- Liao X, Yang L, Chen X, Chen J. (2017) Identification of microRNA expression profiles in the gill, intestine and hepatic caecum of Branchiostoma belcheri. Protein Cell 8(4), 302-307.
The origin of vertebrate-specific characters and functional systems is one of the most important questions in the evolutionary biology (Holland and Chen, 2001). Amphioxus, the most basal chordate, is considered as the sister of vertebrates based on the recent molecular phylogenetic evidences, and it is used as an ideal model organism to study the origin and evolution of vertebrate organ systems including immune system (Yu and Holland, 2009). Three digestive organs, gill slits, hepatic caecum and intestine in amphioxus were also considered as primitive immune organs of amphioxus (Schmitz et al., 2000). In addition to the respiratory and digestive function, the amphioxus gill is regarded as “the first immune defense organ” and plays a natural immune defense role by working as a physical barrier. The intestine is serving as a site of continuous immunological interaction (Yuan et al., 2015). Meanwhile, the hepatic caecum of amphioxus, as a prototype of the vertebrate liver, is also considered as a potential immunological organ in the amphioxus, playing an important role in acute phase response (APR) (Wang and Zhang, 2011). The immune responsive cells including lymphocyte-like cells and macrophage-like cells were found in the gill and intestine of amphioxus, respectively (Huang et al., 2011). Furthermore, the conserved molecules and signaling pathways involved in innate immune system were also identified in these organs in the amphioxus (Huang et al., 2011). Though the importance of these organs in digestive system and the value of these tissues for study of immune system evolution are demonstrated (Yuan et al., 2015), the molecular characters of these tissues are not revealed comprehensively.