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Characterization and functional analysis of BmSR-B1 for phytosterol uptake
Mika Takeshima1, Mari H Ogihara2, Hiroshi Kataoka1
1Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
Insects need dietary sterols for survival. This study identifies silkworm Scavenger Receptor class B type1 (BmSR-B1) proteins responsible for selectively taking up dietary phytosterols into insect tissues.
Area of Science:
- Insect physiology
- Molecular biology
- Biochemistry
Background:
- Insects are sterol auxotrophs, requiring dietary sterols like cholesterol.
- Phytophagous insects utilize dietary phytosterols as a cholesterol precursor.
- Lipophorin (Lp) transports sterols, but phytosterol uptake mechanisms remain unclear.
Purpose of the Study:
- To characterize Scavenger Receptor class B type1 (SR-B1) from Bombyx mori (BmSR-B1) in phytosterol uptake.
- To investigate the role of BmSR-B1 in transporting dietary sterols into insect tissues.
Main Methods:
- Sterol quantification using Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS).
- Gene expression analysis of Bmsr-b1 in silkworm tissues.
- Functional characterization of BmSR-B1 homologs in BmN and S2 cells incubated with purified Lp.
Main Results:
- Midgut and fat body showed higher phytosterol concentrations compared to brain and prothoracic glands.
- Specific BmSR-B1 genes (Bmsr-b1_2, 3, 4, 6, 10) were expressed in midgut and fat body.
- BmSR-B1_3 and BmSR-B1_4 facilitated the selective uptake of campesterol and β-sitosterol into cultured cells.
Conclusions:
- BmSR-B1 proteins are involved in the selective uptake of dietary phytosterols into insect cells.
- This study elucidates a key mechanism for phytosterol absorption in silkworms.
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