Ribosomal Protein S6 Gene Haploinsufficiency Is Associated with Activation of a p53-Dependent Checkpoint during Gastrulation

Abstract

Nascent ribosome biogenesis is required during cell growth. To gain insight into the importance of this process during mouse oogenesis and embryonic development, we deleted one allele of the ribosomal protein S6 gene in growing oocytes and generated S6-heterozygous embryos. Oogenesis and embryonic development until embryonic day 5.5 (E5.5) were normal. However, inhibition of entry into M phase of the cell cycle and apoptosis became evident post-E5.5 and led to perigastrulation lethality. Genetic inactivation of p53 bypassed this checkpoint and prolonged development until E12.5, when the embryos died, showing decreased expression of D-type cyclins, diminished fetal liver erythropoiesis, and placental defects. Thus, a p53-dependent checkpoint is activated during gastrulation in response to ribosome insufficiency to prevent improper execution of the developmental program.

Global growth deficiencies in mice lacking the ribosomal protein HIP/RPL29

“…In the current report, the absence of HIP/ RPL29 was associated with an apparent 2.5-fold decrease in abundance of RPS6 protein in vitro. A recent report demonstrated that RPS6 protein haploinsufficiency was associated with perigastrulation lethality (Panic et al, 2006). Consistent with these data, RPS6 protein levels were not significantly altered in embryonic tissues lacking HIP/RPL29 protein.…”

“…Primary mouse embryonic fibroblasts (PMEFs) isolated from these mice display enhanced protein synthesis and accelerated cell division to compensate for their small cell size phenotype due to impaired growth (Ruvinsky et al, 2005). More recently, RPS6 heterozygosity was found to be incompatible with embryonic life during gastrulation (Panic et al, 2006). In another study carried out in mice, a spontaneous semidominant and homozygous lethal mutation called Belly spot (Bst) was found to harbor a short deletion mutation in the first intron of the Rpl24 gene, resulting in abnormal splicing and reduced production of RPL24 protein levels (Oliver et al, 2004).…”

Ribosomal Protein S19 Deficiency Leads to Reduced Proliferation and Increased Apoptosis but Does Not Affect Terminal Erythroid Differentiation in a Cell Line Model of Diamond-Blackfan Anemia

“…We speculate that these defects in ribosome biogenesis may induce a state of "nucleolar stress" that indirectly activates the p53 pathway that leads to transcriptional activation of p21 and p27 and prolonged G1 cell cycle phase [37,38]. Induction of this nucleolar stress signal could explain the prolonged G1 cell cycle phenotypes seen in RPS6-and RPL24-deficient mice [39,40], as well as the increased proportion of cells in G0/G1 and accumulation of p21 and p27 in RPS19-deficient cells.…”

Ribosome biogenesis surveillance: probing the ribosomal protein-Mdm2-p53 pathway

“…T-cell-specific homozygous deletion of Rps6 resulted in complete impairment of T-cell development, whereas haploinsufficiency negatively altered T-cell accumulation in the spleen and lymph nodes in a process dependent on p53 (Sulic et al, 2005). Moreover, deletion of a single Rps6 allele in growing oocytes was sufficient to support embryonic development until day E5.5, when p53 was subsequently activated to induce apoptosis, resulting in perigastrulation lethality (Panic et al, 2006). However, although ablation of Rps6 in mouse liver was shown to activate p53 in an Rpl11-dependent manner, it did so in the absence of nucleolar disruption (Fumagalli et al, 2009), suggesting that inherent nucleolar breakdown may not be a necessary requirement for transmitting ribosome biogenesis stress signals to p53.…”