N-Cadherin mediated cell rearrangements shape embryonic macrophage cluster

Drosophila embryonic macrophages are highly motile phagocytic and secretory cells which are essential for embryonic development. Embryonic migration and dispersal of these cells along pre-determined routes is invariably tied to their functions such that misrouting or delay in macrophage migration has serious consequences for embryogenesis and adult homeostasis. In this study, we describe early steps of macrophage migration from their site of origin in the head mesoderm to the germband and show that hemocytes start moving as an epithelial-like cluster with N-Cadherin based Adherens junctions. The cells within the cluster move in a co-ordinated manner and exhibit cell rearrangements mediated through junction shrinkage. We found that N-Cadherin is dynamically relocalized during cluster extension and modulating N-Cadherin levels results in hemocyte dispersal away from their main axis of migration which affects migration into the germband. We therefore elucidate a novel multi-tiered mechanism which ensures that macrophages are positioned appropriately to regulate their distribution in the embryo.