Fig. 1. Myod^fh261 mutants have delayed muscle differentiation.

A. Schematic of Myod gene and protein showing the fh261 arginine to stop mutation within the helix-loop-helix domain, which is essential for dimerisation and DNA binding. B. Dual immunodetection of Myod and slow myosin in embryos from a myod^fh261/+ incross, genotyped by sequencing of genomic PCR. Dorsal view, anterior to top. C. In situ mRNA hybridization reveals reduction in myod mRNA in embryos from a myod^fh261/+ incross. Wholemount, anterior to top. D-F. In situ mRNA hybridization for indicated probes on myod^fh261 mutants and their siblings. D. Adaxial slow precursors show reduced myog and smyhc1 at 10s and miR-206 at 15s, but actin mRNA appeared less affected (white arrowheads). Fast muscle precursors had no myog or miR-206 expression at this stage (black arrowheads). Dorsal flatmount, anterior to top. E. eng2a expression is reduced in myod^fh261 mutant in regions of muscle pioneers (black arrowhead) and medial fast fibres (red arrowhead). Lateral wholemount, anterior to left. F. Embryos labelled for fast mylz2 with Fast Red were cryo-sectioned at the region indicated (arrow, left panels). Immunofluorescent detection of Pax3/7 protein revealed increased nuclei in the lateral somite in myod^fh261 mutants (yellow arrowheads). Dorsoventral extent of fast myhz1 mRNA (bracket, right panels) is reduced in myod^fh261 mutants at 24 hpf. Lateral wholemounts, anterior to left. Bars = 100 μm.