The claustrum coordinates cortical slow-wave activity.

During sleep and awake rest, the neocortex generates large-scale slow-wave (SW) activity. Here, we report that the claustrum coordinates neocortical SW generation. We established a transgenic mouse line that enabled the genetic interrogation of a subpopulation of claustral glutamatergic neurons. These neurons received inputs from and sent outputs to widespread neocortical areas. The claustral neuronal firings mostly correlated with cortical SW activity. In vitro optogenetic stimulation of the claustrum induced excitatory postsynaptic responses in most neocortical neurons, but elicited action potentials primarily in inhibitory interneurons. In vivo optogenetic stimulation induced a synchronized down-state featuring prolonged silencing of neural activity in all layers of many cortical areas, followed by a down-to-up state transition. In contrast, genetic ablation of claustral neurons attenuated SW activity in the frontal cortex. These results demonstrate a crucial role of claustral neurons in synchronizing inhibitory interneurons across wide cortical areas for the spatiotemporal coordination of SW activity.

[Early Diagnosis of Cancer Using Nematoda C. elegans].

Cancer is the leading cause of death in Japan, and one in two people experience cancer in their lifetime. Early diagnosis of cancer is the most important for increasing survival rate of cancer, which is also expected to contribute to decrease budget impact of cancer, but participation rate of cancer screening is still low in Japan. Currently, people need to take multiple examinations to detect different types of cancer, which increases the cost, time and pain burdens for the examinees. Therefore, it is desirable to develop cheaper, non-invasive, as well as sensitive cancer screening methods that can detect multiple types of cancer at the same time. Most of the existing cancer screening tests including imaging diagnosis depend on artificial devices, which usually require high cost to achieve high sensitivity. We have developed a new technique, N-NOSE, which takes advantage of the good olfaction of nematode C. elegans to detect cancer smell in urine samples. N-NOSEexhibited 95.8% sensitivity and 95.0% specificity on 242 urine samples of 10 cancers types tested including those of early stages. C. elegans is easy to be maintained in a laboratory with low cost. In addition, as C. elegans is a hermaphroditic organism with homogeneous genetic background, they show stable and reproducible behavioral results. Therefore, N-NOSEis expected to offer a reasonable and non-invasive cancer screening method which is suitable for regular health checkup.

Rab8a and Rab8b are essential for several apical transport pathways but insufficient for ciliogenesis.

The small GTP-binding protein Rab8 is known to play an essential role in intracellular transport and cilia formation. We have previously demonstrated that Rab8a is required for localising apical markers in various organisms. Rab8a has a closely related isoform, Rab8b. To determine whether Rab8b can compensate for Rab8a, we generated Rab8b-knockout mice. Although the Rab8b-knockout mice did not display an overt phenotype, Rab8a and Rab8b double-knockout mice exhibited mislocalisation of apical markers and died earlier than Rab8a-knockout mice. The apical markers accumulated in three intracellular patterns in the double-knockout mice. However, the localisation of basolateral and/or dendritic markers of the double-knockout mice seemed normal. The morphology and the length of various primary and/or motile cilia, and the frequency of ciliated cells appeared to be identical in control and double-knockout mice. However, an additional knockdown of Rab10 in double-knockout cells greatly reduced the percentage of ciliated cells. Our results highlight the compensatory effect of Rab8a and Rab8b in apical transport, and the complexity of the apical transport process. In addition, neither Rab8a nor Rab8b are required for basolateral and/or dendritic transport. However, simultaneous loss of Rab8a and Rab8b has little effect on ciliogenesis, whereas additional loss of Rab10 greatly affects ciliogenesis.

Tbr2 deficiency in mitral and tufted cells disrupts excitatory-inhibitory balance of neural circuitry in the mouse olfactory bulb.

The olfactory bulb (OB) is the first relay station in the brain where odor information from the olfactory epithelium is integrated, processed through its intrinsic neural circuitry, and conveyed to higher olfactory centers. Compared with profound mechanistic insights into olfactory axon wiring from the nose to the OB, little is known about the molecular mechanisms underlying the formation of functional neural circuitry among various types of neurons inside the OB. T-box transcription factor Tbr2 is expressed in various types of glutamatergic excitatory neurons in the brain including the OB projection neurons, mitral and tufted cells. Here we generated conditional knockout mice in which the Tbr2 gene is inactivated specifically in mitral and tufted cells from late embryonic stages. Tbr2 deficiency caused cell-autonomous changes in molecular expression including a compensatory increase of another T-box member, Tbr1, and a concomitant shift of vesicular glutamate transporter (VGluT) subtypes from VGluT1 to VGluT2. Tbr2-deficient mitral and tufted cells also exhibited anatomical abnormalities in their dendritic morphology and projection patterns. Additionally, several non-cell-autonomous phenotypes were observed in parvalbumin-, calbindin-, and 5T4-positive GABAergic interneurons. Furthermore, the number of dendrodendritic reciprocal synapses between mitral/tufted cells and GABAergic interneurons was significantly reduced. Upon stimulation with odorants, larger numbers of mitral and tufted cells were activated in Tbr2 conditional knockout mice. These results suggest that Tbr2 is required for not only the proper differentiation of mitral and tufted cells, but also for the establishment of functional neuronal circuitry in the OB and maintenance of excitatory-inhibitory balance crucial for odor information processing.

