Retinotectal topography is ensured early in development when specific areas of the retina project neurons to stereotypedregions in the visual tectum. The nasal to temporal (NT) and dorsal to ventral distribution of Eph/ephryns in the retina will direct the retinal ganglion cells (RGCs) to generate the proper connections in the tectum. An open question is what controls the distribution of Eph/ephryns in the retina NT pattern. Wnt pathway antagonists induce telencephalon whereas diencephalic fate is promoted by Wnt activity. The eye field is situated between these brain territories and thus we speculate that Intermediate, graded levels of Wnt activity, may confer NTpolarity to the prospective RGSc.
We plan to address the role of Wnt pathway in the NT polarisation of the 'prospective retinal cells using zebrafish as a model organism. To study the retina NT pattern we will analyse the expression pattern of genes restricted to NT retina. These will be used as readout of NT pattern when we modify Wnt activity in the retina primordia. To study the role of Wnt pathway in the retina patterning we will perform lack and gain activity experiments. To establish the cells in the prospective eye field, which originate the NT region of the retina, we will perform a fate map of the zebrafish eyefield. We will then be able to modify Wnt activity in specific NT regions of the eye field. The local activity modulation will be driven by transplantation of cells expressing positive and negative Wnt modulators.
The modification of the NT pattern after cell transplantation will be assessed by:
1. Analysing the expression of NT molecular markers.
2. Study of the topographic distribution of RGC axonal arborisation in the tectum out of transplanted cells.
These two approaches will link the change in t he pattern of markers expressed differentially in the NT retina to the functional changes visualised by the projections of RGCs spatial distribution in the tectum.
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