A brief, light-triggered pulse of chemokine secretion rapidly enhances cell interactions in vivo in mouse tissue and in zebrafish. (A) Experimental scheme for optogenetic control of chemokine release in mouse tissue. The ear dermis from an anesthetized LysM-GFP mouse was surgically exposed and seeded with HEK293T cells expressing Cxcl2-YFP-2xUVR8. (B) Distribution of Cxcl2-YFP-2xUVR8 before and after PA. (C) Representative images of ear tissue with mouse neutrophils (red) and HEK293T cells (yellow). Arrows indicate contacts between the cells. (D) Number of contacts formed between individual HEK293T cells and neutrophils before and after PA, normalized to number of neutrophils in the field and relative to no PA condition (n = 63 Cxcl2-YFP-2xUVR8-transfected; n = 48 mock GFP-transfected HEK293T cells, pooled data from 2 to 4 250 × 250 μm regions of interest per mouse and at least 3 mice per experimental condition, paired t test). (E) Experimental scheme for optogenetic control of chemokine release in zebrafish. Mock or zebrafish Cxcl8-YFP-UVR8–transfected HEK293T cells were locally transplanted in transgenic mpx:Lifeact-Ruby zebrafish larvae and mounted for imaging and photoactivation. (F) Distribution of Cxcl8-YFP-UVR8 before and after PA. (G) Representative images of zebrafish neutrophils (red) in the area of HEK293T cell implantation (yellow). (H) Number of contacts formed between individual HEK293T cells and neutrophils before and after PA, normalized to number of neutrophils in the field and relative to no PA condition (n = 43 Cxcl8-YFP-UVR8–transfected and n = 18 mock GFP-transfected HEK293T cells, pooled data from 3 larvae in 2 independent experiments, paired t test). Error bars represent standard error of the mean. Scale bar = 25 µm in all images.