Carotenoids are pigment molecules that animals use to produce bright red and yellow skin and feather coloration and that industry uses as important supplements in aquiculture and in human health products. To derive red pigments, most animals, including birds, ingest yellow carotenoids like lutein and biochemically alter them by adding a chemical group known as a ketone. This reaction is stimulated by an enzyme, known as a ketolase, that has yet to be identified in any animal. The best place to isolate this unidentified ketolase enzyme is in the retina of chicken embryos because it is known that red pigments are first produced in chicken in the retina, 18 days after laying, while still in the egg. By comparing the genes expressed in the retina of chicken embryos on day 15 versus day 18, the researchers will be able to isolate the possible enzyme. Once it has been identified the researchers will place the gene in bacteria to make sure that it functions to convert yellow carotenoid pigments to red carotenoid pigments. The vertebrate ketolase will be a major discovery in zoology because it is the enzyme responsible for most red coloration in fish, lizards, and birds. A vertebrate ketolase also has substantial value to agriculture and the food additive industry as a more efficient means to synthesize astaxanthin, which is used as a red food additive and aquaculture supplement. If new products and synthetic processes are developed from the ketolase research, there is the potential for job creation and economic stimulation. Undergraduate students will learn cutting edge molecular techniques while participating in this project.
Brilliant color displays are among the most dramatic—and puzzling—traits in nature. In many birds and fish, carotenoid coloration ranges from yellow to red among individuals in a population. In such species, redder individuals are preferred as mates by females, tend to win contests, and are in better physical condition, but the mechanisms that link the hue of color displays to performance remain obscure. In particular, there is essentially no information on the genes that control carotenoid-based pigmentation in animals. One gene in particular—the gene that codes for the beta-carotene ketolase enzyme—is hypothesized to be key to the production of red coloration in birds and fish because this enzyme catalyzes the modification of dietary yellow pigments into red pigments. However, the ketolase has never been characterized in a vertebrate. Finding the vertebrate ketolase is important because knowledge of the genes that control ornamentation, like red coloration, will result in more powerful studies of the mechanisms, functions, and evolution of ornamental traits, and permit more rigorous testing of fundamental sexual selection theory. Animal coloration is a key species-isolating mechanism, so understanding the genetics of coloration will be important to studies of speciation. To identify the ketolase, we studied the transcripts from the retinas of chickens held in different light environments. The ketolase produces red retinal carotenoids (e.g. astaxanthin) for color vision, and ketolase genes are down- or up-regulated in chickens from low- and high-light conditions, respectively. In the transcript sequence, we screened the population of up-regulated genes to identify the ketolase. To date we have discovered five candidate genes for the ketolase with one primary candidate identified. We now have to express the candidate gene in a bacterial cell to demonstrate that it is capable of converting yellow precursor carotenoids to red products. The ultimate goal of this study is to uncover the genetic architecture of ornamental coloration so as to better understand the processes of mate choice and sexual selection. The b-carotene ketolase also holds potential to be an important commercial product. Production of ketolated carotenoids is a multi-million dollar business that currently relies on expensive laboratory synthesis. If the beta-carotene ketolase permitted this process to be performed more efficiently and cheaply, it could be the foundation for new US industries.
