Microbial colonization of the infant gastrointestinal tract (GIT) begins at birth, is shaped by the maternal microbiota, and is profoundly altered by antibiotic treatment. Antibiotic treatment of mothers during pregnancy influences colonization of the GIT microbiota of their infants. The role of the GIT microbiota in regulating adaptive immune function against systemic viral infections during infancy remains undefined. We used a mouse model of perinatal antibiotic exposure to examine the effect of GIT microbial dysbiosis on infant CD8+ T cell–mediated antiviral immunity. Maternal antibiotic treatment/treated (MAT) during pregnancy and lactation resulted in profound alterations in the composition of the GIT microbiota in mothers and infants. Streptococcus spp. dominated the GIT microbiota of MAT mothers, whereas Enterococcus faecalis predominated within the MAT infant GIT. MAT infant mice subsequently exhibited increased and accelerated mortality following vaccinia virus infection. Ag-specific IFN-γ–producing CD8+ T cells were reduced in sublethally infected MAT infant mice. MAT CD8+ T cells from uninfected infant mice also demonstrated a reduced capacity to sustain IFN-γ production following in vitro activation. We additionally determined that control infant mice became more susceptible to infection if they were born in an animal facility using stricter standards of hygiene. These data indicate that undisturbed colonization and progression of the GIT microbiota during infancy are necessary to promote robust adaptive antiviral immune responses.

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Edited by Eric R. FearonGlycogen synthase kinase-3 (GSK-3) is a constitutively active, ubiquitously expressed protein kinase that regulates multiple signaling pathways. In vitro kinase assays and genetic and pharmacological manipulations of GSK-3 have identified more than 100 putative GSK-3 substrates in diverse cell types. Many more have been predicted on the basis of a recurrent GSK-3 consensus motif ((pS/pT)XXX(S/T)), but this prediction has not been tested by analyzing the GSK-3 phosphoproteome. Using stable isotope labeling of amino acids in culture (SILAC) and MS techniques to analyze the repertoire of GSK-3-dependent phosphorylation in mouse embryonic stem cells (ESCs), we found that ϳ2.4% of (pS/pT)XXX(S/T) sites are phosphorylated in a GSK-3-dependent manner. A comparison of WT and Gsk3a;Gsk3b knock-out (Gsk3 DKO) ESCs revealed prominent GSK-3-dependent phosphorylation of multiple splicing factors and regulators of RNA biosynthesis as well as proteins that regulate transcription, translation, and cell division. Gsk3 DKO reduced phosphorylation of the splicing factors RBM8A, SRSF9, and PSF as well as the nucleolar proteins NPM1 and PHF6, and recombinant GSK-3␤ phosphorylated these proteins in vitro. RNASeq of WT and Gsk3 DKO ESCs identified ϳ190 genes that are alternatively spliced in a GSK-3-dependent manner, supporting a broad role for GSK-3 in regulating alternative splicing. The MS data also identified posttranscriptional regulation of protein abundance by GSK-3, with ϳ47 proteins (1.4%) whose levels increased and ϳ78 (2.4%) whose levels decreased in the absence of GSK-3. This study provides the first unbiased analysis of the GSK-3 phosphoproteome and strong evidence that GSK-3 broadly regulates alternative splicing. Glycogen synthase kinase-3 (GSK-3)2 is a ubiquitously expressed, highly conserved serine/threonine kinase that plays a central role in multiple signaling pathways, most prominently as an antagonist of insulin/AKT and Wnt/␤-catenin signaling pathways (1). Unlike most protein kinases, GSK-3 is constitutively active and in general is inhibited by upstream signaling. GSK-3 was first identified as a protein kinase that phosphorylates and inhibits glycogen synthase, the rate-limiting enzyme in glycogen synthesis (2) and was later shown to antagonize canonical Wnt signaling (1). However, GSK-3 is now known to regulate a broad range of cellular processes, including cytoskeletal organization, circadian rhythm, cell growth and survival, immune responses, and developmental processes (1).In metazoans, GSK-3 is encoded by two similar genes, Gsk3a and Gsk3b, with 98% amino acid sequence identity in the catalytic domains of mammalian GSK-3␣ and GSK-3␤. The two genes are partially redundant, and mice with complete loss of Gsk3a are viable due to compensation by Gsk3b. However, Gsk3b loss-of-function mutations in mice are embryonic or neonatal lethal (3,4), and the Gsk3a;Gsk3b DKO is lethal in early embryogenesis (5, 6). Furthermore, DKO mouse ESCs maintain expression of pluripotency markers and are unab...

Cells adjust to hypoxic stress within the tumor microenvironment by downregulating energy-consuming processes including translation. To delineate mechanisms of cellular adaptation to hypoxia, we performed RNA-Seq of normoxic and hypoxic head and neck cancer cells. These data revealed a significant down regulation of genes known to regulate RNA processing and splicing. Exon-level analyses classified > 1,000 mRNAs as alternatively spliced under hypoxia and uncovered a unique retained intron (RI) in the master regulator of translation initiation, EIF2B5. Notably, this intron was expressed in solid tumors in a stage-dependent manner. We investigated the biological consequence of this RI and demonstrate that its inclusion creates a premature termination codon (PTC), that leads to a 65kDa truncated protein isoform that opposes full-length eIF2Bε to inhibit global translation. Furthermore, expression of 65kDa eIF2Bε led to increased survival of head and neck cancer cells under hypoxia, providing evidence that this isoform enables cells to adapt to conditions of low oxygen. Additional work to uncover -cis and -trans regulators of EIF2B5 splicing identified several factors that influence intron retention in EIF2B5: a weak splicing potential at the RI, hypoxia-induced expression and binding of the splicing factor SRSF3, and increased binding of total and phospho-Ser2 RNA polymerase II specifically at the intron retained under hypoxia. Altogether, these data reveal differential splicing as a previously uncharacterized mode of translational control under hypoxia and are supported by a model in which hypoxia-induced changes to cotranscriptional processing lead to selective retention of a PTC-containing intron in EIF2B5.

Summary Alternative splicing contributes to gene expression dynamics in many tissues, yet its role in auditory development remains unclear. We performed whole exome sequencing in individuals with sensorineural hearing loss (SNHL) and identified pathogenic mutations in Epithelial Splicing Regulatory Protein 1 (ESRP1). Patient derived iPSCs showed alternative splicing defects that were restored upon repair of an ESRP1 mutant allele. To determine how ESRP1 mutations cause hearing loss we evaluated Esrp1−/− mouse embryos and uncovered alterations in cochlear morphogenesis, auditory hair cell differentiation and cell fate specification. Transcriptome analysis revealed impaired expression and splicing of genes with essential roles in cochlea development and auditory function. Aberrant splicing of Fgfr2 blocked stria vascularis formation due to erroneous ligand usage, which was corrected by reducing Fgf9 gene dosage. These findings implicate mutations in ESRP1 as a cause of SNHL and demonstrate the complex interplay between alternative splicing, inner ear development, and auditory function.