Christophorou Nicolas A D, Bailey Andrew P, Hanson Sven, Streit Andrea
Department of Craniofacial Development, King's College London, Guy's Campus, Tower Wing Floor 27, London SE1 8RT, UK.
Dev Biol. 2009 Dec 15;336(2):327-36. doi: 10.1016/j.ydbio.2009.09.025. Epub 2009 Sep 23.
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.
在脊椎动物中，颅基板形成头部感觉神经系统的关键部分。所有颅基板都起源于一个共同的区域，即基板前区，并通过Six1/4和Eya1/2基因的表达来识别，这些基因控制着无脊椎动物和脊椎动物感觉发育的不同方面。虽然So和Eya能在果蝇中诱导异位眼，但它们在脊椎动物中的同源物在非基板外胚层中诱导基板的能力尚未得到探索。在这里，我们表明Six1和Eya2参与外胚层模式形成，并协同诱导基板前基因表达，同时抑制神经板和神经嵴命运。然而，它们不足以在未来的表皮中诱导异位感觉基板。Six1靶基因的激活对于基板前基因的表达、正常基板形态以及基板特异性Pax蛋白表达是必需的。这些发现表明，与果蝇中Pax6同源物无眼蛋白在Six和Eya上游起作用不同，在早期脊椎动物基板发育中，这些基因之间的调控关系是相反的。
