Constitutive activation of jak2a. (A) Amino acid sequence alignment of zebrafish (ZF) jak2a, human (HM) and mouse (MO) jak2, and Drosophila (DP) hopscotch at the JH2 domain. The conserved glutamic residue was marked with an asterisk. (B-E) Injection of jak2a^ca had no effect on gross morphology at 24 hpf (B,C) and 48 hpf (D,E). Each image is representative of at least 3 experiments using more than 10 embryos each time. (F-H) Quantitative analyses showed that jak2a^ca resulted in increased erythropoiesis (F,G) and stat5 phosphorylation (H). The latter was also increased in chordin morphant embryos. Each graph is representative of 3 separate experiments using 20 (F,G) and 30 (H) embryos each time.