Modeling of axonal endoplasmic reticulum network by spastic paraplegia proteins

Axons contain a smooth tubular endoplasmic reticulum (ER) network that is thought to be continuous with ER throughout the neuron; the mechanisms that form this axonal network are unknown. Mutations affecting reticulon or REEP proteins, with intramembrane hairpin domains that model ER membranes, cause an axon degenerative disease, hereditary spastic paraplegia (HSP). We show that Drosophila axons have a dynamic axonal ER network, which these proteins help to model. Loss of HSP hairpin proteins causes ER sheet expansion, partial loss of ER from distal motor axons, and occasional discontinuities in axonal ER. Ultrastructural analysis reveals an extensive ER network in axons, which shows larger and fewer tubules in larvae that lack reticulon and REEP proteins, consistent with loss of membrane curvature. Therefore HSP hairpin-containing proteins are required for shaping and continuity of axonal ER, thus suggesting roles for ER modeling in axon maintenance and function.RCUK | Biotechnology and Biological Sciences Research Council (BBSRC): Lu Zhao, Cahir J O'Kane, BB/L021706/1; Wellcome: Martin Stofanko, Cahir J O'Kane, 08136; European Commission (EC): Lu Zhao, Niamh C O'Sullivan, Sophie Zaessinger, Olivier Blard, MCSA fellowships 220851,220874,236777,660516; Yousef Jameel Foundation: Belgin Yalçın; Singapore A*STAR Scholarship: Zi Han Kang, BM/RES/07/005; Cambridge Commonwealth, European and International Trust (Cambridge Commonwealth, European & International Trust): Belgin Yalçın, Anood Sohail; Pakistan Higher Education Council Scholarship: Anood Sohail; Motor Neurone Disease Association (MNDA): Alex L Patto, Studentship 861-792 The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication

The Nanos3-3′UTR Is Required for Germ Cell Specific NANOS3 Expression in Mouse Embryos

BACKGROUND: The regulation of gene expression via a 3' untranslated region (UTR) plays essential roles in the discrimination of the germ cell lineage from somatic cells during embryogenesis. This is fundamental to the continuation of a species. Mouse NANOS3 is an essential protein required for the germ cell maintenance and is specifically expressed in these cells. However, the regulatory mechanisms that restrict the expression of this gene in the germ cells is largely unknown at present. METHODOLOGY/PRINCIPAL FINDINGS: In our current study, we show that differences in the stability of Nanos3 mRNA between germ cells and somatic cells is brought about in a 3'UTR-dependent manner in mouse embryos. Although Nanos3 is transcribed in both cell lineages, it is efficiently translated only in the germ lineage. We also find that the translational suppression of NANOS3 in somatic cells is caused by a 3'UTR-mediated mRNA destabilizing mechanism. Surprisingly, even when under the control of the CAG promoter which induces strong ubiquitous transcription in both germ cells and somatic cells, the addition of the Nanos3-3'UTR sequence to the coding region of exogenous gene was effective in restricting protein expression in germ cells. CONCLUSIONS/SIGNIFICANCE: Our current study thus suggests that Nanos3-3'UTR has an essential role in translational control in the mouse embryo

An apicobasal gradient of Rac activity determines protrusion form and position

Each cell within a polarised epithelial sheet must align and correctly position a wide range of subcellular structures, including actin-based dynamic protrusions. Using in vivo inducible transgenes that can sense or modify Rac activity, we demonstrate an apicobasal gradient of Rac activity that is required to correctly form and position distinct classes of dynamic protrusion along the apicobasal axis of the cell. We show that we can modify the Rac activity gradient in genetic mutants for specific polarity proteins, with consequent changes in protrusion form and position and additionally show, using photoactivatable Rac transgenes, that it is the level of Rac activity that determines protrusion form. Thus, we demonstrate a mechanism by which polarity proteins can spatially regulate Rac activity and the actin cytoskeleton to ensure correct epithelial cell shape and prevent epithelial-to-mesenchymal transitions

Notch inhibits Yorkie activity in Drosophila wing discs.

