The Fezf2-Ctip2 genetic pathway regulates the fate choice of subcortical projection neurons in the developing cerebral cortex

Pyramidal neurons in the deep layers of the cerebral cortex can be classified into two major classes: callosal projection neurons and long-range subcortical neurons. We and others have shown that a gene expressed specifically by subcortical projection neurons, Fezf2, is required for the formation of axonal projections to the spinal cord, tectum, and pons. Here, we report that Fezf2 regulates a decision between subcortical vs. callosal projection neuron fates. Fezf2(-/-) neurons adopt the fate of callosal projection neurons as assessed by their axonal projections, electrophysiological properties, and acquisition of Satb2 expression. Ctip2 is a major downstream effector of Fezf2 in regulating the extension of axons toward subcortical targets and can rescue the axonal phenotype of Fezf2 mutants. When ectopically expressed, either Fezf2 or Ctip2 can alter the axonal targeting of corticocortical projection neurons and cause them to project to subcortical targets, although Fezf2 can promote a subcortical projection neuron fate in the absence of Ctip2 expression.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:A network of genetic repression and derepression specifies projection fates in the developing neocortex

Neurons within each layer in the mammalian cortex have stereotypic projections. Four genes—Fezf2, Ctip2, Tbr1, and Satb2—regulate these projection identities. These genes also interact with each other, and it is unclear how these interactions shape the final projection identity. Here we show, by generating double mutants of Fezf2, Ctip2, and Satb2, that cortical neurons deploy a complex genetic switch that uses mutual repression to produce subcortical or callosal projections. We discovered that Tbr1, EphA4, and Unc5H3 are critical downstream targets of Satb2 in callosal fate specification. This represents a unique role for Tbr1, implicated previously in specifying corticothalamic projections. We further show that Tbr1 expression is dually regulated by Satb2 and Ctip2 in layers 2–5. Finally, we show that Satb2 and Fezf2 regulate two disease-related genes, Auts2 (Autistic Susceptibility Gene2) and Bhlhb5 (mutated in Hereditary Spastic Paraplegia), providing a molecular handle to investigate circuit disorders in neurodevelopmental diseases.     

Modeling local and cross-species neuron number variations in the cerebral cortex as arising from a common mechanism

A massive increase in the number of neurons in the cerebral cortex, driving its size to increase by five orders of magnitude, is a key feature of mammalian evolution. Not only are there systematic variations in cerebral cortical architecture across species, but also across spatial axes within a given cortex. In this article we present a computational model that accounts for both types of variation as arising from the same developmental mechanism. The model employs empirically measured parameters from over a dozen species to demonstrate that changes to the kinetics of neurogenesis (the cell-cycle rate, the progenitor death rate, and the “quit rate,” i.e., the ratio of terminal cell divisions) are sufficient to explain the great diversity in the number of cortical neurons across mammals. Moreover, spatiotemporal gradients in those same parameters in the embryonic cortex can account for cortex-wide, graded variations in the mature neural architecture. Consistent with emerging anatomical data in several species, the model predicts (i) a greater complement of neurons per cortical column in the later-developing, posterior regions of intermediate and large cortices, (ii) that the extent of variation across a cortex increases with cortex size, reaching fivefold or greater in primates, and (iii) that when the number of neurons per cortical column increases, whether across species or within a given cortex, it is the later-developing superficial layers of the cortex which accommodate those additional neurons. We posit that these graded features of the cortex have computational and functional significance, and so must be subject to evolutionary selection.Changes in brain structure follow a remarkably stable pattern over ∼450 My in the vertebrate lineage: it is always the same brain parts that become enlarged when overall brain size increases (1). Moreover, in studies of individual variation in humans and other mammals, when overall brain size is larger, those same divisions as would be predicted by looking at brain enlargement across taxa are also found to be preferentially enlarged (2, 3). Such regularities in brain scaling from the individual to the taxon level suggest that the developmental mechanisms which generate central nervous systems are strongly conserved across species (4).To tease apart the features of the isocortex contributed by the scaling of conserved developmental mechanisms from those features which might be specially selected for in a given niche or species, we have created an empirically informed, mathematical model of cortical neurogenesis. The model elucidates how the dials and levers made available by conserved developmental mechanisms allow selection to shape the basic landscape of the embryonic cortex. The extent to which any particular cortical area (e.g., a visual or language area) has been a special subject of selection can be better evaluated given the baselines provided by this evolutionary developmental or “evo-devo” model.The modeling approach presented here provides an explicit structure to assimilate known data and predict unknowns, both for developmental kinetic parameters and for the resultant time courses of neuronal and progenitor cell populations, for the entire range of mammalian brain sizes and across a spatial axis within the respective cortices. Our model incorporates important insights from several previously published mathematical models of cortical neurogenesis which focus on more limited sets of species or which consider spatial variations in a single species (5–10).     

