Abstract
Formation of yellow-red color cocoons in the silkworm, Bombyx mori, occurs as the result of the selective delivery of carotenoids from the midgut to the silk gland via the hemolymph. This process of pigment transport is thought to be mediated by specific cellular carotenoids carrier proteins. Previous studies indicated that two proteins, Cameo2 and CBP, are associated with the selective transport of lutein from the midgut into the silk gland in Bombyx mori. However, the exact roles of Cameo2 and CBP during the uptake and transport of carotenoids are still unknown. In this study, we investigated the respective contributions of these two proteins to lutein and β-carotene transport in Bombyx mori as well as commercial cell-line. We found that tissues, expressed both Cameo2 and CBP, accumulate lutein. Cells, co-expressed Cameo2 and CBP, absorb 2 fold more lutein (P<0.01) than any other transfected cells, and the rate of cellular uptake of lutein was concentration-dependent and reached saturation. From immunofluorescence staining, confocal microscopy observation and western blot analysis, Cameo2 was localized at the membrane and CBP was expressed in the cytosol. What’s more, bimolecular fluorescence complementation analysis showed that these two proteins directly interacted at cellular level. Therefore, Cameo2 and CBP are necessarily expressed in midguts and silk glands for lutein uptake in Bombyx mori. Cameo2 and CBP, as the membrane protein and the cytosol protein, respectively, have the combined effect to facilitate the cellular uptake of lutein.
Highlights
Natural colored silk fabric possesses broad market prospects and valuable economic benefits [1]
In 03-520 [Y, +C], both Cameo1 and Cameo2 mRNA were expressed in midguts, but only Cameo1 mRNA existed in silk glands from last instar larvae stage at 3 days of age
Carotenoid-binding protein (CBP) mRNA was expressed in both midguts and silk glands from Jianpuzhai and 03-520; no CBP mRNA was detected in Qiubai and Dazao
Summary
Natural colored silk fabric possesses broad market prospects and valuable economic benefits [1]. As one of the most important natural colored silk-spinning insects in the world, Bombyx mori divide into white cocoon strains, yellow-red cocoon strains and green cocoon strains [2]. The yellow-red cocoon strains have varies colored cocoons (including yellow, golden yellow, flesh, pink and rust). The main coloring pigments in yellow-red cocoons are carotenoids [3,4]. Bombyx mori cannot synthesize carotenoids by themselves [5]. Instead, they can ingest carotenoids from the mulberry leaves to produce yellow-red silk [6,7,8,9]. The mechanism of absorption and transport of carotenoids from the midgut into the silk gland via hemolymph is still unclear
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