SummaryDNA repair deficiency leads to genome instability and hence human disease. Depletion of the RNA processing factor Y14/RBM8A in cultured cells or Rbm8a haplodeficiency in the developing mouse cortex results in the accumulation of DNA damage. Y14 depletion differentially affected the expression of DNA damage response (DDR) factors and induced R-loops, both of which threaten genomic stability. Immunoprecipitation coupled with mass spectrometry revealed DDR factors as potential Y14-interacting partners. Further results confirmed that Y14 interacts with Ku and several DDR factors in an ATM-dependent manner. Y14 co-fractionated with Ku in chromatin-enriched fractions and further accumulated on chromatin upon DNA damage. Y14 knockdown delayed recruitment of DDR factors to DNA damage sites and formation of γH2AX foci and also led to Ku retention on chromatin. Accordingly, Y14 depletion compromised the efficiency of DNA end joining. Therefore Y14 likely plays a direct role in DNA damage repair via its interaction with DDR factors.

RBM4 promotes differentiation of neuronal progenitor cells and neurite outgrowth of cultured neurons via its role in splicing regulation. In this study, we further explored the role of RBM4 in neuronal differentiation. During neuronal differentiation, energy production shifts from glycolysis to oxidative phosphorylation. We found that the splice isoform change of the metabolic enzyme pyruvate kinase M (PKM) from PKM2 to PKM1 occurs during brain development and is impaired in RBM4-deficient brains. The PKM isoform change could be recapitulated in human mesenchymal stem cells (MSCs) during neuronal induction. Using a PKM minigene, we demonstrated that RBM4 plays a direct role in regulating alternative splicing of PKM. Moreover, RBM4 antagonized the function of the splicing factor PTB and induced the expression of a PTB isoform with attenuated splicing activity in MSCs. Overexpression of RBM4 or PKM1 induced the expression of neuronal genes, increased the mitochondrial respiration capacity in MSCs, and, accordingly, promoted neuronal differentiation. Finally, we demonstrated that RBM4 is induced and is involved in the PKM splicing switch and neuronal gene expression during hypoxiainduced neuronal differentiation. Hence, RBM4 plays an important role in the PKM isoform switch and the change in mitochondrial energy production during neuronal differentiation.KEYWORDS alternative splicing, hypoxia, mesenchymal stem cells, neuronal differentiation, pyruvate kinase M T he splicing regulator RBM4 modulates alternative splicing of a number of transcripts involved in cell differentiation and tumorigenesis (1, 2). Previous studies demonstrated the role of RBM4 in differentiation of muscle and pancreas cells and adipocytes (3-5). We recently reported that RBM4 is also involved in neuronal differentiation of mouse embryonal carcinoma P19 cells and neural progenitor-derived cells (1). RBM4 promotes the expression of Numb splice isoforms that function during neuronal differentiation as well as neurite outgrowth. Mesenchymal stem cells (MSCs) are adult bone marrow stromal cells that can differentiate into a variety of cell types, including neurons, and have potential in regenerative therapy for neurological diseases (6). In this study, we assessed whether RBM4 can also modulate neuronal differentiation of MSCs and explored the underlying mechanism.Cellular energy metabolism undergoes a dynamic change during development. In principle, anabolic glycolysis dominates in embryonic stem cells and permits rapid cell proliferation similar to that in cancer cells (7,8). Most adult stem cells exhibit low glycolysis activity in a quiescent state and undertake active glycolysis while proliferat-

RBM4 modulates alternative exon selection of Numb and up-regulates proneural Mash1 gene expression, possibly via specific Numb isoforms. RBM4 overexpression promotes neuronal cell differentiation. Moreover, RBM4 is essential for neurite outgrowth in primary cortical neurons by modulating specific Numb isoform expression.

This new model successfully recapitulates intestinal hypernociception induced by stress or Giardia. Colonic CCK contributes to visceral hypersensitivity caused by stress, but not by Giardia, partly via NGF-dependent neurite outgrowth.

The RNA-binding motif 4 (RBM4) protein participates in cell differentiation via its role in regulating the expression of tissue-specific or developmentally regulated mRNA splice isoforms. RBM4 is expressed in embryonic brain during development; it is initially enriched in the ventricular zone/subventricular zone and subsequently distributed throughout the cerebral cortex. knockout brain exhibited delayed migration of late-born neurons. Using electroporation, we confirmed that knockdown of RBM4 impaired cortical neuronal migration. RNA immunoprecipitation with high-throughput sequencing identified (), which encodes a critical reelin signaling adaptor, as a potential target of RBM4. knockout embryonic brain showed altered isoform ratios. Overexpression of RBM4 promoted the inclusion of exons 7 and 8 (7/8), whereas its antagonist polypyrimidine tract-binding protein 1 (PTBP1) acted in an opposite manner. RBM4 directly counteracted the effect of PTBP1 on exon 7/8 selection. Finally, we showed that the full-length Dab1, but not exon 7/8-truncated Dab1, rescued neuronal migration defects in RBM4-depleted neurons, indicating that RBM4 plays a role in neuronal migration via modulating the expression of Dab1 splice isoforms. Our findings imply that RBM4 is necessary during brain development and that its deficiency may lead to developmental brain abnormality.