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

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 (abdominal-A) and Abd-B (Abdominal-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 (Longitudinals lacking), Lolal (Lola like), and Cg (Combgap) repress Abd-B expression, whereas Prg (Piragua) and Svp (Seven up) 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 (Cleavage Under Targets & Release Using Nuclease) analyses identified dTCF/Pangolin 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.