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Hypobranchial placodes in Xenopus laevis give rise to hypobranchial ganglia, a novel type of cranial ganglia


Recently, a novel type of neurogenic placode was described in anurans. These hypobranchial placodes were recognized as ectodermal thickenings situated ventral to the second and third pharyngeal pouch that give rise to neurons of unknown fate. Here, the development of hypobranchial placodes in Xenopus laevis is described in more detail using in situ hybridization and immunohistochemistry for various placodal (Six1, Eya1) and neurogenic (NGNR-1, NeuroD, Delta-1, Hu, acetylated tubulin) markers. Moreover, the fate of hypobranchial placodes was determined by analyzing tadpoles that had received orthotopic grafts of ventral branchial arch ectoderm at embryonic stages from donor embryos injected with the lineage tracer green fluorescent protein. The neurogenic epibranchial and hypobranchial placodes are shown to develop in certain subregions of a broader branchial placodal area as defined by Six1 and Eya1 expression, viz., adjacent to the dorsal and ventral tip of the pharyngeal pouches, respectively. Grafting experiments show that each of the two hypobranchial placodes gives rise to a small and previously undescribed hypobranchial ganglion (identified by its immunoreactivity for the neuron-specific Hu protein) of unknown function located in the ventral branchial arch region. No contributions of hypobranchial placodes to any other ganglia (including cardiac ganglia and the ganglia of branchiomeric nerves located dorsal to pharyngeal pouches) were found.

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I thank Marion Ahlbrecht and Katja Ahrens for technical support, Mario Wullimann for critical reading of the manuscript, and Gerhard Roth and Dietmar Blohm for providing lab space. Sally Moody and Chris Kintner kindly provided plasmids to obtain in situ probes for Six1, NeuroD, NGNR-1, and Delta1. The pCMTEGFP plasmid was a kind gift from Doris Wedlich. The 9E10 antibody developed by J.M. Bishop was obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by The University of Iowa, Department of Biological Science, Iowa City, IA 52242, USA.

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Correspondence to Gerhard Schlosser.

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This research was supported by grants 450/5-1 and 450/5-3 from the German Science Foundation

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Schlosser, G. Hypobranchial placodes in Xenopus laevis give rise to hypobranchial ganglia, a novel type of cranial ganglia. Cell Tissue Res 312, 21–29 (2003).

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  • Epibranchial placodes
  • Neurogenesis
  • Cranial nerves
  • NeuroD, Eya1
  • Xenopus laevis (Anura)