Biology subjects

Bienz, M.

Publications and source records attributed to Bienz, M..

5 recordsLinked to original sources

bioRxiv2025

Dishevelled drives Wnt-stimulated disassembly of primary cilia through a unique PDZ-mediated binding mode with Daple and Girdin

Dishevelled is a pivotal cytoplasmic hub protein that transmits Wnt signals to various cytoplasmic effectors to specify cell fates and behaviors during animal development. The molecular mechanisms by which Dishevelled directs Wnt outputs towards {beta}-catenin or other non-canonical effectors remain unclear. Its PDZ domain is dispensable for signaling to {beta}-catenin but essential for multiple non-canonical Wnt responses in Drosophila and vertebrate systems. None of its functionally relevant binding partners are known even though a broad range of PDZ-binding ligands have been identified. Here, we combined proximity labeling with structural and biophysical analysis to discover that Daple and its Girdin-L paralog bear unique extended C-terminal PDZ-binding motifs that bind to the PDZ domain of the main human Dishevelled paralog DVL2 with exceptionally high affinity. Assays in HEK293T cells revealed that deletions of these motifs or their cognate PDZ domain of DVL2 resulted in elongated primary cilia and rendered these cilia unresponsive to Wnt5a-stimulated disassembly following serum starvation. We conclude that an unprecedented molecular interaction between Dishevelled and Daple or Girdin-L underpins the disassembly of these ciliary organelles with universal links to signaling and cell cycle progression. One-sentence summaryThe PDZ domain of Dishevelled engages in unique interactions with the C-termini of Daple or Girdin-L to mediate the disassembly of primary cilia in response to Wnt5a.

cell biology↗

bioRxiv2024

Functional specialization of Arabidopsis VEL polymerization domains in the switch to Polycomb silencing

Cold-induced epigenetic silencing of Arabidopsis FLOWERING LOCUS C (FLC) requires the Polycomb Repressive Complex 2 and accessory proteins VIN3 and VRN5. VIN3 and VRN5 interact via head-to-tail VEL polymerization domains, but how these functionally contribute to the switch to an epigenetically silenced state remains poorly understood. Here, we determine that VIN3 VEL polymerization involves higher order nuclear VIN3 assemblies in vivo, promotes strong chromatin association and efficient H3K27me3 nucleation. However, we also show that the polymerization domains of VIN3 and VRN5 are not equivalent: VRN5 VEL domain is not required for silencing despite its role in physically connecting VIN3 with the PRC2 complex and VRN5 VEL is unable to functionally replace VIN3 VEL in vivo. Both VIN3 and VRN5 homologs are present throughout angiosperm species, suggesting a functional requirement for maintaining different polymerization modalities. This work reveals distinct roles for multifunctional polymerization domains of Polycomb accessory proteins underpinning the onset of epigenetic silencing.

plant biology↗

bioRxiv2023

Distinct accessory roles of Arabidopsis VEL proteins in Polycomb silencing

Polycomb Repressive Complex 2 (PRC2) mediates epigenetic silencing of target genes in animals and plants. In Arabidopsis, PRC2 is required for the cold-induced epigenetic silencing of the FLC floral repressor locus to align flowering with spring. During this process, PRC2 relies on VEL accessory factors, including the constitutively expressed VRN5 and the cold-induced VIN3. The VEL proteins are physically associated with PRC2, but their individual functions remain unclear. Here, we show an intimate association between recombinant VRN5 and multiple components within a reconstituted PRC2, dependent on a compact conformation of VRN5 central domains. Key residues mediating this compact conformation are conserved amongst VRN5 orthologs across the plant kingdom. By contrast, VIN3 interacts with VAL1, a transcriptional repressor that binds directly to FLC. These associations differentially affect their role in H3K27me deposition: both proteins are required for H3K27me3, but only VRN5 is necessary for H3K27me2. Although originally defined as vernalization regulators, VIN3 and VRN5 co-associate with many targets in the Arabidopsis genome that are modified with H3K27me3. Our work, therefore, reveals the distinct accessory roles for VEL proteins in conferring cold-induced silencing on FLC, with broad relevance for PRC2 targets generally.

plant biology↗

bioRxiv2020

Feedback control of Wnt signaling based on histidine cluster co-aggregation between Naked/NKD and Axin

Feedback control is a universal feature of cell signaling pathways. Naked/NKD is a widely conserved feedback regulator of Wnt signaling which controls animal development and tissue homeostasis. Naked/NKD destabilizes Dishevelled, which assembles Wnt signalosomes to inhibit the {beta}-catenin destruction complex via recruitment of Axin. Here, we discover that the molecular mechanism underlying Naked/NKD function relies on its assembly into ultrastable decameric core aggregates via its conserved C-terminal histidine cluster (HisC). HisC aggregation is facilitated by Dishevelled and depends on accumulation of Naked/NKD during prolonged Wnt stimulation. Naked/NKD HisC cores co-aggregate with a conserved histidine cluster within Axin, to destabilize it along with Dishevelled, possibly via the autophagy receptor p62 which binds to HisC aggregates. Consistent with this, attenuated Wnt responses are observed in CRISPR-engineered flies and human epithelial cells whose HisC has been deleted. Thus, HisC aggregation by Naked/NKD provides context-dependent feedback control of prolonged Wnt responses.

cell biology↗

bioRxiv2020

Limited Dishevelled/Axin oligomerization determines efficiency of Wnt/β-catenin signal transduction

In Wnt/{beta}-catenin signaling, the transcriptional coactivator {beta}-catenin is regulated by its phosphorylation in a complex that includes the scaffold protein Axin and associated kinases. Wnt binding to its coreceptors activates the cytosolic effector Dishevelled (Dvl), leading to the recruitment of Axin and the inhibition of {beta}-catenin phosphorylation. This process requires interaction of homologous DIX domains present in Dvl and Axin, but is mechanistically undefined. We show that Dvl DIX forms antiparallel, double-stranded oligomers in vitro, and that Dvl in cells forms oligomers typically <10 molecules at endogenous expression levels. Axin DIX (DAX) forms small single-stranded oligomers, but its self-association is stronger than that of DIX. DAX caps the ends of DIX oligomers, such that a DIX oligomer has at most four DAX binding sites. The relative affinities and stoichiometry of the DIX-DAX interaction provide a mechanism for efficient inhibition of {beta}-catenin phosphorylation upon Axin recruitment to the Wnt receptor complex.

biochemistry↗