Shivaei, S.; Cheung, K. Y. M.; Yadav, A.; Hurvitz, I. U.; Lee, S.; Revilla, J.; Rabut, C.; Criado-Hidalgo, E.; Zhang, R. J.; Shapiro, M. G.

Ultrasound imaging and acoustic reporter genes provide unique capabilities for in vivo biological imaging by leveraging ultrasound\'s ability to visualize opaque tissues with high spatiotemporal resolution. But until now, the expression of acoustic reporter genes - based on gas vesicle (GV) proteins - has been limited to ex vivo-modified cells due to the complexity of the GV gene cluster, precluding valuable in situ applications. Here, we develop a system capable of introducing GV genes directly into native tissues via stoichiometric multi-AAV delivery. We validate this system in the mouse brain, demonstrating well-tolerated in situ gene expression and repeated ultrasound imaging over more than a month in the same animal. Furthermore, by placing GV genes under the control of immediate early gene promoters, we demonstrate the ability to track in vivo gene expression changes arising from elevated neural activity during epileptic seizures. This work connects ultrasound to in situ transcriptional dynamics happening inside the opaque tissues of living creatures.