Genome-wide identification and expression analysis of lysine-specific demethylase (KDM) genes in the echiuran worm Urechis unicinctus and the association of Jumonji domain containing 6 (Jmjd6) with antioxidant defense.

Histone lysine-specific demethylases (KDMs) are key epigenetic regulators, yet studies on KDM genes in marine annelids remain limited. In this study, we identified 21 KDM genes belonging to 14 subfamilies from the genome of the intertidal echiuran worm Urechis unicinctus. Using publicly available transcriptomic sequencing data, we performed detailed expression analyses of KDM genes across different developmental stages, multiple adult tissues, and under various environmental stress conditions. Expression profiles revealed that most KDM genes peaked during early embryonic development and were predominantly expressed in nephridia and body wall tissues. A total of 19 KDM genes responded to sulfide stress, among which two exhibited type I transcriptional memory and nine exhibited type II transcriptional memory. Extreme temperature and ultraviolet exposure also induced differential expression of multiple KDM paralogs. Notably, jmjd6-3 (Jumonji domain-containing 6-3) responded to the highest number (four) of stress conditions, suggesting its functional importance. Furthermore, we conducted a study examining pharmacological inhibition at the organism-level (using the specific inhibitor SKLB325) that suggested Jumonji domain-containing protein 6 (Jmjd6) is functionally linked to antioxidant defense, as its inhibition significantly reduced the expression of antioxidant genes, the activity of superoxide dismutase, and the total antioxidant capacity under high-temperature stress conditions. This study provides a foundation for exploring the roles of KDM genes in environmental stress responses of marine benthic organisms.