The peripheral nervous system of the head is derived from cranial ectodermal placodes and neural crest cells. Placodes arise from thickenings in the cranial ectoderm that invaginate or ingress to form sensory ganglia and the paired sense organs. We have combined embryological techniques with array technology to identify genes that are expressed as a consequence of placode induction. As a secondary screen, we used whole mount in situ hybridization to determine the expression of candidate genes in various placodal domains. The results reveal 52 genes that are found in one or more placodes, including the olfactory, trigeminal, and otic placodes. Expression of some of these genes is retained in placodal derivatives. Furthermore, several genes are common to both neural crest and ectodermal placodes. This study presents the first array of candidate genes implicated in placode development, providing numerous new molecular markers for various stages of placode formation. Importantly, the results uncover previously unknown commonalities in genes expressed by multiple placodes and shared properties between placodes and other migratory cells, like neural crest cells.
Bibliographical noteFunding Information:
We would like to thank Anitha Rao for technical support, Titus Brown for his help with bioinformatics programs, Dr. Jonathan Rast for answering questions regarding the library screen, and Drs. Vivian Lee and Lisa Taneyhill Ziemer for their critical reviews of the manuscript. This work was funded in part by NIH F32 DE14131-03 and NIH RO1 DE016459-05.
- Neural crest