Beschreibung
Xenopus oocyte nuclei are giant organelles whose mechanical integrity is provided by an extensive intranuclear F‑actin network. Organization and maintenance of cytoplasmic equivalents involve large sets of accessory proteins. We here report on the development of a novel phalloidin-based affinity matrix that we used to identify the nuclear F‑actin interactome of Xenopusoocytes. This approach revealed a compilation of proteins that strikingly differed from the respective cytoplasmic interactome. We designate previously known F‑actin binders, chromatin remodelers and DNA binding proteins in a novel role as nuclear F‑actin interactors. A major constituent of the nuclear F‑actin network turned out to be a fully unexpected component, namely a novel kinesin that bundles F‑actin filaments. This protein possesses features that allow contact to two different cytoskeletal systems. Indeed, following germinal vesicle break down, Kin3I contacts a structure called the transient microtubule array, which serves as precursor of the meiotic spindle. At the end of the first asymmetric cell division of the oocyte, we observed a striking localization of Kin3I to the resulting polar body, indicating that Kin3I might be involved in its extrusion.