WDR75

WDR75 is a nucleolar component of the small subunit (SSU) processome that supports biogenesis of the small ribosomal subunit, a role conserved from its yeast ortholog Nan1/Utp17 (PMID:15356263, PMID:34611297). Within the early SSU processome it is positioned near the 5'ETS, ITS1, and U3 snoRNA elements of the nascent 35S pre-rRNA, and it binds an evolutionarily conserved motif in the external transcribed spacer of rRNA to help assemble the particle (PMID:35076539, PMID:39932919). In human cells WDR75 is required for pre-rRNA transcription: its depletion lowers levels of the RNA Polymerase I subunit RPA194 and impairs pre-rRNA processing, including A0/A0-type cleavage (PMID:34611297, PMID:42099922). Loss of WDR75 function triggers the nucleolar stress response, activating the RPL5/RPL11-dependent p53 checkpoint with downstream p21 induction, driving impaired proliferation and cellular senescence; under nucleolar stress WDR75 itself relocalizes to nucleolar caps (PMID:34611297, PMID:42099922). Compound-heterozygous WDR75 variants in patient-derived cells produce these same processing and p53-pathway defects, linking WDR75 dysfunction to human disease (PMID:42099922).

1. 2004 Medium

   Established that the WDR75 ortholog is a constituent of the ribosome-biogenesis machinery whose loss blocks the cell cycle, defining its core cellular role.

   Evidence Genetic depletion of SSU processome proteins in S. cerevisiae and S. pombe with cell cycle readouts

   PMID:15356263

   Open questions at the time

   • Yeast ortholog only — human function not directly tested here
   • Molecular function of Nan1/Utp17 within the complex not resolved
2. 2021 High

   Connected human WDR75 to pre-rRNA transcription and the nucleolar stress checkpoint, showing how its loss converts a biogenesis defect into a p53-mediated proliferative arrest.

   Evidence siRNA knockdown in U2OS, fractionation, immunofluorescence of GFP-WDR75 under nucleolar stress, western blots for RPA194 and p53, proliferation/senescence assays

   PMID:34611297

   Open questions at the time

   • Mechanism by which WDR75 maintains RPA194 levels not defined
   • Single lab; cap relocalization function unknown
3. 2022 Medium

   Placed the ortholog architecturally near specific pre-rRNA spacer and U3 snoRNA elements, indicating direct engagement with the nascent transcript during early assembly.

   Evidence Tethered-MNase structural probing of yeast pre-ribosomal particles

   PMID:35076539

   Open questions at the time

   • Yeast system; human contacts inferred
   • Functional consequence of these contacts not tested
4. 2022 Low

   Identified Wdr75 as a positive regulator of stem-cell self-renewal, extending its biogenesis role to a developmental/proliferative phenotype.

   Evidence Genome-wide CRISPR-Cas9 knockout screen in mouse ESCs with sgRNA depletion readout

   PMID:35019759

   Open questions at the time

   • Screen-based hit with limited Wdr75-specific mechanistic follow-up
   • Link to ribosome biogenesis in this context not established
5. 2025 Low

   Argued that the rRNA-binding interface of WDR75 is under purifying selection, supporting a functionally constrained direct contact with the ETS motif.

   Evidence Comparative evolutionary and structural-prediction analysis of 70 mammalian WDR75 sequences

   PMID:39932919

   Open questions at the time

   • Computational only — no direct biochemical binding assay
   • Beta-sheet residue contacts not experimentally validated
6. 2026 Medium

   Tied WDR75 variants to human disease by showing patient and CRISPR-engineered cells recapitulate the pre-rRNA processing defect and p53-pathway activation.

   Evidence Pre-rRNA processing assays and p21 western blotting in patient-derived and CRISPR/Cas9-edited cells carrying compound-heterozygous variants

   PMID:42099922

   Open questions at the time

   • Authors note association rather than proven causality
   • Specific disease entity and full clinical mechanism not established here

• How WDR75 mechanistically sustains RNA Pol I subunit RPA194 levels and couples SSU processome assembly to the p53 checkpoint remains unresolved.
• No direct biochemical demonstration of human WDR75–rRNA binding
• Mechanism linking WDR75 loss to RPA194 reduction unknown
• Structure of human SSU processome with WDR75 not determined