Fig. 3

The Exclusive Asymmetric Function of tjp1b Postsynaptically Is Necessary and Sufficient for Electrical Synapse Formation

(A and B) Schematics of chimeric larval circuits with the presynaptic Mauthner (A) or postsynaptic CoLo (B) derived from a transgenic donor. The genotype of the donor cell and host varies and is noted on the left of each set of images below.

(C–H) Dorsal views of chimeric larvae with GFP-marked cells (green) transplanted from a transgenic donor embryo into an unmarked host. Larvae are stained with anti-zebrafish-Cx35.5 (cyan), anti-zebrafish-Cx34.1 (yellow), and anti-human Tjp1 (magenta). Boxes denote location of single Z-plane zoom images in the ′ panels. (C and D) Control transplants from wild-type (wt) M/CoLo:GFP transgenic into a wild-type host. (E and F) Transplants from tjp1b mutant M/CoLo:GFP transgenic into a wild-type host. (G and H) Transplants from wild-type M/CoLo:GFP transgenic into a tjp1b mutant host.

(I and J) Quantification of the ratio of Cx36 at donor-associated synapses to host synapses in chimeric embryos. Removing tjp1b function postsynaptically (I) results in a significant loss of Cx36 staining (p = 0.0002) while providing tjp1b function postsynaptically in a mutant (J) results in a significant restoration of Cx36 staining (p = 0.0005). The height of the bar represents the mean of the sampled data with each circle representing the average of 3–10 transplant-associated M/CoLo synapses within an animal.

(K) Molecular model of postsynaptically localized Tjp1b required for asymmetric Cxs at the electrical synapse. Tjp1 may dimerize using its second PDZ domain [23] and thereby cluster Cxs at the synapse. Molecular asymmetry may create functional asymmetry at these synapses.

See associated data and statistics in Data S1.