Autonomous function of <i>Antennapedia</i> in adult muscle precursors directly connects Hox genes to adult muscle development

The evolutionarily conserved Hox genes define segment identities along the anterior-posterior axis and are expressed in most cell types within each segment, performing specific functions tailored to cellular needs. It has been suggested previously that Drosophila adult flight muscles in the second thoracic segment (T2) develop without direct Hox gene input, relying instead on ectodermal signals to shape their identity. However, our research, leveraging single-cell transcriptomics of Drosophila wing discs and Hox perturbation experiments using CRISPR technology and gain-of-function assays, unveiled a more intricate regulatory landscape. We found that the Hox protein Antennapedia (Antp) is essential for adult flight muscle development, acting in two crucial ways: by regulating the cell cycle rate of adult muscle precursors (AMPs) through repression of proliferation genes, and by guiding flight muscle fate via regulation of Hedgehog (Hh) signalling during cell fate establishment. Antp, along with its co-factor Apterous (Ap), directly interacts with the patched (ptc) locus to control its expression in AMPs. These findings challenge the notion of T2 as a 'Hox-free' zone, highlighting the indispensable role of low-level Antp expression in adult muscle development.