Hecw controls oogenesis and neuronal homeostasis by promoting the liquid state of ribonucleoprotein particles

Valentina Fajner,Simona Polo,Emanuele Martini,Amanda Oldani,Giuliana Cesare,Elena Maspero,Francesco Napoletano,Thomas Vaccari,Dario Parazzoli,Simona Sala,Roberto Cerbino,Fabio Giavazzi

doi:10.1038/s41467-021-25809-8

Abstract

Specialised ribonucleoprotein (RNP) granules are a hallmark of polarized cells, like neurons and germ cells. Among their main functions is the spatial and temporal modulation of the activity of specific mRNA transcripts that allow specification of primary embryonic axes. While RNPs composition and role are well established, their regulation is poorly defined. Here, we demonstrate that Hecw, a newly identified Drosophila ubiquitin ligase, is a key modulator of RNPs in oogenesis and neurons. Hecw depletion leads to the formation of enlarged granules that transition from a liquid to a gel-like state. Loss of Hecw activity results in defective oogenesis, premature aging and climbing defects associated with neuronal loss. At the molecular level, reduced ubiquitination of the Fmrp impairs its translational repressor activity, resulting in altered Orb expression in nurse cells and Profilin in neurons.

Highlights

Specialised ribonucleoprotein (RNP) granules are a hallmark of polarized cells, like neurons and germ cells
By searching the Drosophila genome, we identified a single ortholog of human HECW1 and 2, encoded by the uncharacterised gene CG42797, whose protein product shares co-linearity and 40% overall similarity with the corresponding human proteins
Extensive amino acid sequence identity is present in two WW domains required for substrate interaction and in the catalytic HECT domain (Fig. 1a and Supplementary Fig. 1a)

Summary

Introduction

Specialised ribonucleoprotein (RNP) granules are a hallmark of polarized cells, like neurons and germ cells. NEDD4 ligases modify multiple substrates by monoubiquitination[13,14] or by addition of K63-linked Ub chains[15] to support a variety of cellular functions, such as protein trafficking, signalling regulation or lysosomal degradation By virtue of such multifaceted activity, the NEDD4 family of HECT ligases is known to contribute to a wide range of physiological and pathologic processes, including immune regulation, viral infection, tumorigenesis and neurological disorders[16]. We investigate the molecular, cellular and organismal functions of a previously uncharacterised member of the NEDD4 family in Drosophila to reveal an unexpected and pivotal role for non-degradative ubiquitination in maintaining the liquid state of germ- and neuronal RNP granules

Methods

Results

Conclusion