Valentina Fajner

Ubiquitination is one of the most abundant and versatile post-translation modifications in eukaryotes, and it plays
an important role in many biological processes by affecting protein activity, interactions, localization and
stability. E3 ligases (E3s) have a key function as ubiquitin-substrate matchmakers, providing specificity to the
reaction, yet little is known about the targets and functions of the majority of E3s.
We identified and characterized dHecw, a novel member of the Drosophila melanogaster Nedd4 family of
ubiquitin E3s. dHecw is the single ortholog of the human HECT ligases HECW1 and HECW2, which are the
less characterized members of the family. dHecw expression is tightly regulated in the central nervous system
and in the ovary, and is down-modulated during aging. Catalytic inactive dHecw mutants and dHecw KO flies,
generated by CRISPR/Cas9 technology, presented signs of neurodegeneration, as short lifespan, limited motor
function and brain tissue vacuolization. They also showed premature decline in fertility due to germline specific
defects in oogenesis. dHecw interactome, identified by mass spectrometry analysis, presents several
ribonucleoparticles (RNPs) components, including dFmr1, a translational repressor that controls localized
mRNA translation in developing embryo. We demonstrated that dFmrp is a dHecw substrate in vitro, and we
found a genetic interaction among the two proteins. Our investigation of the functional outcome of dFmrp
ubiquitination suggests that it does not cause dFmrp degradation but, instead, it impacts on its function/interaction
network. Altogether, our data suggest that dHecw is a novel player involved in the dynamic regulation of RNPs
required for neuronal health and fertility.