Characteristics and Genomic Localization of Nurse Shark (Ginglymostoma cirratum) IgNAR

The variable domain of IgNAR shows great potential in biological medicine and therapy. IgNAR has been discovered in sharks and rays, with the nurse shark (<i>Ginglymostoma cirratum</i>) IgNARs being the most extensively studied among sharks. Despite being identified in nurse sharks over 30 years ago, the characteristics and genomic localization of IgNAR remain poorly defined, with significant gaps even in the latest released genome data. In our research, we localized the IgNAR loci in the nurse shark genome and resolved the previously missing regions. We identified three IgNAR loci, designated <i>GcIgNAR1</i>, <i>GcIgNAR2</i>, and <i>GcIgNAR3</i>, with only <i>GcIgNAR1</i> and <i>GcIgNAR2</i> being expressed. GcIgNAR1 and GcIgNAR2 belong to type I and type II IgNARs, respectively, and each exhibits several different isoforms. Most nurse shark IgNARs possess five constant domains. However, we found transcripts of GcIgNAR1 and GcIgNAR2 lacking two constant domains, C4 and C5, which differ from the IgNAR of the whitespotted bamboo shark. The protein structures of GcIgNAR1 and GcIgNAR2, generated by AlphaFold3, confirmed the accuracy of the IgNAR loci we identified. Our findings advance scientific understanding of IgNAR in nurse sharks and facilitate future research and medical applications.