SUMMARYThe robust regenerative ability of planarians depends on a population of somatic stem cells called neoblasts, which are the only mitotic cells in adults and are responsible for blastema formation after amputation. The molecular mechanism underlying neoblast differentiation associated with blastema formation remains unknown. Here, using the planarian Dugesia japonica we found that DjmkpA, a planarian mitogen-activated protein kinase (MAPK) phosphatase-related gene, was specifically expressed in blastema cells in response to increased extracellular signal-related kinase (ERK) activity. Pharmacological and genetic [RNA interference (RNAi)] approaches provided evidence that ERK activity was required for blastema cells to exit the proliferative state and undergo differentiation. By contrast, DjmkpA RNAi induced an increased level of ERK activity and rescued the differentiation defect of blastema cells caused by pharmacological reduction of ERK activity. These observations suggest that ERK signaling plays an instructive role in the cell fate decisions of blastema cells regarding whether to differentiate or not, by inducing DjmkpA as a negative regulator of ERK signaling during planarian regeneration.

The Temperament and Character Inventory was translated into Japanese, and, to confirm the psychometric properties of the inventory, three samples were recruited from a nonpatient population. In nonpatient population A (N = 555), the full version (240 items) of the inventory with dichotomous measuring, along with the General Health Questionnaire and the Social Desirability Scale, were distributed to the subjects. Factor analyses of the subscales showed that the factor structure of the inventory was consistent with Cloninger's theory. Correlations of the scale scores with the General Health Questionnaire and the Social Desirability Scale scores were almost negligible, indicating that the scale is resistant to the current psychopathology and response bias. In this and the other two university student samples (ns = 395 and 377), Cronbach coefficients alpha of the scale scores were substantially high except for the short version (125 items) of the inventory with dichotomous measures. The Japanese version of the inventory appears to have internal reliability and content and construct validity in a Japanese population.

The neoblasts are the only somatic stem cells in planarians possessing pluripotency, and can give rise to all types of cells, including germline cells. Recently, accumulated knowledge about the transcriptome and expression dynamics of various pluripotent somatic stem cells has provided important opportunities to understand not only fundamental mechanisms of pluripotency, but also stemness across species at the molecular level. The neoblasts can easily be eliminated by radiation. Also, by using fluorescence activated cell sorting (FACS), we can purify and collect many neoblasts, enabling identification of neoblast-related genes by comparison of the gene expression level among intact and X-ray-irradiated animals, and purified neoblasts. In order to find such genes, here we employed the high coverage expression profiling (HiCEP) method, which enables us to observe and compare genome-wide gene expression levels between different samples without advance sequence information, in the planarian D. japonica as a model organism of pluripotent stem cell research. We compared expression levels of ~17,000 peaks corresponding to independent genes among different samples, and obtained 102 peaks as candidates. Expression analysis of genes identified from those peaks by in situ hybridization revealed that at least 42 genes were expressed in the neoblasts and in neoblast-related cells that had a different distribution pattern in the body than neoblasts. Also, single-cell PCR analysis of those genes revealed heterogeneous expression of some genes in the neoblast population. Thus, using multidimensional gene expression analyses, we were able to obtain a valuable data set of neoblast-related genes and their expression patterns.

A series of experiments were performed to investigate why two peaks (D and E) of the five dissolved phase peaks in hyperpolarized 129 Xe rat head spectra appeared inconsistently in previous work. Specifically, spectra were acquired under conditions of various shim states, anaesthetics, and arterial ligation. The shimming experiments showed that slice-shimming can be used to improve resolution of the dissolved phase peaks, but even so, subtle changes in the shim state that may dramatically alter the shape of peak E remain poorly understood. Also, the inability to shim gas spaces and tissue simultaneously may explain why In previous work, five dissolved phase peaks were found in hyperpolarized 129 Xe (HypXe) rat head spectra (1). The sources of the peaks were investigated by comparing spectra acquired from normal rats with spectra taken from rats after ligating the major arteries feeding nonbrain tissue, the external carotid arteries (ECAs), and the pterygopalatine arteries (PPAs). The results indicated that the dominant peak (peak A in (1); see also Fig. 1a and Table 1 in this paper) originates from brain tissue, while two other peaks originate from xenon in nonbrain tissue (B) and blood (C). The origins of the remaining two peaks (D and E) were unresolved because they did not appear consistently in the preand postligation spectra. From the data available at that time, three factors were isolated as possible reasons for the inconsistent appearance of the latter two peaks. The factors were: the low SNR of the measurements, the anaesthetic used to subdue the animals, and the fact that the ligated and unligated spectra were not from the same animal. Of these factors, the first has now been addressed by technical

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