Origin and progeny of reactive gliosis: A source of multipotent cells in the injured brain

Reactive gliosis is the universal reaction to brain injury, but the precise origin and subsequent fate of the glial cells reacting to injury are unknown. Astrocytes react to injury by hypertrophy and up-regulation of the glial-fibrillary acidic protein (GFAP). Whereas mature astrocytes do not normally divide, a subpopulation of the reactive GFAP(+) cells does so, prompting the question of whether the proliferating GFAP(+) cells arise from endogenous glial progenitors or from mature astrocytes that start to proliferate in response to brain injury. Here we show by genetic fate mapping and cell type-specific viral targeting that quiescent astrocytes start to proliferate after stab wound injury and contribute to the reactive gliosis and proliferating GFAP(+) cells. These proliferating astrocytes remain within their lineage in vivo, while a more favorable environment in vitro revealed their multipotency and capacity for self-renewal. Conversely, progenitors present in the adult mouse cerebral cortex labeled by NG2 or the receptor for the platelet-derived growth factor (PDGFRalpha) did not form neurospheres after (or before) brain injury. Taken together, the first fate-mapping analysis of astrocytes in the adult mouse cerebral cortex shows that some astrocytes acquire stem cell properties after injury and hence may provide a promising cell type to initiate repair after brain injury.     

快速眼动睡眠剥夺引起大鼠皮质PERK活化及药物干预

目的观察不同时间快速眼动睡眠剥夺引起大鼠皮质PERK活化和磷酸化elF2α蛋白表达的变化以及依达拉奉干预的作用。方法将60只Sprague-Dawle大鼠随机分为正常对照组(5只),环境对照组(5只)和睡眠剥夺组(50只)。其中睡眠剥夺组又分为模型组,生理盐水组和依达拉奉组3个亚组。采用改良多平台睡眠剥夺法建立大鼠快速眼动睡眠剥夺模型,通过Western blot技术观察快速眼动睡眠剥夺后大鼠额叶PERK活化和磷酸化elF2α蛋白表达的变化规律,并考察依达拉奉对这些指标的影响。结果与正常对照组和环境对照组比较,不同时间快速眼动睡眠剥夺后大鼠皮质激活了磷酸化的PERK和磷酸化elF2α蛋白表达,表达水平显示了先升后降的变化规律。依达拉奉干预后两指标明显下降(P<0.01)。结论睡眠剥夺启动了内质网应激反应过程中未折叠蛋白应答通路之一,依达拉奉可能是通过减轻内质网应激而起到脑保护作用。     

皮质下脑梗死患者初级运动皮质结构损伤和运动功能恢复的相关性研究

目的探讨脑梗死后结构损伤和功能代偿脑区的相关性,为阐述脑梗死后运动功能恢复的机制提供理论基础。方法选择运动功能恢复较好的慢性期单侧基底节区脑梗死患者28例(脑梗死组),健康体检者25例(对照组),功能MRI采用组块设计,进行患手虚握运动以及高分辨率结构像采集,采用统计参数图比较2组脑灰质体积和执行运动任务时脑激活的不同。结果与对照组比较,脑梗死组患侧半球M1区(感兴趣区1)及丘脑灰质体积减少。患手运动时,脑梗死组患侧半球M1区(感兴趣区2)及颞上回激活增强。感兴趣区1和感兴趣区2重叠,重叠区占灰质体积减少脑区(感兴趣区1)的21.9%。结论 M1结构损伤区及其周围正常脑区均参与运动功能的恢复,而与感觉功能有密切关系的M1区背侧的持续性激活增强可能对运动功能的恢复起更主要的作用。     

