Biology subjects

Mlodzik, M.

Publications and source records attributed to Mlodzik, M..

9 recordsLinked to original sources

bioRxiv2025

The Wnt co-receptor Arrow-LRP5/6 is required for Planar Cell Polarity establishment in Drosophila

Wnt-signaling, via {beta}-catenin or the planar cell polarity (PCP) branch, is crucial for development, tissue homeostasis, and linked to many diseases. LRP5/6, arrow (arr) in Drosophila, is the obligate co-receptor in Wnt/{beta}-catenin signaling, with ligand binding to a Frizzled (Fz) family member and LRP5/6 mediating formation of the signalosome complex with Dishevelled (Dsh/Dvl in mammals) and Axin. Current models for Wnt/PCP signaling omit Arr/LRP5/6 and the notion is that it functions without these co-receptors. Here we show that arr/LRP5/6 is positively required in Wnt/PCP signaling. In Drosophila, loss of arr results in PCP mediated cellular orientation defects, aberrant wing hair formation, and loss of polarity, as described for core PCP factors fz, fmi/Celsr, and dsh. In the eye, arr mutant tissue displays cell fate changes in photoreceptors R3/R4 and chirality defects, classical PCP phenotypes. During Wnt/PCP establishment, defects are manifest as reduced levels of Fmi/Celsr and Dsh along with loss of their asymmetric localization. Functional interactions indicate that Fz can recruit Arr, and this potentiates Fz and Dsh function in PCP signaling in all tissues tested. Taken together, our data support an essential Arr/LRP5/6 function in promoting Wnt/Fz-Dsh PCP-complex activity.

developmental biology↗

bioRxiv2025

A novel conserved protein associates with the IFT-A complex to mediate nuclear translocation of β-catenin in Wg/Wnt-signaling

Wingless (Wg)/Wnt signaling is critical throughout development and tissue homeostasis and associated with many disease states. Canonical Wg/Wnt-signaling is mediated by {beta}-catenin (Arm in Drosophila) with IFT-A/Kinesin-2 complex promoting nuclear translocation of {beta}-catenin/Arm upon pathway activation. Although IFT-A is essential for nuclear translocation of {beta}-catenin/Arm, existing data suggests additional proteins are involved in this process. Here, we have identified a novel, evolutionarily conserved protein, Pasovec (Psv), as a critical component required for nuclear {beta}-catenin/Arm localization. We demonstrate that Psv functionally interacts with the IFT-A/Kinesin2 complex and physically associates with IFT140, a core component of IFT-A. The Psv-IFT140 interaction is independent of Wg/Wnt-signaling activation. Importantly, Psv contains a nuclear localization sequence (NLS), which is critical for its own nuclear localization and that of {beta}-catenin/Arm upon Wg/Wnt-signaling activation. Psv with a mutated NLS can act as an inhibitor of Wg/Wnt-signaling. Altogether, this study describes a new factor required for Wg/Wnt-signaling, with its mutant phenotypes resembling wg and {beta}-catenin/arm mutants, that functions during the nuclear translocation process of {beta}-catenin/Arm.

developmental biology↗

bioRxiv2023

Wg/Wnt-signaling induced nuclear translocation of β-catenin is attenuated by a β-catenin peptide through its interaction with IFT-A in development and cancer cells

Wnt/Wingless (Wg) signaling is critical for many developmental patterning processes and linked to diseases, including cancer. Canonical Wnt-signaling is mediated by {beta}-catenin, Armadillo/Arm in Drosophila transducing signal activation to a nuclear response. The IFT-A/Kinesin-2 complex is required to promote the nuclear translocation of {beta}-catenin/Arm. Here, we define a small conserved N-terminal Arm/{beta}-catenin (Arm34-87) peptide, which binds IFT140, as a dominant interference tool to attenuate Wg/Wnt-signaling in vivo. Expression of Arm34-87 is sufficient to antagonize endogenous Wnt/Wg-signaling activation resulting in marked reduction of Wg-signaling target gene expression. This effect is modulated by endogenous levels of Arm and IFT140, with the Arm34-87 effect being enhanced or suppressed, respectively. Arm34-87 thus inhibits Wg/Wnt-signaling by interfering with the nuclear translocation of endogenous Arm/{beta}-catenin. Importantly, this mechanism is conserved in mammals with the equivalent {beta}-catenin34-87 peptide blocking nuclear translocation and pathway activation, including in cancer cells. Our work indicates that Wnt-signaling can be regulated by a defined N-terminal peptide of Arm/{beta}-catenin, and thus this might serve as an entry point for potential therapeutic applications to attenuate Wnt/{beta}-catenin signaling.

