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在很大程度上是未知的，例如与类胡萝卜素吸收和运输有关的腔内和细胞内因素。类胡萝卜素转运突变体为研究昆虫脂质特异性转运体提供了独特的研究工具。在+^Y基因中，除类胡萝卜素外，其他脂类的转运正常，只有叶黄素的转运受到影响。运送到血淋巴的类胡萝卜素的数量在野生型中是突变型的100倍。从家蚕幼虫中分离到一种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仅存在于显性Y基因的幼虫中。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可能参与上皮细胞对类胡萝卜素的吸收和运输。RFLP定位分析几乎可以肯定Y基因编码CBP。在Y和+^Y突变体中，通过南、北杂交发现了CBP基因和CBP mRNA。Y株和+^Y株的CBP cDNA序列没有差异。目前尚不清楚为什么+^Y菌株不能制造CBP。+^Y可能在与CBP表达相关的调控区域发生突变。

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.