Samir Merabet

The spatial organization of the genome within the nucleus is critical for gene regulation, yet the mechanisms by which transcription factors (TFs) orchestrate this process remain poorly understood. Here, we demonstrate that the Drosophila Hox protein Ultrabithorax (Ubx) represses autophagy-related ( atg ) genes by tethering their loci to the nuclear periphery. This repressive activity relies on the interaction with the nuclear lamina component Lamin-C (LamC). Furthermore, we identify that DNA-binding of Ubx is determinant for both the physical interaction with nucleoplasmic LamC and the repression of atg genes in vivo. Together, our findings reveal a mechanism whereby a Hox TF functions as a spatial anchor, positioning target genes within a LamC-rich nuclear compartment to ensure efficient transcriptional repression.

In March 2026 happened a two-days’ workshop in the historical guest house of the University of Heidelberg, with the participation of 18 professors and researchers from US and Europe. The workshop was entitled “HOX- and TALE transcription factors: From developmental regulatory networks to disease states”, which recalled previous workshops organized under the European COST action between 2010 and 2020. HOX- and TALE-homeodomain (HD) family proteins are highly conserved developmental transcription factors (TFs) that were originally characterized as major instructors providing spatial-temporal coordinates along the antero-posterior axis in bilaterian embryos. HOX and TALE are also known to play a number of additional functions during embryogenesis, as well as during the adult life. Not surprisingly, several diseases and malformations result from the aberrant expression or function of HOX- and/or TALE-encoding genes in human.The workshop revealed novel functional and molecular aspects of HOX and TALE in the context of different animal model systems and regulatory pathways. It also illustrated the power of most recent technologies associated with dedicated bioinformatics tools in deciphering HOX/TALE molecular complexity at an unprecedented level in vivo. Time was dedicated for stimulating discussions and the workshop was also a good opportunity to put together seniors and more junior/new comers in the HOX/TALE field. Over these two days, the HOX/TALE community not only demonstrated its remarkable dynamism but also raised key questions that are sure to inspire exciting research for years to come

A number of human diseases results from abnormal protein-protein interactions (PPIs) involving key regulatory proteins. Therefore, an important strategy in therapeutics consists in developing inhibitory molecules that should ideally be specific for the aberrant PPI. In this context, it is critical to evaluate the number of PPIs that could be affected by the candidate molecule and to analyze the inhibitory potential before and after the formation of the PPI. Surprisingly, these two molecular aspects are rarely considered, due to a lack of appropriate methodological approaches. In this study, we present a novel methodology that captures drug-sensitive PPIs by considering drug-induced cellular functions in live cell conditions. As a proof-of-concept, we identified interactions of the human core signaling protein ERK1 that are specifically affected by two different inhibitory molecules. In addition, we used a complementary set of innovative tools that allowed visualizing the inhibitory effect on ERK1/cofactor protein complexes after their assembly in living cells. Overall, our work establishes a unique methodological approach for deciphering drug activity for potentially any target bait protein of interest.

Pioneer transcription factors have the unique ability to open chromatin at enhancers to implement new cell fates. They also provide epigenetic memory through demethylation of enhancer DNA, but the underlying mechanisms remain unclear. We now show that the pioneer paired box 7 (PAX7) triggers DNA demethylation using two replication-dependent mechanisms, including direct PAX7 interaction with the E3 ubiquitin-protein ligase (UHRF1)-DNA methyltransferase 1 (DNMT1) complex that is responsible for DNA methylation maintenance. PAX7 binds to UHRF1 and prevents its interaction with DNMT1, thus blocking activation of its enzyme activity. The ten-eleven translocation DNA dioxygenase (TET) DNA demethylases also contribute to the replication-dependent loss of DNA methylation. Thus, PAX7 hijacks UHRF1 to block activation of DNMT1 after replication, leading to loss of DNA methylation by dilution, and the process is assisted by the action of TET demethylases.

