Robles, E., Filosa, A., and Baier, H. (2013) Precise lamination of retinal axons generates multiple parallel input pathways in the tectum. The Journal of neuroscience : the official journal of the Society for Neuroscience. 33(11):5027-5039.
The axons of retinal ganglion cells (RGCs) form topographic connections in the optic tectum, recreating a two-dimensional
map of the visual field in the midbrain. RGC axons are also targeted to specific positions along the laminar axis of the tectum.
Understanding the sensory transformations performed by the tectum requires identification of the rules that control the formation
of synaptic laminae by RGC axons. However, there is little information regarding the spatial relationships between multiple
axons as they establish laminar and retinotopic arborization fields within the same region of neuropil. Moreover, the contribution
of RGC axon lamination to the processing of visual information is unknown. We used Brainbow genetic labeling to visualize
groups of individually identifiable axons during the assembly of a precise laminar map in the larval zebrafish tectum. Live
imaging of multiple RGCs revealed that axons target specific sublaminar positions during initial innervation and maintain
their relative laminar positions throughout early larval development, ruling out a model for lamina selection based on iterative
refinements. During this period of laminar stability, RGC arbors undergo structural rearrangements that shift their relative
retinotopic positions. Analysis of cell-type-specific lamination patterns revealed that distinct combinations of RGCs converge
to form each sublamina, and this input heterogeneity correlates with different functional responses to visual stimuli. These
findings suggest that lamina-specific sorting of retinal inputs provides an anatomical blueprint for the integration of visual
features in the tectum.