Genomic structure of Hstx2 modifier of Prdm9-dependent hybrid male sterility in mice

ABSTRACTF1 hybrids between mouse inbred strains PWD and C57BL/6 represent the most thoroughly genetically defined model of hybrid sterility in vertebrates. Hybrid male sterility can be fully reconstituted from three components of this model, namely the Prdm9 hybrid sterility gene, intersubspecific homeology of Mus musculus musculus and Mus musculus domesticus autosomes, and the X-linked Hstx2 locus. Hstx2 modulates the extent of Prdm9-dependent meiotic arrest and harbors two additional genetic factors responsible for intersubspecific introgression-induced oligospermia (Hstx1) and reduced global meiotic recombination rate (Meir1). To facilitate positional cloning and to overcome the recombination suppression within the 4.3 Mb genomicDob interval encompassing the Hstx2 locus we designed Hstx2-CRISPR and SPO11/Cas9 transgenes aimed to induce DNA double-strand breaks specifically within the Hstx2 locus. The resulting recombinant reduced the Hstx2 locus to 2.70 Mb (Chr X:66.51-69.21 Mb). The newly defined Hstx2 still operates as the major X-linked factor of the F1 hybrid sterility, controls meiotic chromosome synapsis, and modifies meiotic recombination rate. Despite extensive further crosses, the 2.70 Mb Hstx2 interval behaved as a recombination cold spot with reduced PRDM9-mediated H3K4 hotspots and absence of DMC1-defined DNA DSB hotspots. To search for structural anomalies as a possible cause of recombination suppression we used optical mapping of the Hstx2 interval and observed high incidence of subspecies-specific structural variants along the X chromosome, with a striking copy number polymorphism of the microRNA Mir465 cluster. Finally, we analyzed the role of one of the Hstx2 candidate genes, the Fmr1 neighbor (Fmr1nb) gene in male fertility.Article summaryEarly meiotic arrest of mouse intersubspecific hybrids depends on the interaction between the Prdm9 gene and Hybrid sterility X2 (Hstx2) locus on chromosome X. Lustyk et al. conducted high-resolution genetic and physical mapping of the Hstx2 locus, reduced it to 2.7 Mb interval within a constitutive recombination cold spot and found that the newly defined Hstx2 still operates as the X-linked hybrid sterility factor, controls meiotic chromosome synapsis, and modifies recombination rate. Optical mapping of the Hstx2 genomic region excluded inversion as a cause of recombination suppression and revealed a striking copy number polymorphism of the microRNA Mir465 cluster.

Low-Copy Number Polymorphism in DEFA1/DEFA3 Is Associated with Susceptibility to Hospital-Acquired Infections in Critically Ill Patients

DEFA1/DEFA3, genes encoding human neutrophil peptides (HNP) 1–3, display wide-ranging copy number variations (CNVs) and is functionally associated with innate immunity and infections. To identify potential associations between DEFA1/DEFA3 CNV and hospital-acquired infections (HAIs), we enrolled 106 patients with HAIs and 109 controls in the intensive care unit (ICU) and examined their DEFA1/DEFA3 CNVs. DEFA1/DEFA3 copy number ranged from 2 to 16 per diploid genome in all 215 critically ill patients, with a median of 7 copies. In HAIs, DEFA1/DEFA3 CNV varied from 2 to 12 with a median of 6, which was significantly lower than that in controls (2 to 16 with a median of 8, p=0.017). Patients with lower DEFA1/DEFA3 copy number (CNV < 7) were far more common in HAIs than in controls (52.8% in HAIs versus 35.8% in controls; p=0.014; OR, 2.010; 95% CI, 1.164–3.472). The area under the receiver operating characteristic (AUROC) of DEFA1/DEFA3 CNV combined with clinical characteristics to predict the incidence of HAIs was 0.763 (95% CI 0.700–0.827), showing strong predictive ability. Therefore, lower DEFA1/DEFA3 copy number contributes to higher susceptibility to HAIs in critically ill patients, and DEFA1/DEFA3 CNV is a significant hereditary factor for predicting HAIs.