大鼠的局灶性脑缺血再灌注损伤分区及再灌注时间窗

目的　研究脑缺血早期神经元损伤、半暗带及再灌注时间窗。方法　采用线栓法制做大鼠大脑中动脉梗阻 /再灌注模型。动物分为 :正常对照组 ;假手术组 ;缺血 (不再灌注 ) 30min组 ;缺血 (不再灌注 ) 1 ,2 ,4,6 ,2 4h ;缺血 1 ,2 ,3h后再灌注 2 4h组。每组 6只。恒温冰冻切片 ,行微管相关蛋白 (MAP2 )免疫组化染色 ;嗜银Ⅲ染色法复染 ;甲苯胺蓝染色。结果　MAP2免疫染色可显示神经元形态和皮质结构 ,显示缺血 30min的神经元病变。病变可分为 :中心区———MAP2阳性消失区 ;半暗带———MAP2阳性减弱伴选择性表达增强 ;继发损伤反应区———MAP2表达增强。缺血 6h内半暗带被迅速扩大的中心区取代 ,同时半暗带的神经元病变进行性加重。再灌注的时间窗应在缺血 3h以内。嗜银神经元集中分布于中心区边缘 ,半暗带也有散在分布 ,MAP2表达增强的神经元不易被银染。结论　MAP2表达增加可能是神经元对抗缺血的保护性反应 ;MAP2免疫染色是显示半暗带的理想的组织学方法     

大鼠持续性局灶脑缺血后Fas基因表达及其与神经元凋亡的关系

目的 研究成年大鼠持续性局灶脑缺血后Fas基因表达以及与缺血后细胞凋亡的关系。方法 用右侧近端大脑中动脉电凝术,建立大鼠持续性局灶脑缺血模型。分别在电凝术后3、6、12、24、48、72和120h取材,用原位末端标记(TUNEL)检测细胞凋亡,用原位RT-PCR法检测Fas mRNA表达并进行半定量分析。结果 梗死灶周边区细胞从12h开始表达Fas mRNA,24h达到高峰,48和、72h逐渐下降,120h已经检测不到。缺血后3、6、12、24和48h未见凋亡细胞,72h在梗死灶周边区域出现散在的凋亡细胞,120h仍然有凋亡细胞,分布范围与数量与72h相似。Fas mRNA原位杂交信号阳性细胞的出现明显早于凋亡细胞,数量明显多于后,而细胞形态和分布区域相似。结论 大鼠局灶性脑缺血可诱导梗死灶周边区域Fas mRNA的表达,Fas基因可能介导了脑缺血后细胞凋亡的发生。     

Handedness and its genetic influences are associated with structural asymmetries of the cerebral cortex in 31,864 individuals

Roughly 10% of the human population is left-handed, and this rate is increased in some brain-related disorders. The neuroanatomical correlates of hand preference have remained equivocal. We resampled structural brain image data from 28,802 right-handers and 3,062 left-handers (UK Biobank population dataset) to a symmetrical surface template, and mapped asymmetries for each of 8,681 vertices across the cerebral cortex in each individual. Left-handers compared to right-handers showed average differences of surface area asymmetry within the fusiform cortex, the anterior insula, the anterior middle cingulate cortex, and the precentral cortex. Meta-analyzed functional imaging data implicated these regions in executive functions and language. Polygenic disposition to left-handedness was associated with two of these regional asymmetries, and 18 loci previously linked with left-handedness by genome-wide screening showed associations with one or more of these asymmetries. Implicated genes included six encoding microtubule-related proteins: TUBB, TUBA1B, TUBB3, TUBB4A, MAP2, and NME7—mutations in the latter can cause left to right reversal of the visceral organs. There were also two cortical regions where average thickness asymmetry was altered in left-handedness: on the postcentral gyrus and the inferior occipital cortex, functionally annotated with hand sensorimotor and visual roles. These cortical thickness asymmetries were not heritable. Heritable surface area asymmetries of language-related regions may link the etiologies of hand preference and language, whereas nonheritable asymmetries of sensorimotor cortex may manifest as consequences of hand preference.

