Chemokine ccl33 is a key regulator of fish barbel development

Abstract

Barbels are integumentary sense organ that can be found in fishes, reptiles and amphibians. Barbel structures are relatively simple, consisting of central rod of cartilage, nerve trunk, artery and taste bud. The cell types in barbels were highly conserved with that in human. So, the barbel provided a good system for studying angiogenesis, neural pathfinding, wound healing, scar formation and other key processes in vertebrate physiology. More than one century ago, people attempted to find the evolution and formation of the barbels. However, it is still unclear which genes regulate the barbel development, and the origin of the barbels. Bottlenose catfish (Ageneiosus Marmoratus), a catfish species but lacking the sensory organ barbels, serves as an ideal model to determine the genomic basis for barbel development and its regeneration. Through comparative genome and transcriptome subtraction analysis, here I report a chemokine gene, ccl33, as a key regulator of barbel development and regeneration. The ccl33 gene is present in fish with barbels but absent from fish without barbels. It has multiple copies in channel catfish, of which three copies, ccl33.4, ccl33.6, and ccl33.7 were differentially expressed during barbel regeneration, in a fashion concordant with the timing of barbel regeneration. Knockout of ccl33 genes in zebrafish resulted in various phenotypes including complete loss of barbels, reduced barbel sizes, curly barbels, and reduced body size and weak performance, suggesting that ccl33 is a key regulator of barbel development, and may be important for normal development and immunological functions.