A dual role for the βPS integrin myospheroid in mediating Drosophila embryonic macrophage migration

Throughout embryonic development, macrophages not only constitute the first line of defense against infection but also help to sculpt organs and tissues of the embryo by removing dead cells and secreting extracellular matrix components. Key to their function is the ability of embryonic macrophages to migrate and disperse throughout the embryo. Yet despite these important developmental functions, little is known about the molecular mechanisms underlying embryonic macrophage migration in vivo. Integrins are key regulators of many of the adult macrophage responses, but their role in embryonic macrophages remains poorly characterized. Here, we have used Drosophila macrophages (haemocytes) as a model system to address the role of integrins during embryonic macrophage dispersal in vivo. We show that the main βPS integrin, myospheroid, affects haemocyte migration in two ways; by shaping the 3-dimensional environment in which haemocytes migrate and by regulating the migration of haemocytes themselves. Live imaging reveals a requirement for myospheroid within haemocytes for coordinating the microtubule and actin dynamics, and in enabling haemocyte developmental dispersal, contact repulsion and inflammatory migration towards wounds.