Robust designation of meiotic crossover sites by CDK-2 through phosphorylation of the MutSγ complex

Crossover formation is essential for proper segregation of homologous chromosomes during meiosis. Here, we show that Caenorhabditis elegans cyclin-dependent kinase 2 (CDK-2) partners with cyclin-like protein COSA-1 to promote crossover formation by promoting conversion of meiotic double-strand breaks into crossover–specific recombination intermediates. Further, we identify MutSγ component MSH-5 as a CDK-2 phosphorylation target. MSH-5 has a disordered C-terminal tail that contains 13 potential CDK phosphosites and is required to concentrate crossover–promoting proteins at recombination sites. Phosphorylation of the MSH-5 tail appears dispensable in a wild-type background, but when MutSγ activity is partially compromised, crossover formation and retention of COSA-1 at recombination sites are exquisitely sensitive to phosphosite loss. Our data support a model in which robustness of crossover designation reflects a positive feedback mechanism involving CDK-2–mediated phosphorylation and scaffold-like properties of the MSH5 C-terminal tail, features that combine to promote full recruitment and activity of crossover–promoting complexes.

Akkommodationsfähigkeit unter Einbeziehung refraktiver, biometrischer und demographischer Parameter

PURPOSE

The aim of this study was to evaluate the accommodation ability in healthy phakic eyes in relation to refraction and biometric parameters in order to get comparable results for patients with the accommodative 1 CU posterior chamber lens.

METHODS

The study included 120 normal eyes of 120 patients (77 males, 43 females, mean age: 40+/-18, range: 11-70 years). The inclusion criteria were spherical equivalent for distance refraction <2 D, astigmatism <1.5 D, and a best-corrected visual acuity > or =0.8. Exclusion criteria were diabetes, glaucoma, cataract, traumas, or previous surgery. Subjects were divided into six age groups at increments of 10 years. Each group consisted of 20 subjects. Measurements included subjective and objective refraction (D), the accommodation ability (D) assessed with an accommodometer, and biometric parameters using the IOLMaster. In addition, the relation of anterior chamber depth and length of the eye was calculated for analyzing the relationship of anterior eye segment and accommodation.

RESULTS

The spherical equivalent for distance refraction was 0.04+/-0.6 D with a range of -1.5 to 2.0 D. There was no sex-related significant difference of accommodation range. The accommodation range (D) decreased significantly with increasing age (p<0.0001, r=-0.895). The highest decrease could be found between the ages of 30 and 50 years. In subsequent years, the decline in accommodation ability was comparatively less. In association with the anterior chamber depth and the relation of anterior chamber depth and length of the eye, the accommodation ability fell with increasing age (p<0.001). The length of the eye did not correlate with the accommodation ability (p=0.8).

CONCLUSION

There is a strong relationship between accommodation ability and age. Accommodation ability decreases strongly from the 3rd to the 5th decade; after that the loss of accommodation ability is relatively lower. The increase in lens thickness during the life span can implicate a correlation between the change of anterior chamber depth in relation to the length of the eye and a decrease of accommodation ability. Our results confirm Duane's hypothesis of accommodation and age.

Cognitive and physiologic responses to EMG biofeedback and three types of pseudofeedback during a muscular relaxation task

Four groups of normal human subjects were tested for their ability to reduce frontal muscle tension levels during presentation of veridical auditory biofeedback or auditory pseudofeedback. A double-blind methodology was used. Three groups of subjects assigned to the pseudofeedback conditions received a feedback signal that was not contingent on EMG activity but that followed one of three different patterns. One group received a truly random signal, the second received a signal that gradually increased in frequency (apparent failure), and the third received a signal that gradually decreased in frequency (apparent success). Dependent measures included both physiologic (frontal and neck EMG) and subjective reactions to the relaxation task. The different patterns of pseudofeedback did produce reliably different subjective responses, suggesting that the manipulations succeeded in producing unequal nonspecific effects that were unrelated to the feedback contingency specifically. However, these differential subjective effects were not strongly reflected in the physiologic responses since the differences in EMG levels among the four groups did not differ significantly at any stage of training. An analysis of the integrity of the double-blind procedure showed that although experimenters were effectively kept blind to group assignment, subjects' responding suggested a response bias as well as the possibility that the double-blind was breached. The utility of the double-blind methodology in biofeedback experiments is discussed and suggestions for future research are offered.

Effect of iodoacetate on T lymphocytes of young AKR mice

The influence of sulphydryl inhibitor iodoacetate on properties characteristically associated with T-lymphocytes was examined in young AKR mice. Thymocytes from mice receiving 100 microgram of iodoacetate showed a decrease in cortisone sensitivity, and responded more vigorously to phytohemagglutinin (PHA). Spleen cells from treated mice also exhibited greater reactivity to both PHA and concanavalin A (Con A). The uptake of 14C-iodoacetate by the thymus, spleen, lymph nodes, bone marrow, liver and kidneys also was investigated. One hour, 2 h and 18 h after the intraperiotoneal injection of 10-3 M iodoacetate, the thymus demonstrated a higher incorporation of the labelled compound than did the spleen, lymph nodes or other organs examined. These findings provide further evidence to indicate that the immuno-enhancement observed following iodoacetate treatment is related to its effect on T lymphocytes.