During development, tissues and organs must coordinate growth and patterning so they reach the right size and shape. During larval stages, a dramatic increase in size and cell number of Drosophila wing imaginal discs is controlled by the action of several signaling pathways. Complex cross-talk between these pathways also pattern these discs to specify different regions with different fates and growth potentials. We show that the Notch signaling pathway is both required and sufficient to inhibit the activity of Yorkie (Yki), the Salvador/Warts/Hippo (SWH) pathway terminal transcription activator, but only in the central regions of the wing disc, where the TEAD factor and Yki partner Scalloped (Sd) is expressed. We show that this cross-talk between the Notch and SWH pathways is mediated, at least in part, by the Notch target and Sd partner Vestigial (Vg). We propose that, by altering the ratios between Yki, Sd and Vg, Notch pathway activation restricts the effects of Yki mediated transcription, therefore contributing to define a zone of low proliferation in the central wing discs

Differential Trypanosome Surface Coat Regulation by a CCCH Protein That Co-Associates with procyclin mRNA cis-Elements

The genome of Trypanosoma brucei is unusual in being regulated almost entirely at the post-transcriptional level. In terms of regulation, the best-studied genes are procyclins, which encode a family of major surface GPI-anchored glycoproteins (EP1, EP2, EP3, GPEET) that show differential expression in the parasite's tsetse-fly vector. Although procyclin mRNA cis-regulatory sequences have provided the paradigm for post-transcriptional control in kinetoplastid parasites, trans-acting regulators of procyclin mRNAs are unidentified, despite intensive effort over 15 years. Here we identify the developmental regulator, TbZFP3, a CCCH-class predicted RNA binding protein, as an isoform-specific regulator of Procyclin surface coat expression in trypanosomes. We demonstrate (i) that endogenous TbZFP3 shows sequence-specific co-precipitation of EP1 and GPEET, but not EP2 and EP3, procyclin mRNA isoforms, (ii) that ectopic overexpression of TbZFP3 does not perturb the mRNA abundance of procyclin transcripts, but rather that (iii) their protein expression is regulated in an isoform-specific manner, as evidenced by mass spectrometric analysis of the Procyclin expression signature in the transgenic cell lines. The TbZFP3 mRNA-protein complex (TbZFP3mRNP) is identified as a trans-regulator of differential surface protein expression in trypanosomes. Moreover, its sequence-specific interactions with procyclin mRNAs are compatible with long-established predictions for Procyclin regulation. Combined with the known association of TbZFP3 with the translational apparatus, this study provides a long-sought missing link between surface protein cis-regulatory signals and the gene expression machinery in trypanosomes. © 2009 Walrad et al

Oskar allows nanos mRNA translation in Drosophila embryos by preventing its deadenylation by Smaug/CCR4.

Anteroposterior patterning of the Drosophilaembryo depends on a gradient of Nanos protein arising from the posterior pole. This gradient results from both nanos mRNA translational repression in the bulk of the embryo and translational activation of nanos mRNA localized at the posterior pole. Two mechanisms of nanos translational repression have been described, at the initiation stepand after this step. Here we identify a novel level of nanos translational control. We show that the Smaug protein bound to thenanos3UTR recruits the deadenylation complex CCR4-NOT, leading to rapid deadenylation and subsequent decay of nanos mRNA.Inhibition of deadenylation causes stabilization of nanos mRNA, ectopic synthesis of Nanos protein and head defects. Therefore, deadenylation is essential for both translational repression and decay of nanos mRNA. We further propose a mechanism for translational activation at the posterior pole. Translation of nanos mRNA at the posterior pole depends on oskar function. We show that Oskar prevents the rapid deadenylation of nanos mRNA by precluding its binding to Smaug, thus leading to its stabilization and translation. This study provides insights into molecular mechanisms of regulated deadenylation by specific proteins and demonstrates its importance in developmen

Research data supporting "Modeling of axonal endoplasmic reticulum network by spastic paraplegia proteins"

The supporting data include sequence analyses, microscopy, electron microscopy, quantitative analyses and reconstructions of images, and statistical analyses, for each figure presented in the paper.Listed in 10.7554/eLife.2388

Viral hijacking of the TENT4–ZCCHC14 complex protects viral RNAs via mixed tailing

© 2020, The Author(s), under exclusive licence to Springer Nature America, Inc. TENT4 enzymes generate ‘mixed tails’ of diverse nucleotides at 3′ ends of RNAs via nontemplated nucleotide addition to protect messenger RNAs from deadenylation. Here we discover extensive mixed tailing in transcripts of hepatitis B virus (HBV) and human cytomegalovirus (HCMV), generated via a similar mechanism exploiting the TENT4–ZCCHC14 complex. TAIL-seq on HBV and HCMV RNAs revealed that TENT4A and TENT4B are responsible for mixed tailing and protection of viral poly(A) tails. We find that the HBV post-transcriptional regulatory element (PRE), specifically the CNGGN-type pentaloop, is critical for TENT4-dependent regulation. HCMV uses a similar pentaloop, an interesting example of convergent evolution. This pentaloop is recognized by the sterile alpha motif domain–containing ZCCHC14 protein, which in turn recruits TENT4. Overall, our study reveals the mechanism of action of PRE, which has been widely used to enhance gene expression, and identifies the TENT4–ZCCHC14 complex as a potential target for antiviral therapeutics11sci