Histone deacetylase inhibitors de-repress tyrosine hydroxylase expression in the olfactory bulb and rostral migratory stream

Most olfactory bulb (OB) interneurons are derived from neural stem cells in the subventricular zone (SVZ) and migrate to the OB via the rostral migratory stream (RMS). Mature dopaminergic interneurons in the OB glomerular layer are readily identified by their synaptic activity-dependent expression of tyrosine hydroxylase (TH). Paradoxically, TH is not expressed in neural progenitors migrating in the RMS, even though ambient GABA and glutamate depolarize these progenitors. In forebrain slice cultures prepared from transgenic mice containing a GFP reporter gene under the control of the Th 9 kb upstream regulatory region, treatment with histone deacetylase (HDAC) inhibitors (either sodium butyrate, Trichostatin A or Scriptaid) induced Th-GFP expression specifically in the RMS independently of depolarizing conditions in the culture media. Th-GFP expression in the glomerular layer was also increased in slices treated with Trichostatin A, but this increased expression was dependent on depolarizing concentrations of KCl in the culture media. Th-GFP expression was also induced in the RMS in vivo by intra-peritoneal injections with either sodium butyrate or valproic acid. Quantitative RT-PCR analysis of neurosphere cultures confirmed that HDAC inhibitors de-repressed Th expression in SVZ-derived neural progenitors. Together, these findings suggest that HDAC function is critical for regulating Th expression levels in both neural progenitors and mature OB dopaminergic neurons. However, the differential responses to the combinatorial exposure of HDAC inhibitors and depolarizing culture conditions indicate that Th expression in mature OB neurons and neural progenitors in the RMS are regulated by distinct HDAC-mediated mechanisms.     

外周输入依赖的嗅球颗粒细胞的突触结构可塑性

活动依赖的突触结构可塑性是学习和记忆的基础.哺乳动物,尤其是啮齿类动物,具有高度发达的嗅觉系统和惊人的气味学习和记忆能力.本研究以CNGA2敲除而导致外周输入缺失的小鼠为模型,研究嗅球内活动依赖的突触结构可塑性.利用特异性的突触前和突触后标记物,发现外周输入缺失减少了突触标记蛋白突触素(synaptophysin)和抑制性突触标记蛋白桥蛋白(gephyrin)在嗅球外网状层和颗粒细胞层中的表达;兴奋性突触标记蛋白囊泡谷氨酸转运蛋白1(VGluT1)的表达水平只在外网状层中有显著下降,而在颗粒细胞层中没有明显变化.进一步通过活体质粒电转标记嗅球颗粒细胞后发现,CNGA2敲除小鼠颗粒细胞上位于外网状层中的远端树突棘密度显著减小,而位于颗粒细胞层中的近端树突棘密度没有明显变化.这些结果表明颗粒细胞上的树-树突触具有对外周活动依赖的结构可塑性,而轴-树突触则无.     

Deficits of olfactory interneurons in polysialyltransferase‐ and NCAM‐deficient mice

The neurogenic niche of the anterior subventricular zone (SVZ) persistently generates neuroblasts, which migrate along the rostral migratory stream (RMS) into the olfactory bulb (OB), where they differentiate into granule and periglomerular cells. Loss of the neural cell adhesion molecule NCAM or its post‐translational modification polysialic acid (polySia) impairs migration causing accumulations of cells in the proximal RMS and decreased OB volume. Polysialylation of NCAM is implemented by two polysialyltransferases, ST8SIA2 and ST8SIA4, with overlapping functions. Here, we used mice with Ncam1 and polysialyltransferase deletions to analyze how partial or complete loss of polySia synthesis or a combined loss of polySia and NCAM affects the RMS and the interneuron composition in the OB. Numerous calretinin (CR)‐positive cells were detected dispersed around the RMS in Ncam1 knockout, St8sia2, St8sia4 double‐knockout, and St8sia2, St8sia4, Ncam1 triple‐knockout mice, as well as in St8sia2 ^?/? but not in St8sia4 ^?/? mice. These changes were not reflected by reductions of CR‐positive cells in the granule or glomerular layer of the OB. Instead, calbindin‐positive periglomerular interneurons were strongly reduced in all polySia‐NCAM negative mice and slightly attenuated in St8sia2 ^?/? as well as in the St8sia4 ^?/? mice, which were devoid of ectopic CR‐positive cells along the RMS. Consistent with the early developmental generation of calbindin‐ as compared with CR‐positive OB interneurons, this phenotype was fully developed at postnatal day 5. Together, these results demonstrate that the early development of calbindin‐positive periglomerular interneurons depends on the presentation of polySia on NCAM and requires the activity of both polysialyltransferases. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 421–433, 2016     