cell biology↗

bioRxiv2022

A Van Gogh/Vangl tyrosine phosphorylation switch regulates its interaction with core Planar Cell Polarity factors Prickle and Dishevelled

Epithelial tissues can be polarized along two axes, in addition to apical-basal polarity they are often also polarized within the plane of the epithelium, known as planar cell polarity (PCP). PCP depends upon the conserved Wnt/Frizzled (Fz) signaling factors, including Fz itself and Van Gogh (Vang/Vangl). Here, taking advantage of the complementary features of Drosophila wing and mouse skin PCP establishment, we dissect how Vang phosphorylation on a specific conserved tyrosine residue affects its interaction with two cytoplasmic core PCP factors, Dsh/Dvl and Pk. We demonstrate that Pk and Dsh/Dvl bind to Vang/Vangl in an overlapping region centered around this tyrosine. Strikingly, Vang/Vangl2 phosphorylation promotes its binding to Pk, a key effector of the Vang/Vangl complex, and inhibits its interaction with Dsh/Dvl, and thus phosphorylation of this tyrosine appears to promote the formation of the mature and stable Vang/Vangl-Pk complex during PCP establishment. Interestingly, as our single point mutations allow selective binding inhibition of either Dsh or Pk, we can demonstrate for the first time that Dsh interaction with Vang is physiologically important, as all single point mutations fail to rescue the Vang null mutant wing phenotype.

developmental biology↗

bioRxiv2022

Par3/Bazooka promotes Notch pathway target gene activation

The conserved bazooka (baz/par3) gene acts as a key regulator of asymmetrical cell divisions across the animal kingdom. Associated Par3/Baz-Par6-aPKC protein complexes are also well known for their role in the establishment of apical/basal cell polarity in epithelial cells. Here we define a novel, positive function of Baz/Par3 in the Notch pathway. Using Drosophila wing and eye development, we demonstrate that Baz is required for Notch signaling activity and optimal transcriptional activation of Notch target genes. Baz appears to act independently of aPKC in these contexts, as knockdown of aPKC does not cause Notch loss-of-function phenotypes. Using transgenic Notch constructs, our data positions Baz activity downstream of activating Notch cleavage steps and upstream of Su(H)/CSL transcription factor complex activity on Notch target genes. We demonstrate a biochemical interaction between NICD and Baz, suggesting that Baz is required for NICD activity before NICD binds to Su(H). Taken together, our data define a novel role of the polarity protein Baz/Par3, as a positive and direct regulator of Notch signaling through its interaction with NICD.

developmental biology↗

bioRxiv2022

The conserved Pelado/ZSWIM8 protein regulates actin dynamics by promoting linear actin filament polymerization

Actin filament polymerization can be branched or linear, which depends on the associated regulatory proteins. Competition for Actin monomers occurs between proteins that induce branched or linear actin polymerization. Cell specialization requires the regulation of actin filaments to allow the formation of cell-type specific structures, like cuticular hairs in Drosophila, formed by linear actin filaments. Here, we report the functional analysis of CG34401/pelado, a gene encoding a SWIM domain containing protein, conserved throughout the animal kingdom. Mutant pelado epithelial cells display actin hair elongation defects. This phenotype is reversed by increasing Actin monomer levels or by either pushing linear actin polymerization or reducing branched actin polymerization. The same behavior occurs in hemocytes, where Pelado is essential to induce filopodia, a linear actin-based structure. We further show that this function of Pelado, ZSWIM8 in mammals, is conserved in human cells, where Pelado inhibits branched actin polymerization in a cell migration context. In summary, our data indicate that the function of Pelado/ZSWIM8 in regulating actin cytoskeletal dynamics is conserved, favoring linear actin polymerization at the expense of branched filaments.

