Figure 1

(a) Fluorescent micrograph of a skin fibroblast incubated with fluorescent dextran, shows perinuclear accumulation of vesicles at 15 min postincubation (See Ref. 9 for more images). A cartoon of MT structure is superimposed. The coordinates used to locate vesicles are also shown—$r$ and $\eta =r/(r+b)$. (b) A schematic showing the multiple states of a vesicle—(i) $s=0$: freely diffusing with diffusivity $D_0$, (ii) $s=1$: bound to MT, plus end movement with speed $v_{+}$ and (iii) $s=-1$: bound to MT, minus end movement with speed $v_{-}$. Binding/unbinding rates are described by first-order rate constants $k_{\pm }$ and $k_{\pm }^{\prime }$, respectively, which, in turn, determine the fraction $f$ of particles undergoing directed transport at a given time, $f=\frac{K_{+}+K_{-}}{K_{+}+K_{-}+1},K_{+}=k_{+}/k_{-}^{\prime }\mathrm{\text{and}}{K}_{-}=k_{-}/k_{-}^{\prime }$.Reuse & Permissions

Figure 2

Confinement of vesicle motion to one dimension. (a) Trajectories of 350 actively transported vesicles are plotted such that the geometric center of the nucleus of the parent cell is shifted to the origin (star). Scale bar is $20\mu \mathrm{m}$. (b) Mean squared displacements averaged over all active trajectories, for the whole trajectory (▪) and radial ($○$) and orthoradial ($△$) projections of the trajectory. Mean squared displacements were fitted to $⟨r^2⟩=a{t}^{\gamma }$ separately for the radial and orthoradial components and, respectively, yielded $\gamma =1.46$ and 0.93 showing directed transport in radial direction and diffusive transport in the orthoradial direction. The orthoradial diffusion coefficient was estimated to be $0.009\mu {\mathrm{m}}^2/\sec $.Reuse & Permissions

Figure 3

Distribution of frame to frame speeds in the plus (solid) and minus (open) directions for dextran (triangles) and PEI-DNA (circles). Inset: Distribution of run lengths in the plus and minus directions (same legend) is also identical. These distributions are fitted to an exponential function to obtain $⟨v_{+}⟩=⟨v_{-}⟩=⟨v⟩=0.33\mu \mathrm{m}/\sec$, ($r^2=0.96$) and $k_{+}^{\prime }=k_{-}^{\prime }=k^{\prime }=0.34\mathrm{se}{\mathrm{c}}^{-1}$ ($r^2=0.99$). See Ref. 9, Sec. F for a comparison with other systems in literature.Reuse & Permissions

Figure 4

(a) Concentration of vesicles $c(r,t)$. (i) PEI-DNA vesicles at short time (12–30 min postincubation, $●$). Similar curves were observed for other vesicles and are not shown for clarity, (ii) Distribution of dextran ($\square$) at 10–30 min, LDL ($△$) at 30–150 min, and PEI-DNA ($○$) at 60–180 min postincubation. Over these time periods, the distribution does not change. Asterisks mark the abscissae where short time data ($●$) are statistically different from long time data ($○$), $p<0.05$. (b) Distribution of vesicles $p(\eta ,t)$. PEI-DNA containing vesicles at short time (12–30 min postincubation) showing $p(\eta )=2\eta$, ($r^2=0.9$ for a linear fit, $●$); at intermediate times (30–45 min, $\diamond$); and at long times (60–180 min, $○$) and distribution of dextran ($\square$) and LDL ($△$) containing vesicles at quasi-steady-state. (c) Immunolabeled microtubules (anti-$\alpha$ tubulin, [15]) with the nuclear and cell membranes superimposed. Arrow points towards the MTOC and (d) concentration of MTs in pixel $\mathrm{\text{intensity}}/\mu {\mathrm{m}}^2$ ($○$) and concentration of PEI-DNA vesicles in $\#/\mu {\mathrm{m}}^2$ ($●$) as a function of distance from the nuclear membrane.Reuse & Permissions

Figure 5

(a) Average mean squared displacement for simulated trajectories (solid line) and the experimentally measured trajectories ($○$). A clear crossover from the sub-ballistic to diffusive regime occurs between $t=10–100\sec $. See Ref. 9 for a discussion of MSD at very short time scales ($t<1$). Inset: Variation of $\gamma$, (where $\mathrm{MSD}\sim t^{\gamma }$) with $t$ for measured trajectories ($●$) and simulated trajectories (solid line). (b) Comparison of predicted and observed time required for 95% equilibration for dextran ($\square$), LDL ($△$), and PEI-DNA ($●$). In the presence of nocodazole (▽), a microtubule-destabilizing drug, $t$ approaches infinity, calculated here by assuming $D^{\mathrm{eff}}=D_0={10}^{-3}\mu {\mathrm{m}}^2/\sec$.Reuse & Permissions