Expression of FGFR1, FGFR2 and FGFR3 during early neural development in the chick embryo.

Studies involving chick embryos have implicated FGFs in neural induction and patterning as well as in other developmental events. Detailed analyses of FGF receptor expression at early stages of neural development have not been reported for the chick embryo and are incomplete for other vertebrate classes. Here we show the expression patterns of three FGF receptors, (FGFR1, FGFR2 and FGFR3) in embryonic stages between gastrulation and limb bud formation, focussing particularly on neural tissues. Between neural induction and neurulation, all three receptors are expressed in the neural plate albeit with distinct and overlapping distributions. During early neuromere formation FGFR1 transcripts are present throughout the neural tube, while transcripts for FGFR2 and FGFR3 become restricted to regions of the diencephalon and spinal cord. A little later, FGFR2 and FGFR3 are additionally expressed in the anterior midbrain and within the hindbrain. During later neuromere development, FGFR1 transcripts become localised to the telencephalon, anterior dorsal diencephalon and throughout the midbrain and hindbrain, whereas FGFR2 mRNA is restricted to dorsal telencephalon, dorsoanterior midbrain and hindbrain. FGFR3 is also expressed in anterior midbrain and hindbrain during this developmental period, and is additionally expressed in the posterior telencephalon, in the pretectum, and at the zona limitans intrathalamica. The observed expression patterns of all three receptors within the hindbrain, including rhombomere boundaries, are complex and dynamic. Expression patterns within the somites, eye, head mesenchyme, branchial arches, limb buds, nephric kidney and pharynx are also described.