UNC-83 is a nuclear-specific cargo adaptor for kinesin-1-mediated nuclear migration

Abstract

Intracellular nuclear migration is essential for many cellular events including fertilization, establishment of polarity, division and differentiation. How nuclei migrate is not understood at the molecular level. The C. elegans KASH protein UNC-83 is required for nuclear migration and localizes to the outer nuclear membrane. UNC-83 interacts with the inner nuclear membrane SUN protein UNC-84 and is proposed to connect the cytoskeleton to the nuclear lamina. Here, we show that UNC-83 also interacts with the kinesin-1 light chain KLC-2, as identified in a yeast two-hybrid screen and confirmed by in vitro assays. UNC-83 interacts with and recruits KLC-2 to the nuclear envelope in a heterologous tissue culture system. Additionally, analysis of mutant phenotypes demonstrated that both KLC-2 and the kinesin-1 heavy chain UNC-116 are required for nuclear migration. Finally, the requirement for UNC-83 in nuclear migration could be partially bypassed by expressing a synthetic outer nuclear membrane KLC-2::KASH fusion protein.Our data support a model in which UNC-83 plays a central role in nuclear migration by acting to bridge the nuclear envelope and as a kinesin-1 cargo-specific adaptor so that motor-generated forces specifically move the nucleus as a single unit.

Cell Biology of theCaenorhabditis elegansNucleus

“…Instead, the mechanism underlying the nuclear migration phenotypes is linked to NE-associated molecular motors. UNC-83 interacts with the kinesin 1 light chain KLC-2 and the dynein regulators BICD-1, NUD-2, and DLC-1 (Meyerzon et al 2009a;. Inhibition of kinesin 1 (klc-2, unc-116) or dynein (dhc-1, dlc-1, bicd-1, lis-1, nud-2) activity causes defects in hyp7 nuclear migration, whereas artificially tethering KLC-2 to the NE can rescue unc-83 nuclear migration defects, arguing that a major role of UNC-83 is to serve as a nuclear anchor for kinesin and dynein motors (Meyerzon et al 2009a;.…”

“…UNC-83 interacts with the kinesin 1 light chain KLC-2 and the dynein regulators BICD-1, NUD-2, and DLC-1 (Meyerzon et al 2009a;. Inhibition of kinesin 1 (klc-2, unc-116) or dynein (dhc-1, dlc-1, bicd-1, lis-1, nud-2) activity causes defects in hyp7 nuclear migration, whereas artificially tethering KLC-2 to the NE can rescue unc-83 nuclear migration defects, arguing that a major role of UNC-83 is to serve as a nuclear anchor for kinesin and dynein motors (Meyerzon et al 2009a;. Based on detailed time-lapse microscopy including analysis of microtubule dynamics, it has been proposed that the involvement of two different molecular motors increases the efficiency of nuclear migration by accommodating for bidirectional movements to bypass "roadblocks" .…”

toca-1 Is in a Novel Pathway That Functions in Parallel with a SUN-KASH Nuclear Envelope Bridge to Move Nuclei in Caenorhabditis elegans

“…The screen presented here was designed to identify novel mechanisms that function in parallel to SUN-KASH bridges. Our model system, C. elegans larval P-cell nuclear migration, is better suited for identifying such pathways than embryonic dorsal hyp7 precursors where the mechanisms of UNC-84 and UNC-83 were elucidated (McGee et al 2006;Meyerzon et al 2009;Tapley et al 2011). SUN-KASH bridges are absolutely required for nuclear migration in the embryonic hypodermis at all temperatures.…”

“…In the cytoplasm, UNC-83 acts as the nuclear-specific cargo adaptor to recruit the microtubule motors kinesin-1 and dynein to the cytoplasmic surface of the nucleus. Kinesin-1 then provides the mechanical forces to move nuclei while dynein mediates bidirectional movements of nuclei to avoid cellular roadblocks (Meyerzon et al 2009;. Similar SUN-KASH nuclear-envelope bridges are conserved from yeast to humans Starr 2011).…”

How plants LINC the SUN to KASH

“…10,29 UNC-83 in turn targets kinesin-1 and/or dynein to the nuclear periphery, and the force provided by the motor proteins drives the nuclear migration in C. elegans hypodermal P cells and embryonic hypodermal cells. [30][31][32] ANC-1 interacts with F-actin and is required for nuclear anchorage in the adult C. elegans syncytial hypodermis. 10 SUN-KASH complexes can also link chromosomes to the cytoskeleton.…”