“…Although the worm genome expresses a single Gli homolog (TRA-1) primarily involved in sex-determination ( Hodgkin and Brenner, 1977 ; Hodgkin, 1987 ; Ellis, 2020 ), the nematode HHLS pathway lacks the canonical Hedgehog intracellular transduction pathway, and the evolutionary function of the PTR and HRP family expansions remains unclear ( Baker et al, 2021 ). HHLS genes have been involved in C. elegans epithelial function and development ( Hao et al, 2006a ; Liegeois et al, 2006 ; Soloviev et al, 2011 ), cuticular structure and patterning ( Zugasti et al, 2005 ; Hao et al, 2006b , c ; Liegeois et al, 2006 ; Kouns et al, 2011 ; Chiyoda et al, 2021 ; Cohen et al, 2021 ), sensory organ formation ( Michaux et al, 2000 ; Liegeois et al, 2007 ; Oikonomou et al, 2011 ; Wang et al, 2017 ; van der Burght et al, 2020 ), neurogenesis ( Kume et al, 2019 ) and axonal guidance ( Riveiro et al, 2017 ), immunity ( Roberts et al, 2010 ; Lightfoot et al, 2016 ), lipid homeostasis ( Lin and Wang, 2017 ; Del Castillo et al, 2021 ), reproduction ( Kuwabara et al, 2000 ; Templeman et al, 2020 ), and longevity ( Ji et al, 2021 ). In particular, the HHLS pathway was found to mediate the impact of microbial metabolites on host lipid metabolism ( Lin and Wang, 2017 ), supporting a direct role in host-nematode interactions that could in part explain the diversification of HRP ligands and PTR receptors.…”