Kif26b, a kinesin family gene, regulates adhesion of the embryonic kidney mesenchyme.

The kidney develops through reciprocal interactions between two precursor tissues: the metanephric mesenchyme and the ureteric bud. We previously demonstrated that the zinc finger protein Sall1 is essential for ureteric bud attraction toward the mesenchyme. Here, we show that Kif26b, a kinesin family gene, is a downstream target of Sall1 and that disruption of this gene causes kidney agenesis because of impaired ureteric bud attraction. In the Kif26b-null metanephros, compact adhesion between mesenchymal cells adjacent to the ureteric buds and the polarized distribution of integrin alpha8 were impaired, resulting in failed maintenance of Gdnf, a critical ureteric bud attractant. Overexpression of Kif26b in vitro caused increased cell adhesion through interactions with nonmuscle myosin. Thus, Kif26b is essential for kidney development because it regulates the adhesion of mesenchymal cells in contact with ureteric buds.

Notch2 activation in the embryonic kidney depletes nephron progenitors.

Successive activation of Wnt4 and Notch2 generates nephrons from the metanephric mesenchyme. Mesenchymal-to-epithelial transition requires Wnt4, and normal development of the proximal nephron (epithelia of glomeruli and proximal tubules) requires Notch2. It is unknown, however, whether Notch2 dictates the fate of the proximal nephron directly. Here, we generated a mutant strain of mice with activated Notch2 in Six2-containing nephron progenitor cells of the metanephric mesenchyme. Notch2 activation did not skew the cell fate toward the proximal nephron but resulted in severe kidney dysgenesis and depletion of Six2-positive progenitors. We observed ectopic expression of Wnt4 and premature tubule formation, similar to the phenotype of Six2-deficient mice. Activation of Notch2 in the progenitor cells suppressed Pax2, an upstream regulator of Six2, possibly through Hesr genes. Taken together, these data suggest that a positive feedback loop exists between Notch2 and Wnt4, and that Notch2 stabilizes, rather than dictates, nephron fate by shutting down the maintenance of undifferentiated progenitor cells, thereby depleting this population.

Trb2, a mouse homolog of tribbles, is dispensable for kidney and mouse development.

Glomeruli comprise an important filtering apparatus in the kidney and are derived from the metanephric mesenchyme. A nuclear protein, Sall1, is expressed in this mesenchyme, and we previously reported that Trb2, a mouse homolog of Drosophila tribbles, is expressed in the mesenchyme-derived tissues of the kidney by microarray analyses using Sall1-GFP knock-in mice. In the present report, we detected Trb2 expression in a variety of organs during gestation, including the kidneys, mesonephros, testes, heart, eyes, thymus, blood vessels, muscle, bones, tongue, spinal cord, and ganglions. In the developing kidney, Trb2 signals were detected in podocytes and the prospective mesangium of the glomeruli, as well as in ureteric bud tips. However, Trb2 mutant mice did not display any apparent phenotypes and no proteinuria was observed, indicating normal glomerular functions. These results suggest that Trb2 plays minimal roles during kidney and mouse development.

Children's and adults' neural bases of verbal and nonverbal 'theory of mind'.

Theory of mind (ToM) - our ability to predict behaviors of others in terms of their underlying intentions - has been examined through verbal and nonverbal false-belief (FB) tasks. Previous brain imaging studies of ToM in adults have implicated medial prefrontal cortex (mPFC) and temporo-parietal junction (TPJ) for adults' ToM ability. To examine age and modality related differences and similarities in neural correlates of ToM, we tested 16 adults (18-40 years old) and 12 children (8-12 years old) with verbal (story) and nonverbal (cartoon) FB tasks, using functional magnetic resonance imaging (fMRI). Both age groups showed significant activity in the TPJ bilaterally and right inferior parietal lobule (IPL) in a modality-independent manner, indicating that these areas are important for ToM during both adulthood and childhood, regardless of modality. We also found significant age-related differences in the ToM condition-specific activity for the story and cartoon tasks in the left inferior frontal gyrus (IFG) and left TPJ. These results suggest that depending on the modality adults may utilize different brain regions from children in understanding ToM.

Cultural and linguistic effects on neural bases of 'Theory of Mind' in American and Japanese children.

Theory of Mind (ToM) has been defined as our ability to predict behaviors of others in terms of their underlying intentions. While the developmental trajectory of ToM had been thought to be invariant across cultures, several ToM studies conducted outside the Anglo-American cultural or linguistic milieus have obtained mixed results. To examine effects of culture/language on the development of neural bases of ToM, we studied 12 American monolingual children and 12 Japanese bilingual children with second-order false-belief story and cartoon tasks, using functional magnetic resonance imaging (fMRI). While a few brain regions such as ventro-medial prefrontal cortex (vmPFC) and precuneus were recruited by both cultural/linguistic groups, several brain areas including inferior frontal gyrus (IFG) and temporo-parietal junction (TPJ) were employed in a culture/language-dependent manner during the ToM tasks. These results suggest that the neural correlates of ToM may begin to vary depending upon cultural/linguistic background from early in life.

