Activation of Six1 target genes is required for sensory placode formation.
In vertebrates, cranial placodes form crucial parts of the sensory nervous system in the head. All cranial placodes arise from a common territory, the preplacodal region, and are identified by the expression of Six1/4 and Eya1/2 genes, which control different aspects of sensory development in invertebrates as well as vertebrates. While So and Eya can induce ectopic eyes in Drosophila, the ability of their vertebrate homologues to induce placodes in non-placodal ectoderm has not been explored. Here we show that Six1 and Eya2 are involved in ectodermal patterning and cooperate to induce preplacodal gene expression, while repressing neural plate and neural crest fates. However, they are not sufficient to induce ectopic sensory placodes in future epidermis. Activation of Six1 target genes is required for expression of preplacodal genes, for normal placode morphology and for placode-specific Pax protein expression. These findings suggest that unlike in the fly where the Pax6 homologue Eyeless acts upstream of Six and Eya, the regulatory relationships between these genes are reversed in early vertebrate placode development.
Christophorou
Nicolas A D
NA
Department of Craniofacial Development, King's College London, Guy's Campus, Tower Wing Floor 27, London SE1 8RT, UK.
Bailey
Andrew P
AP
Hanson
Sven
S
Streit
Andrea
A
D000818:Animals; D002642:Chick Embryo; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology; D051762:PAX2 Transcription Factor / Q000235:genetics; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000502:physiology
D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D051762:PAX2 Transcription Factor; C497318:PAX2 protein, human; C099236:SIX1 protein, human; C106938:EYA2 protein, human; D017027:Protein Tyrosine Phosphatases