Roughly 90% of the human population is right-handed and 10% left-handed, and this strong bias is broadly consistent across cultures, ethnicities, and history (1–5). Hand motor control is performed primarily by the contralateral brain hemisphere, such that right-handedness reflects left-hemisphere dominance for hand articulation, and vice versa (6). Behavioral precursors of hand preference are established in the developing human fetus (7, 8), probably through a genetically regulated program of asymmetrical brain development (9–12). Left-handedness occurs at increased frequencies in neurodevelopmental and psychiatric conditions, including intellectual disability (13), autism (14), and schizophrenia (15). This suggests overlapping genetic and developmental contributions to altered brain asymmetry and psychiatric conditions. However, it is important to stress that the large majority of left-handed people do not have these conditions.Despite decades of research, the brain anatomical correlates of hand preference have remained uncertain. Some MRI studies have reported slightly altered laterality of the sensorimotor cortex around the central sulcus as well as temporal auditory cortex in left-handed people—while other studies found no effects at all (16–22). Most of these studies focused on hypothesis-driven regions of interest rather than mapping across the entire cerebral cortex, and they used different methods of analysis and measurement. The results were conflicting, not replicated or negative, possibly due to small sample sizes; the largest number of left-handers in any of these studies was 198 (16). Cortex-wide screening using atlas-defined regions has also not shown robust associations with hand preference (23, 24), even in as many as 608 left-handers versus 7,243 right-handers. One possibility is that brain anatomical correlates of handedness may be too focal to be captured by common atlas-defined parcellations. To this end, atlas-free mapping in a large population sample may provide new insights into how hand preference relates to cerebral cortical structural asymmetry.The most statistically robust association of handedness with brain anatomy reported to date is altered average whole-hemispheric skew, or “torque,” in the horizontal and vertical planes found in 35,338 right-handed versus 3,712 left-handed adults from the UK Biobank (25). However, an association of whole-hemispheric torque with handedness does not identify specific brain regional asymmetries linked to this behavioral trait. Associations of left-handedness have also been reported with increased functional connectivity between left and right language networks in roughly 9,000 UK Biobank individuals (26) in an analysis of resting-state functional MRI data. The asymmetry of intrahemispheric functional connectivity during the resting state has also been associated with hand preference (27). The left hemisphere is dominant for language in more than 95% of the right-handed population but in only around 70% of the left-handed population, which suggests possible developmental and evolutionary relationships between these two functional asymmetries (28–32).In the present study, we mapped cerebral cortical structural asymmetry with respect to hand preference using a large sample and an atlas-free approach: 28,802 adult right-handers and 3,062 left-handers from the UK Biobank measured for asymmetries of cortical surface area and thickness at each of 163,842 vertices in each hemisphere, before down sampling the asymmetry maps to 8,681 vertices to test associations with hand preference. Vertex-wise correspondence between the left and right hemispheres was achieved through resampling each individual’s cortical surface model to a symmetrical template created by interhemispheric coregistration (33, 34). This surface-based registration approach aligns cortical folding patterns across individuals and both hemispheres.Using these data, we first aimed to identify specific clusters of vertices where cortical surface area or thickness asymmetries differed significantly at the group level between right and left-handers, for a uniquely well-powered and precision mapping analysis of the cortical correlates of hand preference. We then used meta-analyzed functional MRI (fMRI) data to annotate the cognitive and behavioral functions of the implicated cortical regions based on independent studies.Handedness is a partly heritable trait with estimates of the heritability due to common genetic polymorphisms ranging from 1.2 to 5.9% across different large-scale studies and cohorts (35, 36) and around 25% in twin-based studies (37). Recent large-scale genome-wide association studies (GWAS) have made progress on the identification of genetic influences on handedness (26, 35, 36) and separately also on brain structural asymmetry (11). However, no study has previously investigated shared genetic influences on handedness and its specific cortical structural correlates. Using genome-wide genotype data for single-nucleotide polymorphisms (SNPs) in the UK Biobank individuals, we tested the SNP-based heritabilities of the cortical asymmetry measures at each regional cluster associated with hand preference, and also the genetic correlations between these regional cortical asymmetries. We then tested if polygenic disposition to left-handedness was associated with the specific cortical regional asymmetries that are associated with this behavioral trait, including the use of causal mediation analyses. In addition, we tested 39 individual SNPs in relation to the asymmetries of these cortical regions—the SNPs were previously implicated in left-handedness by a GWAS of 1,766,671 individuals (36). Together, these analyses would reveal numerous insights into the biology of gene–brain–behavioral links involving human hand preference.     

