本文采用的英格恩产品: CCAA细胞凋亡检测试剂盒(PI)
The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons
Affiliations
- 1 Université Paris-Saclay, CEA, CNRS – Institute for Integrative Biology of the Cell (I2BC), Gif-Sur-Yvette, France.
- 2 Université Paris Cité, CNRS, Institut Jacques Monod, Paris, F-75013, France.
- 3 Génomique Métabolique, Genoscope, Institut François Jacob, CEA, CNRS, Université Evry, Université Paris-Saclay, Evry, 91057, France.
- 4 Institut de Biologie de l’ENS (IBENS), Département de Biologie, École Normale Supérieure, CNRS, INSERM, Université PSL, Paris, 75005, France.
- 5 Université Paris-Saclay, INRAE, URGI, Versailles, 78026, France.
- 6 Université Paris-Saclay, INRAE, BioinfOmics, URGI, Versailles, 78026, France.
- 7 Universite Claude Bernard Lyon 1, LBBE, UMR 5558, CNRS, VAS, Villeurbanne, France.
- 8 Université Paris Cité, UFR Sciences du Vivant, Paris Cedex 13, 75205, France.
- 9 Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, Kraków, 31-016, Poland.
- 10 Institut de Biologie de l’ENS (IBENS), Département de Biologie, École Normale Supérieure, CNRS, INSERM, Université PSL, Paris, 75005, France. emeyer@biologie.ens.fr.
- 11 Université Paris Cité, CNRS, Institut Jacques Monod, Paris, F-75013, France. sandra.duharcourt@ijm.fr.
- 12 Université Paris-Saclay, CEA, CNRS – Institute for Integrative Biology of the Cell (I2BC), Gif-Sur-Yvette, France. linda.sperling@i2bc.paris-saclay.fr.
- PMID: 41992225
- PMCID: PMC13085455
- DOI: 10.1186/s12915-026-02584-w
Abstract
Background: Paramecia belong to the ciliate phylum of unicellular eukaryotes characterized by nuclear dimorphism. A diploid germline micronucleus (MIC) transmits genetic information across sexual generations. A polyploid transcriptionally active somatic macronucleus (MAC) develops at each sexual generation from a copy of the MIC through programmed DNA elimination (PDE) of > 30% of germline DNA. PDE requires the domesticated PiggyMac (Pgm) transposase. Assembly of Paramecium germline genomes has presented an enormous challenge owing to the difficulty of MIC isolation.
Results: We report chromosome-scale short-read MIC assemblies for 7 species from the P. aurelia species complex. We discovered a novel clade of Helitrons, with 9-10-kb transposase ORFs under purifying selection, that have remained active in all P. aurelia lineages. A long-read assembly for P. tetraurelia together with a genetic linkage map provided a nearly telomere-to-telomere assembly.
Conclusions: The ~ 100-Mb genome consists of tiny (300 kb-1.2 Mb) and numerous (~ 160) germline chromosomes with the highest recombination rate ever reported for a eukaryote (420 cM/Mb). The ends of the chromosomes consist of Helitrons inserted in telomeric C4A2 repeats, forming a distinct genomic compartment that is eliminated very early during MAC development in a Pgm-independent manner.
Keywords: Aneuploidy; Ciliate; Comparative genomics; G-quadruplex; Genetic linkage map; Helitron; Horizontal transfer; Nuclear dimorphism; Recombination rate; Telomere.
