"Birth of the cool": Using sea urchin zygotes to study centrosome duplication, cell division, and cytokinesis

The successful division of the cell depends on several morphological events that must be coordinated in a cell cycle dependent fashion. Crucial to this process is the remodeling of the cytoskeleton to both establish the bipolar spindle during mitosis, and cleave the cell into two daughters during cytokinesis. From the standpoint of the cytoskeleton, this process begins during inter-phase with the duplication of the centrosome; it is the two daughter centrosomes that will assemble the poles of the mitotic spindle and establish its necessary bipolarity. Following the cell cycle transition into mitosis, the spindle must assemble in order to properly align the sister chromatids at the center of the cell, and release the "wait anaphase checkpoint". As the spindle transports the disjoined sister chromatids to the spindle poles, the cell must rapidly undergo cytokinesis, cleaving the cell into two - the plane of cleavage being established by the spindle itself. Understanding the temporal regulation and molecular basis for these events has come from extensive experiments using a variety of model systems, and has benefited from cell biological, molecular genetic, and biophysical approaches. One of the earliest and most important model systems for studying mitosis is the sea urchin zygote. With their large size, rapid/synchronous cell cycles, and advantages for conduct of biochemical and cytological investigations on the same system, fertilized sea urchin eggs have revealed many of the fundamental properties of centrosome duplication, cell division and cytokinesis. Here we review several key studies that have utilized the sea urchin zygote to explore mechanisms that coordinate and drive two of the major cytoskeletal events of mitotic division - centrosome duplication and cytokinesis.