title: Development of the thalamo-dorsal ventricular ridge tract in the Chinese soft-shelled turtle, Pelodiscus sinensis.
abstract: With the exception of that from the olfactory system, the vertebrate sensory information is relayed by the dorsal thalamus (dTh) to be carried to the telencephalon via the thalamo-telencephalic tract. Although the trajectory of the tract from the dTh to the basal telencephalon seems to be highly conserved among amniotes, the axonal terminals vary in each group. In mammals, thalamic axons project onto the neocortex, whereas they project onto the dorsal pallium and the dorsal ventricular ridge (DVR) in reptiles and birds. To ascertain the evolutionary development of the thalamo-telencephalic connection in amniotes, we focused on reptiles. Using the Chinese soft-shelled turtle (Pelodiscus sinensis), we studied the developmental course of the thalamic axons projecting onto the DVR. We found, during the developmental period when the thalamo-DVR connection forms, that transcripts of axon guidance molecules, including EphA4 and Slit2, were expressed in the diencephalon, similar to the mouse embryo. These results suggest that the basic mechanisms responsible for the formation of the thalamo-telencephalic tract are shared across amniote lineages. Conversely, there was a characteristic difference in the expression patterns of Slit2, Netrin1, and EphrinA5 in the telencephalon between synapsid (mammalian) and diapsid (reptilian and avian) lineages. This indicates that changes in the expression domains of axon guidance molecules may modify the thalamic axon projection and lead to the diversity of neuronal circuits in amniotes.
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577, Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Tosa
authors.forename: Ayako
authors.initials: A
authors.lastname: Hirao
authors.forename: Ikumi
authors.initials: I
authors.lastname: Matsubara
authors.forename: Masahumi
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Makiko
authors.initials: M
authors.lastname: Fukui
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuratani
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Murakami
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D002681:China; D036386:Ephrin-A5 / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D019579:Neocortex / Q000166:cytology / Q000196:embryology*; D009414:Nerve Growth Factors / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D000075388:Netrin-1; D009830:Olfactory Bulb / Q000166:cytology / Q000196:embryology; D036122:Receptor, EphA4 / Q000378:metabolism; D013788:Thalamus / Q000166:cytology / Q000196:embryology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D014426:Turtles; D000098552:Slit Homolog 2 Protein
chemical_list: D036386:Ephrin-A5; D036341:Intercellular Signaling Peptides and Proteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D025521:Tumor Suppressor Proteins; D000075388:Netrin-1; D036122:Receptor, EphA4; D000098552:Slit Homolog 2 Protein
keywords: amniote; axon guidance molecule; dorsal thalamus; telencephalon; turtle