cell biology↗

bioRxiv2021

Notch-dependent Abl signaling regulates cell motility during ommatidial rotation in Drosophila

A collective cell motility event that occurs during Drosophila eye development, ommatidial rotation (OR), serves as a paradigm for signaling pathway-regulated directed movement of cell clusters. OR is instructed by several signaling events, including the EGFR and Notch pathways, and planar cell polarity (PCP) signaling, all of which are associated with photoreceptor R3 and R4 specification and differentiation. Here, we show that Abl kinase negatively regulates ommatidial rotation through its activity in the R3/R4 pair. Interestingly in wild-type, Abl is localized to apical junctional regions in R4 but not in R3 during OR, and this apical enrichment requires Notch signaling. We further demonstrate that Abl and Notch genetically interact during OR, and Abl co-immunoprecipitates in complexes with Notch in the developing eye disc. Perturbations of Abl interfere with adherens junction dynamics of the ommatidial preclusters, which are critical for the OR process. Taken together, our data suggest a model in which Abl kinase acts directly downstream of the Notch receptor in R4 to fine-tune OR via its input into adherens junction complexes.

developmental biology↗

bioRxiv2019

Notch signaling coordinates ommatidial rotation in the Drosophila eye via transcriptional regulation of the EGF-Receptor ligand Argos

In all metazoans, a small number of evolutionarily conserved signaling pathways are reiteratively used during development to orchestrate critical patterning and morphogenetic processes. Among these, Notch (N) signaling is essential for most aspects of tissue patterning where it mediates the communication between adjacent cells to control cell fate specification. In Drosophila, Notch signaling is required for several features of eye development, including the R3/R4 cell fate choice and R7 specification. Here we show that hypomorphic alleles of Notch - belonging to the Nfacet class - reveal a novel phenotype: while photoreceptor specification in the mutant ommatidia is largely normal, defects are observed in ommatidial rotation (OR), a planar cell polarity (PCP)-mediated morphogenetic cell motility process. We demonstrate that during OR Notch signaling is specifically required in the R4 photoreceptor to upregulate the transcription of argos (aos), an inhibitory ligand to the EGFR, to fine-tune the activity of Egfr signaling. Consistently, the loss-of-function defects of Nfacet alleles and EGFR-signaling pathway mutants are largely indistinguishable. A Notch-regulated aos enhancer confers R4 specific expression arguing that aos is directly regulated by Notch signaling in this context via Su(H)- Mam dependent transcription.

developmental biology↗

bioRxiv2019

Regulation of Numb during planar cell polarity establishment in the Drosophila eye

The establishment of planar cell polarity (PCP) in the Drosophila eye requires correct specification of the R3/R4 pair of photoreceptor cells, determined by a Frizzled mediated signaling event that specifies R3 and induces Delta to activate Notch signaling in the neighboring cell, specifying it as R4. Here, we investigated the role of the Notch signaling negative regulator Numb in the specification of R3/R4 fates and PCP establishment in the Drosophila eye. We observed that Numb is transiently upregulated in R3 at the time of R3/R4 specification. This regulation of Numb levels in developing photoreceptors occurs at the post-transcriptional level and is dependent on Dishevelled, an effector of Frizzled signaling, and Lethal Giant Larva. We detected PCP defects in cells homozygous for numb15, but these defects were due to a loss of function mutation in fat (fatQ805*) being present in the numb15 chromosome. However, mosaic overexpression of Numb in R4 precursors (only) caused PCP defects and numb loss-of-function had a modifying effect on the defects found in a hypomorphic dishevelled mutation. Our results suggest that Numb levels are upregulated to reinforce the bias of Notch signaling activation in the R3/R4 pair, two post-mitotic cells that are not specified by asymmetric cell division.

developmental biology↗