Figure 6.

The extracellular domain of Crb2a is required for Crb2a to mediate photoreceptor adhesion. A. The schematics illustrate the two strategies to transgenically express Crb2a, Crb2a-Δ^EX-mCherry^out, Crb2a-Δ^EX-mCherryⁱⁿ, Crb2a-Δ^EX, Crb3a-mCherry^out, or Crb3a in zebrafish retina. Individual protein domains are labeled as follows: SP, the signal peptide; Ex., the extracellular domain; T, the transmembrane domain; In., the intracellular domain; mC, mCherry; GFP, green florescent protein; -Δ^EX, absence of the extracellular domain. The percentages of transgenic photoreceptors that formed rosettes in 5-dpf crb2a^m289 mutant retinas were quantified and summarized in the table. B, C. Crb2a-Δ^EX-mCherry^out-expressing photoreceptors (red) scattered randomly in the crb2a^m289 mutant retinas. Panels C are magnified images of two transgenic cells that abutted each other but did not appear to adhere (the contours illustrates the lack of flat adhering junctional interface, arrow). D, E. Transgenic photoreceptors that co-expressed Crb2a-Δ^EX and GFP also scattered randomly in the crb2a^m289 mutant retinas. Panels E show magnified images of three transgenic cells, two of which abutted but did not adhere to each other to establish a flat junctional interface (contours, arrow). The lack of Crb2a staining confirmed that the embryo was a crb2a^m289 mutant. See Figure S5 for effects of transgenic expressing Crb2a-Δ^EX-mCherryⁱⁿ, Crb3a-mCherry^out, and Crb3a in either wildtype or crb2a^m289 mutant embryos. Also see Figure S5.