Hox proteins, a sub-group of the homeodomain (HD) transcription factor family, provide positional information for axial patterning in development and evolution. Hox protein functional specificity is reached, at least in part, through interactions with Pbc (Extradenticle (Exd) in Drosophila) and Meis/Prep (Homothorax (Hth) in Drosophila) proteins. Most of our current knowledge of Hox protein specificity stems from the study of anterior and central Hox proteins, identifying the molecular and structural bases for Hox/Pbc/Meis-Prep cooperative action. Posterior Hox class proteins, Abdominal-B (Abd-B) in Drosophila and Hox9-13 in vertebrates, have been comparatively less studied. They strongly diverge from anterior and central class Hox proteins, with a low degree of HD sequence conservation and the absence of a core canonical Pbc interaction motif. Here we explore how Abd-B function interface with that of Exd/Hth using several developmental contexts, studying mutual expression control, functional dependency and intrinsic protein requirements. Results identify cross-regulatory interactions setting relative expression and activity levels required for proper development. They also reveal organ-specific requirement and a binary functional interplay with Exd and Hth, either antagonistic, as previously reported, or synergistic. This highlights context specific use of Exd/Hth, and a similar context specific use of Abd-B intrinsic protein requirements.

Bimolecular Fluorescence Complementation (BiFC) is a powerful molecular imaging method used to visualize protein-protein interactions (PPIs) in living cells or organisms. BiFC is based on the reassociation of hemi-fragments of a monomeric fluorescent protein upon spatial proximity. It is compatible with conventional light microscopy, providing a resolution that is constrained by the diffraction of light to around 250 nm. PAmCherry1, a fluorescent protein compatible for BiFC and Photoactivated Localization Microscopy (PALM), allows the analysis of PPIs with nanometer spatial resolution and single molecule sensitivity. To date, this so-called BiFC-PALM approach has only been described in human cell culture. Here, we present a protocol for performing BiFC-PALM in Drosophila larval salivary glands, using the interaction between the Hox protein Ultrabithorax (Ubx) and the generic Hox cofactor Extradenticle (Exd) as a model system.

Protein interaction networks (or interactomes) are formed progressively, each interaction influencing the next one. Accordingly, a same protein will establish different interactomes depending on its first associated cofactor, thereby diversifying its function in the cell. In contrast to their central role, few methods exist to capture interactomes of dimeric protein complexes. Here, we tackle this issue by introducing an innovative method based on bimolecular fluorescence complementation and the specific binding of a nanobody fused to a proximity-dependent biotinylating enzyme. This method was applied to visualize and capture specific interactions of the cytoplasmic TAZ/14-3-3e and nuclear TAZ/TEAD2 complexes, which are major downstream effectors of the Hippo signaling pathway. Among other interactions, we identified SERPINB4 as a novel regulator of TAZ and 14-3-3e proliferative activity in mesenchymal stromal cells. Molecular dissections in living cells revealed the central role of a unique residue of TAZ for recruiting SERPINB4 specifically in the presence of 14-3-3e. Overall, our work demonstrates the importance of considering binary protein complexes for deciphering interactomes and establishes a novel sensitive method in this perspective.

The quest for targeted therapies is critical in the battle against cancer. The RAS/MAP kinase pathway is frequently implicated in neoplasia, with ERK playing a crucial role as the most distal kinase in the RAS signaling cascade. Our previous research demonstrated that the interaction between ERK and MYD88, an adaptor protein in innate immunity, is crucial for RAS-dependent transformation and cancer cell survival. In this study, we examine the biological consequences of disrupting the ERK-MYD88 interaction through the ERK D-recruitment site (DRS), while preserving ERK’s kinase activity. Our results indicate that EI-52, a small-molecule benzimidazole targeting ERK-MYD88 interaction induces an HRI-mediated integrated stress response (ISR), resulting in immunogenic apoptosis specific to cancer cells. Additionally, EI-52 exhibits anti-tumor efficacy in patient-derived tumors and induces an anti-tumor T cell response in mice in vivo. These findings suggest that inhibiting the ERK-MYD88 interaction may be a promising therapeutic approach in cancer treatment.