PTEN (phosphatase and tensin homologue) is a phosphatase that dephosphorylates both protein and phosphoinositide substrates. It is mutated in a variety of human tumours and has important roles in a diverse range of biological processes, including cell migration and chemotaxis. PTEN's intracellular localization and presumably activity are regulated by chemoattractants in Dictyostelium and mouse neutrophils. However, the mechanisms for its regulation remain elusive. Here we show that RhoA and Cdc42, members of the Rho family of small GTPases, regulate the intracellular localization of PTEN in leukocytes and human transfected embryonic kidney cells. In addition, active RhoA is able to stimulate the phospholipid phosphatase activity of PTEN in human embryonic kidney cells and leukocytes, and this regulation seems to require RhoA's downstream effector, RhoA-associated kinase (Rock). Furthermore, we have identified key residues on PTEN that are required for its regulation by the small GTPase, and show that small GTPase-mediated regulation of PTEN has a significant role in the regulation of chemotaxis.

The specification and differentiation of serotonergic (5-HT) neurons require both extrinsic signaling molecules and intrinsic transcription factors to work in concert or in cascade. Here we identify the genetic cascades that control the specification and differentiation of 5-HT neurons in mice. A major determinant in the cascades is an LIM homeodomain-containing gene, Lmx1b, which is required for the development of all 5-HT neurons in the central nervous system. Our results suggest that, during development of 5-HT neurons, Lmx1b is a critical intermediate factor that couples Nkx2-2-mediated early specification with Pet1-mediated terminal differentiation. Moreover, our data indicate that genetic cascades controlling the caudal and rostral 5-HT neurons are distinct, despite their shared components.

Postmitotic neurons in the developing cortex migrate along radial glial fibers to their proper location in the cortical plate and form the layered structure. Here we report that the radial migration of rat layer II/III cortical neurons requires guidance by the extracellular diffusible factor Semaphorin-3A (Sema3A). This factor is expressed in a descending gradient across the cortical layers, whereas its receptor neuropilin-1 (NP1) is highly expressed in migrating neurons. Downregulation or conditional knockout of NP1 in newborn cortical neurons impedes their radial migration by disrupting their radial orientation during migration without altering their cell fate. Studies in cultured cortical slices further show that the endogenous gradient of Sema3A is required for the proper migration of newborn neurons. In addition, transwell chemotaxis assays show that isolated newborn neurons are attracted by Sema3A. Thus, Sema3A may function as a chemoattractive guidance signal for the radial migration of newborn cortical neurons toward upper layers.

The corpus callosum is the largest commissural system in the mammalian brain, but the mechanisms underlying its development are not well understood. Here we report that neuronal activity is necessary for the normal development and maintenance of callosal projections in the mouse somatosensory cortex. We labeled a subpopulation of layer II/III callosal neurons via in utero electroporation and traced their axons in the contralateral cortex at different postnatal stages. Callosal axons displayed region-and layer-specific projection patterns within the first 2 weeks postnatally. Prenatal suppression of neuronal excitation was achieved via electroporation-induced overexpression of the inward rectifying potassium channel Kir2.1 in layer II/III cortical neurons. This resulted in abnormal callosal projections with many axons extending beyond layers II-III to terminate in layer I. Others failed to terminate at the border between the primary and secondary somatosensory cortices. Blocking synaptic transmission via expression of the tetanus toxin light chain (TeNT-LC) in these axons produced a more pronounced reduction in the projections to the border region, and the eventual disappearance of callosal projections over the entire somatosensory cortex. When Kir2.1 and TeNT-LC were coexpressed, callosal axon targeting exhibited a more severe phenotype that appeared to represent the addition of the effects produced by individual expression of Kir2.1 and TeNT-LC. These results underscore the importance of activity in regulating the developing neural connections and suggest that neuronal and synaptic activities are involved in regulating different aspects of the development of callosal projection.