Ascl1 and Gsh1/2 control inhibitory and excitatory cell fate in spinal sensory interneurons.

Sensory information from the periphery is integrated and transduced by excitatory and inhibitory interneurons in the dorsal spinal cord. Recent studies have identified a number of postmitotic factors that control the generation of these sensory interneurons. We show that Gsh1/2 and Ascl1 (Mash1), which are expressed in sensory interneuron progenitors, control the choice between excitatory and inhibitory cell fates in the developing mouse spinal cord. During the early phase of neurogenesis, Gsh1/2 and Ascl1 coordinately regulate the expression of Tlx3, which is a critical postmitotic determinant for dorsal glutamatergic sensory interneurons. However, at later developmental times, Ascl1 controls the expression of Ptf1a in dIL(A) progenitors to promote inhibitory neuron differentiation while at the same time upregulating Notch signaling to ensure the proper generation of dIL(B) excitatory neurons. We propose that this switch in Ascl1 function enables the cogeneration of inhibitory and excitatory sensory interneurons from a common pool of dorsal progenitors.

Lbx1 and Tlx3 are opposing switches in determining GABAergic versus glutamatergic transmitter phenotypes.

Most neurons in vertebrates make a developmental choice between two principal neurotransmitter phenotypes (glutamatergic versus GABAergic). Here we show that the homeobox gene Lbx1 determines a GABAergic cell fate in the dorsal spinal cord at early embryonic stages. In Lbx1-/- mice, the presumptive GABAergic neurons are transformed into glutamatergic cells. Furthermore, overexpression of Lbx1 in the chick spinal cord is sufficient to induce GABAergic differentiation. Paradoxically, Lbx1 is also expressed in glutamatergic neurons. We previously reported that the homeobox genes Tlx1 and Tlx3 determine glutamatergic cell fate. Here we show that impaired glutamatergic differentiation, observed in Tlx3-/- mice, is restored in Tlx3-/-Lbx1-/- mice. These genetic studies suggest that Lbx1 expression defines a basal GABAergic differentiation state, and Tlx3 acts to antagonize Lbx1 to promote glutamatergic differentiation.

Gsh2 is required for the repression of Ngn1 and specification of dorsal interneuron fate in the spinal cord.

The molecular programs that specify progenitors in the dorsal spinal cord remain poorly defined. The homeodomain transcription factor Gsh2 is expressed in the progenitors of three dorsal interneuron subtypes, dI3, dI4 and dI5 neurons, whereas Gsh1 is only expressed in dI4 and dI5 progenitors. Mice lacking Gsh2 exhibit a selective loss of dI3 interneurons that is accompanied by an expansion of the dI2 progenitor domain. In Gsh2 mutant embryos, expression of the proneural bHLH protein Mash1 is downregulated in dI3 neural progenitors, with Mash1 mutants exhibiting a concordant reduction in dI3 neurons. Conversely, overexpression of Gsh2 and Mash1 leads to the ectopic production of dI3 neurons and a concomitant repression of Ngn1 expression. Our results provide evidence that genetic interactions involving repression of Ngn1 by Gsh2 promote the differentiation of dI3 neurons from class A progenitors.

Tlx3 and Tlx1 are post-mitotic selector genes determining glutamatergic over GABAergic cell fates.

Glutamatergic and GABAergic neurons mediate much of the excitatory and inhibitory neurotransmission, respectively, in the vertebrate nervous system. The process by which developing neurons select between these two cell fates is poorly understood. Here we show that the homeobox genes Tlx3 and Tlx1 determine excitatory over inhibitory cell fates in the mouse dorsal spinal cord. First, we found that Tlx3 was required for specification of, and expressed in, glutamatergic neurons. Both generic and region-specific glutamatergic markers, including VGLUT2 and the AMPA receptor Gria2, were absent in Tlx mutant dorsal horn. Second, spinal GABAergic markers were derepressed in Tlx mutants, including Pax2 that is necessary for GABAergic differentiation, Gad1/2 and Viaat that regulate GABA synthesis and transport, and the kainate receptors Grik2/3. Third, ectopic expression of Tlx3 was sufficient to suppress GABAergic differentiation and induce formation of glutamatergic neurons. Finally, excess GABA-mediated inhibition caused dysfunction of central respiratory circuits in Tlx3 mutant mice.