Cultural and linguistic influence on neural bases of 'Theory of Mind': an fMRI study with Japanese bilinguals.

Theory of mind (ToM)-our ability to predict behaviors of others in terms of their underlying intentions-has been thought to be universal and invariant across different cultures. However, several ToM studies conducted outside the Anglo-American cultural or linguistic boundaries have obtained mixed results. To examine the influence of culture/language on neural bases of ToM, we studied 16 American English-speaking monolinguals and 16 Japanese-English bilinguals with second-order false-belief story tasks, using functional magnetic resonance imaging (fMRI). Several neural correlates of ToM including medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC) were recruited by both cultural/linguistic groups. However, some other brain areas including inferior frontal gyrus (IFG) were employed in a culture/language-specific manner, during the ToM tasks. These results suggest that the ways in which adults understand ToM are not entirely universal.

Detection of apoptosis during planarian regeneration by the expression of apoptosis-related genes and TUNEL assay.

Apoptosis is a tightly organized cell death process that plays a crucial role in metazoan development, but it has not yet been revealed whether apoptotic events are involved in the process of regeneration. Here, we tried to detect apoptotic cells during planarian regeneration using the TdT-mediated dUTP nick-end labeling (TUNEL) assay as well as the expression of apoptosis-related genes. Three novel cDNAs were isolated from a planarian cDNA library and shown to be closely related to other metazoan caspases at the amino acid sequence level. One of these cDNAs, Caspase-like gene 3 (DjClg3), was expressed primarily in apoptotic cells by double detections with the TUNEL assay. Whole mount in situ studies indicated that DjClg3 was expressed in the cells of the mesenchymal space and also around the pharynx of the intact body. Its expression in the regenerating head piece was seen in the blastema and less significantly in the brain, while in the regenerating tail piece, DjClg3 expression was detected uniformly throughout the entire region. In parallel experiments, we performed in situ TUNEL assays to localize the regions where cell death occurred during regeneration and comparable results to the DjClg3 expression patterns were obtained. This is the first report to show that planarians have apoptosis-related genes and the results suggest that the apoptotic mechanism probably takes place to a large extent in normal intact worms as well as during their regeneration. We hypothesize that the presence of apoptosis in planarians may have a role in controlling cell numbers, eliminating unnecessary tissues or cells and remodeling the old tissues of regenerating body parts.

Experience-induced changes in taste identification of monosodium glutamate.

Taste sensitivity for a given subject generally has been thought to be genetically determined and not plastic. Yet experience-inducible changes in human taste and olfactory sensitivities have been reported. To test a taste induction hypothesis, we exposed 17 Americans/Europeans to monosodium glutamate (MSG) in food and then compared their ability to identify MSG taste with that of 2 control groups (18 Americans/Europeans without MSG exposure and 18 Japanese). When tested on Day 11 or 12, the Americans/Europeans exposed to MSG were able to identify MSG at significantly lower concentrations than the Americans/Europeans without MSG exposure. Moreover, Japanese subjects who had prior extensive experience with MSG in Japanese food were able to identify MSG at significantly lower concentrations than the two American/European groups. The differences in identification ability between the two American/European groups challenge the notion of taste sensitivity as stable over time and support the hypothesis of an experience-inducible component in human taste.

Overexpression of Sall1 in vivo leads to reduced body weight without affecting kidney development.

Human SALL1 is a homologue of the Drosophila region-specific homeotic gene sal, and is also known as a causative gene for Townes-Brocks syndrome, which is characterized by multi-organ malformations. We previously demonstrated that mouse Sall1 plays a crucial role in ureteric bud invasion during kidney development, and possibly in nephron progenitor cells in the metanephric mesenchyme. To gain insights into the Sall1 functions in the kidney and other tissues, we generated R26Sall1 mice, in which Rosa26 locus stop sequences flanked by two loxP sites were located upstream of the Sall1 cDNA. This allele allowed exogenous Sall1 expression in a Cre recombinase-dependent manner. R26Sall1 mice were first crossed with CAGCre mice, which expressed Cre recombinase ubiquitously during embryogenesis. Mice expressing Sall1 ubiquitously were smaller in size compared with mice of other genotypes. We then crossed R26Sall1 mice with Six2Cre mice expressing Cre recombinase in the metanephric mesenchyme during kidney development. However, no kidney defects were observed. Taken together, overexpression of Sall1 does not affect kidney development, but does lead to a reduced body weight, suggesting that the optimal dosage of Sall1 is required for normal mouse development.

To be or not to be a flatworm: the acoel controversy.

