Maternal Care under Large Clutches with Small Eggs: The Evolution of Life History Traits in Shield Bugs.

AbstractPatterns in the correlated evolution of parental care and life history traits are long established but controversial. Although parental care is related to large egg size in many taxa, conflicting results have also been reported. To test the evolutionary relationships between parental care and life history traits, we performed phylogenetic comparative analyses using shield bugs (Heteroptera: Acanthosomatidae), in which maternal guarding of eggs and young has repeatedly evolved. Our analyses revealed that female body size affected reproductive resource allocation. Contrary to the expectations of current theories, the acquisition of maternal care was associated with small eggs, large clutches, and large egg resource allocation. There was a greater trade-off between egg size and clutch size in caring species than in noncaring species. Egg and hatchling developmental rates were not correlated with egg size but were slower in caring species than in noncaring species. Analyses of evolutionary transitions suggest that the establishment of large clutches, small eggs, and large egg resource allocation preceded the evolution of maternal care. To our knowledge, this is the first study clarifying the evolution of parental care linked with small eggs in invertebrates.

Reanalysis of cancer mortality using reconstructed organ-absorbed dose: J-EPISODE 1991‒2010.

The Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE) has been conducted since 1990 by the Radiation Effects Association to analyse health effects for nuclear workers. It uses the recorded doses, i.e. dosimeter readings, evaluated inHp(10) for estimation of radiation risk; however, the International Commission on Radiological Protection does not recommend the use of effective doses for epidemiological evaluation and instead recommends the use of organ-absorbed doses for assessing cancer risk. Recently, the J-EPISODE has developed a conversion factor that can convert dosimeter readings to organ-absorbed doses following, in principle, the approach adopted by the International Agency for Research on Cancer 15-Country Collaborative Study. The approach was modified based on recent dosimeter usage practices and the Japanese physique. The aim of this study was to reanalyse the excess relative risk (ERR) of cancer mortality for the J-EPISODE using the previous analysis method but substituting the organ-absorbed dose for the recorded dose to confirm the adaptability and relevance of organ-absorbed doses for the J-EPISODE. The organ-absorbed doses from 1957 to 2010 were reconstructed for the whole cohort. The cancer mortality risk was reanalysed with Poisson regression methods, first by comparing the ERR/Gy for all cancers excluding leukaemia with the risk after excluding lung cancer for the whole cohort of 204 103 participants. In the whole cohort, all cancers excluding leukaemia, lung cancer and non-Hodgkin's lymphoma had statistically significant positive ERR/Gy estimates; leukaemia excluding chronic lymphocytic leukaemia had negative but not statistically significant estimates. Gallbladder cancer and pancreatic cancer showed statistically significant negative. Then, a subcohort of 71 733 respondents was selected based on lifestyle surveys with data on qualitative smoking status as well as quantitative smoking information on pack-years. Pack-years for current smokers and former smokers and years since the cessation of smoking for former smokers were used for the smoking-adjusted model. The most important feature of the J-EPISODE revealed to date was a decreasing tendency of the ERR/Sv by the smoking adjustment. For almost all causes of death such as lung cancer and stomach cancer, the estimated ERR/Gy decreased by the smoking adjustment, although those for the colon, prostate and kidney and other urinary organs were almost the same after the adjustment. This tendency remained unchanged even when using the organ-absorbed dose, indicating the appropriateness of using organ-absorbed doses for further risk analysis. At the same time, it indicated that confounding by smoking seriously biased the radiation risk estimates in the J-EPISODE and thus should be accounted even if organ dose is used.

Direct adjustment for confounding by smoking reduces radiation-related cancer risk estimates of mortality among male nuclear workers in Japan, 1999-2010.

