Use they’re in a position to separate the two daughter nuclei solely by pulling forces exerted through astral microtubules, most like by means of minus-end directed motor activity of cortical dynein [237]. 4. Centrosome-Nucleus Attachment Like all centrosomal structures in vegetative cells, the Dictyostelium centrosome is structurally linked to the cytosolic side from the nucleus through interphase. Not surprisingly, 1 key protein of this linkage may be the nuclear envelope protein Sun1, named soon after the founding members on the Sun-family, i.e., fission yeast Sad1 and Caenorhabditis elegans UNC-84, which share a frequent Sun-domain. In most eukaryotes Sun1 is definitely an inner nuclear membrane protein, forming a trimer and interacting, by way of its Sun-domain, with the so-called KASH-domain proteins (named immediately after Klarsicht, ANC-1, SYNE1 homology) inside the perinuclear space [239]. Since the several KASH domain proteins interact straight or indirectly with all three cytoskeletal components (actin, microtubules, intermediate filaments) the term LINC complicated (linker on the nucleus and cytoskeleton) was coined for the Sun/KASH domain protein heterodimer [240]. In the nuclear side, Sun1 interacts with lamins in animal cells and also in Dictyostelium [241]. Yet, around the cytosolic face of the nuclear envelope the scenario in Dictyostelium appears to be exclusive. Sun1 is present in both nuclear membanes with no powerful bias towards the inner nuclear membrane [124,125] and there is absolutely no clear orthologue to get a KASH domain protein. On account of its similarity to mammalian nesprins, the outer nuclear membrane protein interaptin was discussed as a Dictyostelium KASH domain protein [125,242]. But interaptin is undoubtedly no BI-409306 supplier portion of a LINC complicated, as it lacks the conserved KASH domain and naturally does not interact with Sun1 [125]. Sun1 is nevertheless required for centrosome/nucleus attachment. It co-purifies with isolated centrosomes and is concentrated at the nuclear envelope within the direct vicinity with the centrosome (Figure 4). Sun1 mutants are defective in centrosome/nucleus attachment. It is feasible that the centrosome/nucleus linker employs Sun1 on both sides in the membrane, and that an unknown protein of your perinuclear space mediates this interaction. Even though a direct interaction with Sun1 remains to become proven, the unusual kinesin Kif9 is really a likely candidate for any LINC complicated element in Dictyostelium. Kif9 is definitely an internal motor kinesin, which is usually grouped in to the kinesin-13 family members, which normally act as microtubule depolymerases [130]. Within this group Kif9 is special in containing a 23 residue transmembrane domain close to its C-terminal end, targeting the protein for the outer nuclear envelope exactly where it accumulates inside the pericentrosomal area. Knockout of Kif9 disrupts the centrosome/nucleus linkage and causes dispersal of Sun1, away from the pericentrosomal region in the nuclear envelope [130].Figure 4. Centrosome-Nucleus-Centromere cluster. (A) Immunoelectron microscopy image displaying a single section of an isolated nucleus with the attached centrosome. Nuclei have been labeled with an antibody (-)-Blebbistatin Purity & Documentation against Dictyostelium Sun1 and nanogold conjugated anti-rabbit antibodies. The centrosome (Cn), the centromeric cluster (Cm), the nuclear envelope (NE) along with the endoplasmic reticulum (ER) are indicated (image by Prof. Otto Baumann); (B) Immunofluorescence microscopy image of a Sun1-GFP knock-in cell (green) stained with an antibody against the centrosomal core protein CP91 and anti-rabbit-AlexaFluor 568 conjug.
