Abstract
Purpose :
Sorting of retinal ganglion cell (RGC) axons at the optic chiasm is critical for proper innervation of retinorecipient brain nuclei. Axon sorting is regulated by guidance cues produced by the radial glia and neurons of the chiasm. During axon sorting the axons and the radial glia are in direct contact with the chiasm basement membrane (BM). BMs regulate the extracellular localization of repulsive and attractive cues, however the role of BM components in regulating axon sorting is not completely understood. Here we tested if β2- and γ3-containing laminins regulate the structure of the chiasm and its impact in axon sorting.
Methods :
Organization of the optic chiasm was analyzed histologically at E15.5 in WT (N=3) and Lamb2-/- (N=3) mutants. Routing of RGC axons and innervation of retinorecipient nuclei was determined by labeling RGC axons from one eye anterogradely with DiI in wild-type (WT) (N=4), Lamb2-/- (N=3), Lamc3-/- (N=3), and Lamb2:c3-/- (N=2) mice at P4 and P7. The area of brain nuclei innervation and the retinal projections were measured and used to calculate the proportional area occupied by the RGC terminals and of each projection.
Results :
β2- and γ3-containing laminins are expressed in the BM of the chiasm when the axons are being sorted into the optic tracts. Analysis of chiasm sections at the time of axon sorting showed that the BM of the chiasm is fragmented in Lamb2-/- animals. The radial glia endfeet lose contact with the BM and either retract from or protrude through the BM. At the same time, RGC axons were found to misroute at the chiasm, with a larger proportion of axons being sorted into the ipsilateral projection of Lamb2-/-, Lamc3-/-, and Lamb2:c3-/- than in WT, suggesting that alterations in the chiasm structure may impact axon sorting. Innervation of retinorecipient nuclei, including the suprachiasmatic nucleus (SCN) and dorsal lateral geniculate nucleus (dLGN) was also significantly decreased in Lamb2-/- and Lamc3-/- mutants compared to WT mice.
Conclusions :
Together, these data suggest that β2- and γ3-containing laminins regulate axon sorting by maintaining the integrity of the BM of the chiasm and the structure of the guidance cue producing radial glia. In addition, β2- and γ3-containing laminins also function to regulate the innervation of the SCN and dLGN.
This is a 2020 ARVO Annual Meeting abstract.