Dual roles for a chromatin insulator-H2Av axis in the DNA damage response and hematopoietic development in <i>Drosophila</i>

Chromatin insulator proteins regulate genome architecture and maintain genome integrity, yet how insulator function intersects with the DNA damage response and developmental gene regulation remains poorly understood. Here we show that the Drosophila insulator protein Suppressor of Hairy wing [Su(Hw)] and the histone variant H2Av form a functional axis that operates in both contexts. In response to UV and X-ray irradiation, Su(Hw) enrichment at insulator sites increases and Su(Hw) is required for phosphorylation of H2Av, the Drosophila equivalent of vertebrate H2AX, establishing Su(Hw) as a component of the DNA damage response. Simultaneous mutation of the damage-sensing kinases ATR and ATM disrupts normal Su(Hw) chromatin binding dynamics, further linking insulator activity to the DNA damage signaling network. Beyond genome integrity, Su(Hw) and H2Av interact genetically to control larval hematopoiesis: mutation of His2Av produces melanotic masses and reduced lymph glands, phenotypes that are suppressed in a Su(Hw) dose-dependent manner, while double mutants display supernumerary and overgrown lymph gland lobes. Together, these findings establish dual roles for a chromatin insulator-histone variant axis in which Su(Hw) and H2Av interact to regulate both the cellular response to DNA damage and the transcriptional control of lymph gland development in Drosophila.