What makes a model system great?

With the advent of fluorescently tagged proteins and live cell imaging our understanding of actin cytoskeleton dynamics has been expanding at an unprecedented pace. However, the role of the actin cytoskeleton in numerous cellular processes has been elucidated primarily in cultured cells. The next stage is to understand if these processes and the mechanisms that underpin them transfer from what is essentially a 2-dimensional cell living in isolation to cells in a 3-dimensional community—a tissue. Intravital microscopy holds the promise for being able to visualize the actin cytoskeleton in its native state—a tissue in situ. The greatest challenges at the moment are in developing tractable and meaningful in vivo experimental model systems capable of addressing specific questions about the molecular machinery involved in the assembly and function of complex cytoskeletal structures. In this article we discuss important considerations for establishing such in vivo models and showcase one such model system which has proven successful in revealing the in situ dynamics of actomyosin assembly on large secretory granules.