The bulldog mutations disrupt the sec24d gene and affect craniofacial development.
(A) The bulldog mutations map to chromosome 7 between markers Z13880 and Z13936. The number of recombinants and the corresponding distances in centiMorgans (cM) are indicated below. The genes in the critical region are listed. (B) Electropherograms of wild-type +/+, heterozygous +/- and bulm421 -/- genomic DNA shows the C→T transition (arrows) that results in an amber stop codon (TAG) in place of glutamine at position 811 (Q811X). (C) Schematic diagram of the Sec24D primary protein structure of wild-type and bulldog mutants. (D) bulm606 and sec24d morphant embryos (3.5 ng sec24d-MO) have reduced head size (red arrows), shorter body length and pectoral fins (blue arrows). Alcian blue staining of the head skeleton in the right panels shows short Meckel′s (red arrows), deformed ceratohyals (black arrows) and kinked pectoral fins (blue arrows) in bulm606 and sec24d morphant embryos compared to wild types. Toluidine blue stained coronal sections of craniofacial cartilage in bulm606 and sec24d morphant embryos demonstrate very low amount of ECM material (purple staining) and abnormal shape and packing density of chondrocytes as compared to wild types, all at 4 dpf. Abbreviation: ch, ceratohyal.