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Reyna I Martinez-De Luna, Galina Bachay, Dale D. Hunter, William J Brunken; β2- and γ3-containing laminins regulate axon sorting at the chiasm and SCN
innervation. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6409.
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© ARVO (1962-2015); The Authors (2016-present)
Sorting of retinal ganglion cell (RGC) axons at the optic chiasm is critical for proper innervation of retinorecipient nuclei. Laminins are essential components of the extracellular matrix known to regulate axonal outgrowth but their role in RGC axon sorting and target innervation of retinorecipient nuclei in mammals is currently unknown. Here, we show that β2- and γ3-containing laminins regulate aspects of RGC axon sorting at the optic chiasm, and the innervation of suprachiasmatic nucleus (SCN).
RGC axons were labeled anterogradely with DiI at the optic nerve head of wild-type (WT), Lamb2-/-, Lamc3-/-, and Lamb2:c3-/- mice at P4 and P7. The brains were dissected with the optic nerve and chiasm intact, and imaged. The areas of both ipsilateral and contralateral projections were measured at the chiasm and the relative proportions were calculated for each genotype. Both total SCN area and the area occupied by labeled RGC terminals were measured in vibratome sections. The ratio of innervated vs. total area was compared among WT and laminin mutants. Statistical differences were calculated using One Way ANOVA with Tukey post-test.
At P4, RGC axons misrouted at the optic chiasm, with a larger proportion of axons entering the ipsilateral projection in Lamb2-/- (44%), Lamc3-/- (46%), and Lamb2:c3-/- (42%) than in WT (40%; p<0.0001) mice. Importantly, this increase in the ipsilateral projection was accompanied by axons misrouting to the contralateral eye in the mutants. The proportional area of the SCN innervated by RGC axons was also significantly decreased in Lamb2-/- (49%) and Lamc3-/- (44%) mutants compared to WT (81%; p=0.0131) mice. By P7, the SCN area innervated by RGC axons was comparable in WT and laminin mutants (48% in Lamb2-/-, 60% in Lamc3-/-, 69% in WT; p=0.53). Although RGC axons traveled through the optic tract to reach the LGN, their terminal distribution was aberrant in the Lamb2-/- mutants compared to WT and Lamc3-/- mice. Specifically, regions of dLGN were uninnervated and some axons overshot the dLGN.
These data suggest that β2 and γ3-containing laminins are required for RGC axon sorting at the optic chiasm and for the early innervation of the SCN. Additionally, β2-containing laminins also function to regulate targeting of RGC axons to the dLGN.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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