Generating X: formation of the optic chiasm.
At the optic chiasm, axons from either eye meet and decide whether to cross contralaterally or turn back ipsilaterally. Here, the guidance ligand Slit and its receptor Robo control not whether axons cross (as in other midline decisions), but where the chiasm forms. Whether axons cross is instead controlled by the transcription factor Zic2 and the guidance receptor EphB1, as shown by two papers in the current issues of Neuron and Cell (Herrera et al. and Williams et al.). Surprisingly, this mechanism is conserved evolutionarily from frogs to mammals.
Rasband
Kendall
K
Department of Neurobiology and Anatomy, University of Utah Medical Center, Salt Lake City, UT 84132, USA.
Hardy
Melissa
M
Chien
Chi-Bin
CB
D000818:Animals; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006133:Growth Substances / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D009897:Optic Chiasm / Q000254:growth & development* / Q000378:metabolism*
D006133:Growth Substances