New mode of mitochondrial transport and polarized sorting regulation by Dynein, Milton and Miro

Abstract

Intrinsic cell microtubule (MT) polarity, together with molecular motors and adaptor proteins, determines mitochondrial polarized targeting and MT-dependent transport. In polarized cells, such as neurons, mitochondrial mobility and transport require the regulation of kinesin and dynein by two adaptor proteins, Milton and Miro. Recently, we found that dynein heavy chain 64C (Dhc64C) is the primary motor protein for both anterograde and retrograde transport of mitochondria in the Drosophila bristle. In this study, we revealed that a molecular lesion in the Dhc64C allele that reduced bristle mitochondrial velocity generated a variant that acts as a "slow" dynein in a MT gliding assay, indicative of dynein directly regulating mitochondrial transport. We also showed that in milton RNAi flies, mitochondrial flux into the bristle shaft but not velocity was significantly reduced. Surprisingly, mitochondria retrograde flux but not net velocity was significantly decreased in miro RNAi flies. We thus revealed a new mode of mitochondrial polarized sorting in polarized cell growth, whereby bi-directional mitochondrial transport undertaken exclusively by dynein is regulated by Milton in anterograde direction and by a Miro-dependent switch to retrograde direction.