Since first described, acoels were considered members of the flatworms (Platyhelminthes). However, no clear synapomorphies among the three large flatworm taxa -- the Catenulida, the Acoelomorpha and the Rhabditophora -- have been characterized to date. Molecular phylogenies, on the other hand, commonly positioned acoels separate from other flatworms. Accordingly, our own multi-locus phylogenetic analysis using 43 genes and 23 animal species places the acoel flatworm Isodiametra pulchra at the base of all Bilateria, distant from other flatworms. By contrast, novel data on the distribution and proliferation of stem cells and the specific mode of epidermal replacement constitute a strong synapomorphy for the Acoela plus the major group of flatworms, the Rhabditophora. The expression of a piwi-like gene not only in gonadal, but also in adult somatic stem cells is another unique feature among bilaterians. These two independent stem-cell-related characters put the Acoela into the Platyhelminthes-Lophotrochozoa clade and account for the most parsimonious evolutionary explanation of epidermal cell renewal in the Bilateria. Most available multigene analyses produce conflicting results regarding the position of the acoels in the tree of life. Given these phylogenomic conflicts and the contradiction of developmental and morphological data with phylogenomic results, the monophyly of the phylum Platyhelminthes and the position of the Acoela remain unresolved. By these data, both the inclusion of Acoela within Platyhelminthes, and their separation from flatworms as basal bilaterians are well-supported alternatives.

Switching language switches mind: linguistic effects on developmental neural bases of 'Theory of Mind'.

Theory of mind (ToM)--our ability to predict behaviors of others in terms of their underlying intentions--has been examined through false-belief (FB) tasks. We studied 12 Japanese early bilingual children (8-12 years of age) and 16 late bilingual adults (18-40 years of age) with FB tasks in Japanese [first language (L1)] and English [second language (L2)], using fMRI. Children recruited more brain regions than adults for processing ToM tasks in both languages. Moreover, children showed an overlap in brain activity between the L1 and L2 ToM conditions in the medial prefrontal cortex (mPFC). Adults did not show such a convergent activity in the mPFC region, but instead, showed brain activity that varied depending on the language used in the ToM task. The developmental shift from more to less ToM specific brain activity may reflect increasing automatization of ToM processing as people age. These results also suggest that bilinguals recruit different resources to understand ToM depending on the language used in the task, and this difference is greater later in life.

Wnt signaling is required for antero-posterior patterning of the planarian brain.

Wnt signaling functions in axis formation and morphogenesis in various animals and organs. Here we report that Wnt signaling is required for proper brain patterning during planarian brain regeneration. We showed here that one of the Wnt homologues in the planarian Dugesia japonica, DjwntA, was expressed in the posterior region of the brain. When DjwntA-knockdown planarians were produced by RNAi, they could regenerate their heads at the anterior ends of the fragments, but formed ectopic eyes with irregular posterior lateral branches and brain expansion. This suggests that the Wnt signal may be involved in antero-posterior (A-P) patterning of the planarian brain, as in vertebrates. We also investigated the relationship between the DjwntA and nou-darake/FGFR signal systems, as knockdown planarians of these genes showed similar phenotypes. Double-knockdown planarians of these genes did not show any synergistic effects, suggesting that the two signal systems function independently in the process of brain regeneration, which accords with the fact that nou-darake was expressed earlier than DjwntA during brain regeneration. These observations suggest that the nou-darake/FGFR signal may be involved in brain rudiment formation during the early stage of head regeneration, and subsequently the DjwntA signal may function in A-P patterning of the brain rudiment.

Experience-induced changes in taste identification of monosodium glutamate (MSG) are reversible.

A few studies have reported experience-inducible changes in human taste and olfactory sensitivities. However, no study thus far has systematically characterized the stability of the enhanced sensitivities. In our previous study, we found increases in taste identification ability for monosodium glutamate (MSG) in subjects who had been briefly exposed to MSG in food for 10 days. Here, we tested the temporal stability of the enhanced taste identification ability. First, we exposed a group of 20 subjects to MSG in food and then compared their sensitivities to MSG with those of a control group. When tested on day 11 or 12, the mean MSG taste identification ability of the MSG-exposed group was significantly higher than the control group. Next, 11 of the subjects who were exposed to MSG in food initially, and then stopped being exposed performed significantly poorer in identifying MSG after 10 days of the nonexposure than they did 10 days before. In contrast, nine subjects who were exposed to MSG initially and continued being exposed maintained their high identification levels. These results support earlier finding of the plasticity in the taste identification of MSG and show that the enhanced identification ability can be reversed rapidly when MSG exposure is not sustained.

The murine homolog of SALL4, a causative gene in Okihiro syndrome, is essential for embryonic stem cell proliferation, and cooperates with Sall1 in anorectal, heart, brain and kidney development.

