Molecular Organization of the Ferret Visual Thalamus

Abstract

The visual system encodes and deciphers information using parallel, anatomically segregated, processing streams. To reveal patterns of gene expression in the visual thalamus correlated with physiological processing streams, we designed a custom ferret cDNA microarray. By isolating specific subregions and layers of the thalamus, we identified a set of transcription factors, including Zic2, Islet1, and Six3, the unique distribution profiles of which differentiated the lateral geniculate nucleus (LGN) from the associated perigeniculate nucleus. Within the LGN, odd homeobox1 differentiated the A layers, which contain X cells and Y cells, from the C layers. One neuron-specific protein, Purkinje cell protein 4 (PCP4), was strongly expressed in Y cells in the ferret LGN and in the magnocellular layers of the primate LGN. In the ferret LGN, PCP4 expression began as early as postnatal day 7 (P7), suggesting that Y cells are already specified by P7. These results reveal a rich molecular repertoire that correlates with functional divisions of the LGN.

Mechanisms Underlying Development of Visual Maps and Receptive Fields

“…Also N-cadherin, in collaboration with neural activity, regulates layer specificity of geniculo-cortical projections (Poskanzer et al 2003, Uesaka et al 2007, Yamamoto et al 2000 (Figure 2b). No one has yet reported regarding the molecules that mediate layer-specific targeting of functionally defined visual processing streams, although such cues have been proposed to exist (Meissirel et al 1997;Kawasaki et al 2004). …”

“…Thus, such an injection should lead to a uniform label in V1, not patches. Molecularly distinct portions of theLGNthat corresponded to functionally specific, but not eye-specific, visual pathways have been identified (Kawasaki et al 2004). Still, molecules that mediate ODC formation may exist.…”

Emerging roles for zic genes in early development

“…A similar role for Zic2 in interpreting repulsive cues in undifferentiated tissues during early development remains to be explored. Finally, the zic2 gene is expressed in the cells of the developing and differentiated lateral geniculate nucleus, although the role of Zic2 in this part of the visual thalamus is not known (Kawasaki et al, 2004). Thus, the activities of zic genes are not limited to undifferentiated tissues.…”

Retinal waves regulate afferent terminal targeting in the early visual pathway

“…5) but not in adult mice (22,53)? One possibility is that the laminar structure of the ferret dLGN limits the extent of its developmental plasticity (23)(24)(25)54). Because ferret dLGNs have cellular lamination, unlike the mouse, and also express molecules inhibiting neurite outgrowth between laminae (55), it is likely that retinogeniculate plasticity is reduced at more mature time points.…”

“…Similarly, the fragmentation of the ipsilateral projection in a P25 section was quantified by autocounting clusters of pixels (corresponding to projection patches), with a minimum area of 350 μm 2 and no maximum, excluding pixels corresponding to the MIN and OT. A minimum of 350 μm 2 was chosen as it is the reported average size of dLGN neurons (54), and thus helped to eliminate the counting of artifactual pixels. Retinogeniculate projection patches per square millimeter were calculated by summing the area of all pixels included in the patch count analysis, determining the corresponding area those pixels represented based on preset scales (46 pixels = 100 μm with a 5× objective; 92 pixels = 100 μm with a 10× objective), and dividing by the number of patches counted.…”