DEVELOPMENT OF A DIETARY TAURINE-DEPENDENT ZEBRAFISH STRAIN
Taurine is an essential component of aquafeed formulations for several commercially relevant species. Understanding the specifics of how this amino acid affects fish growth and overall health is critical for evaluating its importance in feed formulations across the board. This is particularly true during an era when the increased incorporation of plant-based ingredients shows promise in terms of sustainability but also raises concerns in terms of certain plant components eliciting an inflammatory response.
In vertebrates, the biosynthesis of taurine from methionine or cysteine can occur by two distinct pathways. Cysteine is oxidized by cysteine dioxygenase (CDO; EC 1.13.11, MW 24 kD) to cysteine sulfinic acid which is converted by CSAD (EC 4.1.1.29, MW 51 kD) to hypotaurine which is then oxidized to taurine. CSAD is one of the rate-limiting enzymes for taurine biosynthesis and the level of its activity determines the need for dietary taurine. The alternate pathway involves incorporation of cysteine into coenzyme A (CoA), followed by the release of cysteamine during CoA turnover. Cysteamine is oxidized to hypotaurine by ADO (EC 4.1.1.29, MW 51 kD). In the CSAD KO mouse, there is an 83% decrease in plasma taurine levels.
We are currently establishing a homozygous breeding population of a taurine-dependent zebrafish line. A csadsa9430 mutant with a nonsense mutation was obtained from the Wellcome Trust Sanger Institute Zebrafish Mutation Project (Cambridge, UK). Because all dietary sources used to raise zebrafish contain taurine, no phenotype has been described for this mutant. A 2013 study that utilized antisense morpholino oligonucleotides to knock down csad demonstrated that affected embryos had increased mortality and cardiac anomalies (Chang et al. in Amino Acids).
It is expected that studies with these knockouts will demonstrate a similar, if not increased, deleterious impact on development and viability of embryos. Furthermore, the strain will be used to assess the impact of taurine and a potential ability to ameliorate effects of pro-inflammatory dietary components. Our laboratory has plans to cross this with two other strains with fluorescent labeling of neutrophils (mpx:GFP) and macrophages (mpeg1:mCherry) in order to specifically examine the role of taurine in mitigating the inflammatory process.