Fig. 11

Evolutionary process of Slit/Robo mediated axonal wiring. In amphibians and amniotes, Slit2-weak region is present in the superficial part of the diencephalon, in which posterior commissure is formed. Robo2 is expressed in axons of the posterior commissure originates from nTPC in the posterior diencephalon. In the zebrafish (24 h post fertilization), slit2 expression domain in the dorsal diencephalon is similar to those of tetrapods, whereas robo2 transcripts are appear to be absent in the homologous region of nTPC. In mammals, Slit/Robo is also used for the development of the newly acquired commissure, such as corpus callous (indicated by the blue dashed ring). cc, corpus callous; Di, diencephalon; Mes, mesencephalon; Met, metencephalon; nTPC, nucleus of the tract of the posterior commissure; PC, posterior commissure; Te, telencephalon; vcc, ventrocaldal cluster