Mutations in SALL4, the human homolog of the Drosophila homeotic gene spalt (sal), cause the autosomal dominant disorder known as Okihiro syndrome. In this study, we show that a targeted null mutation in the mouse Sall4 gene leads to lethality during peri-implantation. Growth of the inner cell mass from the knockout blastocysts was reduced, and Sall4-null embryonic stem (ES) cells proliferated poorly with no aberrant differentiation. Furthermore, we demonstrated that anorectal and heart anomalies in Okihiro syndrome are caused by Sall4 haploinsufficiency and that Sall4/Sall1 heterozygotes exhibited an increased incidence of anorectal and heart anomalies, exencephaly and kidney agenesis. Sall4 and Sall1 formed heterodimers, and a truncated Sall1 caused mislocalization of Sall4 in the heterochromatin; thus, some symptoms of Townes-Brocks syndrome caused by SALL1 truncations could result from SALL4 inhibition.

Planarian fibroblast growth factor receptor homologs expressed in stem cells and cephalic ganglions.

The strong regenerative capacity of planarians is considered to reside in the totipotent somatic stem cell called the 'neoblast'. However, the signal systems regulating the differentiation/growth/migration of stem cells remain unclear. The fibroblast growth factor (FGF)/FGF receptor (FGFR) system is thought to mediate various developmental events in both vertebrates and invertebrates. We examined the molecular structures and expression of DjFGFR1 and DjFGFR2, two planarian genes closely related to other animal FGFR genes. DjFGFR1 and DjFGFR2 proteins contain three and two immunoglobulin-like domains, respectively, in the extracellular region and a split tyrosine kinase domain in the intracellular region. Expression of DjFGFR1 and DjFGFR2 was observed in the cephalic ganglion and mesenchymal space in intact planarians. In regenerating planarians, accumulation of DjFGFR1-expressing cells was observed in the blastema and in fragments regenerating either a pharynx or a brain. In X-ray-irradiated planarians, which had lost regenerative capacity, the number of DjFGFR1-expressing cells in the mesenchymal space decreased markedly. These results suggest that the DjFGFR1 protein may be involved in the signal systems controlling such aspects of planarian regeneration as differentiation/growth/migration of stem cells.

Purification and cDNA cloning of the ovigerous-hair stripping substance (OHSS) contained in the hatch water of an estuarine crab Sesarma haematocheir.

The egg attachment system of an estuarine crab Sesarma haematocheir is formed on the maternal ovigerous hairs just after egg laying, and slips off these hairs just after hatching. The stripping is caused by an active factor that we call OHSS (ovigerous-hair stripping substance), which is released by the embryo upon hatching. OHSS was purified, and its active form had a molecular mass of 25 kDa. The cDNA of OHSS cloned from an embryonic cDNA library was 1759 bp long, encoding 492 amino acids in a single open reading frame (ORF). The C-terminal part of the predicted protein was composed of a trypsin-like serine protease domain, with homology to counterparts in other animals of 33-38%. The predicted protein (54.7 kDa) secreted as a zymogen may be cleaved post-translationally, separating the C-terminal from the N-terminal region. The OHSS gene was expressed in the embryo at least 2 weeks before hatching. Expression was also detected in the zoea larva 1 day after hatching and in the brain of the female. However, it was not detected in the muscle, hepatopancreas or ovigerous seta of the female. Ultrastructural analysis indicated that the material investing maternal ovigerous hair, i.e. the outermost layer (E1) of the egg case, is attached at the special sites (attachment sites) arranged at intervals of 130-160 nm on the hair. It is suggested that OHSS acts specifically at these sites, lysing the bond with the coat, thus disposing of the embryo attachment system. This enables the female to prepare the next clutch of embryos without ecdysis.

FGFR-related gene nou-darake restricts brain tissues to the head region of planarians.

The study of planarian regeneration may help us to understand how we can rebuild organs and tissues after injury, disease or ageing. The robust regenerative abilities of planarians are based upon a population of totipotent stem cells (neoblasts), and among the organs regenerated by these animals is a well-organized central nervous system. In recent years, methodologies such as whole-mount in situ hybridizations and double-stranded RNA have been extended to planarians with the aim of unravelling the molecular basis of their regenerative capacities. Here we report the identification and characterization of nou-darake (ndk), a gene encoding a fibroblast growth factor receptor (FGFR)-like molecule specifically expressed in the head region of the planarian Dugesia japonica. Loss of function of ndk by RNA interference results in the induction of ectopic brain tissues throughout the body. This ectopic brain formation was suppressed by inhibition of two planarian FGFR homologues (FGFR1 and FGFR2). Additionally, ndk inhibits FGF signalling in Xenopus embryos. The data suggest that ndk may modulate FGF signalling in stem cells to restrict brain tissues to the head region of planarians.