Hub connectivity, neuronal diversity, and gene expression in the Caenorhabditis elegans connectome
Fig 6
Correlated gene expression varies as a function of connectedness and connection type.
(A) Left: distribution of CGE for (i) pairs of neurons connected by gap junctions, (ii) pairs of neurons connected by reciprocal chemical synapses, (iii) pairs of neurons connected by unidirectional chemical synapses, (iv) pairs of neurons that are unconnected, shown as a violin plot, with the median of each distribution represented by a horizontal line. CGE is increased in connected (electrical or chemical; reciprocally or unidirectionally) pairs of neurons relative to unconnected pairs (p = 1.8 × 10−78, Wilcoxon rank sum test). Among connected pairs of neurons neurons connected via gap junctions have more similar CGE than connected via chemical synapses (Wilcoxon rank-sum test, p = 5.4 × 10−22). Right: GCE for pairs of neurons labeled as peripheral, feed-in, feed-out, and rich, where hubs are neurons with degree k > 44. The median of each distribution shown as a horizontal line. CGE is significantly higher between hubs (rich links) compared to feeder (p = 5 × 10−22, Wilcoxon rank sum test) and peripheral (p = 3.9 × 10−19, Wilcoxon rank sum test) links. Feed-out links show significantly higher CGE than both feed-in (p = 1.9 × 10−6, Wilcoxon rank sum test) and peripheral links (p = 4.5 × 10−12, Wilcoxon rank sum test). (B) Top: Degree distribution, k, of the C. elegans connectome. Middle: proportion of connections that are: ‘rich’ (hub→hub, red), ‘feed-in’ (nonhub→hub, yellow), ‘feed-out’ (hub→nonhub, orange), or ‘peripheral’ (nonhub→nonhub, blue) as a function of the degree threshold, k, used to define hubs. Note that at high k most neurons are labeled as nonhubs and hence the vast majority of connections are labeled ‘peripheral’. Bottom: Median CGE, , for each connection type as a function of k. The median CGE across all network links is shown as a dotted black line; the topological rich-club regime (determined from the network topology, cf. Fig 5) is shaded gray. Circles indicate a statistically significant increase in CGE in a given link type relative to the rest of the network (one-sided Wilcoxon rank-sum test, p < 0.05).