Olfactory regulation by dopamine and DRD2 receptor in the nose

Olfactory behavior is important for animal survival, and olfactory dysfunction is a common feature of several diseases. Despite the identification of neural circuits and circulating hormones in olfactory regulation, the peripheral targets for olfactory modulation remain relatively unexplored. In analyzing the single-cell RNA sequencing data from mouse and human olfactory mucosa (OM), we found that the mature olfactory sensory neurons (OSNs) express high levels of dopamine D2 receptor (Drd2) rather than other dopamine receptor subtypes. The DRD2 receptor is expressed in the cilia and somata of mature OSNs, while nasal dopamine is mainly released from the sympathetic nerve terminals, which innervate the mouse OM. Intriguingly, genetic ablation of Drd2 in mature OSNs or intranasal application with DRD2 antagonist significantly increased the OSN response to odorants and enhanced the olfactory sensitivity in mice. Mechanistic studies indicated that dopamine, acting through DRD2 receptor, could inhibit odor-induced cAMP signaling of olfactory receptors. Interestingly, the local dopamine synthesis in mouse OM is down-regulated during starvation, which leads to hunger-induced olfactory enhancement. Moreover, pharmacological inhibition of local dopamine synthesis in mouse OM is sufficient to enhance olfactory abilities. Altogether, these results reveal nasal dopamine and DRD2 receptor as the potential peripheral targets for olfactory modulation.

Olfactory behavior is important for food seeking and animal survival. On the other hand, olfactory dysfunction is a common feature of several diseases such as psychiatric disorders, neurodegeneration, and COVID-19 (1–3). Interestingly, the olfactory ability can be regulated by feeding status and external environments (4, 5). Recent studies have made progress in identifying the neural circuits and circulating hormones in olfactory regulation (6–11). However, the peripheral targets modulating olfactory ability remain relatively unexplored (12).Dopamine (DA) is a monoamine neurotransmitter (13, 14), which plays important roles in a variety of brain functions. DA is released by dopaminergic neurons in the central nervous system. In addition, DA can be released by sympathetic nerves in the peripheral tissues including the olfactory mucosa (OM) (15–18). The sympathetic innervation of rodent OM originates predominantly from the superior cervical ganglion (SCG) (17). Tyrosine hydroxylase (TH) is the rate-limiting enzyme for DA synthesis (19). Intriguingly, the Th mRNA is locally translated in the sympathetic nerve axons, which facilitates local DA synthesis (20, 21).There are two types of DA receptors based on sequence homology and function: The excitatory D1-like receptors (DRD1 and DRD5) and inhibitory D2-like receptors (DRD2–DRD4) (22). Activation of DRD2, a Gα_i/o-coupled receptor, can reduce the intracellular levels of cyclic adenosine monophosphate (cAMP). Drd2 is associated with several neuropsychiatric diseases and is the target of some antipsychotic drugs (23–28). In the central nervous system including the olfactory bulb (OB), DA-DRD2 signaling plays important roles in regulating synaptic transmission and plasticity (29–33). However, the function and regulation of DA-DRD2 signaling in the peripheral tissues are relatively less understood.Here we show that DRD2 is expressed in the cilia and somata of mature olfactory sensory neurons (OSNs) in mice. We provide evidence that DA-DRD2 signaling has a tonic inhibition on OSN activity and olfactory function in mice. Intriguingly, hunger greatly reduces the N4-acetylcytidine (ac⁴C) modification of Th mRNA and local DA synthesis in mouse OM, which causes the olfactory enhancement during starvation. We further show that inhibition of local DA synthesis or DRD2 receptor in mouse OM recapitulates enhanced olfactory abilities during starvation. Collectively, these results reveal nasal DA and DRD2 receptor as the potential peripheral targets for olfactory regulation.     

