DNA methylation in a sea lamprey vasotocin receptor gene promoter correlates with tissue- and life-stage-specific mRNA expression

The jawless vertebrate sea lamprey (Petromyzon marinus) genome has a different structure from both invertebrates and jawed vertebrates featuring high guanine–cytosine (GC) content. This raises the question of whether DNA methylation of cytosine–guanine (CpG) dinucleotides could function to regulate lamprey gene transcription. We previously characterized a lamprey arginine vasotocin (AVT) receptor gene (Pm807) possessing characteristics of both arginine vasopressin (AVP) V1A and oxytocin (OXT) receptor genes of jawed vertebrates. Lamprey Pm807 mRNA is highly expressed in adult heart and larval liver but not expressed in adult liver. Using high-resolution melt (HRM) PCR on bisulfite-converted DNA, we pinpointed a region with tissue-specific differences in DNA melt characteristics, indicating differences in methylation level. Sequencing revealed a pattern of methylation at specific CpGs at consistently higher levels in adult heart and larval liver than adult liver. These CpGs are associated with putative transcription factor binding sequences organized similarly to functional OXTR promoters in mammals, suggesting functional similarity in lamprey gene transcription regulation.