STATEMENT 1 Proper localization and functions of macromolecules during cell division are crucial to 2 ensure survival and proliferation of daughter cells. 3 4 ABSTRACT 1 Staufen1 (STAU1) is an RNA-binding protein involved in the posttranscriptional 2 regulation of mRNAs. We report that a large fraction of STAU1 localizes to the mitotic 3 spindle in the colorectal cancer HCT116 and in the non-transformed hTERT-RPE1 cells. 4Spindle-associated STAU1 partly co-localizes with ribosomes and active sites of 5 translation. We mapped the molecular determinant required for STAU1/spindle association 6 within the first 88 N-terminal amino acids, a domain that is not required for RNA binding. 7Interestingly, transcriptomic analysis of purified mitotic spindles reveals that 1054 mRNAs 8 as well as the precursor ribosomal RNA and lncRNAs and snoRNAs involved in 9 ribonucleoprotein assembly and processing are enriched on spindles compared to cell 10 extracts. STAU1 knockout causes the displacement of the pre-rRNA and of 154 mRNAs 11 coding for proteins involved in actin cytoskeleton organization and cell growth, 12 highlighting a role for STAU1 in mRNA trafficking to spindle. These data demonstrate 13 that STAU1 controls the localization of sub-populations of RNAs during mitosis and 14 suggests a novel role of STAU1 in pre-rRNA maintenance during mitosis, ribogenesis 15 and/or nucleoli reassembly. 16 17 18