Lint‐O cooperates with L(3)mbt in target gene suppression to maintain homeostasis in fly ovary and brainYamamoto‐Matsuda, Hitomi; Miyoshi, Keita; Moritoh, Mai; Yoshitane, Hikari; Fukada, Yoshitaka; Saito, Kuniaki; Yamanaka, Soichiro; Siomi, Mikiko C
doi: 10.15252/embr.202153813pmid: 35993198
Loss‐of‐function mutations in Drosophila lethal(3)malignant brain tumor [l(3)mbt] cause ectopic expression of germline genes and brain tumors. Loss of L(3)mbt function in ovarian somatic cells (OSCs) aberrantly activates germ‐specific piRNA amplification and leads to infertility. However, the underlying mechanism remains unclear. Here, ChIP‐seq for L(3)mbt in cultured OSCs and RNA‐seq before and after L(3)mbt depletion shows that L(3)mbt genomic binding is not necessarily linked to gene regulation and that L(3)mbt controls piRNA pathway genes in multiple ways. Lack of known L(3)mbt co‐repressors, such as Lint‐1, has little effect on the levels of piRNA amplifiers. Identification of L(3)mbt interactors in OSCs and subsequent analysis reveals CG2662 as a novel co‐regulator of L(3)mbt, termed “L(3)mbt interactor in OSCs” (Lint‐O). Most of the L(3)mbt‐bound piRNA amplifier genes are also bound by Lint‐O in a similar fashion. Loss of Lint‐O impacts the levels of piRNA amplifiers, similar to the lack of L(3)mbt. The lint‐O‐deficient flies exhibit female sterility and tumorous brains. Thus, L(3)mbt and its novel co‐suppressor Lint‐O cooperate in suppressing target genes to maintain homeostasis in the ovary and brain.
Jag2b‐Notch3/1b‐mediated neuron‐to‐glia crosstalk controls retinal gliogenesisJin, Mengmeng; Zhang, Hui; Xu, Baijie; Li, Yanan; Qin, Huiwen; Yu, Shuguang; He, Jie
doi: 10.15252/embr.202254922pmid: 36047082
In the developing central nervous systems (CNS), neural progenitor cells generate neurons and glia in sequential order. However, the influence of neurons on glia generation remains elusive. Here, we report that photoreceptor cell‐derived Jag2b is required for Notch‐dependent Müller glia (MG) generation in the developing zebrafish retina. In jab2b−/− mutants, differentiating MGs are re‐specified into lineage‐related bipolar neuron fate at the expense of mature MG. Single‐cell transcriptome analysis and knock‐in animals reveal that jab2b is specifically expressed in crx+‐photoreceptor cells during MG generation. Crx promoter‐driven jag2b, but not other Notch ligands, is sufficient to rescue the loss of MGs observed in jag2b−/− mutants. Furthermore, we observe a severe and moderate decrease in the number of MGs in notch3−/− and notch1b−/− mutants, respectively, and the activation of Notch3 or Notch1b rescues the MG loss in jag2b−/− mutants. Together, our findings reveal that the interaction of Jag2b and Notch3/Notch1b mediates the crosstalk between neurons and glial cells to ensure the irreversible differentiation of MG, providing novel mechanistic insights into the temporal specification of glial cell fate in a developing vertebrate CNS structure.
CDK9 and PP2A regulate RNA polymerase II transcription termination and coupled RNA maturationTellier, Michael; Zaborowska, Justyna; Neve, Jonathan; Nojima, Takayuki; Hester, Svenja; Fournier, Marjorie; Furger, Andre; Murphy, Shona
doi: 10.15252/embr.202154520pmid: 35980303
CDK9 is a kinase critical for the productive transcription of protein‐coding genes by RNA polymerase II (pol II). As part of P‐TEFb, CDK9 phosphorylates the carboxyl‐terminal domain (CTD) of pol II and elongation factors, which allows pol II to elongate past the early elongation checkpoint (EEC) encountered soon after initiation. We show that, in addition to halting pol II at the EEC, loss of CDK9 activity causes premature termination of transcription across the last exon, loss of polyadenylation factors from chromatin, and loss of polyadenylation of nascent transcripts. Inhibition of the phosphatase PP2A abrogates the premature termination and loss of polyadenylation caused by CDK9 inhibition, indicating that this kinase/phosphatase pair regulates transcription elongation and RNA processing at the end of protein‐coding genes. We also confirm the splicing factor SF3B1 as a target of CDK9 and show that SF3B1 in complex with polyadenylation factors is lost from chromatin after CDK9 inhibition. These results emphasize the important roles that CDK9 plays in coupling transcription elongation and termination to RNA maturation downstream of the EEC.
Phytochrome B enhances seed germination tolerance to high temperature by reducing S‐nitrosylation of HFR1Ying, Songbei; Yang, Wenjun; Li, Ping; Hu, Yulan; Lu, Shiyan; Zhou, Yun; Huang, Jinling; Hancock, John T; Hu, Xiangyang
doi: 10.15252/embr.202154371pmid: 36062942
Light and ambient high temperature (HT) have opposite effects on seed germination. Light induces seed germination through activating the photoreceptor phytochrome B (phyB), resulting in the stabilization of the transcription factor HFR1, which in turn sequesters the suppressor PIF1. HT suppresses seed germination and triggers protein S‐nitrosylation. Here, we find that HT suppresses seed germination by inducing the S‐nitrosylation of HFR1 at C164, resulting in its degradation, the release of PIF1, and the activation of PIF1‐targeted SOMNUS (SOM) expression to alter gibberellin (GA) and abscisic acid (ABA) metabolism. Active phyB (phyBY276H) antagonizes HFR1 S‐nitrosylation and degradation by increasing S‐nitrosoglutathione reductase (GSNOR) activity. In line with this, substituting cysteine‐164 of HFR1 with serine (HFR1C164S) abolishes the S‐nitrosylation of HFR1 and decreases the HT‐induced degradation of HFR1. Taken together, our study suggests that HT and phyB antagonistically modulate the S‐nitrosylation level of HFR1 to coordinate seed germination, and provides the possibility to enhance seed thermotolerance through gene‐editing of HFR1.
Structural insights into the assembly and activation of the IL‐27 signaling complexJin, Yibo; Fyfe, Paul K; Gardner, Scott; Wilmes, Stephan; Bubeck, Doryen; Moraga, Ignacio
doi: 10.15252/embr.202255450pmid: 35920255
Interleukin 27 (IL‐27) is a heterodimeric cytokine that elicits potent immunosuppressive responses. Comprised of EBI3 and p28 subunits, IL‐27 binds GP130 and IL‐27Rα receptor chains to activate the JAK/STAT signaling cascade. However, how these receptors recognize IL‐27 and form a complex capable of phosphorylating JAK proteins remains unclear. Here, we used cryo electron microscopy (cryoEM) and AlphaFold modeling to solve the structure of the IL‐27 receptor recognition complex. Our data show how IL‐27 serves as a bridge connecting IL‐27Rα (domains 1–2) with GP130 (domains 1–3) to initiate signaling. While both receptors contact the p28 component of the heterodimeric cytokine, EBI3 stabilizes the complex by binding a positively charged surface of IL‐27Rα and Domain 1 of GP130. We find that assembly of the IL‐27 receptor recognition complex is distinct from both IL‐12 and IL‐6 cytokine families and provides a mechanistic blueprint for tuning IL‐27 pleiotropic actions.