library_construction_protocol: Bone marrow cells were isolated by flushing femurs, tibias, ilia and humerus with PBS. Cells were filtered through a 70µM cell strainer to obtain single cell suspensions and cell number was assessed by counting with a hemocytometer. Cell suspensions were first enriched for lineage-negative cells by MACS using Mouse Lineage cell depletion kit (Miltenyi Biotec) before staining for cell-surface antigens. Cells were stained for 30 minutes using the following rat anti-mouse monoclonal antibodies: Lineage cocktail (145-2C11, RA3-6B2, RB6-8C5, M1/70 and TER-119)-PE, CD34 (RAM34) -FITC, CD150 (Q8-480)-BV421, CD150 (mShad150) - PerCP-eFluor710, CD48 (HM48-1) -APC-Cy7, CD127 (SB/199) -V450. All reagents were purchased from ThermoFisher Scientific, BD Bioscience or BioLegend. For polysome profiling analysis, 1-2x10^6 CD127- MyPs pooled from 5 Elp3fl/fl and 10 Elp3HscKO mice were FACS-sorted in biological triplicate on a FACS Aria 2 (BD Bioscience) Pellets were lyzed in hypotonic buffer as in (Liang et al., 2017, https://doi.org/10.1093/nar/gkx940) and 10% of each sample, corresponding to total RNA, were directly lyzed in Trizol and snap-frozen. The remaining cells were further loaded in a non-linear gradient as described in (Liang et al., 2017). Fractions corresponding to heavy polysomes were pooled, lyzed in Trizol and snap-frozen. RNA was extracted using Direct-zol™ RNA MiniPrep Plus (Zymo Research) and cleaned of potential DNA contamination with RNeasy MinElute Cleanup Kit (Qiagen). cDNA was synthesized with 10 ng of total RNA using the SMART-SeqTM v4 UltraTM Low input RNA Kit for Sequencing (Clontech Laboratories) and amplified by 7 cycles of locked-DNA PCR. The sequencing library was generated using the Nextera XT DNA Library Preparation (Illumina) according to the manufacturer's instructions. Libraries were submitted to quality control on a QIAxcel (Qiagen) and to quantification using a KAPA Library Quantification Kit (Kapa Biosystems). Libraries were subsequently normalized and pooled.