Mouse Strains with an Active H2-Ea Meiotic Recombination Hot Spot Exhibit Increased Levels of H2-Ea-Specific DNA Breaks in Testicular Germ Cells

Abstract

We devised a sensitive method for the site-specific detection of rare meiotic DNA strand breaks in germ cell-enriched testicular cell populations from mice that possess or lack an active recombination hot spot at the H2-Ea gene. Using germ cells from adult animals, we found an excellent correlation between the frequency of DNA breaks in the 418-bp H2-Ea hot spot and crossover activity. The temporal appearance of DNA breaks was also studied in 7-to 18-day-old mice with an active hot spot during the first waves of spermatogenesis. The number of DNA breaks detected rose as leptotene and zygotene spermatocytes populate the testis with a peak at day 14 postpartum, when leptotene, zygotene, and early pachytene spermatocytes are the most common meiotic prophase I cell types. The number of DNA breaks drops precipitously 1 day later, when middle to late pachytene spermatocytes become the dominant subtype. The recombination-related breaks in the hot spot likely reflect SPO11-induced double-strand breaks and/or recombination intermediates containing free 3 hydroxyl groups.Meiotic recombination leads to crossover events critical for the proper segregation of homologous chromosomes. It has been known for decades that recombination events may not be randomly distributed along each chromosome. The result is that some regions exhibit a recombination frequency greater than that expected based on the genome average relationship between physical distance and crossing over (reviewed in references 2, 31, 37, 38, and 54). These so-called recombination hot spots have been found in every organism examined carefully. A number of crossover hot spots exist in the mouse major histocompatibility complex (MHC; also called H-2) (see Fig.

Assessing human germ‐cell mutagenesis in the Postgenome Era: A celebration of the legacy of William Lawson (Bill) Russell

“…The trend for sex bias might indicate a higher level of complexity in male vs. female gametogenesis or greater pleiotropy among the genes that control female reproduction. Molecular studies indicate that many of these mutants affect mitotic proliferation of primordial germ cells or meiotic mechanisms of chromatid cohesion and recombination [Qin et al, 2004]. Future studies will test the epistatic relationship of these new mutants to previously characterized meiotic mutants.…”

Regulating double-stranded DNA break repair towards crossover or non-crossover during mammalian meiosis

“…These Spo11-oligo covalent molecules, where Spo11 is bound to the 5 ¶ end of a short oligonucleotide (15Y30 bp long), are thought to result from the processing of Spo11YDNA cleavage complexes that have been released by an unknown endonuclease activity. DNA breaks have also been visualized in mouse testis sections by assays allowing the detection of ends with 3 ¶ overhangs (Zenvirth et al 2003), and at a mouse CO hotspot by the use of terminal transferase (Qin et al 2004). One property of initiation by DSB and repair as depicted in Figure 1 is that the initiating chromosome is the recipient of information.…”

Recombination Hotspots in Nonallelic Homologous Recombination

“…There is recent evidence that DSBs form preferentially in hotspot regions in mice (29), but otherwise it remains to be proven that mammalian HR hotspots also result from preferential initiation by DSBs. Evidence from sperm-typing (30) and population genetic studies suggest that the majority of recombination intermediates at meiotic AHR hotspots are resolved as gene conversions rather than as crossovers, but there is also evidence of variation in the gene conversion/crossover ratio between hotspots (30).…”