Identification, evolution and expression of a CD36 homolog in the basal chordate amphioxus Branchiostoma japonicum

CD36, as one member of scavenger receptor class B (SRB) family, is a transmembrane glycoprotein and has been associated with diverse normal physiological processes and pathological conditions. However, little is known about it in amphioxus, a model organism for insights into the origin and evolution of vertebrates. In this paper, CD36 homologs in amphioxus were identified. Evolutionary analysis suggested that amphioxus BfCD36F-a/b, which were more similar to vertebrate CD36, might represent the primitive form before the splitting of CD36, SRB1 and SRB2 genes during evolution. Then the BjCD36F-a cDNA was cloned from Branchiostoma japonicum using RACE technology. Real-time PCR and in situ hybridization revealed the expression of BjCD36F-a in all the tissues detected with the highest expression in the hepatic caecum. The BjCD36F-a expression was obviously up-regulated after feeding and down-regulated during fasting, indicating a role of BjCD36F-a in feeding regulation. Besides, the up-regulation expression of BjCD36F-a transcripts was also found after either Lipoteichoic acid (LTA) treatment in the BjCD36F-a-transfected FG cells or Escherichia coli (E. coli) challenge in vivo, implying an immune-related function for BjCD36F-a. Collectively, we identify and characterize a conserved gene that is important in the fundamental process of immune and nutritional regulation. These are the first such data in amphioxus, laying a foundation for further study of their physiological functions.