Kaori Yamanaka

Critical function of Prdm14 for the establishment of the germ cell lineage in mice

Specification of germ cell fate is fundamental in development and heredity. Recent evidence indicates that in mice, specification of primordial germ cells (PGCs), the common source of both oocytes and spermatozoa, occurs through the integration of three key events: repression of the somatic program, reacquisition of potential pluripotency and ensuing genome-wide epigenetic reprogramming. Here we provide genetic evidence that Prdm14, a PR domain–containing transcriptional regulator with exclusive expression in the germ cell lineage and pluripotent cell lines, is critical in two of these events, the reacquisition of potential pluripotency and successful epigenetic reprogramming. In Prdm14 mutants, the failure of these two events manifests even in the presence of Prdm1 (also known as Blimp1), a key transcriptional regulator for PGC specification. Our combined evidence demonstrates that Prdm14 defines a previously unknown genetic pathway, initiating independently from Prdm1, for ensuring the launching of the mammalian germ cell lineage.

A signaling principle for the specification of the germ cell lineage in mice.

Specification of the germ cell lineage is vital to development and heredity. In mice, the germ cell fate is induced in pluripotent epiblast cells by signaling molecules, yet the underlying mechanism remains unknown. Here we demonstrate that germ cell fate in the epiblast is a direct consequence of Bmp4 signaling from the extraembryonic ectoderm (ExE), which is antagonized by the anterior visceral endoderm (AVE). Strikingly, Bmp8b from the ExE restricts AVE development, thereby contributing to Bmp4 signaling. Furthermore, Wnt3 in the epiblast ensures its responsiveness to Bmp4. Serum-free, defined cultures revealed that, in response to Bmp4, competent epiblast cells uniformly expressed key transcriptional regulators Blimp1 and Prdm14 and acquired germ-cell properties, including genome-wide epigenetic reprogramming, in an orderly fashion. Notably, the induced cells contributed to both spermatogenesis and fertility of offspring. By identifying a signaling principle in germ cell specification, our study establishes a robust strategy for reconstituting the mammalian germ cell lineage in vitro.

Complex genome-wide transcription dynamics orchestrated by Blimp1 for the specification of the germ cell lineage in mice

Specification of germ cell fate is fundamental in development. With a highly representative single-cell microarray and rigorous quantitative PCR analysis, we defined the genome-wide transcription dynamics that create primordial germ cells (PGCs) from the epiblast, a process that exclusively segregates them from their somatic neighbors. We also analyzed the effect of the loss of Blimp1, a key transcriptional regulator, on these dynamics. Our analysis revealed that PGC specification involves complex, yet highly ordered regulation of a large number of genes, proceeding under the strong influence of mesoderm induction but specifically avoiding developmental programs such as the epithelial-mesenchymal transition, Hox cluster activation, cell cycle progression, and DNA methyltransferase machinery. Remarkably, Blimp1 is essential for repressing nearly all the genes normally down-regulated in PGCs relative to their somatic neighbors. In contrast, it is dispensable for the activation of approximately half of the genes up-regulated in PGCs, uncovering the Blimp1-independent events for PGC specification. Notably, however, highly PGC-specific genes exhibited distinct correlations to Blimp1 in wild-type embryos, and these correlations faithfully predicted their expression impairments in Blimp1 mutants. Moreover, their expression overlaps within single cells were severely damaged without Blimp1, demonstrating that Blimp1 exerts positive influence on their concerted activation. Thus, Blimp1 is not a single initiator but a dominant coordinator of the transcriptional program for the establishment of the germ cell fate in mice.

Mechanisms and State of the Art of Transcranial Magnetic Stimulation

In 1985, Barker et al. built a transcranial magnetic stimulation (TMS) device with enough power to stimulate dorsal roots in the spine. They quickly realized that this machine could likely also noninvasively stimulate the superficial cortex in humans. They waited a while before using their device over a human head, fearing that the TMS pulse might magnetically “erase the hard-drive” of the human brain. Almost 10 years later, in 1994, an editorial in this journal concerned whether TMS might evolve into a potential antidepressant treatment. In the intervening years, there has been an explosion of basic and clinical research with and about TMS. Studies are now uncovering the mechanisms by which TMS affects the brain. It does not “erase the hard-drive” of the brain, and it has many demonstrated research and clinical uses. This article reviews the major recent advances with this interesting noninvasive technique for stimulating the brain, critically reviewing the data on whether TMS has anticonvulsant effects or modulates cortical-limbic loops.

