A CD36-related transmembrane protein is coordinated with an intracellular lipid-binding protein in selective carotenoid transport for cocoon coloration.
The transport pathway of specific dietary carotenoids from the midgut lumen to the silk gland in the silkworm, Bombyx mori, is a model system for selective carotenoid transport because several genetic mutants with defects in parts of this pathway have been identified that manifest altered cocoon pigmentation. In the wild-type silkworm, which has both genes, Yellow blood (Y) and Yellow cocoon (C), lutein is transferred selectively from the hemolymph lipoprotein to the silk gland cells where it is accumulated into the cocoon. The Y gene encodes an intracellular carotenoid-binding protein (CBP) containing a lipid-binding domain known as the steroidogenic acute regulatory protein-related lipid transfer domain. Positional cloning and transgenic rescue experiments revealed that the C gene encodes Cameo2, a transmembrane protein gene belonging to the CD36 family genes, some of which, such as the mammalian SR-BI and the fruit fly ninaD, are reported as lipoprotein receptors or implicated in carotenoid transport for visual system. In C mutant larvae, Cameo2 expression was strongly repressed in the silk gland in a specific manner, resulting in colorless silk glands and white cocoons. The developmental profile of Cameo2 expression, CBP expression, and lutein pigmentation in the silk gland of the yellow cocoon strain were correlated. We hypothesize that selective delivery of lutein to specific tissue requires the combination of two components: 1) CBP as a carotenoid transporter in cytosol and 2) Cameo2 as a transmembrane receptor on the surface of the cells.
Sakudoh
Takashi
T
Division of Radiological Protection and Biology, National Institute of Infectious Diseases, Shinjuku, Tokyo 162-8640, Japan.
Iizuka
Tetsuya
T
Narukawa
Junko
J
Sezutsu
Hideki
H
Kobayashi
Isao
I
Kuwazaki
Seigo
S
Banno
Yutaka
Y
Kitamura
Akitoshi
A
Sugiyama
Hiromu
H
Takada
Naoko
N
Fujimoto
Hirofumi
H
Kadono-Okuda
Keiko
K
Mita
Kazuei
K
Tamura
Toshiki
T
Yamamoto
Kimiko
K
Tsuchida
Kozo
K
D000595:Amino Acid Sequence; D000818:Animals; D012831:Bombyx / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D050556:Fatty Acid-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008040:Genetic Linkage; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D014975:Lutein / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010858:Pigmentation / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D047011:Silk / Q000737:chemistry* / Q000378:metabolism; D019076:Transgenes
D018955:CD36 Antigens; D002352:Carrier Proteins; D050556:Fatty Acid-Binding Proteins; D019476:Insect Proteins; D008565:Membrane Proteins; D047011:Silk; D002338:Carotenoids; D014975:Lutein