Gene co-expression network analysis reveal core responsive genes in Parascaris univalens tissues following ivermectin exposure
Anthelmintic resistance threatens the effectiveness of critical drugs like ivermectin (IVM) against the equine parasite roundworm, Parascaris univalens. This study leveraged gene co-expression network analysis to elucidate tissue-specific transcriptional responses and to identify core genes implicated in IVM response in P. univalens. Adult worms (n=28) were exposed to 10-11 M and 10-9 M IVM in vitro for 24 hours. RNA-sequencing examined transcriptional changes in the anterior end and intestine. Differential expression analysis revealed pronounced tissue differences, with the intestine exhibiting substantially more transcriptional activity. Gene co-expression network analysis identified seven modules significantly associated with IVM response. Within these, 219 core genes were detected, largely expressed in the intestine and spanning diverse biological processes. After 10-11 M IVM, intestinal core genes showed transcriptional suppression, cell cycle inhibition, and ribosomal alterations. Interestingly, genes PgR028_g047 (sorb-1), PgB01_g200 (gmap-1) and PgR046_g017 (col-37 & col-102) switched from downregulation at 10-11 M to upregulation at 10-9 M IVM. The 10-9 M concentration induced cuticle and membrane integrity core genes in the intestine. No clear core gene patterns were visible in the anterior end after 10-11 M IVM. However, after 10-9 M IVM, the anterior end mostly displayed downregulation, indicating disrupted transcriptional regulation.  An interesting find was the non-modular calcium-signaling gene, PgR047_g066 (gegf-1), uniquely connected 71 genes across four modules. These genes were enriched for transmembrane signaling activity, suggesting that PgR047_g066 (gegf-1) could have a key signaling role. By unveiling tissue-specific expression patterns and highlighting biological processes through unbiased core gene detection, this study reveals intricate IVM responses in P. univalens. These findings can guide functional validations to further resistance mechanism understanding.