Developmental trajectory of Caenorhabditis elegans nervous system governs its structural organization
Fig 8
The developmental duration of functional circuit neurons are strongly indicative of their process length and connectivity.
(A) Distribution of differentiation times of neurons that belong to any of nine functional circuits identified from behavioral assays. Note that the entire complement of neurons belonging to three functional circuits [shown using solid lines] have differentiated before hatching, while those for others [shown using broken lines] are completed later. (B) The distribution of neurons having short, medium and long processes [indicated at left], among the different functional circuits [right]. We note a correlation between the morphological feature of neurite length and the development time of functional circuit neurons, viz., those in the circuits completed before hatching predominantly have short processes, while those in circuits that are completed later mostly have medium to long processes (the exceptions being thermotaxis and CO2 sensation circuits that comprise a majority of short process neurons). (C) Comparison between the distributions of the number of incoming and outgoing synaptic connections (kin [top panel] and kout [middle panel], respectively), as well as, gap junctions (kgap [bottom panel]) of neurons in the entire somatic nervous system (blue) and of the subset of functional circuit neurons (red). We note that the distribution of outgoing synaptic connections for the functional circuit neurons is significantly different from that for the entire network, as indicated by the result of a two-sample Kolmogorov-Smirnov test at 1% level of significance (hKS = 1), but this is not the case for incoming synaptic connections or gap junctions (hKS = 0). (D) Dispersion of kin (top panel), kout (middle) and kgap (bottom) for the functional circuit neurons differentiating at various times is shown in terms of the adjoining box plots where neurons are clustered into four groups according to the developmental stage during which they are born, viz., Embryo, L1, L2 or L3. In general, the distributions are far more broad for the early born neurons (Embryo) compared to those born later (L1-L3). Focusing on the functional circuit neurons that develop in the embryonic stage, we note that the distribution of incoming connections is more skewed than that for outgoing connections. The distribution of gap junctions is even more skewed, with outliers lying very far from the median.