title: Hepatocytes lacking thioredoxin reductase 1 have normal replicative potential during development and regeneration.
abstract: Cells require ribonucleotide reductase (RNR) activity for DNA replication. In bacteria, electrons can flow from NADPH to RNR by either a thioredoxin-reductase- or a glutathione-reductase-dependent route. Yeast and plants artificially lacking thioredoxin reductases exhibit a slow-growth phenotype, suggesting glutathione-reductase-dependent routes are poor at supporting DNA replication in these organisms. We have studied proliferation of thioredoxin-reductase-1 (Txnrd1)-deficient hepatocytes in mice. During development and regeneration, normal mice and mice having Txnrd1-deficient hepatocytes exhibited similar liver growth rates. Proportions of hepatocytes that immunostained for PCNA, phosphohistone H3 or incorporated BrdU were also similar, indicating livers of either genotype had similar levels of proliferative, S and M phase hepatocytes, respectively. Replication was blocked by hydroxyurea, confirming that RNR activity was required by Txnrd1-deficient hepatocytes. Regenerative thymidine incorporation was similar in normal and Txnrd1-deficient livers, further indicating that DNA synthesis was unaffected. Using genetic chimeras in which a fluorescently marked subset of hepatocytes was Txnrd1-deficient while others were not, we found that the multigenerational contributions of both hepatocyte types to development and to liver regeneration were indistinguishable. We conclude that, in mouse hepatocytes, a Txnrd1-independent route for the supply of electrons to RNR can fully support DNA replication and normal proliferative growth.
authors.affiliation: Veterinary Molecular Biology, Montana State University, Bozeman, MT 59718, USA.
authors.forename: MaryClare F
authors.initials: MF
authors.lastname: Rollins
authors.forename: Dana M
authors.initials: DM
authors.lastname: van der Heide
authors.forename: Carla M
authors.initials: CM
authors.lastname: Weisend
authors.forename: Jean A
authors.initials: JA
authors.lastname: Kundert
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Comstock
authors.forename: Elena S
authors.initials: ES
authors.lastname: Suvorova
authors.forename: Mario R
authors.initials: MR
authors.lastname: Capecchi
authors.forename: Gary F
authors.initials: GF
authors.lastname: Merrill
authors.forename: Edward E
authors.initials: EE
authors.lastname: Schmidt
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects / Q000235:genetics; D006498:Hepatectomy; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D006918:Hydroxyurea / Q000494:pharmacology; D008099:Liver / Q000196:embryology / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D008115:Liver Regeneration; D051379:Mice; D008810:Mice, Inbred C57BL; D038081:Organogenesis / Q000235:genetics; D057093:Orphan Nuclear Receptors / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D054481:Thioredoxin Reductase 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: C485736:Nr2e3 protein, mouse; D057093:Orphan Nuclear Receptors; D054481:Thioredoxin Reductase 1; D006918:Hydroxyurea