Fig. 8.

Working model of the Prdm1a gene regulatory network during pectoral fin development. Prdm1a acts downstream of pectoral fin initiation and tbx5a (Fig. 6A,B), but upstream of induction and Fgf signaling. Prdm1a directly binds to regulatory sequences of and activates fgfr1a (Fig. 7G), allowing Fgf10a to bind (Fig. 6C-G). Fgf10a then activates Fgf8a in the apical fold (Fig. 6H-L), signaling pectoral fin outgrowth and differentiation. Prdm1a also directly binds to putative enhancers and promoter regions of smo (Fig. 7G), a receptor in Shh signaling. shha is expressed in the zone of polarizing activity (Fig. 6Q,R). It is required for anterior/posterior patterning as well as regulating fgf8a expression. Dashed arrows illustrate additional feedback loops that have been demonstrated in mice and/or chick but have not yet been shown in zebrafish. Finally, Prdm1a directly binds to putative enhancers of dlx5a and dlx6a, additional fin outgrowth markers (Fig. 6M-P).