Differences between the anterior and posterior populations of Ciona vCENs.

(A): Schematized representation of the Ciona larval CENs (adapted from [41]). (B): Whole mount view of a hatching larva electroporated with the pVGluT::EGFP reporter construct and immunostained with an anti-GFP antibody to show the general organization of the tail PNS. The posterior vCENs emit long axons (red arrowhead) and are contacted by axons from the dorsal CENs (yellow arrowhead), while the anterior vCENs do not establish contacts with other CENs (gap between the blue arrows). (C, C′): Differences in the birth time of anterior and posterior vCENs. Ci-etr expression in initial- (C) and early-tailbud stages (C′) embryos show that the posterior vCENs are born slightly earlier than the anterior vCENs. (D–E′): closeup showing the long axons of the posterior vCENs (red arrowheads) and their connexions with the dorsal CENs (yellow arrowheads). (F, F′): closeup showing that the anterior vCENs emit only very short axonal extensions (white arrowheads). (G): Quantification of the morphometric differences between anterior and posterior vCENs at hatching larva stage. The axonal length of 42 randomly chosen EGFP-expressing vCENs from 14 larvae was plotted against the position of their cell body along the tail. K-means parameter cluster analysis of the scatterplot reveals the existence of two distinct clusters of 21 points each. The centroid coordinates of the anterior (red) cluster are: axonal length = 15.9 µm, distance from trunk/tail junction = 233.8 µm, those of the posterior (yellow) cluster are: axonal length = 173,8 µm, distance from trunk/tail junction = 565.4 µm.