ABSTRACT
The specific molecular determinants that govern progenitor expansion and final compartment size in the myogenic lineage, either during gestation or during regenerative myogenesis, remain largely obscure. Recently, we retrieved d-asb11 from a zebrafish screen designed to identify gene products that are downregulated during embryogenesis upon terminal differentiation and identified it as a potential regulator of compartment size in the ectodermal lineage. A role in mesodermal derivatives remained, however, unexplored. Here we report pan-vertebrate expression of Asb11 in muscle compartments, where it highly specifically localizes to the Pax7(+) muscle satellite cell compartment. Forced expression of d-asb11 impaired terminal differentiation and caused enhanced proliferation in the myogenic progenitor compartment both in in vivo and in vitro model systems. Conversely, introduction of a germline hypomorphic mutation in the zebrafish d-asb11 gene produced premature differentiation of the muscle progenitors and delayed regenerative responses in adult injured muscle. Thus, the expression of d-asb11 is necessary for muscle progenitor expansion, whereas its downregulation marks the onset of terminal differentiation. Hence, we provide evidence that d-asb11 is a principal regulator of embryonic as well as adult regenerative myogenesis.
Subject(s)
Gene Expression Regulation, Developmental , Muscle Development , Regeneration , Suppressor of Cytokine Signaling Proteins/metabolism , Zebrafish Proteins/metabolism , Zebrafish/metabolism , Alleles , Animals , Blastomeres/cytology , Blastomeres/metabolism , Cell Count , Cell Differentiation , Cell Proliferation , Cells, Cultured , Embryo, Nonmammalian/cytology , Embryo, Nonmammalian/metabolism , Germ-Line Mutation , Immunohistochemistry , Mice , Models, Animal , Muscle, Skeletal/cytology , Muscle, Skeletal/injuries , Muscle, Skeletal/metabolism , PAX7 Transcription Factor/genetics , PAX7 Transcription Factor/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Satellite Cells, Skeletal Muscle/cytology , Satellite Cells, Skeletal Muscle/metabolism , Suppressor of Cytokine Signaling Proteins/genetics , Transfection , Zebrafish/embryology , Zebrafish/genetics , Zebrafish Proteins/geneticsABSTRACT
Interleukin-10 (IL-10) plays an indispensable role in mucosal tolerance by programming dendritic cells (DCs) to induce suppressor Th-cells. We have tested the modulating effect of L. lactis secreting human IL-10 (L. lactis(IL-10)) on DC function in vitro. Monocyte-derived DC incubated with L. lactis(IL-10) induced effector Th-cells that markedly suppressed the proliferation of allogenic Th-cells as compared to L. lactis. This suppressive effect was only seen when DC showed increased CD83 and CD86 expression. Furthermore, enhanced production of IL-10 was measured in both L. lactis(IL-10)-derived DC and Th-cells compared to L. lactis-derived DC and Th-cells. Neutralizing IL-10 during DC-Th-cell interaction and coculturing L. lactis(IL-10)-derived suppressor Th-cells with allogenic Th-cells in a transwell system prevented the induction of suppressor Th-cells. Only 130 pg/mL of bacterial-derived IL-10 and 40 times more exogenously added recombinant human IL-10 were needed during DC priming for the generation of suppressor Th-cells. The spatially restricted delivery of IL-10 by food-grade bacteria is a promising strategy to induce suppressor Th-cells in vivo and to treat inflammatory diseases.
ABSTRACT
ECS (Elongin BC-Cul2/Cul5-SOCS-box protein) ubiquitin ligases recruit substrates to E2 ubiquitin-conjugating enzymes through a SOCS-box protein substrate receptor, an Elongin BC adaptor and a cullin (Cul2 or Cul5) scaffold which interacts with the RING protein. In vitro studies have shown that the conserved amino acid sequence of the cullin box in SOCS-box proteins is required for complex formation and function. However, the in vivo importance of cullin boxes has not been addressed. To explore the biological functions of the cullin box domain of ankyrin repeat and SOCS-box containing protein 11 (d-Asb11), a key mediator of canonical Delta-Notch signaling, we isolated a zebrafish mutant lacking the Cul5 box (Asb11(Cul)). We found that homozygous zebrafish mutants for this allele were defective in Notch signaling as indicated by the impaired expression of Notch target genes. Importantly, asb11(Cul) fish were not capable to degrade the Notch ligand DeltaA during embryogenesis, a process essential for the initiation of Notch signaling during neurogenesis. Accordingly, proper cell fate specification within the neurogenic regions of the zebrafish embryo was impaired. In addition, Asb11(Cul) mRNA was defective in the ability to transactivate a her4::gfp reporter DNA when injected in embryos. Thus, our study reporting the generation and the characterization of a metazoan organism mutant in the conserved cullin binding domain of the SOCS-box demonstrates a hitherto unrecognized importance of the SOCS-box domain for the function of this class of cullin-RING ubiquitin ligases and establishes that the d-Asb11 cullin box is required for both canonical Notch signaling and proper neurogenesis.
Subject(s)
Neurons/metabolism , Receptors, Notch/metabolism , Signal Transduction , Suppressor of Cytokine Signaling Proteins/physiology , Zebrafish Proteins/physiology , Animals , Basic Helix-Loop-Helix Transcription Factors/genetics , Basic Helix-Loop-Helix Transcription Factors/metabolism , Binding Sites/genetics , Cell Proliferation , Cullin Proteins/metabolism , Embryo, Nonmammalian/cytology , Embryo, Nonmammalian/embryology , Embryo, Nonmammalian/metabolism , Gene Expression Regulation, Developmental , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Immunoblotting , In Situ Hybridization , Intracellular Signaling Peptides and Proteins , Membrane Proteins/genetics , Membrane Proteins/metabolism , Microscopy, Confocal , Mutation , Neurons/cytology , Receptors, Notch/genetics , Reverse Transcriptase Polymerase Chain Reaction , Suppressor of Cytokine Signaling Proteins/genetics , Suppressor of Cytokine Signaling Proteins/metabolism , Zebrafish/embryology , Zebrafish/genetics , Zebrafish/metabolism , Zebrafish Proteins/genetics , Zebrafish Proteins/metabolismABSTRACT
In canonical Delta-Notch signalling, expression of Delta activates Notch in neighbouring cells, leading to downregulation of Delta in these cells. This process of lateral inhibition results in selection of either Delta-signalling cells or Notch-signalling cells. Here we show that d-Asb11 is an important mediator of this lateral inhibition. In zebrafish embryos, morpholino oligonucleotide (MO)-mediated knockdown of d-Asb11 caused repression of specific Delta-Notch elements and their transcriptional targets, whereas these were induced when d-Asb11 was misexpressed. d-Asb11 also activated legitimate Notch reporters cell-non-autonomously in vitro and in vivo when co-expressed with a Notch reporter. However, it repressed Notch reporters when expressed in Delta-expressing cells. Consistent with these results, d-Asb11 was able to specifically ubiquitylate and degrade DeltaA both in vitro and in vivo. We conclude that d-Asb11 is a component in the regulation of Delta-Notch signalling, important in fine-tuning the lateral inhibition gradients between DeltaA and Notch through a cell non-autonomous mechanism.