Tolerability and safety of high daily doses of repetitive transcranial magnetic stimulation in healthy young men

Abstract: Repetitive transcranial magnetic stimulation (rTMS) is an experimental technology that involves a powerful magnetic pulse applied to the scalp, which is sufficient to cause neuronal depolarization. Transcranial magnetic stimulation has been used in treatment studies for psychiatric disorders, primarily unipolar depression, and as a tool to map brain function. Although thousands of rTMS sessions have been given with few side effects, rTMS can produce serious adverse effects such as an unintended seizure. Safety guidelines for frequency, duration, and intensity of rTMS have aided in the prevention of such adverse side effects. However, the total dose (number of stimuli) able to be delivered safely to human subjects within a day or within a week has not been established. For example, previous rTMS studies as a treatment for depression consisted of delivering 800 to 3000 magnetic pulses per day, with 8000 to 30,000 magnetic pulses over 2 to 3 weeks. This study examined whether high doses of rTMS within a day or over a week would produce significant side effects. As part of a study to examine rTMS effects in sleep deprivation, we exposed healthy men to 12,960 magnetic pulses a day for up to 3 days in 1 week. This equals 38,880 magnetic pulses over 1 week, which is likely one of the largest exposures of TMS to date. Despite this intense treatment regimen, we failed to produce significant side effects. Doses of up to 12,960 pulses per day appear safe and tolerable in healthy young men.

A comprehensive, non-invasive visualization of primordial germ cell development in mice by the Prdm1-mVenus and Dppa3-ECFP double transgenic reporter.

The ability to monitor the development of a given cell lineage in a non-invasive manner by fluorescent markers both in vivo and in vitro provides a great advantage for the analysis of the lineage of interest. To date, a number of transgenic or knock-in mouse strains, in which developing germ cells are marked with fluorescent reporters, have been generated. We here describe a novel double transgenic reporter mouse strain that expresses membrane-targeted Venus (mVenus), a brighter variant of yellow fluorescent protein (YFP), under the control of Prdm1 (Blimp1) regulatory elements and enhanced cyan fluorescent protein (ECFP) under the control of Dppa3 (Stella/Pgc7). The double transgenic strain unambiguously marked Prdm1 expression in the lineage-restricted precursors of primordial germ cells (PGCs) in the proximal epiblast at embryonic day (E) 6.25 and specifically illuminated Prdm1- and Dppa3-positive migrating PGCs after E8.5. The double transgenic reporter also precisely recapitulated dynamic embryonic expression of Prdm1 outside the germ cell lineage. Moreover, we derived ES cells that bore both transgenes. These cells made a robust contribution both to the germ and somatic cell lineages in chimeras with accurate Prdm1-mVenus and Dppa3-ECFP expression. The transgenic strain and the ES cells will serve as valuable experimental materials not only for analyzing the origin and properties of the germ cell lineage in vivo, but also for establishing a culture system to efficiently induce proper germ cells with temporally coordinated Prdm1 and Dppa3 expression in vitro.

Transcranial Magnetic Stimulation of the Parietal Cortex Facilitates Spatial Working Memory: Near-Infrared Spectroscopy Study

The present study investigated whether transcranial magnetic stimulation (TMS) to the parietal cortex improves the performance of healthy persons in a spatial working memory (WM) task. The effect of TMS on the frontal cortex was examined by measuring oxygenated hemoglobin (oxy-Hb) with near-infrared spectroscopy. Fifty-two healthy persons received either 100% resting motor threshold TMS at 5 Hz (real TMS) or sham TMS while engaged in a spatial WM task or a control visuospatial attention task. TMS was applied to either the left or the right parietal cortex during the delay period of the task. Reaction times improved in the spatial WM task, but not in the control task, with real TMS, whereas sham TMS had no effect. This improvement was only observed when TMS was applied to the right parietal cortex. Application of real TMS to the right parietal cortex also significantly increased frontal oxy-Hb levels during the WM task, but reduced oxy-Hb during the control task. These results suggest that TMS to the right parietal cortex may selectively facilitate spatial WM. Hemispheric asymmetry and the frontoparietal network theory may explain the observed effect of right parietal TMS on spatial WM.

