Research Highlight: Molecular signatures of neural connectivity in the olfactory cortex

In the mouse, the piriform olfactory cortex is known to transmit odor information to other brain areas (involved in cognition, context, or behavior) but how the specificity of efferent cortical connectivity is organized at the cellular level remains unknown. To address the molecular identity of piriform neurons subsets, the ENP group leader Alexander Fleischmann and coll. used laser-capture micro-dissection and RNA deep sequencing to identify genes and neural tracing experiments to characterize the antomical organization of distinct sub-classes of piriform neurons. Combining technologies reveals that layer-specific genes discriminate between different sub-classes of neurons independent of whether they were segregated in one layer or mingled together within a layer. Interestingly, these molecular signatures of neural connectivity are maintained even if the neuronal network  organization is scrambled (reeler mice). This suggests that as in the neuromuscular map, the specificity of the neuronal response in the olfactory cortex primarly depends on the molecular identity of the neurons rather than their neural sub-localisation.

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Molecular signatures of neural connectivity in the olfactory cortex, Assunta Diodato, Marion Ruinart de Brimont, Yeong Shin Yim, Nicolas Derian, Sandrine Perrin, Juliette Pouch, David Klatzmann, Sonia Garel, Gloria B Choi & Alexander Fleischmann, Nature Communications 7, 12238 (2016)


Figure 1: Expression of the layer-specific genes in neocortex and (olfactory) piriform cortex. (Left) Coronal section of the adult mouse brain. (Right) Immunohistochemical analysis of Cux1 and Ctip2 expression in neocortex (top) and olfactory (piriform) cortex (bottom). Note that superficial and deep layer-specific gene expression patterns are reversed, and that in contrast to neocortex, Cux1 and Ctip2 are co-expressed in a subpopulation of piriform neurons (insert, in yellow). Cux1 and Ctip2 specify piriform neurons projecting to the olfactory bulb and the medial prefrontal cortex (for details, see Diodato et al., Nature. Comm., 2016).