Developmental patterning of adipose tissue by <i>abd-A</i> and <i>Abd-B</i> homeotic genes in <i>Drosophila melanogaster</i>

The Bithorax Complex (BX-C) homeobox proteins specify segmental identities along the anterior-posterior axis during embryogenesis in Drosophila. Differential expression of the BX-C genes abd-A and Abd-B distinguishes abdominal from thoracic adipocytes, but the mechanisms underlying this heterogeneity remain unknown. Here, we identify cis-regulatory elements (CREs) and DNA-binding proteins that regulate abdomen-specific expression of abd-A and Abd-B in the larval fat body. Fine-mapping analyses identified a 627-bp CRE within the Abd-B locus and an approximately 6-kb CRE within the abd-A locus that are sufficient to drive region-specific expression. Yeast one-hybrid screening and functional analyses revealed that Lola, Lolal, and Combgap (Cg) repress Abd-B expression, whereas Piragua (Prg) and Seven up (Svp) activate Abd-B transcription. We further show that lola and prg are repressed by Abd-B, whereas lolal and svp are activated by Abd-B, forming a feedback regulatory network. Wnt signaling modulates this network by promoting lola and lolal expression and repressing svp. CUT&RUN analyses identified dTCF/Pan occupancy at the lola, lolal, and svp loci and Abd-B occupancy at the lola and lolal loci, suggesting that a subset of these interactions is direct. Together, these findings define a gene regulatory network that controls Abd-B expression in the larval fat body and provide a molecular mechanism for establishing adipocyte heterogeneity along the anterior-posterior axis.