Bioinformatic identification of cytochrome b5 homologues from the parasitic nematode Ascaris suum and the free-living nematode Caenorhabditis elegans highlights the crucial role of A. suum adult-specific secretory cytochrome b₅ in parasitic adaptation

Proteomics of Nasonia vitripennis and the effects of native Wolbachia infection on N. vitripennis

Background

Nasonia vitripennis, a parasitic wasp, is a good model organism to study developmental and evolutionary genetics and to evaluate the interactions between insect hosts and their symbionts. Wolbachia may be the most prevalent endosymbiont among insect species due to their special ability to improve the fitness of the infected hosts. Transinfection of bacteria or fungi could substantially alter the expression of host immune system components. However, few studies have focused on the effects of native Wolbachia infection. Accordingly, in this study, we evaluated the proteomics of N. vitripennis following Wolbachia infection.

Methods

We studied the proteomics of N. vitripennis following native Wolbachia infection and in antibiotic-treated Wolbachia-free samples using isobaric tags for relative and absolute quantification-liquid chromatography tandem mass spectrometry, accompanying with some ecological experiments.

Results

In total, 3,096 proteins were found to be associated with a wide range of biological processes, molecular functions, and cellular components. Interestingly, there were few significant changes in immune or reproductive proteins between samples with and without Wolbachia infection. Differentially expressed proteins were involved in the binding process, catalytic activity, and the metabolic process, as confirmed by quantitative reverse transcription polymerase chain reaction.

Discussion

Invasion of any pathogen or bacterium within a short time can cause an immunoreaction in the host. Our results implied that during the long process of coexistence, the immune system of the host was not as sensitive as when the symbiont initially infected the host, implying that the organisms had gradually adjusted to cohabitation.

Identification of cytochrome b5 CYTB-5.1 and CYTB-5.2 in C. elegans; evidence for differential regulation of SCD

Unsaturated fatty acids (UFAs) play crucial roles in living organisms regarding development, energy metabolism, stress resistance, etc. The biosynthesis of UFAs starts from the introduction of the first double bond by stearoyl-CoA desaturase (SCD), converting saturated fatty acids (SFAs) to monounsaturated fatty acids (MUFAs). This desaturation is considered to be an aerobic process that requires cytochrome b5 reductase, cytochrome b5 and SCD. However, this enzyme system remains elusive in Caenorhabditis elegans. Here, we show that inactivation by RNAi knockdown or mutation (gk442189) of putative cytochrome b5 genes cytb-5.1 led to reduced conversion of C18:0 to C18:1(n-9) by SCD desaturases FAT-6/7 in C. elegans. On the contrary, cytb-5.2RNAi and cytb-5.2(gk113588) mutant worms showed decreased conversion of C16:0 to C16:1(n-7) by FAT-5 desaturase. Dietary supplementation with C18:1(n-9) and C18:2(n-6) also showed that CYTB-5.1 is likely required for the activity of FAT-6/7 desaturases, but not for FAT-1 to FAT-4 desaturases. Interestingly, co-immunoprecipitation (Co-IP) demonstrated that either FAT-7 or FAT-5 has ability to interact with both CYTB-5.1 and CYTB-5.2. Moreover, RNAi knockdown of cytb-5.1 upregulates the transcriptional and translational expression of fat-5 to fat-7, which may be due to the feedback induction by reduced C18:1(n-9) and downstream fatty acids. Furthermore, both CYTB-5.1 and CYTB-5.2 are involved in fat accumulation, fertility and lifespan in worms, which may be independent of changes in fatty acid compositions. Collectively, these findings for the first time reveal the differential regulation of various SCDs by distinct cytochrome b5 CYTB-5.1 and CYTB-5.2 in the biosynthesis of UFAs in C. elegans.