title: Species differences in early patterning of the avian brain.
abstract: The telencephalon is proportionately larger in parrots than in galliformes (chicken-like birds), whereas the midbrain tectum is proportionately smaller. We here test the hypothesis that the adult species difference in midbrain proportion is due to an evolutionary change in early brain patterning. In particular, we compare the size of the early embryonic midbrain between parakeets (Melopsittacus undulatus) and bobwhite quail (Colinus virgianus) by examining the expression domains of transcription factors Pax6 and Gbx2, which are expressed in the forebrain and hindbrain, respectively. Because these expression domains form rostral and caudal borders with the presumptive midbrain when this region is specified (Hamburger-Hamilton stages 9-11), they allow us to measure and compare the sizes of a molecularly defined presumptive midbrain in the two species. Based on published data from older embryos, we predicted that the molecularly defined midbrain territory is significantly larger in quail than parakeets. Indeed, our data show that normalized midbrain length is 33% greater in quail and that the midbrain to forebrain ratio is 28% greater. This is strong evidence of a significant species difference in early brain patterning.
authors.affiliation: Department of Neurobiology and Behavior, University of California, Irvine (UCI), California 92697, USA. lukemcgowan1@yahoo.com
authors.forename: Luke
authors.initials: L
authors.lastname: McGowan
authors.forename: Eric
authors.initials: E
authors.lastname: Kuo
authors.forename: Arnaud
authors.initials: A
authors.lastname: Martin
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Monuki
authors.forename: Georg
authors.initials: G
authors.lastname: Striedter
mesh_terms: D000818:Animals; D001717:Birds / Q000235:genetics; D005136:Eye Proteins / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics; D008636:Mesencephalon / Q000033:anatomy & histology* / Q000196:embryology; D009929:Organ Size; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics; D010240:Parakeets / Q000033:anatomy & histology* / Q000196:embryology / Q000235:genetics; D011784:Quail / Q000033:anatomy & histology* / Q000196:embryology / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D013045:Species Specificity
chemical_list: D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins