Expression levels of the tetratricopeptide repeat protein ttc39b co-vary with carotenoid-based skin color in cichlid fish

Carotenoid pigments play a major role in animal body coloration, and the underlying genetic mechanisms are currently attracting increasing research attention. Here, we used RNA sequencing (RNA-Seq) to test for differential gene expression between three pairs of related cichlid fish taxa, which differ in terms of red and yellow carotenoid-based body coloration. Five genes were differentially expressed in all three yellow versus red skin contrasts (dhrsx, nlrc3, tcaf2, urah, and ttc39b), but only the tetratricopeptide repeat (TPR) protein coding gene ttc39b was consistently higher expressed in the red skin samples. The RNA-Seq results were confirmed by quantitative PCR. Elevated ttc39b expression has recently been associated with the presence of yellow carotenoids in the skin of another cichlid fish, and we therefore suggest that the expression differences of ttc39b in the present study may be related to the higher carotenoid concentrations in red compared to yellow skin samples, as opposed to the presence or absence of red carotenoids.