Intra-manchette transport employs both microtubule and actin tracks

Abstract

The manchette is a transient microtubule based structure that plays a vital role in nuclear shaping during spermio-genesis. It comprises thousands of microtubules (MTs) that build a scaffold around the distal half of the nucleus. The manchette distributes proteins and vesicles during spermio-genesis in a process called intra-manchette transport (IMT). The current hypothesis is that IMT shares many similarities with intra-flagellar transport (IFT) and utilizes both MTs and filamentous actin (F-actin). However, IMT is still poorly understood as direct visualization of IMT complexes is missing, and the presence of F-actin has not been experimentally shown. Here, we use proteomics and cryogenic-electron tomography (cryo-ET) to identify and visualize IMT components. We find that F-actin is an integral part of the manchette with two different spatial organizations, namely bundles and single filaments, providing tracks for transport as well as having structural and mechanical roles. We further uncover that IMT on MTs is mediated by two distinct transport machineries: a dynein-mediated transport of soluble cargo and a dynein-independent transport for vesicles. Our results provide new insights into the manchettes function as a transport scaffold, highlighting its significance for the polarization of spermatids during spermiogenesis.