title: Initial specification of the epibranchial placode in zebrafish embryos depends on the fibroblast growth factor signal.
abstract: In vertebrates, cranial sensory ganglia are mainly derived from ectodermal placodes, which are focal thickenings at characteristic positions in the embryonic head. Here, we provide the first description of the early development of the epibranchial placode in zebrafish embryos using sox3 as a molecular marker. By the one-somite stage, we saw a pair of single sox3-expressing domains appear lateral to the future hindbrain. The sox3 domain, which is referred to here as the early lateral placode, is segregated during the early phase of segmentation to form a pax2a-positive medial area and a pax2a-negative lateral area. The medial area subsequently developed to form the otic placode, while the lateral area was further segregated along the anteroposterior axis, giving rise to four sox3-positive subdomains by 26 hr postfertilization. Given their spatial relationship with the expression of the markers for the epibranchial ganglion, as well as their positions and temporal changes, we propose that these four domains correspond to the facial, glossopharyngeal, vagal, and posterior lateral line placodes in an anterior-to-posterior order. The expression of sox3 in the early lateral placode was absent in mutants lacking functional fgf8, while implantation of fibroblast growth factor (FGF) beads restored the sox3 expression. Using SU5402, which inhibits the FGF signal, we were able to demonstrate that formation of both the early lateral domains and later epibranchial placodes depends on the FGF signal operating at the beginning of somitogenesis. Together, these data provide evidence for the essential role of FGF signals in the development of the epibranchial placodes.
authors.affiliation: Department of Life Science, Graduate School of Science and Engineering, Saitama University, Sakura-ku, Saitama, Japan. mnikaido@post.saitama-u.ac.jp
authors.forename: Masataka
authors.initials: M
authors.lastname: Nikaido
authors.forename: Kazunao
authors.initials: K
authors.lastname: Doi
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hibi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kikuchi
authors.forename: Kyo
authors.initials: K
authors.lastname: Yamasu
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004475:Ectoderm / Q000502:physiology*; D051524:Fibroblast Growth Factor 8 / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D017950:Ganglia, Sensory / Q000196:embryology*; D006609:High Mobility Group Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D011758:Pyrroles / Q000494:pharmacology; D055748:SOXB1 Transcription Factors; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology*
chemical_list: D004268:DNA-Binding Proteins; C496457:Fgf8 protein, mouse; D006609:High Mobility Group Proteins; D011758:Pyrroles; D055748:SOXB1 Transcription Factors; C105686:SU 5402; C527786:Sox3 protein, mouse; D014157:Transcription Factors; D051524:Fibroblast Growth Factor 8