Abstract The adult zebrafish heart can regenerate after injury, but the earliest gene expression changes that trigger this process remain poorly understood. Here we show that in vivo single-cell RNA metabolic labeling, which marks newly made RNA in individual cells, can capture rapid responses in the adult zebrafish heart after injury. Within the first 6 h, we detect activation of innate immune programs, including Toll-like receptor signaling, in a subset of macrophage-like immune cells. Analysis of a larger single-cell dataset indicates that neutrophils also contribute to this early response. Guided by these data, we show that macrophage-specific inhibition of the Toll-like receptor adaptor MyD88 reduces the pro-inflammatory macrophage response at the injury site and improves early hallmarks of regeneration. Our work establishes RNA metabolic labeling as a useful approach for measuring acute responses in vivo at single-cell resolution and identifies early immune-cell activation as a tunable component of heart regeneration.
Mintcheva et al. (Tue,) studied this question.