Grna mutants fail to regenerate the tail fin after resection. (A) Experimental workflow. grna^+/+ or grna^−/− 48 hpf embryos were subjected to caudal tail resection immediately after the end of the notochord. Bright field imaging of the wound was taken every 24 hours for 3 days (72 hpw, equivalent to 120 hpf). (B) Representative images of tail fins from grna^+/+ (top panel) or grna^−/− (bottom panel) larvae at the indicated times. Black lines indicate where the tail fins were resected. (C) Quantification of the regenerated tail fin area of grna^+/+ (n = 5) and grna^−/− (n = 5) larvae from panel B. (D) Schematic representation of signaling occurring during myeloid cell differentiation. Briefly, Pu.1 and Irf8 positively regulate granulin expression, which in turn controls the expression of rgs2 and cebpa for the differentiation of myeloid progenitors into neutrophils expressing mpx and lyz or macrophages (mpeg1 and mfap4). Granulin blocks gata1 expression, inhibiting erythroid development and the expression of the erythroid-related genes alas2, epb41b, and hbae4. Granulin expression levels are indicated in green. Error bars indicate SEM.  **P < .001; ***P < .0001.