Midbrain dopamine neurons (mDA) are important regulators of diverse physiological functions, including movement, attention, and reward behaviors. Accordingly, aberrant function of dopamine neurons underlies a wide spectrum of disorders, such as Parkinson's disease (PD), dystonia, and schizophrenia. The distinct functions of the dopamine system are carried out by neuroanatomically discrete subgroups of dopamine neurons, which differ in gene expression, axonal projections, and susceptibility in PD. The developmental underpinnings of this heterogeneity are undefined. We have recently shown that in the embryonic CNS, mDA originate from the midbrain floor plate, a ventral midline structure that is operationally defined by the expression of the molecule Shh. Here, we develop these findings to reveal that in the embryonic midbrain, the spatiotemporally dynamic Shh domain defines multiple progenitor pools. We deduce 3 distinct progenitor pools, medial, intermediate, and lateral, which contribute to different mDA clusters. The earliest progenitors to express Shh, here referred to as the medial pool, contributes neurons to the rostral linear nucleus and mDA of the ventral tegmental area/interfascicular regions, but remarkably, little to the substantia nigra pars compacta. The intermediate Shh؉ progenitors give rise to neurons of all dopaminergic nuclei, including the SNpc. The last and lateral pool of Shh؉ progenitors generates a cohort that populates the red nucleus, Edinger Westphal nucleus, and supraoculomotor nucleus and cap. Subsequently, these lateral Shh؉ progenitors produce mDA. This refined ontogenetic definition will expand understanding of dopamine neuron biology and selective susceptibility, and will impact stem cell-derived therapies and models for PD.dopamine ͉ Sonic hedgehog ͉ lineage ͉ substantia nigra

The floor plate, an essential ventral midline organizing center that produces the morphogen Shh, has distinct properties along the neuraxis. The neurogenic potential of the floor plate and its underlying mechanisms remain unknown. Using Shh as a driver for lineage analysis, we found that the mouse midbrain, but not the hindbrain, floor plate is neurogenic, giving rise to dopamine (DA) neurons. Distinct spatiotemporal Shh and Wnt expression may distinguish the neurogenetic potential of these structures. We discovered an inhibitory role for Shh: removal of Shh resulted in neurogenesis from the hindbrain midline and, conversely, high doses of Shh inhibited proliferation and DA neuron production in midbrain cultures. We found that Wnt/beta-catenin signaling is necessary and sufficient for antagonizing Shh, DA progenitor marker induction and promotion of dopaminergic neurogenesis. These findings demonstrate how the dynamic interplay of canonical Wnt/beta-catenin signaling and Shh may orchestrate floor plate neurogenesis or a lack thereof.

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MicroRNAs, by modulating gene expression, have been implicated as regulators of various cellular and physiological processes, including differentiation, proliferation, and cancer. Here, we study the role of microRNAs in Schwann cell (SC) differentiation by conditional removal of the microRNA processing enzyme Dicer1. We reveal that both male and female mice lacking Dicer1 in SC (Dicer1 conditional knock-outs) display a severe neurological phenotype resembling congenital hypomyelination. Ultrastructural analyses show that many SC lacking Dicer1 are stalled in differentiation at the promyelinating state and fail to myelinate axons. Gene expression analyses reveal a failure to extinguish genes characteristic of the undifferentiated state such as Sox2, Jun, and Ccnd1. Sox2 and Jun are well characterized negative regulators of SC differentiation. Consistent with Sox2/Jun maintenance, Egr2, a master regulator of the myelinating program, is drastically downregulated and likely accounts for the myelination defect. We posit a model wherein microRNAs are critical for downregulation of antecedent programs of gene expression. In SC differentiation, this is particularly relevant in the key developmental transition from a promyelinating to myelinating SC.

