Characterisation of the role and regulation of Ultrabithorax in sculpting fine-scale leg morphology

Abstract

Hox genes are expressed during embryogenesis and determine the regional identity of animal bodies along the antero-posterior axis. However, they also function post-embryonically to sculpt fine-scale morphology. To better understand how Hox genes are integrated into post-embryonic gene regulatory networks, we further analysed the role and regulation of Ultrabithorax (Ubx) during leg development in Drosophila melanogaster. Ubx regulates several aspects of bristle and trichome patterning on the femurs of the second (T2) and third (T3) leg pairs. We found that repression of trichomes in the proximal posterior region of the T2 femur by Ubx is likely mediated by activation of the expression of microRNA-92a and microRNA-92b by this Hox protein. Furthermore, we identified a novel enhancer of Ubx that recapitulates the temporal and regional activity of this gene in T2 and T3 legs. We then used transcription factor (TF) binding motif analysis in regions of accessible chromatin in T2 leg cells to predict and functionally test TFs that may regulate the Ubx leg enhancer. We also tested the role of the Ubx co-factors Homothorax (Hth) and Extradenticle (Exd) in T2 and T3 femurs. We found several TFs that may act upstream or in concert with Ubx to modulate trichome patterning along the proximo-distal axis of developing femurs and that the repression of trichomes also requires Hth and Exd. Taken together our results provide insights into how Ubx is integrated into a post-embryonic gene regulatory network to determine fine-scale leg morphology.

Cis-regulatory modes of Ultrabithorax inactivation in butterfly forewings

“…The Ultrabithorax ( Ubx ) gene encodes a Hox family transcription factor involved in the specification of segment identities in arthropods ( Hughes and Kaufman, 2002 ; Heffer and Pick, 2013 ). In insects, the conserved expression of Ubx in the metathoracic (T3) segment is required for their differentiation from Ubx-free tissues in the mesothorax (T2), and has been a key factor for the specialization of metathoracic serial appendages including T3 legs ( Mahfooz et al, 2007 ; Refki et al, 2014 ; Tomoyasu, 2017 ; Feng et al, 2022 ; Buffry et al, 2023 ) and hindwings or their derivatives ( Tomoyasu, 2017 ; Loker et al, 2021 ). The mechanisms of Ubx segment-specific expression have been intensively studied in D. melanogaster ( Mallo and Alonso, 2013 ; Hajirnis and Mishra, 2021 ), where Hox genes are separated into two genomic loci, the Antennapedia (ANT-C, Antp ) and Bithorax clusters (BX-C).…”

The functional evolution of collembolan Ubx on the regulation of abdominal appendage formation

“…Typically, Hox genes are organized in a cluster on the chromosome and exhibit both spatial and temporal collinearity in their expression patterns (Durston et al, 2011). Dll ( Distal-less ) serves as a marker gene for the appendage primordium in a wide variety of animals (Panganiban et al, 1997), within some groups of pancrustaceans (including crustaceans and hexapods) (Browne & Patel, 2000; Cohen et al, 1991; Jockusch et al, 2004), it acts as a downstream target of Ubx ( Ultrabithorax ) (Buffry et al, 2023; Cohen, 1990; Galant & Carroll, 2002; Gebelein et al, 2002; Palopoli & Patel, 1998; Ronshaugen et al, 2002). In Drosophila melanogaster , the Ubx gene generates six isoforms ( Ib , Ia , IIb , IIa , IVb , IVa ) via alternative splicing events, with variation in the architecture of the linker region between the YPWM motif and homeodomain (HD domain) (Geyer et al, 2015; Passner et al, 1999; Reed et al, 2010).…”

The functional evolution of collembolan Ubx on the regulation of abdominal appendage formation

“…Typically, Hox genes are organized in a cluster on the chromosome and exhibit both spatial and temporal collinearity in their expression patterns (Durston et al, 2011). Within the group of pancrustaceans (including crustaceans and hexapods), Dll (Distal-less) serves as a marker gene for the appendage primordium (Abzhanov & Kaufman, 2000;Cohen et al, 1991;Jockusch et al, 2004;Panganiban et al, 1997) and acts as a downstream target of Ubx (Ultrabithorax) (Buffry et al, 2023;Cohen, 1990;Galant & Carroll, 2002;Gebelein et al, 2002;Palopoli & Patel, 1998). In Drosophila melanogaster, the Ubx gene generates six isoforms (Ib, Ia, IIb, IIa, IVb, IVa) via alternative splicing events, with variation in the architecture of the linker region between the YPWM motif and homeodomain (HD domain) (Geyer et al, 2015;Passner et al, 1999;Reed et al, 2010).…”