Fig. 1: MRE11 is required for resection initiation.

a Early meiotic recombination steps and sequencing strategy. i, SPO11 (magenta ellipses) cuts DNA via a covalent protein–DNA intermediate that is nicked (arrowheads) to give an entry point(s) for exonuclease(s). Bi-directional resection releases SPO11-oligo complexes and exposes ssDNA tails. ii, Two-step resection model: MRE11 hands off to other exonucleases. iii, Sequencing adapters are ligated to duplex ends after removal of ssDNA. Adapted from Fig. 1A of ref. ³⁴ under a CC-BY 4.0 license (https://creativecommons.org/licenses/by/4.0/). b Conditional deletion of Mre11. c Reduced MRN protein in immunoblots of whole testis lysates from 5–7 wk old Mre11-cKO animals. Numbers below the MRE11 blot indicate amounts of a dilution series of wild-type (wt) lysate or band intensities for mutants relative to wild type, normalized to loading control (tubulin). d Seminiferous tubule sections at 5–7 wk stained for MRE11 (brown). In wild type, all cells except elongated spermatids stained positive for MRE11. In Mre11-cKO, tubules were categorized based on presence of MRE11-positive spermatocytes. Arrowheads, examples of MRE11-positive spermatogonia (red) or spermatocytes with (purple) or without (green) MRE11 staining. e Quantification of tubule classes in (d). Number of animals tested: n = 1 for wild type and n = 2 for Mre11-cKO (mean ± range). f Strand-specific S1-seq [reads per million mapped reads (RPM)] at a representative DSB hotspot. Signals from three (wild type) or two (Spo11^–/– and Mre11-cKO) biological replicate libraries were averaged and plotted after smoothing (151-bp Hann window). Choice of ages is explained in Methods. SPO11-oligo sequencing throughout is from our previous study³⁷. The y-axis baseline for each plot is 0. g Stereotyped distribution of resection endpoints around DSB hotspots. Heatmaps (data in 40-bp bins) show strand-specific reads around SPO11-dependent DSB hotspots from wild type (n = 13,960 from our previous study³⁷). Each hotspot is shown as a horizontal line, strongest at the top. Sequencing signals were locally normalized by dividing by the total signal in a 4001-bp window around each hotspot’s center. Each hotspot thus has a total value of 1, to facilitate comparisons of spatial patterns between hotspots of different strengths. Arrowheads, the position of subsidiary peaks. Source data are provided as a Source data file.