Mutant worms

Japanese scientists say they have genetically engineered silkworms to produce a specific colour.

The author of the study, Takashi Sakudoh of the University of Tokyo, says understanding the pigment transport system of silkworms could "pave the way for genetic manipulation of the colour and pigment content of silk".

In nature, silkworm cocoon colours vary from white, yellow, straw, salmon, pink and green. The colours in the silk are from natural pigments absorbed when the silkworms eat mulberry leaves.

Japanese researchers have observed in silkworms that produce white silk that the "yellow blood", or Y gene, was mutated. A segment of DNA had been deleted. The Y gene enables silkworms to extract carotenoids, yellow-coloured compounds, from mulberry leaves.

The scientists have found that mutated insects produced a non-functional form of the carotenoid-binding protein (CBP), known to aid pigment uptake.

Using genetic engineering techniques, the researchers introduced pristine Y genes into the mutant insects. The engineered worms produced working CBP and yellow-coloured cocoons. The yellow colour became more vivid after rounds of crossbreeding.

The study, published in the Proceedings of the National Academy of Sciences of the United States, says the silk fibres could be produced in a flesh colour and a reddish colour.