ACTR3B (actin-related protein 3B) is a component of the Arp2/3 complex that regulates actin cytoskeleton organization and branched actin network formation 1. As an ATP-binding protein within this complex, ACTR3B functions together with nucleation-promoting factors to control actin polymerization and is essential for stress fiber formation in fibroblasts 1. The gene plays a critical role in cellular cytoskeletal dynamics, as demonstrated by impaired actin regulation when NSD1-regulated ACTR3B expression is suppressed 1. ACTR3B expression is dysregulated in multiple disease contexts. In colorectal cancer, elevated ACTR3B expression driven by lncRNA AC009022.1 (through miR-497-5p suppression) promotes cell proliferation, migration, and invasion 2. Conversely, ACTR3B expression is downregulated in diffuse large B-cell lymphoma associated with high PD-L1 or IDO1 expression 3. ACTR3B has also been identified as differentially expressed in non-obstructive azoospermia spermatogenic cells 4 and in kidney tissue of female offspring exposed to paternal pre-conceptional unhealthy diet 5. Additionally, ACTR3B functions as a hub gene associated with normal brain aging processes 6, and variants in ACTR3B have been identified in cemento-ossifying fibroma tumors 7 and pregnancy-related complications 8.