Netrins regulate axon path-finding during development, but the underlying mechanisms are not well understood. Here, we provide evidence for the involvement of the unconventional myosin X (Myo X) in netrin-1 function. We find that Myo X interacts with the netrin receptor deleted in colorectal cancer (DCC) and neogenin, a DCC-related protein. Expression of Myo X redistributes DCC to the cell periphery or to the tips of neurites, whereas its silencing prevents DCC distribution in neurites. Moreover, expression of DCC, but not neogenin, stimulates Myo X-mediated formation and elongation of filopodia, suggesting that Myo X function may be differentially regulated by DCC and neogenin. The involvement of Myo X in netrin-1 function was further supported by the effects of inhibiting Myo X function in neurons. Cortical explants derived from mouse embryos expressing a motor-less Myo X exhibit reduced neurite outgrowth in response to netrin-1 and chick commissural neurons expressing the motor-less Myo X, or in which Myo X is silenced using microRNA (miRNA), show impaired axon projection in vivo. Taken together, these results identify a novel role for Myo X in regulating netrin-1 function.

The transient receptor potential canonical (TRPC) channels are Ca2+-permeable, nonselective cation channels with different biological functions, but their roles in brain are largely unknown. Here we report that TRPC6 was localized to excitatory synapses and promoted their formation via a CaMKIV-CREB-dependent pathway. TRPC6 transgenic mice showed enhancement in spine formation, and spatial learning and memory in Morris water maze. These results reveal a previously unknown role of TRPC6 in synaptic and behavioral plasticity.

Protease-activated receptors (PAR) are G protein-coupled receptors that function as cell-surface sensors for coagulant proteases, as well as other proteases associated with the tumor microenvironment. PAR1 is activated by thrombin whereas the upstream coagulant protease VIIa bound to tissue factor and Xa can activate both PAR1 and PAR2. PAR1 has been implicated in tumor cell growth, migration, and invasion whereas the function of PAR2 in these processes is largely unknown. Towards defining the functional importance of PAR2 in cancer cells, we used small interfering RNAs to deplete highly invasive breast cancer cells of endogenous PAR proteins. Our findings strongly suggest that PAR2 is critical for MDA-MB-231 and BT549 breast cancer cell migration and invasion towards NIH 3T3 fibroblast conditioned medium. To define the relative importance of PAR1 versus PAR2 in mediating factor VIIa and Xa responses, we assessed signaling in cancer cells lacking either endogenous PAR1 or PAR2 proteins. Strikingly, in MDA-MB-231 cells depleted of PAR2, we observed a marked inhibition of VIIa and Xa signaling to phosphoinositide hydrolysis and extracellular signalregulated kinase 1/2 activation whereas signaling by VIIa and Xa remained intact in PAR1-deficient cells. Factor VIIa and Xa-induced cellular migration was also impaired in MDA-MB-231 cells deficient in PAR2 but not in cells lacking PAR1. Together, these studies reveal the novel findings that PAR2, a second protease-activated G protein-coupled receptor, has a critical role in breast cancer cell migration and invasion and functions as the endogenous receptor for coagulant proteases

Many studies have suggested that childhood maltreatment increase risk of adulthood major depressive disorder (MDD) and predict its unfavorable treatment outcome, yet the neural underpinnings associated with childhood maltreatment in MDD remain poorly understood. Here, we seek to investigate the whole-brain functional connectivity patterns in MDD patients with childhood maltreatment. Resting-state functional magnetic resonance imaging was used to explore intrinsic or spontaneous functional connectivity networks of 18 MDD patients with childhood neglect, 20 MDD patients without childhood neglect, and 20 healthy controls. Whole-brain functional networks were constructed by measuring the temporal correlations of every pairs of brain voxels and were further analyzed by using graph-theory approaches. Relative to the healthy control group, the two MDD patient groups showed overlapping reduced functional connectivity strength in bilateral ventral medial prefrontal cortex/ventral anterior cingulate cortex. However, compared with MDD patients without a history of childhood maltreatment, those patients with such a history displayed widespread reduction of functional connectivity strength primarily in brain regions within the prefrontal-limbic-thalamic-cerebellar circuitry, and these reductions significantly correlated with measures of childhood neglect. Together, we showed that the MDD groups with and without childhood neglect exhibited overlapping and segregated functional connectivity patterns in the whole-brain networks, providing empirical evidence for the contribution of early life stress to the pathophysiology of MDD.