PCNA activates the MutLγ endonuclease to promote meiotic crossing over.

During meiosis, crossover recombination connects homologous chromosomes to direct their accurate segregation1. Defective crossing over causes infertility, miscarriage and congenital disease. Each pair of chromosomes attains at least one crossover via the formation and biased resolution of recombination intermediates known as double Holliday junctions2,3. A central principle of crossover resolution is that the two Holliday junctions are resolved in opposite planes by targeting nuclease incisions to specific DNA strands4. The endonuclease activity of the MutLγ complex has been implicated in the resolution of crossovers5-10, but the mechanisms that activate and direct strand-specific cleavage remain unknown. Here we show that the sliding clamp PCNA is important for crossover-biased resolution. In vitro assays with human enzymes show that PCNA and its loader RFC are sufficient to activate the MutLγ endonuclease. MutLγ is further stimulated by a co-dependent activity of the pro-crossover factors EXO1 and MutSγ, the latter of which binds Holliday junctions11. MutLγ also binds various branched DNAs, including Holliday junctions, but does not show canonical resolvase activity, implying that the endonuclease incises adjacent to junction branch points to achieve resolution. In vivo, RFC facilitates MutLγ-dependent crossing over in budding yeast. Furthermore, PCNA localizes to prospective crossover sites along synapsed chromosomes. These data highlight similarities between crossover resolution and the initiation steps of DNA mismatch repair12,13 and evoke a novel model for crossover-specific resolution of double Holliday junctions during meiosis

PCNA activates the MutLγ endonuclease to promote meiotic crossing over.

During meiosis, crossover recombination connects homologous chromosomes to direct their accurate segregation1. Defective crossing over causes infertility, miscarriage and congenital disease. Each pair of chromosomes attains at least one crossover via the formation and biased resolution of recombination intermediates known as double Holliday junctions2,3. A central principle of crossover resolution is that the two Holliday junctions are resolved in opposite planes by targeting nuclease incisions to specific DNA strands4. The endonuclease activity of the MutLγ complex has been implicated in the resolution of crossovers5-10, but the mechanisms that activate and direct strand-specific cleavage remain unknown. Here we show that the sliding clamp PCNA is important for crossover-biased resolution. In vitro assays with human enzymes show that PCNA and its loader RFC are sufficient to activate the MutLγ endonuclease. MutLγ is further stimulated by a co-dependent activity of the pro-crossover factors EXO1 and MutSγ, the latter of which binds Holliday junctions11. MutLγ also binds various branched DNAs, including Holliday junctions, but does not show canonical resolvase activity, implying that the endonuclease incises adjacent to junction branch points to achieve resolution. In vivo, RFC facilitates MutLγ-dependent crossing over in budding yeast. Furthermore, PCNA localizes to prospective crossover sites along synapsed chromosomes. These data highlight similarities between crossover resolution and the initiation steps of DNA mismatch repair12,13 and evoke a novel model for crossover-specific resolution of double Holliday junctions during meiosis

Obstructive sleep apnea and incident type 2 diabetes

OBJECTIVES: To determine whether severity of obstructive sleep apnea is associated with incident diabetes in middle-aged and older adults. METHODS: A prospective analysis of 1,453 non-diabetic participants of both the Atherosclerosis Risk in Communities Study and the Sleep Heart Health Study (mean age 63 years, 46% male) had in-home polysomnography (1996–1998) and were followed for incident diabetes. Using the apnea-hypopnea index derived from home polysomnography, study participants were categorized as follows: <5.0 (normal), 5.0–14.9 (mild), 15.0–29.9 (moderate), and ≥30.0 events/h (severe). Incident diabetes was ascertained during annual follow-up telephone calls through 2013. RESULTS: During a median follow-up of 13 years, there were 285 incident diabetes cases among the 1453 participants. Participants with severe obstructive sleep apnea were at greater risk of incident diabetes compared to persons classified as normal after adjustment for confounders including body mass index and waist circumference (1.71 [1.08, 2.71]). The association between severe obstructive sleep apnea and incident diabetes was similar when analyses were restricted to obese individuals. CONCLUSIONS: Severe obstructive sleep apnea was associated with greater risk of incident diabetes, independent of adiposity in a community-based sample. Healthcare professionals should be cognizant of the high prevalence of OSA in the general population and the potential link to incident diabetes