Rent1, a trans-effector of nonsense-mediated mRNA decay, is essential for mammalian embryonic viability

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.

Nonsense surveillance regulates expression of diverse classes of mammalian transcripts and mutes genomic noise

“…Given the number and diversity of transcripts regulated by NMD, the process has probably been functionally integrated into additional developmental and homeostatic mechanisms. This may explain the unique dependence of mammals on NMD for viability 28 and limit therapeutic strategies based on modulation of the pathway. NMD also mutes a noisy genome and may thus provide tolerance for nonproductive events that occur through genome evolution.…”

Caspases shutdown nonsense-mediated mRNA decay during apoptosis

“…In the event of a molecular dysfunction, such as NMD arrest during embryogenesis, apoptosis and eventually embryonic lethality can occur. For instance, the absence of UPF1 in 3.5 days post coitum (dpc) results in blastocysts death by apoptosis, 18 while the lack of SMG1 leads to embryonic death at day 8.5 dpc by apoptosis. 37 However, NMD inhibition in vivo does not always lead to activation of apoptosis.…”

“…16,17 NMD is a necessary component in the development and maintenance of healthy cells and organisms. For example, UPF1 is an essential gene since the inactivation of UPF1 protein leads to an early embryonic death in mouse, 18 thus implicating NMD as a critical proofreading and/or regulatory component in early organismal development. However, the question of whether NMD is required after cells have committed to proceed along a pathway that culminates in cell death has not been investigated.…”

Introns in UTRs: Why we should stop ignoring them

“…Insights & Perspectives ..... complete embryogenesis, with the most prominent defects observed in heart, brain, and hematopoietic development [45,47,73,74]. The neural development program incorporates NMD in at least two important ways, both with widespread effects.…”