The chick pallium displays divergent expression patterns of chick orthologues of mammalian neocortical deep layer-specific genes

Toshiyuki Fujita, Naoya Aoki, Eiko Fujita, Toshiya Matsushima, Koichi J. Homma, Shinji Yamaguchi
2019 Scientific Reports  
The avian pallium is organised into clusters of neurons and does not have layered structures such as those seen in the mammalian neocortex. The evolutionary relationship between sub-regions of avian pallium and layers of mammalian neocortex remains unclear. One hypothesis, based on the similarities in neural connections of the motor output neurons that project to sub-pallial targets, proposed the cell-type homology between brainstem projection neurons in neocortex layers 5 or 6 (L5/6) and those
more » ... in the avian arcopallium. Recent studies have suggested that gene expression patterns are associated with neural connection patterns, which supports the cell-type homology hypothesis. However, a limited number of genes were used in these studies. Here, we showed that chick orthologues of mammalian L5/6-specific genes, nuclear receptor subfamily 4 group A member 2 and connective tissue growth factor, were strongly expressed in the arcopallium. However, other chick orthologues of L5/6-specific genes were primarily expressed in regions other than the arcopallium. Our results do not fully support the cell-type homology hypothesis. This suggests that the cell types of brainstem projection neurons are not conserved between the avian arcopallium and the mammalian neocortex L5/6. Our findings may help understand the evolution of pallium between birds and mammals.
doi:10.1038/s41598-019-56960-4 pmid:31892722 pmcid:PMC6938507 fatcat:fwzyavmyejghdki5dq67lqavdq