A causal relationship between protracted exposure to low-dose rate radiation and health effects remains unclear despite extensive international studies of nuclear workers. One potential reason is that radiation epidemiological studies that adjust for tobacco smoking, which heavily influences mortality, have been limited. In the present study, we examined radiation-related cancer risk by directly assessing the possible confounding effect of smoking, using data from two questionnaire surveys performed among Japanese nuclear workers in 1997 and 2003. Mortality follow-up was carried out for 71 733 male respondents for an average of 8.2 years during the observation period of 1999-2010. The mean cumulative dose was 25.5 mSv at the end of the follow-up period. Estimates of excess relative risk per Sv (ERRs/Sv) were obtained by Poisson regression. By adjusting for smoking directly on the basis of a linear dose-response model, we quantified the confounding effects of smoking on radiation risks. Statistically significant ERRs/Sv were found for all causes, all diseases, all non-cancer diseases, and liver cancer: 0.97 (90% confidence interval: 0.23, 1.78), 1.32 (0.40, 2.34), 1.87 (0.47, 3.49), and 4.78 (0.09, 11.68), respectively, without adjustment for smoking. However, the ERRs/Sv were no longer statistically significant after adjustment for smoking: 0.45 (-0.22, 1.19), 0.77 (-0.08, 1.72), 1.28 (-0.03, 2.79), and 3.89 (-0.46, 10.34), respectively. The ERRs/Sv for all cancers excluding leukaemia and lung cancer were not significant before adjustment for smoking, but declined after adjustment for smoking. The present study demonstrates that in this cohort of workers, smoking heavily distorts radiation risk estimates of mortality. The possibility of confounding by smoking depends on how strongly smoking is correlated with radiation exposure. If a correlation between smoking and radiation dose is suggested, smoking is an important confounder when assessing the radiation and health risks.

Corrigendum: direct adjustment for confounding by smoking reduces radiation-related cancer risk estimates of mortality among male nuclear workers in Japan, 1999-2010.

We found some trivial errors which might confuse reader. The errors can be identified as the following two types. (1) The one is that misuse of "ERR" and "ERR/Sv". We denoted "Table 4 shows ERRs/Sv and 90% CIs ..." in line 7 of page 366. While we denoted "ERR and 90% CI for all cancers, excluding leukaemia, by dose category ..." in title of Table 4. The values described in Table 4 were ERR by dose category and not ERR/Sv. In addition, the explanation about the model that derived ERR by dose category is better to be added. Therefore, the description mentioned above should be changed as follows. (Misprinted) Table 4 shows ERRs/Sv and 90% CIs for all cancers excluding leukaemia by dose category. (Corrected) Table 4 shows ERRs which were defined as follow equation and 90% CIs for all cancers excluding leukaemia by dose category. λ=λ0 (a,c,y,r,s)exp(α1z1+α2z2+α3z3) (1+ßi di) where di is the dose category, and ßi is the ERR by dose category. The lowest dose category was set as reference. (2) The other were errors in surface caput of several tables. We described "ERR without adjustment for smoking" and "ERR with adjustment for smoking" in Table 4. These are correct description. However, "ERR with adjustment for smoking" was described as "For smoking" in Table 2. In addition, "Without adjustment" and "With adjustment" denoted in the surface caput of Table 5, 6, 7 should be denoted as "Without adjustment for smoking" and "With adjustment for smoking". The author wishes to apologies for the errors. .

Maternal care in Acanthosomatinae (Insecta: Heteroptera: Acanthosomatidae)--correlated evolution with morphological change.

BACKGROUND: Maternal care (egg-nymph guarding behavior) has been recorded in some genera of Acanthosomatidae. However, the origin of the maternal care in the family has remained unclear due to the lack of phylogenetic hypotheses. Another reproductive mode is found in non-caring species whose females smear their eggs before leaving them. They possess pairs of complex organs on the abdominal venter called Pendergrast's organ (PO) and spread the secretion of this organ onto each egg with their hind legs, which is supposed to provide a protective function against enemies. Some authors claim that the absence of PO may be associated with the presence of maternal care. No study, however, has tested this hypothesis of a correlated evolution between the two traits. RESULTS: We reconstructed the molecular phylogeny of the subfamily Acanthosomatinae using five genetic markers sequenced from 44 species and one subspecies with and without maternal care. Eight additional species from the other two acanthosomatid subfamilies were included as outgroups. Our results indicated that maternal care has evolved independently at least three times within Acanthosomatinae and once in the outgroup species. Statistical tests for correlated evolution showed that the presence of maternal care is significantly correlated with the secondary loss or reduction of PO. Ancestral state reconstruction for the node of Acanthosoma denticaudum (a non-caring species in which egg smearing with developed POs occurs) and A. firmatum (a caring species with reduced POs) suggested egg smearing was still present in their most recent common ancestor and that maternal care in A. firmatum has evolved relatively recently. CONCLUSIONS: We showed that maternal care is an apomorphic trait that has arisen multiple times from the presence of PO within the subfamily Acanthosomatinae. The acquisition of maternal care is correlated with the reduction or loss of PO, which suggests an evolutionary trade-off between the two traits resulting from physiological costs. This prediction also implies that presence of maternal care can be highly expected for those groups lacking behavioral data, which invariably also lack the organ. No secondary loss of maternal care was detected in the present tree. We suggest that the loss of maternal care may be suppressed due to the vulnerability of the PO-free condition, which thus maintains maternal care.

