Effects of thioredoxin reductase-1 deletion on embryogenesis and transcriptome

Abstract

Thioredoxin reductases (Txnrd)1 maintain intracellular redox homeostasis in most organisms. Metazoans Txnrds also participate in signal transduction. Mouse embryos homozygous for a targeted null mutation of the txnrd1 gene, encoding the cytosolic thioredoxin reductase, were viable at embryonic day 8.5 (E8.5) but not at E9.5. Histology revealed that txnrd1 −/− cells were capable of proliferation and differentiation; however, mutant embryos were smaller than wild-type littermates and failed to gastrulate. In situ marker gene analyses indicated primitive streak mesoderm did not form. Microarray analyses on E7.5 txnrd −/− and txnrd +/+ littermates showed similar mRNA levels for peroxiredoxins, glutathione reductases, mitochondrial Txnrd2, and most markers of cell proliferation. Conversely, mRNAs encoding sulfiredoxin, IGF-binding protein 1, carbonyl reductase 3, glutamate cysteine ligase, glutathione S-transferases, and metallothioneins were more abundant in mutants. Many gene expression responses mirrored those in thioredoxin reductase 1-null yeast; however mice exhibited a novel response within the peroxiredoxin catalytic cycle. Thus, whereas yeast induce peroxiredoxin mRNAs in response to thioredoxin reductase disruption, mice induced sulfiredoxin mRNA. In summary, Txnrd1 was required for correct patterning of the early embryo and progression to later development. Conserved responses to Txnrd1 disruption likely allowed proliferation and limited differentiation of the mutant embryo cells.

Selenoproteins: Molecular Pathways and Physiological Roles

“…Similar to TR1, multiple TR3 isoforms have been described (352). Both TR1 and TR3 are present in all vertebrates, and knockout of either of them leads to embryonic lethality in mice (29,67,160). The third TR homolog in mammals is thioredoxin/glutathione reductase (TGR, also designated TR2, TxnRd3, and TrxR3).…”

Protein cysteine sulfinic acid reductase (sulfiredoxin) as a regulator of cell proliferation and drug response

“…Based on current sequence databases, Srx appears to be present in eukaryotes and cyanobacteria, whereas homologs of the peroxiredoxin family members have been found in Archeae and Eubacteria. Moreover, functional roles for Srx seem to be different in yeast and mammals (Basu and Koonin, 2005;Bondareva et al, 2007). Oxidative stress can markedly upregulate Srx transcript and protein levels.…”

“…It is apparent that Srx expression patterns are species specific and functionalities may differ. For example, whereas yeast induces peroxiredoxin mRNAs in response to thioredoxin reductase disruption, mice induce Srx as well as other redox relevant mRNAs such as glutamate cysteine ligase, GSTs and metallothioneins (Bondareva et al, 2007). The functions of peroxiredoxins in H 2 O 2 scavenging and signaling require thioredoxin and Srx.…”

DNA Replication in Animal Systems Lacking Thioredoxin Reductase I

“…It was anticipated that all eukaryotic systems might depend primarily on the Trx system to supply electrons to RNR for DNA replication. Consistent with this, mice homozygous for a spontaneous null mutation of the gsr gene showed no defects in growth or DNA replication (Rogers et al, 2004), and mice zygotically homozygous-null for either the txn1 gene encoding cytosolic Trx1 (Matsui et al, 1996) or the txnrd1 gene encoding cytosolic TrxR1 (Bondareva et al, 2007;Jakupoglu et al, 2005), are both embryonic-lethal. From these findings, it was inferred that, in mice under normal conditions, the GSH pathway may be superfluous for replication, yet the cytosolic Trx pathway is critical (Jakupoglu et al, 2005).…”

“…Some recent advances have come from the development of mouse models bearing targeted "conditional" alleles of the gene encoding thioredoxin reductase I (TrxR1, also called Txnrd1 or TR1), which can be disrupted in a cell type-or developmental stage-specific manner. Whereas these models are yielding some exciting insights into the Trx and GSH systems in embryonic development, stress responses, toxicology, cancer, and other processes (Bondareva et al, 2007;Branco et al, 2011;Carvalho et al, 2008;Jakupoglu et al, 2005;Mandal et al, 2010;Rogers et al, 2004;Suvorova et al, 2009;Tipple et al, 2007;Zhang and Lu, 2007), the current treatise will emphasize the interplay of these pathways in supporting DNA replication in animal systems. The enormity of the body of literature on the Trx, GSH, and RNR systems precludes an exhaustive review of these materials, and it is my intention to cover these subjects in only a cursory manner to set the backdrop for understanding these systems in the context of DNA replication in animals.…”