Nesprins anchor kinesin-1 motors to the nucleus to drive nuclear distribution in muscle cells

Abstract

During skeletal muscle development, nuclei move dynamically through myotubes in a microtubule-dependent manner, driven by the microtubule motor protein kinesin-1. Loss of kinesin-1 leads to improperly positioned nuclei in culture and in vivo. Two models have been proposed to explain how kinesin-1 functions to move nuclei in myotubes. In the cargo model, kinesin-1 acts directly from the surface of the nucleus, whereas in an alternative model, kinesin-1 moves nuclei indirectly by sliding anti-parallel microtubules. Here, we test the hypothesis that an ensemble of Kif5B motors acts from the nuclear envelope to distribute nuclei throughout the length of syncytial myotubes. First, using an inducible dimerization system, we show that controlled recruitment of truncated, constitutively active kinesin-1 motors to the nuclear envelope is sufficient to prevent the nuclear aggregation resulting from depletion of endogenous kinesin-1. Second, we identify a conserved kinesin light chain (KLC)-binding motif in the nuclear envelope proteins nesprin-1 and nesprin-2, and show that recruitment of the motor complex to the nucleus via this LEWD motif is essential for nuclear distribution. Together, our findings demonstrate that the nucleus is a kinesin-1 cargo in myotubes and that nesprins function as nuclear cargo adaptors. The importance of achieving and maintaining proper nuclear position is not restricted to muscle fibers, suggesting that the nesprin-dependent recruitment of kinesin-1 to the nuclear envelope through the interaction of a conserved LEWD motif with kinesin light chain might be a general mechanism for cell-typespecific nuclear positioning during development.

Centrifugal Displacement of Nuclei Reveals Multiple LINC Complex Mechanisms for Homeostatic Nuclear Positioning

“…A kinesin-1– nesprin-2 interaction contributes to nuclear spacing in syncytial myotubes [16], but forward nuclear recentering primarily occurred toward MT minus ends and depended on dynein (Figure 3). Dynein and nesprin-2 contribute to centrosomal-directed nuclear movement in migrating neurons, and dynein has been reported to associate with nesprin-2 [13, 41].…”

“…For example, in C. elegans ANC-1 interacts with actin filaments through paired calponin homology (CH) domains [8], whereas UNC-83 engages MTs through kinesin-1 and cytoplasmic dynein motor proteins [9]. In mammalian cells, nesprin-1G and nesprin-2G (“G” refers to the giant isoform) have paired CH domains that interact with actin filaments [10-12], but also engage MTs through MT motors [13-16]. Nesprin-2G's interaction with actin filaments is reinforced by its interaction with two other actin binding proteins, FHOD1 and fascin [17, 18].…”

“…During mouse brain development, nesprin-2 contributes to nuclear movement necessary for neuronal migration, probably by interacting with MTs through kinesin and/or dynein motors [13]. Similarly, nesprin-2 contributes to nuclear spacing in multi-nucleated myotubes by interacting with MTs via kinesin-1 [16]. Nesprin-4 interacts with kinesin-1 to move the nucleus away from the centrosome in epithelial cells and disruption of nesprin-4 leads nuclear positioning defects in hair cells and deafness [21, 25].…”

Muscle Development: Nucleating Microtubules at the Nuclear Envelope

“…The additional model is the cargo model. The Holzbaur lab showed that Nesprin-1 and Nesprin-2 recruit kinesin-1 to cargo, the nucleus, through their LEWD motifs that binds directly to kinesin light chains [19]. This model is distinct from the microtubule-nucleation model because mutating the LEWD motif in Nesprin-1α did not disrupt the microtubule-nucleation activity of Nesprin-1α [7].…”

Nuclear envelope: positioning nuclei and organizing synapses

“…Together, these results suggest LINC complexes are primarily involved in centrosome-mediated nuclear translocations, where mechanical forces are exerted by kinesin-1 and dynein whose direct interactions with KASH proteins are conserved in evolution [28,44–47]. Actin networks may also contribute to this force, since an actin-dependent pathway acts in parallel with SUN/KASH interactions to move nuclei in C. elegans [48].…”