ZYP1-mediated recruitment of PCH2 to the synaptonemal complex remodels the chromosome axis leading to crossover restriction

Chromosome axis-associated HORMA domain proteins (HORMADs), e.g. ASY1 in Arabidopsis, are crucial for meiotic recombination. ASY1, as other HORMADs, is assembled on the axis at early meiosis and depleted when homologous chromosomes synapse. Puzzlingly, both processes are catalyzed by AAA+ ATPase PCH2 together with its cofactor COMET. Here, we show that the ASY1 remodeling complex is temporally and spatially differently assembled. While PCH2 and COMET appear to directly interact in the cytoplasm in early meiosis, PCH2 is recruited by the transverse filament protein ZYP1 and brought to the ASY1-bound COMET assuring the timely removal of ASY1 during chromosome synapsis. Since we found that the PCH2 homolog TRIP13 also binds to the ZYP1 homolog SYCP1 in mouse, we postulate that this mechanism is conserved among eukaryotes. Deleting the PCH2 binding site of ZYP1 led to a failure of ASY1 removal. Interestingly, the placement of one obligatory crossover per homologous chromosome pair, compromised by ZYP1 depletion, is largely restored in this separation-of-function zyp1 allele suggesting that crossover assurance is promoted by synapsis. In contrast, this zyp1 allele, similar to the zyp1 null mutant, showed elevated type I crossover numbers indicating that PCH2-mediated eviction of ASY1 from the axis restricts crossover formation.

A national approach to diabetes foot risk stratification and foot care

The Scottish Diabetes Foot Action Group (SDG) has developed and introduced a national strategy plan for diabetic foot care across Scotland. This has involved the implementation of an evidence-based national foot screening and risk stratification programme that has already covered 61% of the population in just the first two years. Nationally agreed patient information foot leaflets and professional education material have been introduced, and a consensus for antibiotic use in the diabetic foot has been published. Information on multidisciplinary specialist foot services has been collected, indicating that 58% of Health Board areas have consultants with dedicated sessions in their job plan to a foot clinic, and 42% had integrated orthotic involvement. The SDG aims to increase these figures. Work has been undertaken to support local podiatry networks and improve communication between the specialist centre and the community. At a national level the SDG is working with Foot in Diabetes UK (FDUK) to recognize key podiatry skills by developing core competencies and a competency framework for the diabetes podiatrist and diabetes orthotist. The annual Scottish Diabetes Survey indicates some improvement in amputation rates with prevalence decreasing from 0.8% to 0.5%, and improved recording of foot ulceration at a national level. This national strategy has helped highlight the importance and difficulties facing diabetes foot care and should help to continue to improve the quality of care of people with diabetes who have foot-related problems.

Measuring the accuracy of different ways to identify the 'at-risk' foot in routine clinical practice

AIMS

We aimed to identify which individual risk factors best predict foot ulceration in routine clinical practice and whether an integrated clinical tool is a better screening tool for future foot ulceration.

METHODS

Routinely collected clinical information on foot and general diabetes indicators were recorded on the regional diabetes electronic register. Follow-up data on foot ulceration were collected from the same electronic record, the local multidisciplinary foot clinic and community and hospital podiatry paper records. Data were electronically linked to see which criteria best predicted future foot ulceration.

RESULTS

Foot risk scores were recorded on 3719 patients (44% female, mean age 59±15years) across community and hospital clinics. Overall, 851 (22.9%) had insensitivity to monofilaments, in 629 (17.2%) both pulses were absent and 184 (4.9%) had a prior ulcer. In multivariate analysis, the strongest predictors of foot ulceration were prior ulcer, insulin treatment, absent monofilaments, structural abnormality and proteinuria and retinopathy. The sensitivity of predicting foot ulceration was 52% for prior ulcer, 61% for absent monofilaments, 75% for 'high risk' on an integrated risk score and 91% for high and moderate risk combined. The corresponding specificities were 99, 81, 89 and 61%. Positive likelihood ratio was 52 for prior ulcer and 6.8 for foot risk, with negative likelihood ratios of 0.48 and 0.15, respectively.

CONCLUSIONS

Integrated foot risk scores are more sensitive than individual clinical criteria in predicting future foot ulceration and are likely to be better screening tools, where excluding false negative results is of paramount importance.