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Fig. 8. Model of RA signaling during pectoral fin development. Expression of
aldh1a2 during the formation of somites 2-7 is required to induce
tbx5 in the lateral plate mesoderm (lpm) between 12-13 hpf, after
which RA signaling is maintained from ventral somites flanking the pectoral
fin field to establish a prepattern of posterior fates in the developing fin
buds. Arrows indicate genetic interactions between somite-derived RA and fin
mesenchyme, and are based on this and previous studies
(Neumann et al., 1999;
Yelon et al., 2000).