基于Lp-PLA2水平分析急性脑梗死与颈动脉粥样硬化斑块的关系

目的探讨急性脑梗死患者脂蛋白相关磷脂酶A2(Lp-PLA2)水平的变化特点及其与颈动脉粥样硬化斑块的关系。方法选取2013年6月至2014年10月来我院就诊确诊的82例急性脑梗死患者作为脑梗死组,并选取同期我院体检者82例作为对照组,彩色多普勒超声检测颈总动脉粥样硬化斑块,ELISA检测血清Lp-PLA2水平,Spearman相关分析急性脑梗死患者血清Lp-PLA2水平变化特点及其与梗死面积、颈动脉粥样硬化斑块Crouse积分之间的关系。结果脑梗死组Lp-PLA2、hs-CRP、TG、TC及LDLC的水平显著高于对照组,HDLC水平显著低于对照组(P0.05);颈动脉粥样硬化斑块Ⅰ级、Ⅱ级和Ⅲ级三组间Crouse积分、Lp-PLA2水平比较具有显著性差异,且随分级增加Lp-PLA2水平升高(P0.05);急性脑梗死患者Lp-PLA2水平随神经功能损伤程度增加而升高,Lp-PLA2水平与Crouse积分、梗死面积呈正相关(r=0.823和r=0.879,P0.05)。结论 Lp-PLA2水平与动脉粥样硬化性脑梗死有关,可反映患者颈动脉粥样硬化斑块及脑梗死面积情况,可作为脑梗死预测指标。     

Effect of ischemia on noradrenergic and energy-related metabolites in the cerebral cortex of young and adult gerbils

Relationships between ischemic changes in the cerebral cortical content of energy and noradrenergic metabolites were evaluated in young and adult gerbils. Groups of 3-week- and 3-month-old gerbils were subjected to 5 or 15 min of bilateral carotid artery occlusion alone or with 1 hr of release. Ischemia of 5 and 15 min depleted energy-related metabolites but did not affect the content of either norepinephrine or homovanillic acid in young and adult gerbils. At l h of reflow, after 5 and 15 min of ischemia, the levels of norepinephrine significantly decreased, while those of homovanillic acid increased in the adult but not in the young gerbils. At this time a complete recovery of energy reserves was seen in both the young and the adult gerbils. These results indicate that the ischemic change in homeostasis of energy metabolism is not directly associated with that of the noradrenergic system in young and adult cerebral cortex.     

The contribution of alcohol,thiamine deficiency and cirrhosis of the liver to cerebral cortical damage in alcoholics

The relative roles of alcohol toxicity, thiamine deficiency and cirrhosis of the liver in the pathogenesis of alcohol-related brain damage are unclear. Brain shrinkage and neuronal loss from four regions of the cortex was determined in 22 alcoholics with the Wernicke-Korsakoff Syndrome (WKS), cirrhosis of the liver or neither of these complications and compared to 22 age-matched non-alcoholic controls. Brain shrinkage was most marked in those alcoholics with WKS. Neuronal loss occurred only from the superior cortex and was of equal magnitude in all alcoholic subgroups. In an animal model of alcohol abuse and thiamine deficiency, neuronal loss from the cerebral cortex occurred in a time-dependent manner. Furthermore, those cells which contained the calcium-binding protein parvalbumin appeared to be preferentially damaged in this model.