MeCP2 Rett mutations affect large scale chromatin organization.

Rett syndrome is a neurological, X chromosomal-linked disorder associated with mutations in the MECP2 gene. MeCP2 protein has been proposed to play a role in transcriptional regulation as well as in chromatin architecture. Since MeCP2 mutant cells exhibit surprisingly mild changes in gene expression, we have now explored the possibility that Rett mutations may affect the ability of MeCP2 to bind and organize chromatin. We found that all but one of the 21 missense MeCP2 mutants analyzed accumulated at heterochromatin and about half of them were significantly affected. Furthermore, two-thirds of all mutants showed a significantly decreased ability to cluster heterochromatin. Three mutants containing different proline substitutions (P101H, P101R and P152R) were severely affected only in heterochromatin clustering and located far away from the DNA interface in the MeCP2 methyl-binding domain structure. MeCP2 mutants affected in heterochromatin accumulation further exhibited the shortest residence time on heterochromatin, followed by intermediate binding kinetics for clustering impaired mutants. We propose that different interactions of MeCP2 with methyl cytosines, DNA and likely other heterochromatin proteins are required for MeCP2 function and their dysfunction lead to Rett syndrome.

A Risk Comparison of Non-cancer Mortality between Lifestyle, Socioeconomic Status, and Radiation among Japanese Nuclear Workers (J-EPISODE).

ABSTRACT: Many epidemiological studies have been conducted to investigate the health effects of low-dose radiation. Most of these investigations have focused on cancer, and fewer studies have examined non-cancer topics than cancer subjects. The purpose of this study is to compare the relative risks of non-cancer mortality from low-dose radiation with lifestyle factors (such as smoking habits) and socioeconomic status (such as years of education). The cohort consisted of 43,692 males who responded to a lifestyle questionnaire survey conducted from 2003 to 2004 among nuclear workers in Japan. Missing questionnaire data were imputed by multiple imputation, each variable was categorized, and the relative risks for the reference group were calculated using Poisson regression. The total number of observed person-years was 300,000, and the mean age and dose were 55.2 y and 24.5 mSv (10-y lagged dose), respectively. For many of the causes of death in this analysis, significantly high risks existed for lifestyle differences, such as smoking, alcohol consumption, frequency of medical examination, breakfast intake, sleep, and BMI, but few for socioeconomic status. Radiation showed no significantly high risks. Taken together, the risk of non-cancer mortality from low-dose radiation is likely smaller than that from lifestyle factors.

A Risk Comparison between Lifestyle, Socioeconomic Status, and Radiation: A Cohort Study of Cancer Mortality among Japanese Nuclear Workers (J-EPISODE).

ABSTRACT: The health effects of low-dose radiation exposure have been a source of controversy. One possible reason is that epidemiological studies that compare radiation risk with other factors, such as lifestyle or socioeconomic status, have been limited. The aim of this study is to conduct a comparison of the cancer risk of mortality between radiation, lifestyle habits (such as smoking), and socioeconomic status (such as years of education) among Japanese nuclear workers. We assembled a cohort of 41,742 male nuclear workers in Japan who answered a lifestyle questionnaire survey conducted during 2003-2004. To exclude systematic errors caused by missing values, we used multiple imputation and Poisson regression to estimate relative risks and confidence intervals for lifestyle habits, socioeconomic status, and radiation. The total person-y from 2005 to 2010 were 215,000. The mean age and cumulative dose were 54.9 y and 24.8 mSv (10-y lagged dose), respectively. Significantly high relative risks were determined for smoking, alcohol consumption, frequency of medical examination, breakfast intake, sleep, and body mass index. Further, significantly high relative risks of radiation were shown for lung cancer and smoking-related cancers. Since the simultaneous inclusion of radiation and non-radiation variables in the model for relative risk (RR) calculation means that the calculated radiation RR is the result of adjustment by other variables, the risk of cancer from low-dose radiation, if any, is less than smoking and probably less than other lifestyle factors.

