Retroviral lineage analysis reveals dual contribution from ectodermal placodes and neural crest cells to avian olfactory sensory and GnRH neurons.

The origin of the neurons and glia in the olfactory system of vertebrates has been controversial, with different cell types attributed to being of ectodermal placode versus neural crest lineage, depending upon the species. Here, we use replication incompetent avian (RIA) retroviruses to perform prospective cell lineage analysis of either presumptive olfactory placode or neural crest cells during early development of the chick embryo. Surprisingly, the results reveal a dual contribution from both the olfactory placode and neural crest cells to sensory neurons in the nose and Gonadotropin Releasing Hormone (GnRH) neurons migrating to the olfactory bulb. We also confirm that olfactory ensheathing glia are solely derived from the neural crest. Finally, our results show that neural crest cells and olfactory placode cells contribute to p63 positive cells, likely to be basal stem cells of the olfactory epithelium. Taken together, these finding provide evidence for previously unknown contributions of neural crest cells to some cell types in the chick olfactory system and help resolve previous discrepancies in the literature.