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Fig. 1 The laser-pointer optical microheater and local hsp70l:GFP transgene induction. (a) Laser pointer light was focused through a lens onto the end of a 13″ long optic fiber that was mounted on a micromanipulator under a stereomicroscope. Inset shows the coated end of the optical fiber (arrow) contacting the trunk of a 72 hpf zebrafish larva mounted in agarose. (b) Close-up view of the laser pointer microheater assembly. (1) Variable power supply (2) 75 mW red beam laser pointer, (3) clamp to depress the laser pointer switch, (4) laser pointer holder, (5) lens, (6) post holder, (7) fiber clamp, (8) 50 μm core optical fiber, (9) translation stage. (c) Digital thermometer used to determine the temperature of the laser tip (arrow). Inset shows close-up of the heater tip contacting a k-type thermocouple (black arrow). (d-f) Examples of local transgene activation in Tg(hsp70l:GFP) embryos, lateral views of the trunk (see A inset). Somitic tissue was heated for 25 minutes using different sized fiber tips calibrated to 41°C. Insets show different sized tips over a micrometer. (d) GFP expressing muscle fibers (arrows) in a 36 hpf embryo 4 hours after heat shock (120 μm diameter (50 μm core) optical fiber tip). (e) GFP expressing cells (arrow) in a 24 hpf embryo 4 hours after heat shock using a 50 μm diameter tip. (f) GFP expression in a few lateral cells of a 24 hpf embryo 4 hours after local heat shock using a 30 μm diameter tip. (g) Mock treatment (no laser light) in the region of somite 9 (left inset) did not activate gene expression. Local heat shock in the region of somite 12 (right inset) in the same embryo activated transgene expression in somites 12 and 13 (arrow). Scale bars: d-f, 100 μm; g, 50 μm.