Identification of genetic regulators of transcellular chaperone signalling in C. elegans

The maintenance of a functional proteome is key to cellular health. Because of this, cells have developed highly conserved protective mechanisms termed stress responses, which act to promote proteostasis. Stress responses have conventionally been considered from a cell-autonomous perspective. However, increasing evidence shows that they can also act in a cell-non-autonomous manner to influence systemic proteostasis. An example of this is transcellular chaperone signalling (TCS) in the nematode C. elegans, which is activated by tissue-specific perturbations in expression of the chaperone hsp-90. Activation of TCS by tissue-specific depletion of hsp-90 leads to inter-tissue upregulation of the chaperone hsp-70 and confers organismal benefits such as improved heat stress resistance. However, the mechanisms underlying TCS activation in this manner are currently not well characterised.

In order to better understand TCS, this study took a dual approach using strains in which hsp-90 is constitutively knocked down either in the intestine or pan-neuronally. Firstly, the organismal effects of TCS activation were investigated through whole-organism transcriptome profiling, enabling identification of genes which are differentially expressed in these strains. The second approach aimed to identify genes required for transcellular hsp-70 upregulation, which might indicate a specific intercellular pathway. This involved a forward genetic screen with whole-genome sequencing and SNP mapping in the strain harbouring intestine-specific hsp-90 knockdown. To further investigate genes identified by these approaches, a tissue-specific RNAi screen was then performed in the same strain. This confirmed 29 genes as tissue-specific modulators of TCS, subsequently denoted TCS cross(X)-Tissue (txt) genes. Furthermore, bioinformatics in combination with functional genetic analysis and survival assays identified a potential mechanism for hsf-1-independent hsp-70 upregulation, in a proposed pathway involving the PDZ domain protein C50D2.3 and the transcription factor ceh-58. This brings us closer to understanding the signalling pathways underlying TCS, and the potential benefits of activating organismal proteostasis mechanisms.