Muscle β1 homologs in zebrafish. A) A phylogenetic tree constructed from β1 subunit sequences of Mus musculus, Xenopus laevis, Torpedo californica, Torpedo marmorata, Takifugu rubripes, and Danio rerio. Zebrafish sequences are shown in red. The presumed location of the fish specific genome duplication is indicated with an arrowhead. B) In situ hybridization of zebrafish β1a and β1b at 24 and 72 hpf. Scale 100 µm. C) Absolute copy number of β1a and β1b transcripts determined by real time PCR of whole larvae at 1, 2, 3, 8, and 21 dpf. Averages and standard deviations are shown. D) β1 clones conjugated to CFP in the III-IV intracellular loop were expressed in zebrafish muscle cells at 2 dpf. CFP signals (top), α-Btx stainings (middle), and merged images (bottom) are shown. Two β1a clones with different CFP insertion sites did not exhibit synaptic localization (left and middle), while the β1b CFP clone showed the signal of CFP overlapping with the α-Btx staining. Scale 50 µm.