Nicholas, R. E. | Search bioRxiv

bioRxiv2023

Structural variation and DNA methylation shape the centromere-proximal meiotic crossover landscape in Arabidopsis

BackgroundCentromeres load kinetochore complexes onto chromosomes, which mediate spindle attachment and allow segregation during cell division. Although centromeres perform a conserved cellular function, their underlying DNA sequences are highly divergent within and between species. Despite variability in DNA sequence, centromeres are also universally suppressed for meiotic crossover recombination, across eukaryotes. However, the genetic and epigenetic factors responsible for suppression of centromeric crossovers remain to be completely defined. ResultsTo explore the centromere-proximal recombination landscape, we mapped 14,397 crossovers against fully assembled Arabidopsis thaliana genomes. A. thaliana centromeres comprise megabase-scale satellite repeat arrays that load nucleosomes containing the CENH3 histone variant. Each chromosome possesses a structurally polymorphic 3-4 megabase region where crossovers were absent, that includes the satellite arrays, flanked by 1-2 megabase low-recombination zones. The recombination-suppressed regions are enriched for Gypsy/Ty3 retrotransposons, and additionally contain expressed genes with high genetic diversity that initiate meiotic recombination, yet do not crossover. We mapped crossovers at high-resolution in proximity to CEN3, which resolved punctate centromere-proximal hotspots that overlapped gene islands embedded in heterochromatin. Centromeres are densely DNA methylated and the recombination landscape was remodelled in DNA methylation mutants. We observed that the centromeric low-recombining zones decreased and increased crossovers in CG (met1) and non-CG (cmt3) mutants, respectively, whereas the core non recombining zones remained suppressed. ConclusionOur work relates the genetic and epigenetic organisation of the A. thaliana centromeres and flanking pericentromeric heterochromatin to the zones of crossover suppression that surround the CENH3-occupied satellite repeat arrays.

genomics↗

bioRxiv2022

Broad Recognition of Mamu-Bw4 and -A-related MHC class I Ligands by Rhesus Macaque Killer-Cell Immunoglobulin-Like Receptors

Definition of MHC class I ligands of rhesus macaque KIRs is fundamental to NK cell biology in this species as an animal model for infectious diseases, reproductive biology, and transplantation. To provide a more complete foundation for studying NK cell responses, rhesus macaque KIRs representing common allotypes of lineage II KIR genes were tested for interactions with MHC class I molecules representing diverse Mamu-A, -B, -E, -F, -I and -AG alleles. KIR-MHC class I interactions were identified by co-incubating reporter cell lines bearing chimeric KIR-CD3{zeta} receptors with target cells expressing individual MHC class I molecules and were corroborated by staining with KIR IgG-Fc fusion proteins. Ligands for 11 KIRs of previously unknown specificity were identified that fell into two general categories: interactions with multiple Mamu-Bw4 molecules or with Mamu-A-related molecules, including several allotypes of Mamu-AG and the hybrid Mamu-B*045:03 molecule. Although both groups include inhibitory and activating receptors, the majority of KIRs found to interact with Mamu-Bw4 are inhibitory, whereas most of the KIRs that interact with Mamu-AG are activating. We also identified Mamu-A1*012:01 as a ligand for KIR3DLw03*002, which belongs to a phylogenetically distinct group of macaque KIRs with a three amino acid deletion in D0 that is also present in human KIR3DL1/S1 and KIR3DL2. This study more than doubles the number of rhesus macaque KIRs with defined MHC class I ligands and identifies novel interactions with Mamu-AG, -B*045, and -A1*012. These findings support overlapping, but nonredundant, patterns of ligand recognition that reflects extensive functional diversification of these receptors.

immunology↗