No abstract

Summary Pre-mRNA splicing is regulated by developmental and environmental cues, but little is known about how specific signals are transduced in mammalian cells to regulate this critical gene expression step. Here, we report massive reprogramming of alternative splicing in response to EGF signaling. By blocking individual branches in EGF signaling, we found that Akt activation plays a major role, while other branches, such as the JAK/STAT and ERK pathways, make minor contributions to EGF-induced splicing. Activated Akt next branches to SR protein-specific kinases, rather than mTOR, by inducing SRPK autophosphorylation that switches the splicing kinases from Hsp70- to Hsp90-containing complexes. This leads to enhanced SRPK nuclear translocation and SR protein phosphorylation. These findings reveal a major signal transduction pathway for regulated splicing and place SRPKs in a central position in the pathway, consistent with their reputed roles in a large number of human cancers.

Fig. 2. Rapid induction of interchromosomal interactions by nuclear hormone signaling. (A) 3D-FISH confirmation of E 2 -induced (60 min) TFF1:GREB1 interchromosomal interactions in HMECs with the distribution of loci distances measured (box plot with scatter plot) and quantification of colocalization (bar graph) before and after E 2 treatment. Cells exhibiting mono-or biallelic interactions were combined for comparison with cells showing no colocalization; statistical significance in the bar graph was determined by χ 2 test (**, P < 0.001). (B) 2D FISH confirmation of the interchromosomal interactions in HMEC cells by combining chromosome paint (aqua) and specific DNA probes (green and red). (Upper) Illustrates two examples of mock-treated cells. (Lower) Shows the biallelic interactions/ nuclear reorganization after E 2 treatment for 60 min, exhibiting kissing events between chromosome 21 and chromosome 2. (C) Similar analysis on HMECs, but in this case using 3D FISH to paint chromosome 2 (red) and chromosome 21 (green), showing E 2 -induced chromosome 2-chromosome 21 interaction. Both assays revealed neither chromosome 21-chromosome 21 nor chromosome 2-chromosome 2 interactions in response to E 2. (D) Temporal kinetics of GREB1:TFF1 interactions by 3D FISH in HMECs (**, P < 0.001 by χ 2 ). (E-G) Nuclear microinjection of siRNA against ERα, CBP/p300, or SRC1/pCIP prevented E 2 -induced interchromosomal interactions, counting both mono-and biallelic interactions (**, P < 0.001 by χ 2 ). The injection of siER and siDLC1 were done in the same experiment, sharing the same control group. (H) Nuclear microinjection of siRNA against LSD1, which was shown to be required for estrogen-induced gene expression (22), did not block E 2 -induced interchromosomal interactions. The injection of siLSD1 and SRC1/pCIP were done in a single experiment, sharing the same control group.

Neurons and glia in the vertebrate central nervous system arise in temporally distinct, albeit overlapping, phases. Neurons are generated first followed by astrocytes and oligodendrocytes from common progenitor cells. Increasing evidence indicates that axon-derived signals spatiotemporally modulate oligodendrocyte maturation and myelin formation. Our previous observations demonstrate that F3/contactin is a functional ligand of Notch during oligodendrocyte maturation, revealing the existence of another group of Notch ligands. Here, we establish that NB-3, a member of the F3/contactin family, acts as a novel Notch ligand to participate in oligodendrocyte generation. NB-3 triggers nuclear translocation of the Notch intracellular domain and promotes oligodendrogliogenesis from progenitor cells and differentiation of oligodendrocyte precursor cells via Deltex1. In primary oligodendrocytes, NB-3 increases myelin-associated glycoprotein transcripts. Thus, the NB-3/Notch signaling pathway may prove to be a molecular handle to treat demyelinating diseases. Neural progenitor cells (NPCs)1 are self-renewing multipotent cells that can give rise to all types of neural cells, namely neurons, oligodendrocytes (OLs), and astrocytes. Increasing evidence suggests that this fate commitment of NPCs requires molecular cues provided by extracellular molecules and intrinsic signaling involving various transcription factors (1, 2). Our recent study (3) has demonstrated that the F3/Notch signaling pathway via Deltex1 (DTX1) promotes oligodendrocyte precursor cell (OPC) differentiation into oligodendrocytes (OLs) and up-regulates myelin-associated glycoprotein (MAG) expression in both primary OLs and OLN-93 cells, an OL cell line.

No abstract

While liganded nuclear receptors are established to regulate Pol II-dependent transcription units, their role in regulating Pol III-transcribed DNA repeats remains largely unknown. Here, we report that ~2–3% of the ~100,000–200,000 human DR2 Alu repeats in proximity to activated Pol II transcription units are activated by retinoic acid receptor in human embryonic stem cells to generate Pol III-dependent RNAs. These transcripts are processed, initially in a DICER-dependent fashion, into small RNAs (~28–65nt.), referred to as riRNAs, that cause degradation of a subset of critical stem cell mRNAs, including Nanog, modulating exit from the proliferative stem cell state. This regulation requires AGO3-dependent accumulation of processed DR2 Alu transcripts and subsequent recruitment of AGO3-associated decapping complexes to the target mRNA. In this way, the RAR and Pol III-dependent DR2 Alu transcriptional events in stem cells functionally complement the Pol II-dependent neuronal transcriptional program.

Increasing evidence has shown that the Notch signalling pathway regulates oligodendrogliogenesis. Upon binding to classical Delta/Serrate/Lag-2 ligands, Notch signalling promotes generation of oligodendrocyte precursor cells while inhibiting their further differentiation into myelinating oligodendrocytes. In our recent studies, we have found that two neural cell adhesion molecules, F3/contactin and NB-3 interact with Notch receptors and promote oligodendrocyte development. Remarkably, all these F3 and NB-3/Notch cascade-related events required Deltex1 as the intermediate element. Experiments using several animal models further imply the function of F3/Notch signalling in vivo, which designates Notch signalling as a ligand-dependent, multipotential cascade involved in oligodendrocyte development.

Shortly after publication of this paper, concerns were brought to the authors' attention regarding similarities in the plots quantifying the interchromosomal distances derived from FISH images. The authors undertook extensive investigation and confirmed a series of data duplications and transversions in the original dataset. Although they continue to believe the central conclusions of the paper based on confirmation and further studies by other scientists in their laboratories, given the extent of errors in the published plots, the authors feel compelled to retract the paper. They apologize to the scientific community for any confusion these errors may have caused and wish to sincerely thank the colleagues who communicated this problem to them in recent weeks.