ABSTRACT
The ability to detect and degrade transcripts that lack full coding potential is ubiquitous but non-essential in lower eukaryotes, leaving in question the evolutionary basis for complete maintenance of this function. One hypothesis holds that nonsense-mediated RNA decay (NMD) protects the organism by preventing the translation of truncated peptides with dominant negative or deleterious gain-of-function potential. All organisms studied to date that are competent for NMD express a structural homolog of Saccharomyces cerevisiae Upf1p. We have now explored the consequences of loss of NMD function in vertebrates through targeted disruption of the Rent1 gene in murine embryonic stem cells which encodes a mammalian ortholog of Upf1p. Mice heterozygous for the targeted allele showed no apparent phenotypic abnormalities but homozygosity was never observed, demonstrating that Rent1 is essential for embryonic viability. Homozygous targeted embryos show complete loss of NMD and are viable in the pre-implantation period, but resorb shortly after implantation. Furthermore, Rent1(-/-) blastocysts isolated at 3.5 days post-coitum undergo apoptosis in culture following a brief phase of cellular expansion. These data suggest that NMD is essential for mammalian cellular viability and support a critical role for the pathway in the regulated expression of selected physiologic transcripts.
Subject(s)
Codon, Nonsense/physiology , Fetal Viability , Trans-Activators/physiology , Animals , Blastocyst/physiology , Cell Line , Cell Nucleus/ultrastructure , Cell Survival , Cells, Cultured , Codon, Nonsense/genetics , DNA Fragmentation , Germ-Line Mutation , Heterozygote , Mice , Mice, Mutant Strains , Phenotype , Stem Cells/physiology , Trans-Activators/geneticsABSTRACT
All eukaryotes possess the ability to detect and degrade transcripts harboring premature signals for the termination of translation. Despite the ubiquitous nature of nonsense-mediated mRNA decay (NMD) and its demonstrated role in the modulation of phenotypes resulting from selected nonsense alleles, very little is known regarding its basic mechanism or the selective pressure for complete evolutionary conservation of this function. This review will present the current models of NMD that have been generated during the study of model organisms and mammalian cells. The physiological burden of nonsense transcripts and the emerging view that NMD plays a broad and critical role in the regulation of gene expression will also be discussed. Such issues are relevant to the proposal that pharmacological manipulation of NMD will find therapeutic application.
