Developmental trajectory of Caenorhabditis elegans nervous system governs its structural organization
Fig 2
Lineage of neurons affects their synaptic connectivity and spatial localization.
(A) Schematic diagram of a lineage tree of cells resulting from consecutive mitotic divisions of the zygote. The terminal nodes of the tree correspond to terminally differentiated mature cells (shown in red) while other nodes represent progenitors (shown in blue) that appear at different rounds of cell division. Cells born at each round of cell division are indicated by the corresponding rung of the tree they belong to, the numerical value for the rung (shown at the left) being the number of divisions starting from the zygote. The lineage distance l between a pair of mature cells is measured as the total number of cell divisions leading to each from their common progenitor. An example of lineage distance measurement is shown in the figure for the pair of cells a and b which are separated by four cell divisions (the distance of a from each of the intermediate dividing progenitors is indicated in the figure). (B-C) Frequency distributions of the birth time of different neurons (B, separated into the different developmental stages) and the lineage distances for each pair of neurons (C). (D) The probability of a pair of neurons to be connected through a synapse decreases with increasing lineage distance between them, as indicated by a statistically significant linear correlation between the two (r = −0.87, p < 10−7). For gap junctional connections, the correlation is marginally weaker (r = −0.79, p < 10−5). (E-F) Joint probability distributions of lineage distance l along with distance between cell bodies D (E) and birth time difference Δtb (F) between all pairs of neurons. The marginal distributions for the corresponding quantities are also shown. We notice that the distribution of physical distances in (E) exhibit a bimodal nature. However, cells which are closely related in terms of lineage (l < 5) also has a high probability of being physically located nearby (indicated by a prominent peak at the lower end of the distribution of D) which suggests that lineage influences spatial localization of cells. In panel (F), the distribution shows peaks at odd values of the lineage distance (particularly for low Δtb) suggesting that neurons born close in time are located at the same rung on the lineage tree.