Serine protease mediates Ovomermis sinensis-inhibited host immune responses by inducing apoptosis: implications for successful parasitism and host mortality.

BACKGROUND: Mermithid nematodes are entomopathogens that parasitize and kill insect hosts and are used for biological control. It is widely believed that mermithid nematodes kill their host upon nematode emergence, unlike other parasites that depend on virulence factors. In this study, we disproved this theory by demonstrating that the mermithid nematode Ovomermis sinensis mediates host mortality by serine protease-induced apoptosis. RESULTS: Successful parasitism of O. sinensis increased with the infection rate, and the inhibition of host immunity by O. sinensis increased with the parasitic load. A serine protease was identified from the host hemolymph. This protease belongs to the trypsin-like serine protease family, which is an apoptosis-inducing serine protease. Specifically, Os-sp was highly expressed only during the parasitic stage and could be induced by host hemocytes and the fat body. Importantly, host immune effectors (melanization, phenoloxidase activity, and encapsulation) were suppressed by the recombinant protein rOs-sp that induced apoptosis of hemocytes and fat body in a dose-dependent manner, which contributes to host death. CONCLUSION: Serine protease mediates O. sinensis-inhibited host immune responses by inducing apoptosis that is lethal to the insect host. Our findings have broader implications for understanding the mechanism of successful parasitism and killing of host by nematodes. © 2023 Society of Chemical Industry.

Biological evidence for the world's smallest tRNAs.

Due to their function as adapters in translation, tRNA molecules share a common structural organization in all kingdoms and organelles with ribosomal protein biosynthesis. A typical tRNA has a cloverleaf-like secondary structure, consisting of acceptor stem, D-arm, anticodon arm, a variable region, and T-arm, with an average length of 73 nucleotides. In several mitochondrial genomes, however, tRNA genes encode transcripts that show a considerable deviation of this standard, having reduced D- or T-arms or even completely lack one of these elements, resulting in tRNAs as small as 66 nts. An extreme case of such truncations is found in the mitochondria of Enoplea. Here, several tRNA genes are annotated that lack both the D- and the T-arm, suggesting even shorter transcripts with a length of only 42 nts. However, direct evidence for these exceptional tRNAs, which were predicted by purely computational means, has been lacking so far. Here, we demonstrate that several of these miniaturized armless tRNAs consisting only of acceptor- and anticodon-arms are indeed transcribed and correctly processed by non-encoded CCA addition in the mermithid Romanomermis culicivorax. This is the first direct evidence for the existence and functionality of the smallest tRNAs ever identified so far. It opens new possibilities towards exploration/assessment of minimal structural motifs defining a functional tRNA and their evolution.

[Analysis of differentially expressed genes from female and male postparasitic Ovomermis sinensis juveniles].

Mermithidae, as an important natural predator of pests such as Bollworm, has great potential for natural biological control of invasive pests. Unfortunately, the in vitro culture of the nematode has not yet been successful, delaying the commercial application of this pest control method. The key reason for this failure is the inability of the worms to accomplish sex differentiation, sparking a strong interest in this process. Here, we analyzed the differences in gene expression of female and male postparasitic Ovomermis sinensis juveniles by mRNA differential display. In total, 20 gene fragments that had differential expression in male and female worms were isolated, including 8 male- and 12 female-specific ones. Bioinformatics methods were employed to analyze sequences of these fragments, in which ensembl analysis shows 4 fragments have comparable parts with C. elegence's X chromosome, we speculate those fragments are important genes which influence sex differentiation of Ovomermis sinensis, This data provides an idea for further study of the molecular mechanism of sex differentiation in mermithids.

Cellular pattern formation, establishment of polarity and segregation of colored cytoplasm in embryos of the nematode Romanomermis culicivorax.

We have begun to analyze the early embryogenesis of Romanomermis culicivorax, an insect-parasitic nematode phylogenetically distant to Caenorhabditis elegans. Development of R. culicivorax differs from C. elegans in many aspects including establishment of polarity, formation of embryonic axes and the pattern of asymmetric cleavages. Here, a polarity reversal in the germline takes place already in P(1) rather than P(2), the dorsal-ventral axis appears to be inverted and gut fate is derived from the AB rather than from the EMS blastomere. So far unique for nematodes is the presence of colored cytoplasm and its segregation into one specific founder cell. Normal development observed after experimentally induced abnormal partitioning of pigment indicates that it is not involved in cell specification. Another typical feature is prominent midbodies (MB). We investigated the role of the MB region in the establishment of asymmetry. After its irradiation the potential for unequal cleavage in somatic and germline cells as well as differential distribution of pigment are lost. This indicates a crucial involvement of this region for spindle orientation, positioning, and cytoplasmic segregation. A scenario is sketched suggesting why and how during evolution the observed differences between R. culicivorax and C. elegans may have evolved.

[Electrophoretic analysis of isoenzyme and protein patterns of Romanomermis yunanensis and R. culicivorax (Nematoda:Mermithidae)].

Isoenzyme electrophoretic patterns of lactate dehydrogenase (LDH), malate dehydrogenase (MDH), esterase (EST) and peroxidase (PO) of post-parasitic juveniles and adults of Romanomermis yunanensis and R. culicivorax were analysed by disc electrophoresis, respectively. The protein patterns of the two species of Romanomermis were compared by vertical slab SDS polyacrylamide gel electrophoresis. The results showed marked differences in isoenzyme patterns (number of bands and/or Rf) of LDH and MDH between the two species of Romanomermis, but the similar positions of isoenzyme bands denoted a certain genetic relationship between them. No band was found in the isoenzyme patterns of PO and EST. Distinct differences in protein pattern were observed between the two species of Romanomermis, but some common bands in pattern reflected the phylogenetic relationships of these species. The differences of isoenzyme and protein patterns observed in this study have provided the reason for identifying and differentiating the two species of Romanomermis at the molecular level.