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RpS19a depletion alters the haematopoietic translatome to directly drive tissue overgrowth I

ABSTRACT: Counterintuitively, increased tumour predisposition is associated with ribosomal protein (RP) loss. Here, we provide the first evidence that RP depletion can directly drive tissue overgrowth. Haematopoietic compartment-specific knockdown (KD) of RpS19a in the Drosophila lymph gland not only results in haematopoietic stem and progenitor cell (HSPC) loss but also drives excess proliferation and tissue overgrowth. In accordance with continued ribosome assembly and protein synthesis, actively translating ribosomes (polysomes) are detected in RpS19a KD Drosophila S2 cells. The RpS19a KD ribosomes do, however, display heterogeneity and significantly altered stoichiometry of the associated translation initiation factors eIF4A and eIF5. Consistent with altered translation, in addition to increased association between polysomes and mRNA encoding growth promoting genes (e.g. Ras), we observe increased abundance of the ortholog of ribosomal (r)RNA small subunit methyltransferase NEP1. Although uncharacterised in Drosophila, in yeast and human NEP1 is implicated in methylation of 18S rRNA and, thus, 40S assembly and 80S ribosome stability. Moreover, NEP1 (EMG1) mutations in humans underpin Bowen-Conradi syndrome, a ribosomopathy associated with developmental defects, growth failure, and infantile death. Remarkably, NEP1 depletion suppresses the RpS19a KD phenotype, restoring both stem and progenitor cells and suppressing lymph gland overgrowth. We further demonstrate NEP1 depletion significantly decreases methylation of the 18S rRNA residue (Ψ1,279) that is implicated in ribosome assembly. Together, these data suggest the increased NEP1 expression associated with RpS19a KD promotes assembly of pro-proliferative “onco-ribosomes” to drive haematopoietic compartment overgrowth.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE236307 | GEO | 2024/06/30

REPOSITORIES: GEO

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Project description:We use mRNA-seq in combination with polysome profiling to determine translational status for all mRNAs in Drosophila mature oocytes and activated eggs. Puromycin-treated lysates are used as a negative control in polysome profiling experiments. Additionally, we use ribosome footprinting to globally measure translational efficiency of mRNAs in wild type mature oocytes as well as wild type and png mutant activated eggs. Lysates of hand-dissected Drosophila mature oocytes (containing ~540 M-NM-<g of total RNA) were subjected to separation by velocity sedimentation through sucrose gradients. In this way, free mRNAs (present in RNPs fraction) or those comigrating with ribosomal subunits (40S or 60S+80S fractions) or with varying numbers of bound ribosomes (low polysomes (2-4 ribosomes), medium polysomes (5-9 ribosomes), and heavy polysomes (more than 10 ribosomes) can be separated based on their size and collected as sucrose gradient fractions. To compare quantitatively the levels of every mRNA across the polysome gradient fractions, we added 5ng of S. cerevisiae mRNA as an exogenous spike-in to each of the six fractions of interest: RNPs, 40S, 60S+80S, low polysomes, medium polysomes and heavy polysomes. RNA was extraced from these fractions, follwing proteinase K treatment, by hot acid phenol method. In case of unfractionated lysates, RNA was extracted using TRIzol (Invitrogen) according to manufacturerM-bM-^@M-^Ys instructions. mRNA-seq samples were prepared from 1 M-NM-<g of total RNA (in case of sucrose gradient fractions and unfractionated lysates) and subject to Illumina based sequencing. Puromycin-treated lysates of mature oocytes or 0-2h Drosophila activated eggs (containing ~540 M-NM-<g of total RNA) were also subjected to separation by velocity sedimentation through sucrose gradients. Puromycin causes premature termination of elongating ribosomes and thus it can be used to determine whether the mRNAs co-sedimenting with the polysomal peaks (defined here as M-bM-^IM-%5 ribosomes) were actively engaged in translation. As an independent approach to assess translation and obtain information on the position of ribosomes on mRNAs, we employed ribosome footprinting. In addition to analyzing the same samples, as by polysome profiling, we also analyzed png mutant activated eggs by ribosome footprinting. Ribosome footprint profiling measures the number of ribosome-protected fragments (RPFs) derived from the mRNAs of each gene, resulting in a singular value of translational efficiency (TE) for each gene (TE=RPF/RNA).

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RpS19a depletion alters the haematopoietic translatome to directly drive tissue overgrowth I

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