MicroRNAs regulate gene expression in diverse physiological scenarios. Their role in the control of morphogen related signaling pathways has been less studied, particularly in the context of embryonic Central Nervous System (CNS) development. Here, we uncover a role for microRNAs in limiting the spatiotemporal range of morphogen expression and function. Wnt1 is a key morphogen in the embryonic midbrain, and directs proliferation, survival, patterning and neurogenesis. We reveal an autoregulatory negative feedback loop between the transcription factor Lmx1b and a newly characterized microRNA, miR135a2, which modulates the extent of Wnt1/Wnt signaling and the size of the dopamine progenitor domain. Conditional gain of function studies reveal that Lmx1b promotes Wnt1/Wnt signaling, and thereby increases midbrain size and dopamine progenitor allocation. Conditional removal of Lmx1b has the opposite effect, in that expansion of the dopamine progenitor domain is severely compromised. Next, we provide evidence that microRNAs are involved in restricting dopamine progenitor allocation. Conditional loss of Dicer1 in embryonic stem cells (ESCs) results in expanded Lmx1a/b+ progenitors. In contrast, forced elevation of miR135a2 during an early window in vivo phenocopies the Lmx1b conditional knockout. When En1::Cre, but not Shh::Cre or Nes::Cre, is used for recombination, the expansion of Lmx1a/b+ progenitors is selectively reduced. Bioinformatics and luciferase assay data suggests that miR135a2 targets Lmx1b and many genes in the Wnt signaling pathway, including Ccnd1, Gsk3b, and Tcf7l2. Consistent with this, we demonstrate that this mutant displays reductions in the size of the Lmx1b/Wnt1 domain and range of canonical Wnt signaling. We posit that microRNA modulation of the Lmx1b/Wnt axis in the early midbrain/isthmus could determine midbrain size and allocation of dopamine progenitors. Since canonical Wnt activity has recently been recognized as a key ingredient for programming ESCs towards a dopaminergic fate in vitro, these studies could impact the rational design of such protocols.

Pax3 encodes a paired homeobox containing transcription factor that is expressed in neuroepithelium, neural crest, and presomitic mesoderm (1). Homozygous mouse embryos carrying a loss-of-function Pax3 allele (Pax3 Ϫ/Ϫ ) develop open neural tube defects, such as exencephaly or spina bifida (2), and die around embryonic day 14 (E14) 4 as a consequence of heart defects (3). More recently, Pax3 has been shown to function at the nodal point in melanocyte stem cell differentiation (4). Heterozygous embryos (Pax3 ϩ/Ϫ ) are viable but exhibit white patches on their bellies caused by defective development of neural crest-derived melanocytes. This suggests that disruption of the Pax3-dependent developmental program may cause defects in the development of neural crest-derived structures.Two main Pax3-binding sites have been identified and are found in most Pax3 target elements as follows: (i) a binding site derived from the Drosophila Paired (ATTA N5 GTTCC), and (ii) a Pax3 paired domain binding site (CGTCAC(G/A)(C/ G)TT) identified by Epstein et al. (5) by CASTing (DNA-binding site selection assays) in the c-Met promoter region. In addition several paired domains, such as GTTCC, CAGTGT, GTTAT, GTGTGA, and CAAGG (6), as well as the homeodomain ATTA, have been suggested to be "putative Pax3-binding motifs" (7,8). More recently, Corey and Underhill (9) demonstrated that Pax3 can regulate target genes through alternative modes of DNA recognition. They observed that although the microphthalmia-associated transcription factor element is characterized by suboptimal recognition motifs for the paired domain and homeodomain, it sustains a higher level of Pax3 binding than TRP-1, which contains a canonical paired domain site. The basis for this difference involved a context-dependent cooperative binding event requiring both the paired and homeodomain, whereas the paired domain alone was sufficient for TRP-1 recognition.Since Pax3 is important in diverse cellular functions during development, we wanted to identify additional genes regulated by Pax3. To accomplish this we utilized oligonucleotide arrays and RNA isolated from Pax3-transfected cell lines and promoter-based data mining (6). Based on the putative Pax3-binding

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Table tennis involves quick and accurate motor responses during training and competition. Multiple studies have reported considerably faster visuomotor responses and expertise-related intrinsic brain activity changes among table tennis players compared with matched controls. However, the underlying neural mechanisms remain unclear. Herein, we performed static and dynamic resting-state functional magnetic resonance imaging (rs-fMRI) analyses of 20 table tennis players and 21 control subjects using 7T ultra-high field imaging. We calculated the static and dynamic amplitude of low-frequency fluctuations (ALFF) of the two groups. The results revealed that table tennis players exhibited decreased static ALFF in the left inferior temporal gyrus (lITG) compared with the control group. Voxel-wised static functional connectivity (sFC) and dynamic functional connectivity (dFC) analyses using lITG as the seed region afforded complementary and overlapping results. The table tennis players exhibited decreased sFC in the right middle temporal gyrus and left inferior parietal gyrus. Conversely, they displayed increased dFC from the lITG to prefrontal cortex, particularly the left middle frontal gyrus, left superior frontal gyrus-medial, and left superior frontal gyrus-dorsolateral. These findings suggest that table tennis players demonstrate altered visuomotor transformation and executive function pathways. Both pathways involve the lITG, which is a vital node in the ventral visual stream. These static and dynamic analyses provide complementary and overlapping results, which may help us better understand the neural mechanisms underlying the changes in intrinsic brain activity and network organization induced by long-term table tennis skill training.