title: Asynchronous expression and colocalization of Bsep and Mrp2 during development of rat liver.
abstract: In the liver, function of the bile salt export pump (Bsep), a major canalicular exporter of bile salts, is complemented by activity of the multidrug resistance protein 2 (Mrp2), a canalicular organic anions transporter. Mrp2 was found capable of transporting various anticancer drugs out of cells, eventually undermining their therapeutic potential and contributing to multidrug resistance. We employed a RT-PCR, immunoblotting, and immunofluorescence to examine their gene, protein expression, and distribution of antigenic sites in the rat liver during development from 16-day-old fetus to adult animal. Bsep mRNA was almost undetectable before birth. It was first clearly expressed in the liver of newborn rats. On the contrary, Mrp2 mRNA was seen before birth, although at low levels. In concert with mRNA expression, Bsep protein was undetectable before birth, while Mrp2 protein was already expressed. Both proteins were clearly detectable in the postnatal period. Confocal immunofluorescent microscopy showed asynchronous appearance of Bsep and Mrp2 proteins during development but their colocalization in the bile canaliculi once each one is expressed. During the gestational period, a weak immunofluorescence for Mrp2 was observed only in livers of 16-day-old embryos. No fluorescence for Bsep was seen. Both proteins were clearly visualizable after birth, although the pattern of immunostaining varied. These findings provide molecular evidence that expression of both Bsep and Mrp2 during development is transcriptionally regulated. They also point out the differences in relevance to the liver function of the systems responsible for canalicular transport of bile salts versus organic anions.
authors.affiliation: Department of Anatomy and Cell Biology, Kochi Medical School, Nankoku, Kochi 783-8505, Japan. zinchuk@kochi-ms.ac.jp
authors.forename: Vadim S
authors.initials: VS
authors.lastname: Zinchuk
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Okada
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Akimaru
authors.forename: Harumichi
authors.initials: H
authors.lastname: Seguchi
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000032:analysis* / Q000235:genetics*; D000818:Animals; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D005865:Gestational Age; D015151:Immunoblotting; D007150:Immunohistochemistry; D008099:Liver / Q000196:embryology / Q000254:growth & development* / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D024101:Mitochondrial Proteins; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012269:Ribosomal Proteins / Q000032:analysis* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; C093947:MRP2 protein, S cerevisiae; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins