The Dilute domain of Canoe is not essential for Canoe's role in linking adherens junctions to the cytoskeleton but contributes to robustness of morphogenesis

Robust linkage between cell-cell adherens junctions and the actomyosin cytoskeleton allows cells to change shape and move during morphogenesis without tearing tissues apart. The multidomain protein Drosophila Canoe and its mammalian homolog Afadin are critical for this linkage, and in their absence many events of morphogenesis fail. To define underlying mechanisms, we are taking Canoe apart, using Drosophila as our model. Canoe and Afadin share five folded protein domains, followed by a large intrinsically disordered region. The largest of these folded domains is the Dilute domain, which is found in Canoe/Afadin, their paralogs, and members of the MyosinV family. To define the roles of Canoes Dilute domain we have combined biochemical, genetic and cell biological assays. Use of the AlphaFold tools revealed the predicted structure of the Canoe/Afadin Dilute domain, providing similarities and contrasts with that of MyosinV. Our biochemical data suggest one potential shared function: the ability to dimerize. We next generated Drosophila mutants with the Dilute domain cleanly deleted. Surprisingly, these mutants are viable and fertile, and Canoe{Delta}DIL protein localizes to adherens junctions and is enriched at junctions under tension. However, when we reduce the dose of Canoe{Delta}DIL protein in a sensitized assay, it becomes clear it does not provide full wildtype function. Further, canoe{Delta}DIL mutants have defects in pupal eye development, another process that requires orchestrated cell rearrangements. Together, these data reveal the robustness in AJ-cytoskeletal connections during multiple embryonic and postembryonic events, and the power of natural selection to maintain protein structure even in robust systems.