Scorcelletti, M. | bioRxiv Science

bioRxiv2024

Synergistic DNA and RNA binding of the Hox transcription factor Ultrabithorax coordinates splicing and shapes in vivo homeotic functions

The dual interaction of many transcription factors (TFs) with both DNA and RNA is an underexplored issue that could fundamentally reshape our understanding of gene regulation. We address this central issue by investigating the RNA binding activity of the Drosophila Hox TF Ultrabithorax (Ubx) in alternative splicing and morphogenesis. Relying on molecular and genetic interactions, we uncover a homodimerization-dependent mechanism by which Ubx regulates splicing. Notably, this mechanism enables the decoupling of Ubx-DNA and -RNA binding activity in splicing. We identify a critical residue for Ubx-RNA binding and demonstrate the essential role of Ubx-RNA binding ability for its homeotic functions. Overall, we uncover a unique mechanism for Ubx-mediated splicing and underscore the critical contribution of synergistic DNA/RNA binding for its morphogenetic functions. These findings advance our understanding of co-transcriptional regulation and highlight the significance of TF-DNA/RNA synergistic function in shaping gene regulatory networks in living organisms. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/612310v1_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@6b3f84org.highwire.dtl.DTLVardef@116f353org.highwire.dtl.DTLVardef@1c0ceb4org.highwire.dtl.DTLVardef@142906c_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIUbx homodimerization enables decoupling of DNA- and RNA-dependent splicing regulation C_LIO_LIThe homeodomain K58 amino acid is critical for Ubx-RNA binding ability C_LIO_LIUbx-RNA binding ability is essential for splicing regulation C_LIO_LIDual DNA/RNA binding activities shape Ubx homeotic functions C_LI

molecular biology↗

bioRxiv2023

Divergent evolutionary strategies preempt tissue collision in fly gastrulation

Metazoan development proceeds through a series of morphogenetic events that sculpt body plans and organ structures. In the early embryonic stages, morphogenetic processes involving growth and deformation occur concurrently. Forces generated in one tissue can thus increase mechanical stress in the neighboring tissue, potentially disrupting spatial patterning, morphological robustness, and consequently decreasing organismal fitness. How organisms evolved mechanisms to reduce or release inter-tissue stresses remains poorly understood. Here we combined phylogenetic survey across a whole insect order (Diptera), quantitative live imaging, and functional mechanical perturbation to investigate the evolution of mechanical stress management during epithelial expansions in the gastrulating fly embryos. We find that two distinct cellular mechanisms exist in Diptera to prevent the accumulation of compressive stress that can arise when the expanding head and trunk tissues collide. In Cyclorrhapha, a monophyletic dipteran subgroup including the fruit fly Drosophila melanogaster, the head-trunk boundary undergoes active out-of-plane deformation to form a transient epithelial fold, called the cephalic furrow (CF), which acts as a mechanical sink to preempt head-trunk collision. Genetic or optogenetic elimination of the CF leads to tissue buckling, yielding deleterious effects of axial distortion that likely results from unmitigated release of compressive stress. Non-cyclorrhaphan flies, by contrast, lack CF formation and instead display widespread out-of-plane division in the head, which shortens the duration of its expansion and reduces surface area increase. Reorienting head mitosis in Drosophila from in-plane to out-of-plane partially suppresses the need for epithelial out-of-plane deformation, suggesting that out-of-plane division can act as an alternative mechanical sink to prevent tissue collision. Our data suggest that programs of mechanical stress management can emerge abruptly under selective pressure of inter-tissue mechanical conflict in early embryonic development.

developmental biology↗