The Molecular Mechanism of the Cellular Transport of Carotenoids in the silkworm, Bombyx mori

类胡萝卜素吸收的基本方面很大程度上是未知的，例如与类胡萝卜素的吸收和运输有关的腔内和细胞内因子。类胡萝卜素转运蛋白突变体为研究昆虫的脂类特异性转运蛋白提供了独特的研究工具。在+^Y基因中，除类胡萝卜素外，其他脂类的转运都是正常的，只有叶黄素的转运受到影响。野生型的类胡萝卜素转运到血淋巴的量是突变型的100倍。从家蚕幼虫中分离到一个类胡萝卜素结合蛋白(CBP)。免疫印迹分析和免疫细胞化学证实，CBP仅在Y基因显性的幼虫中存在。免疫细胞化学也证实了CBP在中肠上皮细胞刷状缘的定位，提示CBP可能参与了类胡萝卜素在中肠上皮细胞的吸收和运输。RFLP定位分析表明，Y基因编码CBP。经Southern和Northern杂交，在Y和+Y突变体中均检测到CBP基因和CBP基因的表达。Y株和+^Y株的CBP基因序列没有差异。目前尚不清楚+^Y株不能产生CBP的原因。+^Y可能在与CBP表达相关的调控区发生突变。

Fundamental aspects of carotenoid absorption are largely unknown, such as luminal and intracellular factors related to absorb and transport of carotenoid. Carotenoid transport mutants offer unique research tools for studying lipid specific transporter in insects. In the +^Y gene, the transport of the other lipids except carotenoid is normal, only the transfer of lutein is affected. The amount of carotenoids transported to the hemolymph was 100-fold greater in the wild type than in mutants. A carotenoid binding protein (CBP) has been isolated, from Bombyx mori larvae. Immunoblotting analysis and immunocytochemistry confirmed the presence of CBP in larvae with the dominant Y gene only. Immunocytochemistry also verified the localization of CBP in the brush border of the midgut epithelial cells, indicating that CBP might be involved in absorption and transport of carotenoid in the epithelial cell. RFLP mapping analysis shows almost certainly that Y gene encode CBP. In both Y and +^Y mutants, CBP gene and CBP mRNA were found by Southern and Northern hybridization. The difference of sequences of CBP cDNA from Y and +^Y strains was not found. It is not clear why +^Y strain can not make CBP. +^Y might have a mutation on the regulatory region related to CBP expression.