Study of the Role of Transvection in the Regulation of Initiators That Determine Activity of the Regulatory Domains of the Drosophila melanogaster Abd-B Gene

The iab-5 domain regulates transcription of the Abdominal-B (Abd-B) gene in A5 and A6 segments throughout Drosophila development. The iab-5 domain contains an initiator, which determines domain activity, and two enhancers that activate Abd-B in the A5 and A6 cuticle cells, which ensures pigmentation of these segments in adult males. In the present study, we demonstrated that deletion of the iab-5 initiator on one chromosome can negatively affect the initiator located on the homologous chromosome. This is reflected in the appearance of unpigmented spots on segment A5 in males. Isolation of the domain by an insulator and deletion of the boundary sequences that recruit Polycomb proteins enhance the effect of transvection, which inactivates initiator activity in trans. Thus, the interaction between initiators located on homologous chromosomes determines the formation of a stable activation signal for the regulatory domain throughout the development of Drosophila.