The protocadherins, PCDHB1 and PCDH7, are regulated by MeCP2 in neuronal cells and brain tissues: implication for pathogenesis of Rett syndrome.

BACKGROUND: Rett syndrome is a neurodevelopmental and autistic disease caused by mutations of Methyl-CpG-binding protein 2 (MECP2) gene. MeCP2 protein is mainly expressed in neurons and binds to methylated gene promoters to suppress their expression, indicating that Rett syndrome is caused by the deregulation of target genes in neurons. However, it is likely that there are more unidentified neuronal MeCP2-targets associated with the neurological features of RTT. RESULTS: Using a genome-microarray approach, we found 22 genomic regions that contain sites potentially regulated by MeCP2 based on the features of MeCP2 binding, DNA methylation, and repressive histone modification in human cell lines. Within these regions, Chromatin immunoprecipitation (ChIP) analysis revealed that MeCP2 binds to the upstream regions of the protocadherin genes PCDHB1 and PCDH7 in human neuroblastoma SH-SY5Y cells. PCDHB1 and PCDH7 promoter activities were down-regulated by MeCP2, but not by MBD-deleted MeCP2. These gene expression were up-regulated following MeCP2 reduction with siRNA in SH-SY5Y cells and in the brains of Mecp2-null mice. Furthermore, PCDHB1 was up-regulated in postmortem brains from Rett syndrome patients. CONCLUSIONS: We identified MeCP2 target genes that encode neuronal adhesion molecules using ChIP-on-BAC array approach. Since these protocadherin genes are generally essential for brain development, aberrant regulation of these molecules may contribute to the pathogenesis of the neurological features observed in Rett syndrome.

High expression of MeCP2 in JC virus-infected cells of progressive multifocal leukoencephalopathy brains.

Mutations of the methyl CpG binding protein 2 (MeCP2) gene are a major cause of Rett syndrome. To investigate whether the expression of this gene was related to JC virus (JCV) infection, we examined brains of four progressive multifocal leukoencephalopathy (PML) patients. JCV infection was confirmed by immunohistochemical labeling with antibodies against JCV VP1, agnoprotein and large T antigen. MeCP2 expression was examined by immunohistochemistry using a specific polyclonal antibody against MeCP2. In normal brains and uninfected cortices of PML brains, MeCP2 expression was observed in the nuclei of neurons, but not observed in glial and endothelial cell nuclei. However, in PML brains intense immunolabeling was observed in abnormally enlarged glial nuclei of JCV-infected cells. Double immunolabeling using antibodies against large T antigen (visualized as blue) and MeCP2 (visualised as red) revealed dark red JCV-infected nuclei, which confirmed that the JCV infected nuclei expressed MeCP2. We conclude that MeCP2 is highly expressed in the JCV-infected nuclei of PML brain and these results may provide a new insight into the mechanism which regulates the MeCP2 expression in glial cells by the infection of JCV.

[Review of Cohort Studies Among Radiologists, Radiological Technologists, and Nuclear Workers].

A number of epidemiological studies have been conducted to investigate the health effects of low-dose radiation. The author reviewed epidemiological studies among radiologists, radiological technologists, and nuclear workers. Because the results of many epidemiological studies on these subjects have been published, and many studies have measured radiation doses, there is little uncertainty. In the studies among radiologists and radiological technologists, high risks for leukemia, skin cancer, and breast cancer were found in populations that began work before around 1950, but not seen such a tendency for those starting work recent years. The results of the studies among nuclear workers were inconsistent with some reporting that a risk was seen, while others reported no risk. The reason for this may be due to the different analysis methods among the studies.

