Fig. 4 ErbB2 and ErbB3 are required for regeneration. (A) Two zygotic recessive regeneration mutants, kitzelig and hypersensitive, have been identified from a bench mutagenesis screen performed in zebrafish larva. DIC images clearly show that the caudal fin does not regenerate upon amputation on the homozygous mutants after 3 days post-injury (3 dpi). The amputation plane can be identified as the point where the notochord ends abruptly. In the middle and lower panels the amputation plane is marked with a red arrowhead. In contrast, homozygous mutants for a null allele of sox10/colorless do regenerate. The right hand panels are larger magnifications of the left panels. (B) kitzelig and hypersensitive carry mutations on the EGFR members ErbB2 and ErbB3, respectively. FM 4-64 staining of neuromasts (red) of hps larvae at 7 dpf shows strongly increased number of neuromast when compared to wild-type siblings (dorsal view). Both fish carry a FoxD3GFP transgene that labels neural crest derivatives (green). To the right a close up dorsal view of trunk shows neuromast hair cells protruding from every myotome in hps larvae. (C) Mapping placed hps on LG23 with tight linkage to a recently characterized erbB3 homologue. Sequencing confirmed the presence of nonsense mutations in three alleles (plots) and block-diagram shows the resultant truncated proteins (domains: Cysteine-Rich (red), Kinase (green), Furin (blue), Transmembrane (black)). (D) Expression of msxB is affected in erb3 mutants at 3 dpi. Adult fish homozygous for the hps^t21411 allele exhibit a normal pattern of mkp3 expression compared to siblings despite of significant morphological defects on their regenerate. In contrast, the expression of msxB is downregulated in localized areas of homozygous mutants (red arrowheads) compared to controls. These areas exhibit a marked reduction of proliferating progenitor cells as defined by the number of Phospho-HistoneH3 positive cells (see Fig. 8A).