Establishing the appropriate functional connectivity is a fundamental process during brain development. Cells at the origin and in the target area have to be correctly specified to ensure an accurate wiring between them. We are interested in the molecular control of processes such as axon guidance, cell differentiation and synaptogenesis, and are using the mouse and zebrafish as model systems. Visual perception is not only dependent on the correct assembly of the different cell types found in the retina, but also on the correct information transfer to the brain. The retinal ganglion cells send out axons to form connections between the eye and different brain centres. Along their path, these axons have to make several crucial decisions which way to take and with which cells in the target area they form synapses. We study molecules that are involved in these decisions and try to analyse their exact roles. Research in our laboratory has identified several important genes encoding transmembrane proteins, but more recently we have also isolated microRNAs, a novel class of small non-coding RNA factors, controlling axon guidance at the midline. Our current research focuses on the investigation of these molecules during brain development.