Colors of silkworms and beetles

April 25, 2012 § Leave a comment

SIlkworm cocoons

The other day, I learned a new word: ommochrome. Ommochromes are insect pigments derived from tryptophan. A paper in Journal of Biological Chemistry introduced this word into my vocabulary.

It turns out that most of the red, brown and purple colors of insects are the result of ommochromes. Researchers don’t really understand how the final step of ommochrome synthesis takes place. In this JBC paper, which is also a Paper of the Week, Mizuko Osanai-Futahashi and colleagues at the National Institute of Agrobiological Sciences in Japan used genetics to figure out how eggs and eyes of silkworms get their distinctive dark brownish-lilac color.

By studying mutant silkworms that lay orange eggs and have dark red eyes, Osanai-Futahashi and colleagues found the gene involved in biosynthesis of an ommochrome called “ommin.” The protein encoded by this gene is a novel member of a transporter superfamily.

The researchers knocked out its orthologous gene in the red flour beetle (an insect that attacks stored grains) and discovered that the insect developed eye color defects. Osanai-Futahashi and colleagues concluded that the ommin synthesis pathway is conserved in a certain group of insects known as homometabolous insects.

 An interesting tidbit: The gene is absent in the fruitfly, which may explain why they have red, not black, eyes.

Drosophila melanogaster. Image by André Karwath aka Aka

NOTE: Images were taken from http://en.wikipedia.org/wiki/File:Cocoon.jpg (for silkworm cocoons) and http://en.wikipedia.org/wiki/Drosophila_melanogaster (for Drosophila)

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