Modeling organelle transport in branching dendrites with a variable cross-sectional area

Abstract

The purpose of this paper is to develop a method for calculating organelle transport in dendrites with a non-uniform cross-sectional area that depends on the distance from the neuron soma. The model is based on modified Smith-Simmons equations governing molecular motor-assisted organelle transport. The developed method is then applied to simulating organelle transport in branching dendrites with two particular microtubule (MT) orientations reported from experiments. It is found that the rate of organelle transport toward a dendrite's growth cone heavily depends on the MT orientation, and since there is experimental evidence that the MT orientation in a particular region of a dendrite may depend on the dendrite's developmental stage, the obtained results suggest that a rearrangement of the MT structure may depend on the amount of organelles needed at the growth cone.

Keywords: Axons and dendrites; Intracellular organelles; Molecular motors; Motor-assisted transport; Neurons.

Fig. 1

a Schematic diagram of the MT orientation in a dendrite with a mixed polarity orientation in a proximal dendrite and plus-end-out orientation in distal dendrites (dendrite 1), b Schematic diagram of the MT orientation in a dendrite with a mixed polarity orientation in both proximal and distal dendrites (dendrite 2), c kinetic diagram showing various organelle populations and kinetic processes between them

Fig. 2

a Distributions of the number density of free organelles with plus-end-directed motors attached to them, n_0 +, b Distributions of the number density of free organelles with minus-end-directed motors attached to them, n_0 −

Fig. 3

a Distributions of the number density of organelles transported on MTs by plus-end-directed motors, n₊, b Distributions of the number density of organelles transported on MTs by minus-end-directed motors, n₋

Fig. 4

a Distributions of the number densities of organelles transported on MTs anterogradely, n_anterograde, b Distributions of the number densities of organelles transported on MTs retrogradely, n_retrograde

Fig. 5

a Distributions of the rate of organelle transfer due to diffusion, j_diff, b Distributions of the rate of organelle transfer due to motor-driven transport, j_motor

Fig. 6

a Distributions of the total number density of organelles, n_t, b distributions of the total rate of organelle transfer (due to diffusion and motor-driven transport), j