Zebrafish rbm8a and magoh mutants reveal EJC developmental functions and new 3′UTR intron-containing NMD targets

Abstract

Many post-transcriptional mechanisms operate via mRNA 3 0 UTRs to regulate protein expression, and such controls are crucial for development. We show that homozygous mutations in two zebrafish exon junction complex (EJC) core genes rbm8a and magoh leads to muscle disorganization, neural cell death, and motor neuron outgrowth defects, as well as dysregulation of mRNAs subjected to nonsense-mediated mRNA decay (NMD) due to translation termination � 50 nts upstream of the last exon-exon junction. Intriguingly, we find that EJC-dependent NMD also regulates a subset of transcripts that contain 3 0 UTR introns (3 0 UI) < 50 nts downstream of a stop codon. Some transcripts containing such stop codon-proximal 3 0 UI are also NMD-sensitive in cultured human cells and mouse embryonic stem cells. We identify 167 genes that contain a conserved proximal 3 0 UI in zebrafish, mouse and humans. foxo3b is one such proximal 3 0 UI-containing gene that is upregulated in zebrafish EJC mutant embryos, at both mRNA and protein levels, and loss of foxo3b function in EJC mutant embryos significantly rescues motor axon growth defects. These data are consistent with EJC-dependent NMD regulating foxo3b mRNA to control protein expression during zebrafish development. Our work shows that the EJC is critical for normal zebrafish development and suggests that proximal 3 0 UIs may serve gene regulatory function in vertebrates.

The Y14-p53 regulatory circuit in megakaryocyte differentiation and thrombocytopenia

“…Rbm8a haploinsufficiency impairs mouse cortical development due to reduced numbers of progenitors and neurons and the perturbation of cortical lamination ( Mao et al., 2015 ). Morpholino-mediated knockdown of rbm8a in Danio rerio results in disorganized myofibers and motor axon outgrowth defects ( Gangras et al., 2020 ).…”

Eukaryotic initiation factor 4A3 inhibits Wnt/β-catenin signaling and regulates axis formation in zebrafish embryos

“…In mice, the conditional haploinsufficiency of Eif4a3, Y14 (Rbm8a) or Magoh induces apoptosis and p53 ablation rescues apoptosis in the three EJC mutants (Mao et al, 2016). In addition, loss of Y14 (rbma8) or magoh in zebrafish also leads to the apoptotic phenotype as eif4a3 mutant embryos and morphant embryos (Gangras et al, 2020). Therefore, these data suggested that the apoptosis is likely due to the impairment of the EJC complex.…”

Molecular Insights and Prognosis Associated With RBM8A in Glioblastoma

“…RBM8A is a core component of the exon junction complex (EJC), through which it contributes to the formation and development of the nervous system (McSweeney et al, 2020). RBM8A deficiency leads to muscle disorganization, neuronal cell death, and motor neuron growth defects (Gangras et al, 2020); conversely, increased RBM8A expression leads to increased proliferation of cells in the ventricular and subventricular zones, while decreasing the migration of cells toward the cortical plate (Zou et al, 2015). Differential expression and dysfunction of EJC core proteins have been reported in multiple cancers (Degot et al, 2004;Kahles et al, 2018;Liu et al, 2020).…”