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Fig. 6 Adult gpc4-/- zebrafish lack elongated chondrocytes in the adult and juvenile palatoquadrate cartilage. A, B: Magnification of the adult cartilage band connecting the quadrate and metapterygoid bones. The wild type cartilage (A) has three regions: (1) bone overlapping with adjacent cartilage, (2) elongated chondrocytes parallel to the bone border, and (3) a central region of larger, rounded chondrocytes. In gpc4-/- adults, all three regions are modified (B). There is reduced overlap between bone and cartilage and a thickened bone border (region 1), no strongly elongated chondrocytes (region 2), and darker Alcian Blue staining overall (2 and 3). C, D: Outlines of cells traced from the regions between the dotted lines in A and B, respectively. Note the elongated cell boundaries in wild type region 2, which are absent in gpc4-/- mutants. E, F: The adult defect of chondrocyte organization originates in the early larval palatoquadrate (∼8 mm SL). The elongated cartilage cells present in wild type larvae (E) are rounded in gpc4-/- mutants (F). en, endopterygoid; mpt, metapterygoid; q, quadrate; sy, symplectic. Scale bar = 100 μm.