NudE regulates dynein at kinetochores but is dispensable for other dynein functions in the C. elegans early embryo.

Patrícia A Simões,Reto Gassmann,Ana X Carvalho,Ricardo Celestino

doi:10.1242/jcs.212159

Abstract

ABSTRACTIn mitosis, the molecular motor dynein is recruited to kinetochores by the Rod–Zw10–Zwilch complex (RZZ) and Spindly to control spindle assembly checkpoint (SAC) signaling and microtubule attachment. How the ubiquitous dynein co-factors Lis1 and NudE contribute to these functions remains poorly understood. Here, we show that the C. elegans NudE homolog NUD-2 is dispensable for dynein- and LIS-1-dependent mitotic spindle assembly in the zygote. This facilitates functional characterization of kinetochore-localized NUD-2, which is recruited by the CENP-F-like proteins HCP-1 and HCP-2 independently of RZZ–Spindly and dynein–LIS-1. Kinetochore dynein levels are reduced in Δnud-2 embryos, and, as occurs upon RZZ inhibition, loss of NUD-2 delays the formation of load-bearing kinetochore–microtubule attachments and causes chromatin bridges in anaphase. Survival of Δnud-2 embryos requires a functional SAC, and kinetochores without NUD-2 recruit an excess of SAC proteins. Consistent with this, SAC signaling in early Δnud-2 embryos extends mitotic duration and prevents high rates of chromosome mis-segregation. Our results reveal that both NUD-2 and RZZ–Spindly are essential for dynein function at kinetochores, and that the gain in SAC strength during early embryonic development is relevant under conditions that mildly perturb mitosis.

Highlights

Accurate segregation of chromosomes during mitosis depends on attachments between spindle microtubules and the kinetochore, a multi-protein assembly that is localized on the centromeric region of each sister chromatid (Musacchio and Desai, 2017)
We show that the C. elegans NudE/L homolog NUD-2 is dispensable for dynein- and LIS-1-dependent mitotic spindle assembly in the zygote
This facilitates functional characterization of kinetochore-localized NUD-2, which is recruited by the CENP-F-like proteins HCP-1/2 independently of RZZ-Spindly and dynein-LIS-1

Summary

Introduction

Accurate segregation of chromosomes during mitosis depends on attachments between spindle microtubules and the kinetochore, a multi-protein assembly that is localized on the centromeric region of each sister chromatid (Musacchio and Desai, 2017). The molecular motor dynein localizes to the kinetochore and has been implicated in establishing initial contacts with the side of spindle microtubules (Alexander and Rieder, 1991; Pfarr et al, 1990; Steuer et al, 1990). Because chromosome bi-orientation is a stochastic process, cells use a signaling system called the spindle assembly checkpoint (SAC) to generate a diffusible cell cycle inhibitor at kinetochores that have not yet succeeded in establishing end-on microtubule attachments, thereby preventing premature sister chromatid separation that could lead to chromosome loss (Musacchio, 2015). Dynein's microtubule minus end-directed motor activity is thought to contribute to SAC silencing by transporting Mad1/Mad and other checkpoint proteins away from kinetochores towards spindle poles (referred to as 'stripping' or 'streaming') (Howell et al, 2001; Wojcik et al, 2001)

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