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J. Cell Biol.,
Volume 144, Number 6, March 22, 1999 1271-1284
Department of Biochemistry, Weill Medical College of Cornell University, New York 10021
To understand the mechanisms for endocytic
sorting of lipids, we investigated the trafficking of three
lipid-mimetic dialkylindocarbocyanine (DiI) derivatives, DiIC16(3) (1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), DiIC12(3) (1,1'-
didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), and FAST DiI (1,1'-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), in CHO
cells by quantitative fluorescence microscopy. All three
DiIs have the same head group, but differ in their alkyl tail length or unsaturation; these differences are expected to affect their distribution in membrane domains of varying fluidity or curvature. All three DiIs
initially enter sorting endosomes containing endocytosed transferrin. DiIC16(3), with two long 16-carbon saturated tails is then delivered to late endosomes,
whereas FAST DiI, with two cis double bonds in each
tail, and DiIC12(3), with saturated but shorter (12-carbon) tails, are mainly found in the endocytic recycling
compartment. We also find that DiOC16(3) (3,3'- dihexadecyloxacarbocyanine perchlorate) and FAST
DiO (3,3'-dilinoleyloxacarbocyanine perchlorate) behave similarly to their DiI counterparts. Furthermore, whereas a phosphatidylcholine analogue with a
BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore attached at the end of a 5-carbon acyl
chain is delivered efficiently to the endocytic recycling
compartment, a significant fraction of another derivative with BODIPY attached to a 12-carbon acyl chain
entered late endosomes. Our results thus suggest that endocytic organelles can sort membrane components
efficiently based on their preference for association
with domains of varying characteristics.
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