Healthy offspring from freeze-dried mouse spermatozoa held on the International Space Station for 9 months

Significance Radiation on the International Space Station (ISS) is more than 100 times stronger than at the Earth’s surface, and at levels that can cause DNA damage in somatic cell nuclei. The damage to offspring caused by this irradiation in germ cells has not been examined, however. Here we preserved mouse spermatozoa on the ISS for 9 mo. Although sperm DNA was slightly damaged during space preservation, it could be repaired by the oocyte cytoplasm and did not impair the birth rate or normality of the offspring. Our results demonstrate that generating human or domestic animal offspring from space-preserved spermatozoa is a possibility, which should be useful when the “space age” arrives. If humans ever start to live permanently in space, assisted reproductive technology using preserved spermatozoa will be important for producing offspring; however, radiation on the International Space Station (ISS) is more than 100 times stronger than that on Earth, and irradiation causes DNA damage in cells and gametes. Here we examined the effect of space radiation on freeze-dried mouse spermatozoa held on the ISS for 9 mo at –95 °C, with launch and recovery at room temperature. DNA damage to the spermatozoa and male pronuclei was slightly increased, but the fertilization and birth rates were similar to those of controls. Next-generation sequencing showed only minor genomic differences between offspring derived from space-preserved spermatozoa and controls, and all offspring grew to adulthood and had normal fertility. Thus, we demonstrate that although space radiation can damage sperm DNA, it does not affect the production of viable offspring after at least 9 mo of storage on the ISS.

The Japanese version of the Rapid Dementia Screening Test is effective compared to the clock-drawing test for detecting patients with mild Alzheimer's disease.

The Japanese version of the Rapid Dementia Screening Test (RDST‐J) and the clock‐drawing test (CDT) are both brief psychometric screening tools used to detect the severity of Alzheimers disease. It remains unclear, however, which is more effective when screening for mild Alzheimers disease.

Effect of Parietal Transcranial Magnetic Stimulation on Spatial Working Memory in Healthy Elderly Persons - Comparison of Near Infrared Spectroscopy for Young and Elderly

In a previous study, we succeeded in improving the spatial working memory (WM) performance in healthy young persons by applying transcranial magnetic stimulation (TMS) to the parietal cortex and simultaneously measuring the oxygenated hemoglobin (oxy-Hb) level using near-infrared spectroscopy (NIRS). Since an improvement in WM was observed when TMS was applied to the right parietal cortex, the oxy-Hb distribution seemed to support a model of hemispheric asymmetry (HA). In the present study, we used the same study design to evaluate healthy elderly persons and investigated the effect of TMS on WM performance in the elderly, comparing the results with those previously obtained from young persons. The application of TMS did not affect WM performance (both reaction time and accuracy) of 38 elderly participants (mean age  = 72.5 years old). To investigate the reason for this result, we conducted a three-way ANOVA examining oxy-Hb in both young and elderly participants. For the right parietal TMS site in the elderly, TMS significantly decreased the oxy-Hb level during WM performance; this result was the opposite of that observed in young participants. An additional three-way ANOVA was conducted for each of the 52 channels, and a P value distribution map was created. The P value maps for the young participants showed a clearly localized TMS effect for both the WM and control task, whereas the P map for the elderly participants showed less significant channels and localization. Further analysis following the time course revealed that right-side parietal TMS had almost no effect on the frontal cortex in the elderly participants. This result can most likely be explained by age-related differences in HA arising from the over-recruitment of oxy-Hb, differentiation in the parietal cortex, and age-related alterations of the frontal-parietal networks.