Experimental attenuation of Fgf signaling alters regenerative proliferation and growth in a dose-dependent manner. (A-C) Images of 4 dpa fin regenerates (26°C) that were heat-induced once at the indicated temperature and collected and examined for mkp3 expression 5 hours later (violet stain). mkp3 expression is greatest in wild types treated at 38°C (A), less in hsp70:dn-fgfr1 transgenics treated at 37°C (B), and undetectable in transgenics given a strong 38°C induction (C). (D-F) Animals treated in the same way as those in A-C, respectively, were assessed for BrdU incorporation and H3P staining. Blastemal BrdU-labeling density (arrowheads in D) is reduced by the 37°C shock in transgenics (E) and still further by the 38°C shock (F). Brackets in (F) indicate a region of Fgf-dependent proliferation. (G-I) Images of 15 dpa fin regenerates given a daily heat induction; to highlight the extent of regeneration, only the right lobe was amputated. Arrows indicate points of amputation. Wild-type fins induced at 38°C or uninduced transgenic fins regenerated normally (G), those induced at 37°C displayed partial regeneration (H), and those induced at 38°C showed a complete block (I). (J,K) Animals were induced daily at four different temperatures, or had no induction, and regenerative growth was measured at 5, 10, 15 and 20 dpa. Regenerative rates were calculated based on these numbers. A daily heat induction to 37°C nearly halves the rate of regeneration at 5 dpa; daily induction to 38°C blocks regeneration (n=5; * P<0.05, significantly different from no HS, t-test).
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