Canoe's Dilute domain is not essential for linking cell junctions to the cytoskeleton but supports morphogenesis robustness.

Robust linkage between adherens junctions and the actomyosin cytoskeleton allows cells to change shape and move during morphogenesis without tearing tissues apart. The multidomain protein Canoe and its homolog Afadin are critical, as in their absence many events of morphogenesis fail. To define mechanisms, we are taking Drosophila Canoe apart. Canoe has five folded protein domains and a long intrinsically disordered region. The largest is the Dilute domain, shared by Canoe and MyosinV. To define its roles we combined biochemical, genetic and cell biological assays. AlphaFold predicted its structure, providing similarities and contrasts with MyosinV. Biochemical data suggest one potential shared function: the ability to dimerize. We generated mutants with the Dilute domain deleted. Surprisingly, they are viable and fertile. Canoe▵DIL localizes to adherens junctions and is enriched at junctions under tension. However, when its dose is reduced, Canoe▵DIL does not provide fully wildtype function. Further, canoe▵DIL mutants have defects in the orchestrated cell rearrangements of eye development. This reveals the robustness of junction-cytoskeletal connections during morphogenesis and highlights the power of natural selection to maintain protein structure.