Two metazoan osmosensors encoded by GPCR genes in C. elegans

Osmosensors play essential roles in maintaining body fluidic balance in the animal kingdom. However, the molecular identities of osmosensors in mammals are still elusive. TRP channels have been proposed to be candidate osmosensors, but their roles in regulating body fluid homeostasis are still controversial. The major difficulty in identifying osmosensors in animals, is in part because of the lack of efficient screening methods. Here, we designed and conducted a neuronal activity-based genetic screen to identify the first osmosensors in animal kingdom using C. elegans. Previous studies show G proteins are required for C. elegans sensing osmotic stimuli. Thus, we proposed that the osmosensors are GPCRs. To identify the GPCRs enriched in ASH neurons, which are the major osmosensing neurons, we did RNA-seq after FACS sorting for ASH. After screening the enriched GPCRs in ASH, we successfully found one GPCR, OSGR-1, functions as an osmosensor in C. elegans. We also found, its closest paralog, OSGR-2, is also an osmosensor. This is also the first shown that GPCRs are capable of sensing osmolarity, which will facilitate the identification of osmosensors in other animals. To get enriched genes in C. elegans ASH neurons, we used FACS sorting to sort out YFP labeled ASH neurons together with non-YFP cells as controls. RNA-seq was used to map the transcriptome and both Cufflinks/CuffDiff and HTseq/DESeq2 were used to calculate DEG genes.