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Sensory Map Transfer to the Neocortex Relies on Pretarget Ordering of Thalamic Axons.

Lokmane L, Proville R, Narboux-Nême N, Györy I, Keita M, Mailhes C, Léna C, Gaspar P, Grosschedl R, Garel S.

Sensory maps, such as the representation of mouse facial
whiskers, are conveyed throughout the nervous system by
topographic axonal projections that preserve neighboring
relationships between adjacent neurons [1]. In particular,
the map transfer to the neocortex is ensured by thalamocortical axons (TCAs), whose terminals are topographically
organized in response to intrinsic cortical signals [2–5].
However, TCAs already show a topographic order early in
development, as they navigate toward their target [6, 7].
Here, we show that this preordering of TCAs is required for
the transfer of the whisker map to the neocortex. Using
Ebf1 conditional inactivation that specifically perturbs the
development of an intermediate target, the basal ganglia,
we scrambled TCA topography en route to the neocortex
without affecting the thalamus or neocortex. Notably, embryonic somatosensory TCAs were shifted toward the visual
cortex and showed a substantial intermixing along their
trajectory. Somatosensory TCAs rewired postnatally to
reach the somatosensory cortex but failed to form a topo-
graphic anatomical or functional map. Our study reveals
that sensory map transfer relies not only on positional information in the projecting and target structures but also on
preordering of axons along their trajectory, thereby opening
novel perspectives on brain wiring.

Curr Biol. 2013 Apr 23. doi:pii: S0960-9822(13)00364-3