Fig. 7.

Fig. 7.

Failed sclerotome expansion and early depletion may underlie fin loss in smb mutants. The sclerotome is specified in the somites at ∼20 hpf, and in wild types expands from 22-24 hpf. Later, this compartment gives rise to multiple tissues in the fish trunk. We propose that as development progresses and tissues are formed, this progenitor pool becomes depleted. In smb, impaired expansion of the sclerotome leads to a smaller initial pool of progenitors, which depletes earlier, leaving no cells to build late-forming structures like the posterior region of the anal fin and the dorsal fin.