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Kinesin-1 drives the movement of diverse cargoes, and it has been proposed that specific kinesin light chain (KLC) isoforms target kinesin-1 to these different structures. Here, we test this hypothesis using two in vitro motility assays, which reconstitute the movement of rough endoplasmic reticulum (RER) and vesicles present in a Golgi membrane fraction. We generated GST-tagged fusion proteins of KLC1B and KLC1D that included the tetratricopeptide repeat domain and the variable C-terminus. We find that preincubation of RER with KLC1B inhibits RER motility, whereas KLC1D does not. In contrast, Golgi fraction vesicle movement is inhibited by KLC1D but not KLC1B reagents. Both RER and vesicle movement is inhibited by preincubation with the GST-tagged C-terminal domain of ubiquitous kinesin heavy chain (uKHC), which binds to the N-terminal domain of uKHC and alters its interaction with microtubules. We propose that although the TRR domains are required for cargo binding, it is the variable C-terminal region of KLCs that are vital for targeting kinesin-1 to different cellular structures. [ABSTRACT FROM AUTHOR]

While the subcellular organisation of mitochondria is likely to influence many aspects of cell physiology, its molecular control is poorly understood. Here, we have investigated the role of the retrograde motor protein complex, dyneindynactin, in mitochondrial localisation and morphology. Disruption of dynein function, achieved in HeLa cells either by over-expressing the dynactin subunit, dynamitin (p50), or by microinjection of an anti-dynein intermediate chain antibody, resulted in (a) the redistribution of mitochondria to the nuclear periphery, and (b) the formation of long and highly branched mitochondrial structures. Suggesting that an alteration in the balance between mitochondrial fission and fusion may be involved in both of these changes, overexpression of p50 induced the translocation of the fission factor dynamin-related protein (Drp1) from mitochondrial membranes to the cytosol and microsomes. Moreover, a dominant-negative-acting form of Drp1 mimicked the effects of p50 on mitochondrial morphology, while wild-type Drp1 almost completely restored normal mitochondrial distribution in p50 over-expressing cells. Thus, the dynein/dynactin complex plays an unexpected role in the regulation of mitochondrial morphology in living cells, by controlling the recruitment of Drp1 to these organelles. [ABSTRACT FROM AUTHOR]

LIS1, NDE1 and NDEL1 modulate cytoplasmic dynein function in several cellular contexts. However, evidence that they regulate dynein-dependent organelle positioning is limited. Here, we show that depletion of NDE1 or NDEL1 alone profoundly affected the organisation of the Golgi complex but did not cause it to disperse, and slightly affected the position of endocytic compartments. However, striking dispersal of organelles was observed when both NDE1 and NDEL1 were depleted. A substantial portion of NDE1 and NDEL1 is membrane associated, and depletion of these proteins led to complete loss of dynein from membranes. Knockdown of LIS1 also caused the Golgi complex to fragment and disperse throughout the cell, and caused endocytic compartments to relocalise to the periphery. Depletion of LIS1, which is primarily cytosolic, led to partial loss of membrane-associated dynein, without affecting NDE1 and NDEL1. These data suggest that NDE1 and NDEL1 act upstream of LIS1 in dynein recruitment, and/or activation, on the membrane. Consistent with this hypothesis, expression of exogenous NDE1 or NDEL1 rescued the effects of LIS1 depletion on Golgi organisation, whereas LIS1 was only partially effective at rescuing the loss of NDE1 and NDEL1. [ABSTRACT FROM AUTHOR]

Generating the extended endoplasmic reticulum (ER) network depends on microtubules, which act as tracks for motor-driven ER tubule movement, generate the force to extend ER tubules by means of attachment to growing microtubule plus-ends and provide static attachment points. We have analysed ER dynamics in living VERO cells and find that most ER tubule extension is driven by microtubule motors. Surprisingly, we observe that ∼50% of rapid ER tubule movements occur in the direction of the centre of the cell, driven by cytoplasmic dynein. Inhibition of this movement leads to an accumulation of lamellar ER in the cell periphery. By expressing dominant-negative kinesin-1 constructs, we show that kinesin-1 drives ER tubule extension towards the cell periphery and that this motility is dependent on the KLC1B kinesin light chain splice form but not on KLC1D. Inhibition of kinesin-1 promotes a shift from tubular to lamellar morphology and slows down the recovery of the ER network after microtubule depolymerisation and regrowth. These observations reconcile previous conflicting studies of kinesin-1 function in ER motility in vivo. Furthermore, our data reveal that cytoplasmic dynein plays a role in ER motility in a mammalian cultured cell, demonstrating that ER motility is more complex than previously thought. [ABSTRACT FROM AUTHOR]