EMG1 is essential for mouse pre-implantation embryo development

Abstract

BackgroundEssential for mitotic growth 1 (EMG1) is a highly conserved nucleolar protein identified in yeast to have a critical function in ribosome biogenesis. A mutation in the human EMG1 homolog causes Bowen-Conradi syndrome (BCS), a developmental disorder characterized by severe growth failure and psychomotor retardation leading to death in early childhood. To begin to understand the role of EMG1 in mammalian development, and how its deficiency could lead to Bowen-Conradi syndrome, we have used mouse as a model. The expression of Emg1 during mouse development was examined and mice carrying a null mutation for Emg1 were generated and characterized.ResultsOur studies indicated that Emg1 is broadly expressed during early mouse embryonic development. However, in late embryonic stages and during postnatal development, Emg1 exhibited specific expression patterns. To assess a developmental role for EMG1 in vivo, we exploited a mouse gene-targeting approach. Loss of EMG1 function in mice arrested embryonic development prior to the blastocyst stage. The arrested Emg1-/- embryos exhibited defects in early cell lineage-specification as well as in nucleologenesis. Further, loss of p53, which has been shown to rescue some phenotypes resulting from defects in ribosome biogenesis, failed to rescue the Emg1-/- pre-implantation lethality.ConclusionOur data demonstrate that Emg1 is highly expressed during mouse embryonic development, and essential for mouse pre-implantation development. The absolute requirement for EMG1 in early embryonic development is consistent with its essential role in yeast. Further, our findings also lend support to the previous study that showed Bowen-Conradi syndrome results from a partial EMG1 deficiency. A complete deficiency would not be expected to be compatible with a live birth.

Growth arrest in the ribosomopathy, Bowen–Conradi syndrome, is due to dramatically reduced cell proliferation and a defect in mitotic progression

“…However, the dramatic reduction in the EMG1 level in MEFs may indicate that the effect is more severe in mice than in human BCS patients, as residual protein was readily detected in previous studies of BCS patient lymphoblasts or fibroblasts [2,4,5]. As expected, residual levels of mutant EMG1 were detectable in mice, consistent with a rescue from the preimplantation lethality which results when EMG1 is completely absent [8].…”

“…The results are summarized in Table 1. Contrary to the pre-implantation death in Emg1 null mice [8], Emg1 G/G embryos were found between E8.5 and E12.5, indicating that the level of residual protein function provided by the mutant EMG1 protein was adequate to rescue growth beyond implantation. However, only 10.6% of all embryos were homozygous mutants, significantly below the expected Mendelian proportion of 25% (χ 2 = 22.8, p b 0.0001) ( Table 1, "Embryonic total" row).…”

“…We previously generated an Emg1 null (Emg1 −/− ) mouse by replacing exons 2-6 with a SA-IRES-βgeo cassette [8]. Heterozygotes appeared normal, while a complete deficiency was pre-implantation lethal with growth arrested between embryonic day (E) 2.5 and E3.5.…”

Nepro is localized in the nucleolus and essential for preimplantation development in mice

“…Nepro was essential for the development of preimplantation embryos. Developmental arrest or apoptosis before blastocyst formation has been commonly observed in other knockout or knockdown mouse embryos of nucleolar associated genes, such as Fibrillarin (Newton et al 2003), Surf6 (Romanova et al 2006), Bysl (Adachi et al 2007, Rbm19 (Zhang et al 2008), Emg1 (Wu et al 2010), and Wdr36 (Gallenberger et al 2011).…”

Human diseases of the SSU processome

“…EMG1, termed nucleolar essential protein 1 (Nep1) in yeast, is a member of the SSU processome and is thus necessary for small ribosomal subunit assembly and pre-18S rRNA maturation [40]. As expected, the function of EMG1 is necessary for normal mammalian development, as demonstrated by the pre-implantation lethality for EMG1 null mice [41]. EMG1 is highly conserved throughout archaea and eukaryotes.…”