Organ Dose Reconstruction Applicable for a Japanese Nuclear Worker Cohort: J-EPISODE.

ABSTRACT: An evaluation of cancer risk based on organ-absorbed dose is underway for the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE), which has analyzed health effects in association with radiation exposure evaluated with the personal dose equivalent Hp(10). Although the concept of effective dose and its operational definition of Hp(10) are widely used for radiological protection purposes, effective dose is not recommended for epidemiological evaluation. Organ-absorbed dose was instead adopted for the IARC 15-Country Collaborative study (15-Country study), the International Nuclear Workers Study (INWORKS), the Mayak worker study, and the Life Span Study (LSS) of atomic bomb survivors. The reconstruction method in J-EPISODE followed in principle the approach adopted in the 15-Country Study. As part of the approach of J-EPISODE, a conversion factor from photon dosimeter reading to air kerma was developed using dosimeter response data, which were measured by the experiment using an anthropomorphic phantom, and it was confirmed that the 15-Country study's assumption of photon energy and geometry distribution in a work environment applied to Japanese nuclear workers. This article focuses on a method for reconstructing the conversion factor from photon dosimeter reading to organ-absorbed photon dose for a Japanese nuclear worker cohort. The model for estimating the conversion factor was defined under the assumption of a lognormal distribution from three concerned bias factors: (1) a dosimeter reading per air kerma, i.e., dosimeter response; (2) an organ-absorbed dose per air kerma; and (3) a factor relating to the differences in dose concepts and calibration practices between the roentgen dosimeter era and the present. Dosimeter response data were cited from the companion paper. Data on organ-absorbed photon dose per air kerma were estimated using a voxel phantom with the average Japanese adult male height and weight. The bias factor for the recorded dose in the roentgen era was defined, considering the backscatter radiation from the human body. The estimated values of organ-absorbed photon dose per air kerma were almost the same as those in ICRP Publication 116, revealing that the effect of differences in body size was almost negligible. The conversion factors from dosimeter reading to organ-absorbed dose were estimated by period (the roentgen era or from then), nuclear facility type (nuclear power plant or other), dosimeter type, and tissue or organ. The estimated conversion factors ranged from 0.7 to 0.9 (Gy Sv-1). The estimated cumulative organ-absorbed photon dose for the participants of J-EPISODE demonstrated that organ-absorbed dose values were approximately 0.8 times the recorded doses if neglecting dose-unit differences. J-EPISODE reconstructed an organ-absorbed dose conversion factor and will evaluate the risk of cancer mortality and morbidity using the organ-absorbed dose in the future.

MeCP2-dependent repression of an imprinted miR-184 released by depolarization.

Both fragile X syndrome and Rett syndrome are commonly associated with autism spectrum disorders and involve defects in synaptic plasticity. MicroRNA is implicated in synaptic plasticity because fragile X mental retardation protein was recently linked to the microRNA pathway. DNA methylation is also involved in synaptic plasticity since methyl CpG-binding protein 2 (MeCP2) is mutated in patients with Rett syndrome. Here we report that expression of miR-184, a brain-specific microRNA repressed by the binding of MeCP2 to its promoter, is upregulated by the release of MeCP2 after depolarization. The restricted release of MeCP2 from the paternal allele results in paternal allele-specific expression of miR-184. Our finding provides a clue to the link between the microRNA and DNA methylation pathways.

Effect of Radiation Dose Rate on Circulatory Disease Mortality among Nuclear Workers: Reanalysis of Hanford Data.

