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In mouse models of central nervous system injury, Htt is shown to be a key component of the regulatory program associated with reversion of the neuronal transcriptome to a less-mature state.

Detection of dopamine dips by neurons that express dopamine D2 receptors in the striatum is used to refine generalized reward conditioning mediated by dopamine D1 receptors.

Dopamine D2 receptors (D2Rs) are densely expressed in the striatum and have been linked to neuropsychiatric disorders such as schizophrenia(1,2). High-affinity binding of dopamine suggests that D2Rs detect transient reductions in dopamine concentration (the dopamine dip) during punishment learning(3-5). However, the nature and cellular basis of D2R-dependent behaviour are unclear. Here we show that tone reward conditioning induces marked stimulus generalization in a manner that depends on dopamine D1 receptors (D1Rs) in the nucleus accumbens (NAc) of mice, and that discrimination learning refines the conditioning using a dopamine dip. In NAc slices, a narrow dopamine dip (as short as 0.4 s) was detected by D2Rs to disinhibit adenosine A(2A) receptor (A(2A)R)-mediated enlargement of dendritic spines in D2R-expressing spiny projection neurons (D2-SPNs). Plasticity-related signalling by Ca2+/calmodulin-dependent protein kinase II and A(2A)Rs in the NAc was required for discrimination learning. By contrast, extinction learning did not involve dopamine dips or D2-SPNs. Treatment with methamphetamine, which dysregulates dopamine signalling, impaired discrimination learning and spine enlargement, and these impairments were reversed by a D2R antagonist. Our data show that D2Rs refine the generalized reward learning mediated by D1Rs.

Levels of gene expression underpin organismal phenotypes(1,2), but the nature of selection that acts on gene expression and its role in adaptive evolution remain unknown(1,2). Here we assayed gene expression in rice (Oryza sativa)(3), and used phenotypic selection analysis to estimate the type and strength of selection on the levels of more than 15,000 transcripts(4,5). Variation in most transcripts appears (nearly) neutral or under very weak stabilizing selection in wet paddy conditions (with median standardized selection differentials near zero), but selection is stronger under drought conditions. Overall, more transcripts are conditionally neutral (2.83%) than are antagonistically pleiotropic(6) (0.04%), and transcripts that display lower levels of expression and stochastic noise(7-9) and higher levels of plasticity(9) are under stronger selection. Selection strength was further weakly negatively associated with levels of cis-regulation and network connectivity(9). Our multivariate analysis suggests that selection acts on the expression of photosynthesis genes(4,5), but that the efficacy of selection is genetically constrained under drought conditions(10). Drought selected for earlier flowering(11,12) and a higher expression of OsMADS18 (Os07g0605200), which encodes a MADS-box transcription factor and is a known regulator of early flowering(13)-marking this gene as a drought-escape gene(11,12). The ability to estimate selection strengths provides insights into how selection can shape molecular traits at the core of gene action.

Phenotypic selection analysis is used to estimate the type and strength of selection that acts on more than 15,000 transcripts in rice (Oryza sativa), which provides insight into the adaptive evolutionary role of selection on gene expression.

Epithelial-to-mesenchymal transitions (EMTs) are phenotypic plasticity processes that confer migratory and invasive properties to epithelial cells during development, wound-healing, fibrosis and cancer(1-4). EMTs are driven by SNAIL, ZEB and TWIST transcription factors(5,6) together with microRNAs that balance this regulatory network(7,8). Transforming growth factor beta (TGF-beta) is a potent inducer of developmental and fibrogenic EMTs4,9,10. Aberrant TGF-beta signalling and EMT are implicated in the pathogenesis of renal fibrosis, alcoholic liver disease, non-alcoholic steatohepatitis, pulmonary fibrosis and cancer(4,11). TGF-beta depends on RAS and mitogen-activated protein kinase (MAPK) pathway inputs for the induction of EMTs12-19. Here we show how these signals coordinately trigger EMTs and integrate them with broader pathophysiological processes. We identify RAS-responsive element binding protein 1 (RREB1), a RAS transcriptional effector(20,21), as a key partner of TGF-beta-activated SMAD transcription factors in EMT. MAPK-activated RREB1 recruits TGF-beta-activated SMAD factors to SNAIL. Context-dependent chromatin accessibility dictates the ability of RREB1 and SMAD to activate additional genes that determine the nature of the resulting EMT. In carcinoma cells, TGF-beta-SMAD and RREB1 directly drive expression of SNAIL and fibrogenic factors stimulating myofibroblasts, promoting intratumoral fibrosis and supporting tumour growth. In mouse epiblast progenitors, Nodal-SMAD and RREB1 combine to induce expression of SNAIL and mesendoderm-differentiation genes that drive gastrulation. Thus, RREB1 provides a molecular link between RAS and TGF-beta pathways for coordinated induction of developmental and fibrogenic EMTs. These insights increase our understanding of the regulation of epithelial plasticity and its pathophysiological consequences in development, fibrosis and cancer.

RAS and TGF-beta pathways regulate distinct modes of epithelial-to-mesenchymal transition via RAS-responsive element binding protein 1.