were 723 proteins with significant expression differences, including 413 up-regulated proteins and 310 down-regulated proteins. The differentially expressed proteins (DEPs) were enriched in 4519 Gene Ontology enrichment pathways and 320 Kyoto Encyclopedia of Genes and Genomes enrichment pathways. Twenty-two key DEPs related to important functions such as growth and immunity of triploid A. japonicus were screened from the results, among which 20 were up-regulated, such as cathepsin L2 cysteine protease and fibrinogen-like protein A. Arylsulfatase A and zonadhesin were down-regulated. The up-regulated proteins were mainly involved in oxidative stress response, innate immune response, and collagen synthesis in triploid A. japonicus, and the down-regulated proteins were mainly associated with the sterility of triploid A. japonicus. In addition, the transcriptome and proteome were analyzed jointly to support proteome data. In this study, the differences in protein composition between triploid and diploid A. japonicus were analyzed for the first time, and the results revealed the underlying reasons for the growth advantage of triploid A. japonicus.

Species-Specific Gamete Interaction during Sea Urchin Fertilization: Roles of the Egg Jelly and Vitelline Layer

In sea urchins, the sequence of the cellular and molecular events characterizing the fertilization process has been intensively studied. We have learned that to activate the egg, the fertilizing sperm must undergo morphological modifications (the acrosome reaction, AR) upon reaching the outer gelatinous layer enveloping the egg (egg jelly), which triggers the polymerization of F-actin on the sperm head to form the acrosomal process. The AR exposes bindin, an adhesive sperm protein essential for the species-specific interaction with the cognate receptor on the egg vitelline layer. To investigate the specific roles of the egg jelly and vitelline layer at fertilization of sea urchin eggs, Paracentrotus lividus eggs were incubated in acidic seawater, which removes the egg jelly, i.e., experimental conditions that should prevent the occurrence of the AR, and inseminated in the same medium. At variance with the prevailing view, our results have shown that these dejellied P. lividus eggs can still interact with sperm in acidic seawater, albeit with altered fertilization responses. In particular, the eggs deprived of the vitelline layer reacted with multiple sperm but with altered Ca2+ signals. The results have provided experimental evidence that the plasma membrane, and not the vitelline layer, is where the specific recognition between gametes occurs. The vitelline layer works in unfertilized eggs to prevent polyspermy.