Combined loss of prrx1a and prrx1b results in ectopic dorsal cartilage.
(A-F) prrx1a; prrx1b mutants develop ectopic cartilage, both from the dorsal-medial surface of Pq (black arrow) and connecting Pq to the otic cartilage (magenta arrowheads), as well as fusions of Hm to the otic cartilage (yellow arrows). The entopterygoid dermal bone (black arrowhead) that normally forms along the dorsal-medial surface of the Pq is also lost. (G, H) In prrx1a; prrx1b mutants at 36 hpf, barx1 (magenta) is ectopically upregulated in the dorsal first arch (white arrowhead), along the dorsal border of the second arch (white bracket, compare with G), and in the posterior dorsal second arch (white arrow). (I, J) By 48 hpf in prrx1a; prrx1b mutants, ectopic barx1 expression is no longer evident in the posterior first arch (open white arrowhead), and the second arch barx1+ domain is slightly larger than the sibling control (white arrow). sox9a expression (green) is largely normal at this stage in prrx1a; prrx1b mutants. Scale bars in B and F = 100 μm; scale bars in H and J = 20 μm.