# Drosophila Trus, the orthologue of mammalian PDCD2L, is required for proper cell proliferation, larval developmental timing, and oogenesis

## TL;DR

This study shows that the Drosophila protein Trus is essential for normal cell growth, development timing, and egg production, and its absence causes developmental delays and death.

## Contribution

The study identifies Trus as a critical ribosome assembly factor required for development and reveals its role in activating a stress response that affects hormone production.

## Key findings

- Trus is essential for cell proliferation and larval development in Drosophila.
- Trus mutations trigger a ribosomal stress response that reduces ecdysone production, causing developmental delays.
- Trus interacts with RpS2 and eEF1α1, suggesting a role in ribosome biogenesis.

## Abstract

Toys are us (Trus) is the Drosophila melanogaster ortholog of mammalian Programmed Cell Death 2-Like (PDCD2L), a protein that has been implicated in ribosome biogenesis, cell cycle regulation, and oncogenesis. In this study, we examined the function of Trus during Drosophila development. CRISPR/Cas9 generated null mutations in trus lead to partial embryonic lethality, significant larval developmental delay, and complete pre-pupal lethality. In mutant larvae, we found decreased cell proliferation and growth defects in the brain and imaginal discs. Mapping relevant tissues for Trus function using trus RNAi and trus mutant rescue experiments revealed that imaginal disc defects are primarily responsible for the developmental delay, while the pre-pupal lethality is likely associated with faulty central nervous system (CNS) development. Examination of the molecular mechanism behind the developmental delay phenotype revealed that trus mutations induce the Xrp1-Dilp8 ribosomal stress-response in growth-impaired imaginal discs, and this signaling pathway attenuates production of the hormone ecdysone in the prothoracic gland. Additional Tap-tagging and mass spectrometry of components in Trus complexes isolated from Drosophila Kc cells identified Ribosomal protein subunit 2 (RpS2), which is coded by string of pearls (sop) in Drosophila, and Eukaryotic translation elongation factor 1 alpha 1 (eEF1α1) as interacting factors. We discuss the implication of these findings with respect to the similarity and differences in trus genetic null mutant phenotypes compared to the haplo-insufficiency phenotypes produced by heterozygosity for mutants in Minute genes and other genes involved in ribosome biogenesis.

Ribosomes are essential macromolecular machines required for decoding mRNA to make proteins, the major biomolecules that carry out all central cellular functions. As such, their structural and operational integrity is critical to organismal survival, and mutations that disrupt proper stoichiometry or assembly of ribosomes produce serious pathological consequences during an organism’s development and/or adult life. The ribosome assembly factor PDCD2L is highly conserved from yeast to human, yet its overall function and requirement during development are poorly understood. By examining the developmental consequences of null mutations in trus, which encodes the Drosophila PDCD2L ortholog, we demonstrate an essential role for this factor in cell-cycle regulation. Furthermore, disruption of Trus function in mitotically dividing imaginal tissue activates the Xrp1-dilp8 stress response pathway which limits production of ecdysone, the major arthropod molting hormone, leading to severe developmental delay during larval stages. These studies provide new insights on the requirements of this highly conserved ribosome assemble factor during development.