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MOLECULAR DISSECTION OF CRANIOFACIAL DEVELOPMENT USING ZEBRAFISH
Pamela C. Yelick1 and
Thomas F. Schilling2
1 The Forsyth Institute, Department of Cytokine Biology, and Harvard-Forsyth Department of Oral Biology, 140 The Fenway, Boston, MA 02115; pyelick{at}forsyth.org,
2 Department of Developmental and Cell Biology, University of California, Irvine, CA 92697
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Figure 1. Craniofacial skeleton of an adult zebrafish. An x-ray of an adult zebrafish reveals segmented pharyngeal arch skeletal elements that closely resemble those of higher vertebrates. Abbreviations: m, mandible; mx, maxilla; n, nasal; ot, otoliths; pa1-5, pharyngeal arches 1-5; pt, pharyngeal teeth; q, quadrate; and sy, symplectic.
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Figure 2. Components and patterning of the zebrafish pharyngeal skeleton. (A) Neural crest cell and mesodermal components of the zebrafish. Elements within a segment are shaded corresponding to: mandibular, 1 (neural crest; mesoderm); hyoid, 2 (neural crest; mesoderm); branchials, 3-7 (neural crest; mesoderm). Schematic representation of early development, mid-somitogenesis, when head segments are first forming in a generalized vertebrate embryo. Neural crest cells migrate ventrally into pharyngeal arches along three separate migratory streams (1-3). By late embryonic stages, each pharyngeal segment is further subdivided into dorsal and ventral regions, with neural crest lying in a cylinder surrounding mesodermal cores and wrapped in epithelia. By larval stages in the zebrafish, each arch contains segment-specific cartilages derived from neural crest and muscles derived from mesoderm. (B) Schematized, larval pattern of zebrafish pharyngeal cartilages. Segment- and cell-type specification of zebrafish neural crest cells. Anterior-posterior origins of pharyngeal neural crest and mesoderm and medio-lateral organization in the mandibular arch (B). Elements within a segment are shaded as marked: mandibular (neural crest; mesoderm); hyoid (neural crest; mesoderm); and branchial (neural crest; mesoderm). Schematic representation of an early zebrafish embryo, mid-somitogenesis, as neural crest begins to migrate. The hindbrain is segmented into rhombomeres (r2-r7). Neural crest cells migrate to join particular regions of mesoderm in particular arches, depending on their segmental origins adjacent to the hindbrain. Schematic of transverse section (in the plane indicated), showing locations of lateral neural crest that forms neuronal and glial fates and medial crest cells that form cartilage and pigment.
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Figure 3. Adult zebrafish pharyngeal teeth. (A) A lateral view of individual pharyngeal teeth displays the pulp cavity (pc), dentin (d), and enameloid (e) surface, which closely resemble those of mammalian teeth. (B) SEM images display the organization of the three rows of ventral (V), mediodorsal (MD), and dorsal (D) rows of adult teeth. Higher magnification (C) reveals organized dentin tubules and enameloid surface. (D) Sagittal section of 11 adult pharyngeal teeth present on one ceratobranchial 5 arch.
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Figure 4. Conserved gene expression in mammalian teeth and zebrafish pharyngeal arches. The expression patterns of genes expressed in developing zebrafish pharyngeal arches are shown.
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Figure 5. Tooth phenotypes in laf/alk8 and snh/bmp7 zebrafish mutants. Wild-type and mutant embryos at 5 and 8 days of age were stained with Quercetin (100 µg/mL, Sigma) for 3 hrs so that developing pharyngeal teeth could be visualized. At 5 days post-fertilization (dpf), age-matched wild-type siblings exhibit 3 teeth on each cb5 cartilage (panel A), while snh/bmp7 mutants exhibit a single tooth (panel B). At 8dpf, wild-type siblings display 3 well-formed teeth on each of the bilateral cb5 cartilages (panel C),while zygotic laf/alk8 mutants exhibit one tooth that has attached to the cb5 cartilage, and another tooth appears arrested in development (panel D).
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Figure 6. Zebrafish craniofacial mutants. Alcian blue staining of 5-day post-fertilization wild-type and Boston mutants m526 and m533 embryos reveals specific distinct pharyngeal arch phenotypes. Ventral views (top panels) and lateral views (bottom panels) are shown.
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Critical Reviews in Oral Biology & Medicine, Vol. 13, No. 4,
308-322 (2002)
DOI: 10.1177/154411130201300402
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