PPP1R35

PPP1R35 is a resident centriolar protein that drives centriole elongation and the conversion of nascent daughter centrioles into functional centrosomes during the cell cycle (PMID:30168418, PMID:30230954). It occupies the proximal centriole lumen above the cartwheel, where it acts downstream of and in complex with the microcephaly protein RTTN; loss of PPP1R35 yields fewer centrioles, shortened structures lacking distal and microtubule-wall proteins, and failure of centriole elongation (PMID:30168418). PPP1R35 is enriched at newborn daughter centrioles in S/G2 phase and is required for centriole-to-centrosome conversion, acting upstream of CEP295: without PPP1R35, nascent centrioles fail to recruit CEP295 and disintegrate after mitosis when the cartwheel is removed, and this function is independent of its putative PP1-interacting motif (PMID:30230954). In vivo, Ppp1r35 is essential for primary cilia formation, notochord integrity, floor-plate specification, and cell-cycle progression, with its loss causing prometaphase stalling and increased cell death during mammalian development (PMID:32628936). PPP1R35 is a direct phosphorylation substrate of the kinase CDKL5 and interacts with the CDKL5 phospho-target CEP131 (PMID:39136782).

1. 2018 High

   Established that PPP1R35 is a structural centriole-lumen protein required for centriole elongation, placing it in a defined pathway downstream of RTTN.

   Evidence Super-resolution mapping, live-cell imaging, BioID proximity proteomics, and loss-of-function in human cells

   PMID:30168418

   Open questions at the time

   • The molecular activity by which PPP1R35 promotes elongation is undefined
   • Whether the RTTN complex is direct or bridged by other factors is not resolved
   • No structural model of PPP1R35 in the centriole lumen
2. 2018 High

   Defined PPP1R35's cell-cycle-staged role in centriole-to-centrosome conversion, ordering it upstream of CEP295 and showing its function is independent of the predicted PP1-interacting motif.

   Evidence Immunofluorescence, PPP1R35-null cells, epistasis with CEP295, and domain-mutant analysis

   PMID:30230954

   Open questions at the time

   • How PPP1R35 enables CEP295 recruitment mechanistically is unknown
   • The function of the conserved PP1-interacting motif, if any, is unexplained
   • Whether PPP1R35 binds a phosphatase at all remains untested
3. 2020 High

   Demonstrated that PPP1R35 is essential in vivo, linking its centriole/cilia function to embryonic patterning and cell-cycle homeostasis.

   Evidence Mouse homozygous knockout with histological, molecular-marker, cell-death, and proliferation analyses

   PMID:32628936

   Open questions at the time

   • Tissue-specific requirements versus a general centriole defect are not separated
   • Whether ciliary and notochord phenotypes are direct or secondary to cell-cycle stalling is unresolved
4. 2024 Medium

   Identified PPP1R35 as a direct CDKL5 phosphorylation substrate, introducing regulatory control over the protein and a link to centriolar satellite biology via CEP131.

   Evidence Phosphoproteomics in iPSC-derived neurons, in vitro kinase assay, and co-IP with CEP131

   PMID:39136782

   Open questions at the time

   • Functional consequence of the CDKL5 phosphosite on centriole elongation or CCC is untested
   • Whether the CEP131 interaction is direct or part of a larger complex is unclear
   • Single lab; full validation methods not detailed

• The biochemical activity of PPP1R35 and how its phosphorylation by CDKL5 modulates centriole elongation and conversion remain unknown.
• No defined enzymatic or scaffolding activity assigned
• No structural basis for RTTN or CEP295 functional dependence
• No mechanistic link between CDKL5 phosphorylation and centriole function