APC/C(Fzr/Cdh1)-dependent regulation of cell adhesion controls glial migration in the Drosophila PNS

Interactions between neurons and glia are a key feature during the assembly of the nervous system. During development, glial cells often follow extending axons, implying that axonal outgrowth and glial migration are precisely coordinated. We found that the anaphase-promoting complex/cyclosome (APC/C) co-activator fizzy-related/Cdh1 (Fzr/Cdh1) is involved in the non-autonomous control of peripheral glial migration in postmitotic Drosophila neurons. APC/C(Fzr/Cdh1) is a cell-cycle regulator that targets proteins that are required for G1 arrest for ubiquitination and subsequent degradation. We found that Fzr/Cdh1 function is mediated by the immunoglobulin superfamily cell adhesion molecule Fasciclin2 (Fas2). In motor neurons Fzr/Cdh1 is crucial for the establishment of a graded axonal distribution of Fas2. Axonal Fas2 interacts homophilically with a glial isoform of Fas2. Glial migration is initiated along axonal segments that have low levels of Fas2 but stalls in axonal domains with high levels of Fas2 on their surfaces. This represents a simple mechanism by which a subcellular gradient of adhesiveness can coordinate glial migration with axonal growth.