Figure 8. Historical evolution of GKPID-mediated spindle orientation complex.
The center portion shows the phylogeny of Metazoa and closely related taxa. The origin of cell differentiation and spatially organized tissues is marked. The left portion shows major events in the evolution of the components of the spindle orientation complex reconstructed in this study. Duplication of an ancestral gk enzyme (brown) and the key mutations that led to the origin of a GKPID (blue) that could bind other molecules in the complex are shown relative to the phylogeny’s time scale. The apparent date of origin of KHC-73 (black) and Pins (green) are also shown. Dotted green line shows the origin of Pins in a form not yet bound by GKPID. Solid green line shows GKPID-binding form. Horizontal lines indicate binding between proteins. The right portion shows a schematic of the spindle orientation machinery in metazoans, which allows orientation relative to external cues from nearby cells, as well as spindle orientation relative to the internal cell axis as marked by the flagella in both solitary and colonial choanoflagellates.