T-Brain expression in the apical organ of hemichordate tornaria larvae suggests its evolutionary link to the vertebrate forebrain.
T-box genes encode a novel family of sequence-specific activators that appear to play crucial roles in various processes of animal development. Although most of the T-box genes are involved in the mesoderm formation of chordate embryos, mammalian T-Brain is expressed in the developing central nervous system, and defines molecularly distinct domains within the cerebral cortex. Here we report the first invertebrate T-Brain homologue from the hemichordate acorn worm, Ptychodera flava, which we designate Pf-Tbrain. Developmental expression of Pf-Tbrain was examined by whole mount in situ hybridization to various stages of P. flava embryos. A weak, broad in situ hybridization signal of the Pf-Tbrain transcript is first detected during gastrulation in cells around the archenteron, but this signal disappears as gastrulation proceeds. At mid-gastrula an intense signal appears in several apical ectoderm cells of the gastrula. This signal becomes restricted to the apical region, where the eyespots or the light-sensory organ of the tornaria larva form. Expression of Pf-Tbrain in the apical sensory organ of the tornaria and vertebrate T-Brain in the forebrain suggests an evolutionary relationship between the non-chordate deuterostome larval apical sensory organ and the chordate forebrain.
Tagawa
K
K
Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Humphreys
T
T
Satoh
N
N
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate / Q000033:anatomy & histology / Q000196:embryology / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D007814:Larva; D008969:Molecular Sequence Data; D020825:T-Box Domain Proteins / Q000235:genetics*; D014714:Vertebrates / Q000033:anatomy & histology / Q000235:genetics
D018076:DNA, Complementary; D020825:T-Box Domain Proteins