The excess relative risk (ERR) of mortality for circulatory disease among nuclear workers was reanalyzed by taking into consideration the annual dose as the dose rate using publicly available epidemiological data of the Hanford site dedicated to the cohort study of nuclear workers in the US, the UK, and Canada. Values of the dose rate (cut-points) were chosen at 2 mSv y intervals from 2 to 40 mSv y, and risk estimates were made for 32,988 workers, considering the doses accumulated below and above each cut-point to have different effects. Similarly to that in the previous study for cancer by Sasaki et al., examinations of sensitivity analysis were also carried out for different risk models, lag periods, and impacts of adjusting the monitoring period to find the effect of the dose rate. As a result, emergence of a statistically significant difference between ßL1, which is the ERR for the doses accumulated below the specified cut-point, and ßH1, which is the ERR for that above the specified cut-point, was observed for cut-point of the dose rate of 4, 6, 34, 36, and 38 mSv y. While statistically negative values were estimated for ßL1 (4 and 6 mSv y) and for ßH1 (34, 36, and 38 mSv y), the overall relationship between the ERR and the cut-point of the dose rate was found to be similar to that obtained by the analysis of the mortality for all cancers excluding leukemia.

ESTIMATION OF PHOTON ENERGY AND DIRECTION DISTRIBUTIONS AT JAPANESE NUCLEAR POWER PLANTS BASED ON LITERATURE SURVEY FOR J-EPISODE STUDY.

In order to reconstruct organ-absorbed dose from recorded dose for risk estimation in nuclear worker cohort, the preceding study of the International Agency for Research on Cancer (IARC) 15-Country Collaborative Study estimated the organ dose conversion factor from the recorded dose of Hp(10) under the assumption that on average, in the nuclear power plants (NPPs), 10% of the dose received by workers was due to photon energies ranging from 100 to 300 keV and 90% from photon energies ranging from 300 to 3000 keV, with the average geometry being 50% in the antero-posterior geometry and 50% in the isotropic geometry. Similar examination was conducted at the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE). Literature survey disclosed that Japanese electric power companies had jointly conducted the research on energy distribution and incidence direction distribution of gamma rays in working environments during periodical inspection and maintenance as well as during operation in the 1980s. The analysis of the survey results on photon energy and geometry distribution of Japanese NPPs demonstrated appropriateness in applying the IARC study assumption for nuclear workers in Japan and reconstructing organ-absorbed dose in the J-EPISODE. These results in Japan also provide strong evidence to support the robustness and generality of the IARC study assumption, which was estimated based on the judgment of experts at nuclear facilities around the world.

CONVERSION FACTOR FROM DOSEMETER READING TO AIR KERMA FOR NUCLEAR WORKER USING ANTHROPOMORPHIC PHANTOM FOR FURTHER CONVERSION FROM AIR KERMA TO ORGAN-ABSORBED DOSE.

Estimation of cancer risk based on the organ-absorbed dose is underway for the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE). The reconstruction method for the organ-absorbed dose follows the approach adopted in the IARC 15-Country Collaborative Study, which examined the dosemeter response to photon exposure for the old film badge (FB) type, a multi-element FB and a thermoluminescence dosemeter. Until 2000, the dosemeters used in Japan were almost the same in the IARC study, so IARC study data could be used as they were. However, since 2000, the type of dosemeter has been replaced with active personal dosemeters (hereafter called electronic personal dosemeters), radio-photoluminescent glass dosemeters (Glass badge) and optically stimulated luminescence dosemeters (Luminess badge). Hence, it was necessary to collect these data again. A dosemeter response experiment was conducted using a device that irradiated an anthropomorphic phantom in the Japan Atomic Energy Agency calibration laboratories. The aim of the paper is to provide a conversion factor from reading in terms of Hp(10) to air kerma for realistic conditions for further conversion from air kerma to organ-absorbed dose. The obtained dosemeter responses for the dosemeter types currently used in Japan were consistent with those in the IARC study. These data will be utilized for J-EPISODE in reconstructing the organ-absorbed dose.

Bdnf overexpression in hippocampal neurons prevents dendritic atrophy caused by Rett-associated MECP2 mutations.

