Transcriptomes in avian and mammalian brains: tackling evolutionary debates

“The thorniest problem” in comparative neurobiology is the identification of the particular brain region of birds and reptiles that corresponds to the neocortex, a structure unique to mammals. Anatomical, hodological, embryological and gene expression data (based on few select genes) provide conflicting answers. Studies of embryonic neurogenesis and cell migration have informed homology of developmental territories but the striking similarities in lamination, connectivity and physiological properties observed between adult forms derived from non-corresponding pallial regions remain unexplained. Using RNA-seq, we explored which genes are actively transcribed in these regions of controversial ancestry in a representative bird (chicken) and mammal (mouse) at adult stages.