Mining Flatworm Genomes for Endocannabinoid Pathway Enzyme Homologues

Abstract

Endocannabinoid (EC) signalling pathway plays a central role in the normal function of the reproductive, muscular, immune and central nervous system. Two main endogenous endocannabinoids (eCBs), anandamide (AEA) and 2-arachidonoylglycerol (2-AG), are synthesised and degraded in a time-dependent manner within living systems. Enzymatic machinery for the production and destruction of these enzymes has been explored in detail in some mammalian and invertebrate model organisms (such as C. elegans). However, currently no study has explored the enzymatic architecture of the EC pathway in flatworms. The present study has comprehensively investigated the pattern of occurrence of eight EC signalling pathway enzymes (NAPE-1, NAPE-2, DAGL-2, ABHD-5, ABHD-12, FAAH-1, FAAH-2 and FAAH-3) in 33 flatworm species. Homologues of these enzymes were extracted from Wormbase and, using Hidden Markov Model (HMMER) based profiles and Wormbase Parasite BLASTp, these were shortlisted and the hits for these enzymes were validated in flatworm genomes. ABHD-12, with its lowest occurrence in only 14 flatworm species, was deemed to be the least preferred enzyme for the degradation of 2-AG. Furthermore, the occurrence of NAPE1 and NAPE-2 was observed in 17 species. DAGL-2, implicated in 2-AG synthesis, was the most commonly occurring enzyme in the gene set of 32 flatworms. In contrast, the complete absence of FAAH-(1-3) in six flatworm species suggested significant roles for other unexplored fatty acid amide hydrolases in flatworm AEA degradation pathway. In conclusion, the findings from this current study could be employed to investigate the tissue distribution and function of EC pathway enzymes in flatworms using localisation studies and reverse genetics techniques.