Netrin1 is required for neural and glial precursor migrations into the olfactory bulb

Netrin1 (NTN1) deficiency in mouse brain causes defects in axon guidance and cell migration during embryonic development. Here we show that NTN1 is required for olfactory bulb (OB) development at late embryogenesis and at early postnatal stages to facilitate the accumulation of proper numbers of granular and glomerular neuron subtypes and oligodendrocytes into the OB. In addition to the analysis of Ntn1−/− mice we made tissue and neurosphere cultures to clarify the role of NTN1 in the anterior forebrain. We propose that a subset of neural progenitors/precursors requires NTN1 to efficiently enter the rostral migratory stream to migrate into the OB. The analysis of postnatal Ntn1−/− OBs revealed a reduction of specific types of interneurons which have been shown to originate from particular subregions of the lateral ventricle walls. Based on Ntn1 expression in ventral parts of the ventricle walls, we observed a decrease in the mainly ventrally derived type II interneurons that express calcium-binding proteins calretinin and calbindin. Instead, no change in the numbers of dorsally derived tyrosine hydroxylase expressing interneurons was detected. In addition to the specific reduction of type II interneurons, our results indicate that NTN1 is required for oligodendroglial migration into the OB. Furthermore, we characterised the Ntn1 expressing subpopulation of neurosphere-forming cells from embryonic and adult brain as multipotent and self-renewing. However, NTN1 is dispensable for the proliferation of neurosphere forming progenitor cells and for their differentiation.     

Combinatorial Interactions of Two <Emphasis Type="Italic">cis-</Emphasis>Acting Elements,AT-Rich Regions and HSEs,in the Expression of Tomato <Emphasis Type="Italic">Lehsp23.8</Emphasis> upon Heat and Non-Heat Stresses

We previously cloned and analyzed the 1,893-bp promoter region (−1,915 to −23) of the tomato (Lycopersicon esculentum) Lehsp23.8 gene, whose expression is induced by treatment with high or low temperatures, heavy metal, or abscisic acid (ABA). In our present work, we examined how this expression is regulated. A comprehensive quantitative promoter deletion and base-substitution analysis was conducted under various environmental conditions. The proximal region (−565 to −23 bp) of the Lehsp23.8 promoter harbors cis-regulatory elements that conferred high levels of heat-induced expression in transgenic tobacco. Mutation of the five proximal HSEs (HSE1 to 5) of that promoter led to an absence of heat inducibility. The AT-rich regions between −255 bp and −565 bp (AT-rich1 to 4) in the promoter might serve as enhancers for such heat-induced expression. Deletion and HSE mutation analysis indicated that other cis-acting elements also function in response to low temperature, heavy metal, and ABA and that HSE1 to 5 act at least as cis-acting elements in multiple-stress responses of Lehsp23.8. These results reveal that those five proximal HSEs and AT-rich regions function interdependently in the expression of Lehsp23.8 in response to non-heat stresses. Furthermore, the putative elements CRT/DRE, AP-1, and ABRE in that promoter are not required for multiple-stress induction.     

Ras/MEK pathway is required for NGF-induced expression of tyrosine hydroxylase gene

Neurotrophins are essential for the development and survival of catecholaminergic neurons. However, the critical pathway for expression of the tyrosine hydroxylase (TH) gene induced by neurotrophin is still unclear. Here we found that Ras/MEK pathway is required for NGF-induced expression of the TH gene in PC12D cells. Induction of TH mRNA by NGF was abolished by pretreatment of the cells with U0126, an inhibitor for MEK1/2, but not with inhibitors for p38 MAPK, PI3K, and PKA. U0126 inhibited TH promoter activity at the same concentration as it acted on ERK1/2 phosphorylation. A dominant-negative form of Ras suppressed the NGF-induced activation of the TH reporter gene, and transient transfection of cells with wild-type Ras and an active form of MEK1 increased the TH promoter activity. The reporter assay also demonstrated that the Ras/MEK pathway acted on both the AP-1-binding motif and the cAMP-responsive element in the TH promoter.