The expression of the methylated DNA-binding protein MeCP2 increases during neuronal development, which suggests that this epigenetic factor is crucial for neuronal terminal differentiation. We evaluated dendritic and axonal development in embryonic day-18 hippocampal neurons in culture by measuring total length and counting branch point numbers at 4 days in vitro, well before synapse formation. Pyramidal neurons transfected with a plasmid encoding a small hairpin RNA (shRNA) to knockdown endogenous Mecp2 had shorter dendrites than control untransfected neurons, without detectable changes in axonal morphology. On the other hand, overexpression of wildtype (wt) human MECP2 increased dendritic branching, in addition to axonal branching and length. Consistent with reduced neuronal growth and complexity in Rett syndrome (RTT) brains, overexpression of human MECP2 carrying missense mutations common in RTT individuals (R106W or T158M) reduced dendritic and axonal length. One of the targets of MeCP2 transcriptional control is the Bdnf gene. Indeed, endogenous Mecp2 knockdown increased the intracellular levels of BDNF protein compared to untransfected neurons, suggesting that MeCP2 represses Bdnf transcription. Surprisingly, overexpression of wt MECP2 also increased BDNF levels, while overexpression of RTT-associated MECP2 mutants failed to affect BDNF levels. The extracellular BDNF scavenger TrkB-Fc prevented dendritic overgrowth in wt MECP2-overexpressing neurons, while overexpression of the Bdnf gene reverted the dendritic atrophy caused by Mecp2-knockdown. However, this effect was only partial, since Bdnf increased dendritic length only to control levels in mutant MECP2-overexpressing neurons, but not as much as in Bdnf-transfected cells. Our results demonstrate that MeCP2 plays varied roles in dendritic and axonal development during neuronal terminal differentiation, and that some of these effects are mediated by autocrine actions of BDNF.

Dendritic spine pathologies in hippocampal pyramidal neurons from Rett syndrome brain and after expression of Rett-associated MECP2 mutations.

Rett syndrome (RTT) is an X chromosome-linked neurodevelopmental disorder associated with the characteristic neuropathology of dendritic spines common in diseases presenting with mental retardation (MR). Here, we present the first quantitative analyses of dendritic spine density in postmortem brain tissue from female RTT individuals, which revealed that hippocampal CA1 pyramidal neurons have lower spine density than age-matched non-MR female control individuals. The majority of RTT individuals carry mutations in MECP2, the gene coding for a methylated DNA-binding transcriptional regulator. While altered synaptic transmission and plasticity has been demonstrated in Mecp2-deficient mouse models of RTT, observations regarding dendritic spine density and morphology have produced varied results. We investigated the consequences of MeCP2 dysfunction on dendritic spine structure by overexpressing ( approximately twofold) MeCP2-GFP constructs encoding either the wildtype (WT) protein, or missense mutations commonly found in RTT individuals. Pyramidal neurons within hippocampal slice cultures transfected with either WT or mutant MECP2 (either R106W or T158M) showed a significant reduction in total spine density after 48 h of expression. Interestingly, spine density in neurons expressing WT MECP2 for 96 h was comparable to that in control neurons, while neurons expressing mutant MECP2 continued to have lower spine density than controls after 96 h of expression. Knockdown of endogenous Mecp2 with a specific small hairpin interference RNA (shRNA) also reduced dendritic spine density, but only after 96 h of expression. On the other hand, the consequences of manipulating MeCP2 levels for dendritic complexity in CA3 pyramidal neurons were only minor. Together, these results demonstrate reduced dendritic spine density in hippocampal pyramidal neurons from RTT patients, a distinct dendritic phenotype also found in neurons expressing RTT-associated MECP2 mutations or after shRNA-mediated endogenous Mecp2 knockdown, suggesting that this phenotype represent a cell-autonomous consequence of MeCP2 dysfunction.

Effect of Radiation Dose Rate on Cancer Mortality among Nuclear Workers: Reanalysis of Hanford Data.

The excess relative risk of mortality for all cancers excluding leukemia among nuclear workers was reanalyzed by taking the annual dose as the dose rate into consideration using publicly available epidemiological data from the Hanford site dedicated to the cohort study of nuclear workers in the United States, the United Kingdom, and Canada (Three Countries Study). Values of the dose rate (cut points) were chosen at 2 mSv y intervals from 2 to 40 mSv y, and risk estimates were made for 32,988 workers, considering doses accumulated below the cut point and above the cut point to have different effects. Although the procedure to extract the study population and the methodology used for analysis basically followed those in the Three Countries Study, additional examinations were also carried out for different risk models, lag periods, and impacts of adjusting the monitoring period to find the effect of the dose rate. As a result, no statistically significant difference in dose rate was found among the excess relative risks under different calculation conditions.