CenH3

PF3D7_1333700 (CenH3) is the centromere-specific histone H3 variant of Plasmodium falciparum that defines centromeric chromatin and nucleates kinetochore assembly for chromosome segregation (PMID:22507744, PMID:24316361). First identified as a genome-encoded histone variant that escaped detection in acid-extracted histone proteomics, consistent with low abundance or restricted expression (PMID:16410041), CenH3 was subsequently shown by ChIP-seq to occupy a discrete ~4–4.5 kb chromatin region on every P. falciparum chromosome, co-localising with the histone variant PfH2A.Z and excluded from pericentric heterochromatin (PMID:22507744). Its C-terminal histone fold domain—specifically the CATD region and its LLAL residues—is required for centromere targeting and functional chromosome segregation, as canonical H3 fails but CenH3 complements the segregation defect of a yeast Cse4p temperature-sensitive mutant (PMID:24316361). CenH3 provides the platform for inner kinetochore assembly by associating with PfCENP-C, which occupies CenH3-marked loci in vivo, and it further associates with the mitotic spindle (PMID:24316361, PMID:25476240). Across the cell cycle CenH3-marked centromeres cluster to a single nuclear focus during schizogony (PMID:22507744) and, in gametocytes, are captured by a non-mitotic hemispindle in a microtubule-dependent manner (PMID:36030238); conversely, CenH3's own centromeric localisation depends on intact kinetochore assembly, since conditional disruption of PfNDC80/PfNuf2 disrupts the CenH3 mark (PMID:38987258). Beyond these findings, the biophysics of CenH3 nucleosome deposition and its dedicated chaperone machinery have not been characterized in the available corpus.

1. 2006 Medium

   Establishing whether P. falciparum encodes a centromeric H3 variant at all was the first step; genome analysis identified CenH3 but its protein was not detected proteomically, flagging low abundance or restricted expression as a defining feature.

   Evidence genome analysis, mass spectrometry of acid-extracted histones, RT-PCR and immunoblotting in P. falciparum

   PMID:16410041

   Open questions at the time

   • Negative MS detection does not distinguish low abundance from absent expression
   • No localisation or functional data at this stage
   • Cell-cycle expression profile not resolved
2. 2012 High

   Where CenH3 sits in the genome and how it behaves across the cell cycle was unknown; genome-wide ChIP-seq defined discrete ~4–4.5 kb centromeric domains on all chromosomes co-marked with PfH2A.Z, and imaging showed centromere clustering to a single focus during schizogony.

   Evidence ChIP-seq across all 14 chromosomes plus cell-cycle immunofluorescence in P. falciparum

   PMID:22507744

   Open questions at the time

   • Sequence/structural determinants of centromere targeting not defined
   • Mechanism of centromere clustering unknown
   • Deposition machinery not identified
3. 2013 High

   Which region confers CenH3 identity and function was resolved by mapping targeting to the CATD/LLAL residues of the histone fold domain, with heterologous yeast complementation proving functional conservation and co-IP linking CenH3 to PfCENP-C.

   Evidence site-directed mutagenesis, functional complementation of a S. cerevisiae Cse4p ts mutant, and co-immunoprecipitation

   PMID:24316361

   Open questions at the time

   • Structural basis of CATD-mediated targeting in P. falciparum not solved
   • Direct vs indirect nature of the CenH3–PfCENP-C interaction not established
   • In vivo requirement of LLAL residues in the parasite untested
4. 2014 Medium

   Whether CenH3 serves as the assembly platform for the kinetochore was addressed by showing reciprocal association with PfCENP-C and mitotic spindles, with ChIP-PCR placing PfCENP-C at CenH3-marked loci in vivo.

   Evidence co-immunoprecipitation/pull-down and ChIP-PCR in P. falciparum

   PMID:25476240

   Open questions at the time

   • Full inner kinetochore composition anchored by CenH3 not defined
   • Spindle association may be indirect
   • CenH3 role largely inferred from partner characterisation
5. 2022 Medium

   Whether CenH3 organisation extends beyond mitosis was tested in gametocytes, showing CenH3-marked centromeres are captured by a non-mitotic hemispindle and depend on intact microtubules.

   Evidence ultrastructure expansion 3D-EM, immunofluorescence, and trifluralin microtubule depolymerisation in P. falciparum gametocytes

   PMID:36030238

   Open questions at the time

   • Molecular linker between CenH3 centromeres and the hemispindle unknown
   • Functional consequence for gametocyte development not defined
   • Pharmacological perturbation may have off-target effects
6. 2024 Medium

   The directionality of the CenH3–kinetochore relationship was probed by showing that CenH3 localisation itself requires intact kinetochore assembly, since conditional loss of PfNDC80/PfNuf2 disrupts the CenH3 centromere mark.

   Evidence conditional disruption of PfNDC80/PfNuf2 with ultrastructure expansion microscopy using CenH3 as centromere marker in P. falciparum

   PMID:38987258

   Open questions at the time

   • Whether CenH3 is lost or mislocalised is not distinguished
   • Direct vs indirect dependence unresolved
   • Effect on CenH3 deposition kinetics unknown
7. 2025 Low

   CenH3 was leveraged as a validated centromeric reference mark to benchmark a low-input chromatin profiling method, reinforcing its status as the definitive centromere marker.

   Evidence CUT&Tag and DiBioCUT&Tag proximity labelling compared to ChIP-seq in P. falciparum

   PMID:40675147

   Open questions at the time

   • Methods validation only; no new CenH3 mechanism
   • Does not address deposition or dynamics
   • CenH3 used as a tool rather than the object of study

• The CenH3-specific deposition/chaperone machinery, the structural basis of CATD-directed centromere targeting in the parasite, and the epigenetic mechanism specifying centromere position remain unresolved.
• No CenH3 chaperone or loading factor identified
• No structure of a P. falciparum CenH3 nucleosome
• Mechanism of centromere establishment/maintenance unknown