Role of the spindle-pole-body protein ApsB and the cortex protein ApsA in microtubule organization and nuclear migration in Aspergillus nidulans

Abstract

Nuclear migration and positioning in Aspergillus nidulans depend on microtubules, the microtubule-dependent motor protein dynein, and auxiliary proteins, two of which are ApsA and ApsB. In apsA and apsB mutants nuclei are clustered and show various kinds of nuclear navigation defects, although nuclear migration itself is still possible. We studied the role of several components involved in nuclear migration through in vivo fluorescence microscopy using fluorescent-protein tagging. Because ApsA localizes to the cell cortex and mitotic spindles were immobile in apsA mutants, we suggest that astral microtubule-cortex interactions are necessary for oscillation and movement of mitotic spindles along hyphae, but not for post-mitotic nuclear migration. Mutation of apsA resulted in longer and curved microtubules and displayed synthetic lethality in combination with the conventional kinesin mutation ΔkinA. By contrast, ApsB localized to spindle-pole bodies (the fungal centrosome), to septa and to spots moving rapidly along microtubules. The number of cytoplasmic microtubules was reduced in apsB mutants in comparison to the wild type, indicating that cytoplasmic microtubule nucleation was affected, whereas mitotic spindle formation appeared normal. Mutation of apsB suppressed dynein null mutants, whereas apsA mutation had no effect. We suggest that nuclear positioning defects in the apsA and apsB mutants are due to different effects on microtbule organisation. A model of spindle-pole body led nuclear migration and the roles of dynein and microtubules are discussed.

Aspergillus nidulans Dis1/XMAP215 Protein AlpA Localizes to Spindle Pole Bodies and Microtubule Plus Ends and Contributes to Growth Directionality

“…Compared to he wild type (SJW02), the number of MTs was reduced in the ⌬alpA strain. Basically, only one thick MT bundle (according to Veith et al [27]), connecting adjacent nuclei, was visible, in addition to some shorter MTs emerging from the nuclear spindle pole bodies, while in the wild-type strain several single and bundled MTs were present (Fig. 5A, B).…”

“…However, it has to be noted that dynein mutants of A. nidulans do not display the same hyphal growth phenotype. In addition, dynein-mediated MT-cortical interactions are required for nuclear migration and nuclear positioning (27). Both phenomena were not affected in alpA mutants.…”

A Pericentrin-Related Protein Homolog in Aspergillus nidulans Plays Important Roles in Nucleus Positioning and Cell Polarity by Affecting Microtubule Organization

“…Previous studies have shown that proper nuclear distribution first requires the active migration of nuclei, followed by the anchoring of nuclei to the cytoplasm microtubule and then their attachment to the plasma membrane (44,50,51). During this process, microtubule organization, actin cytoskeleton, and motor proteins play important roles; thus, blocking any of their components results in abnormal nuclear trafficking and nuclear distribution (3,32,50,51).…”

A nuclear contortionist: the mitotic migration ofMagnaporthe oryzaenuclei during plant infection

“…Once the plus-ends of astral microtubules bind to Num1, they slide against the cell cortex in a dynein-mediated manner which moves the spindle and eventually the daughter nucleus into the newly formed bud (Heil-Chapdelaine et al 2000). Functional homologs of Num1 are also required for proper nuclear migration in multinucleate fungi, including A. nidulans (Veith et al 2005) and Ashbya gossypii (Grava et al 2011). In M. oryzae , a Num1 homolog, MoAND1, has been characterised (Jeon et al 2014).…”