SID-2 is a conserved extracellular vesicle protein that is not associated with environmental RNAi in parasitic nematodes

Blow, F., Jeffrey, K., Wang-Ngai Chow, F., Nikonorova, I.A., Barr, M.M.,  Cook, A.G.,  Prevo, B., Cheerambathur, D.K.,  and Buck, A.H.

By Natalia Kochanova, Earnshaw Lab

SID-2 is a receptor for dsRNA on the apical membrane of intestinal epithelial cells of C. elegans. The receptors appear to uptake dsRNAs via pH-dependent endocytosis, which is required for systemic gene silencing in the whole organism. Thus, SID-2 and other factors make it very easy to perform RNAi experiments in these worms. However, not all the nematodes are able to uptake dsRNA. For example, Heligmosomoides bakeri, a nematode parasite which infects domestic mice, is refractory to RNAi and until this work it was assumed this was partly due to the absence of SID-2 in its genome.

In this work the team, headed by Amy Buck and Dhanya Cheerambathur, discovered SID-2 in the H.bakeri genome and created C. elegans SID-2 null strains expressing the variant of SID-2 from H. bakeri under C. elegans promoter. As a control, the scientists expressed C. elegans SID-2 under the same conditions. 

Both proteins localised to the apical membrane of intestinal epithelium of transgenic worm. Does it mean that SID-2 from H. bakeri could potentially uptake dsRNAs for C. elegans? 

To answer this question, the team treated developing worms with an siRNA against a gene involved in chromosome segregation that is necessary for embryonic development. The worms expressing the H. bakeri variant of SID-2 developed normally, while C. elegans SID-2 was embryonic lethal in C. elegans at these conditions.

Therefore, either H. bakeri receptor is unable to uptake siRNAs, or it is somehow not connected to the downstream pathway of processing these RNAs and ensuring gene silencing. Intriguingly however the investigators found that SID-2 is highly abundant on extracellular vesicles released from H.bakeri. Since these vesicles can travel out of the worm and into host cells, their work suggests new biological functions of SID-2 outside of the worm. More work will be needed to elucidate precise function of SID-2 orthologues in differing worm species (Blow et al, 2024).