Osamu Ninagi

A carotenoid-binding protein (CBP) plays a crucial role in cocoon pigmentation of silkworm (Bombyx mori) larvae

We examined the role of carotenoid‐binding protein (CBP) in yellow cocoon pigmentation. First, using yellow or white cocoon races, we investigated the linkage between the yellow pigmentation and CBP expression. CBP was expressed only in the silk gland of the yellow cocoon races, which utilize carotenoids for cocoon pigmentation. Furthermore, CBP expression in the silk glands of day 1–7 fifth instar larvae matched the period of carotenoid uptake into the silk gland. Finally, we gave double‐stranded CBP RNA to Bombyx mori (B. mori) larvae to induce RNA interference. The significantly reduced expression of CBP in the silk gland of fifth instar larva was confirmed on day 4 and a decrease in yellow pigmentation was observed in the cocoon. We showed that CBP plays a key role in the yellow cocoon pigmentation caused by carotenoids.

The effect of W chromosome origin on sex-chromosome pairing in ZZWW tetraploid females of the domesticated silkworm, Bombyx mori, and the congenic wild silkworm, Bombyx mandarina.

To analyze the degree of pairing of the Z and W chromosomes in ZZWW tetraploid female silkworms that have the W chromosomes of the domesticated silkworm, Bombyx mori, and those of the wild silkworm, Bombyx mandarina, we induced two types of ZZWW tetraploid female silkworms (Cr4n, Wr4n) through cold treatment of the eggs. The Wr4n female is congenic to the Cr4n female for W chromosomes; namely, the W chromosomes of the Wr4n female are derived from those of B. mandarina. Each of the sex ratios (♀/♂) in filial triploids from the Cr4n females was shown to be in the range of 3.9–5.3 (4.6 as an average of six cases). On the other hand, each of the sex ratios (♀/♂) in filial triploids from the Wr4n females was shown to be in the range of 6.2–9.0 (6.9 as an average of nine cases). The results of a t-test indicated that the difference in sex ratios in the two groups is highly significant (at the 0.1% level). These results suggest that, in the meiosis of the ZZWW tetraploid female, the frequency of pairing of the W chromosome of B. mandarina and the Z chromosome of B. mori is lower than that of the pairing of the W and Z chromosomes of B. mori. Furthermore, the t-test results are evidence that the W chromosomes have undergone significant evolutional change.