Selective pericentromeric heterochromatin dismantling caused by TP53 activation during senescence

Cellular senescence triggers various types of heterochromatin remodeling that contribute to aging. However, the age-related mechanisms that lead to these epigenetic alterations remain elusive. Here, we asked how two key aging hallmarks, telomere shortening and constitutive heterochromatin loss, are mechanistically connected during senescence. We show that, at the onset of senescence, pericentromeric heterochromatin is specifically dismantled consisting of chromatin decondensation, accumulation of DNA breakages, illegitimate recombination and loss of DNA. This process is caused by telomere shortening or genotoxic stress by a sequence of events starting from TP53-dependent downregulation of the telomere protective protein TRF2. The resulting loss of TRF2 at pericentromeres triggers DNA breaks activating ATM, which in turn leads to heterochromatin decondensation by releasing KAP1 and Lamin B1, recombination and satellite DNA excision found in the cytosol associated with cGAS. This TP53–TRF2 axis activates the interferon response and the formation of chromosome rearrangements when the cells escape the senescent growth arrest. Overall, these results reveal the role of TP53 as pericentromeric disassembler and define the basic principles of how a TP53-dependent senescence inducer hierarchically leads to selective pericentromeric dismantling through the downregulation of TRF2.     

发酵液内氨甲酰妥布拉霉素的定量测定

报道了应用一种以测量图象面积为指标的Ｚｙ－３００Ａ多功能抑菌圈测量仪,能够精确、稳定、快速地测定发酵液经薄层层析生物显迹后单组分氨甲酰妥布拉霉素的抑菌斑面积,然后从绘制的标准曲线中直接读取氨甲酸妥布拉霉素在发酵液中的含量,从而排除了其他组分对测定的干扰。试验证明,用Ｚｙ－３００Ａ多功能抑菌圈测量仪测定抗生素薄层层析生物显迹的抑菌斑,具有线性宽、精密度高、重复性强、操作简单方便等优点．本方法的建立为抗生素的纯品检定和多组分抗生素发酵、分离和纯化提供了准确的定量数据．     

转Bt水稻土壤跳虫群落组成及其数量变化

以转Bt水稻恢复系"克螟稻"(Cry1Ab纯合基因型)和"华恢1号"(Cry1Ab+Cry1Ac融合基因型)以及融合基因型转Bt水稻杂交系"Bt汕忧63",及其对照亲本水稻"秀水11"、"明恢63"和"汕优63"稻田土壤跳虫类群为对象,系统研究转Bt水稻种植下土壤跳虫群落组成及其数量动态变化,以评价不同基因型和不同育种品系转Bt水稻种植下稻田土壤生态安全性。结果表明,转Bt水稻种植导致土壤跳虫个别稀有类群的消失,并显著影响半土生和真土生类群以及土壤跳虫总量,但对群落多样性、均匀度和种类丰富度等影响不显著。与对照亲本相比,Cry1Ab转Bt稻田半土生类群和土壤跳虫总量及其种类丰富度指标显著增加了54.7%、44.4%和26.7%;Cry1Ab+Cry1Ac转Bt杂交稻田球角跳属百分比和真土生跳虫数量显著增加了212.3%和180.4%。就恢复系处理而言,与Cry1Ab转Bt水稻相比,Cry1Ab+Cry1Ac转Bt水稻种植导致棘跳属、球角跳属和原等跳属百分比以及半土生跳虫数量分别显著降低了62.1%、56.7%、61.8%和43.4%,同时,显著提高了裔符跳属百分比达88.2%。就Cry1Ab+Cry1Ac融合基因型转Bt水稻而言,与恢复系相比,转Bt杂交稻种植导致球角跳属和原等跳属百分比,半土生类群和土壤跳虫总量及其种类丰富度和群落多样性显著增加了312.9%和171.6%,302.4%和233.2%,以及54.0%和26.7%,同时,显著降低了裔符跳属百分比达65.5%。     

谷氨酸棒杆菌L-天冬氨酸α-脱羧酶在大肠杆菌中的表达及酶转化生产β-丙氨酸

【目的】克隆谷氨酸棒杆菌来源L-天冬氨酸α-脱羧酶基因, 实现其在大肠杆菌中的异源表达, 并进行酶转化L-天冬氨酸合成β-丙氨酸的研究。【方法】PCR扩增谷氨酸棒杆菌L-天冬氨酸α-脱羧酶基因pand, 构建表达载体pET24a(+)-Pand, 转化宿主菌大肠杆菌BL21(DE3), 对重组菌进行诱导表达, 表达产物经DEAE离子交换层析和G-75 分子筛层析纯化后进行酶学性质研究, 然后进行酶转化实验, 说明底物和产物对酶转化的影响。【结果】重组菌SDS-PAGE分析表明Pand表达量可达菌体总蛋白的50%以上, AccQ·Tag法检测酶活达到94.16 U/mL。该重组酶最适反应温度为55 °C, 在低于37 °C时保持较好的稳定性, 最适pH为6.0, 在pH 4.0?7.0范围内有较好的稳定性。酶转化实验说明: 底物L-天冬氨酸和产物β-丙氨酸对转化反应均有抑制作用; 实验建立了较优的酶转化反应方式, 在加酶量为每克天冬氨酸3 000 U时, 以分批加入固体底物L-天冬氨酸的形式, 使100 g/L底物转化率达到97.8%。【结论】重组L-天冬氨酸α-脱羧酶在大肠杆菌中获得高效表达, 研究了酶转化生产β-丙氨酸的影响因素, 为其工业应用奠定了基础。     

凤尾蕨内生真菌的研究Ⅱ——1株产芦丁内生真菌初步研究

报道了从凤尾蕨属井栏边草(Pteris multifida)根状茎中分离出一内生真菌——菌株JJF006,对其形态特征进行了初步研究,并用TLC对该菌株培养物进行了分析。初步结果表明:该真菌液体培养基中含有芦丁成分。     

大兴安岭地区粘细菌资源的多样性及其生物活性

【背景】粘细菌是一类具有社会性行为的高等原核生物,其代谢产物具有丰富、多样、新颖的生物活性,是筛选天然药物的良好资源,具有很大的研究开发应用价值。【目的】分析大兴安岭地区粘细菌资源的多样性;分离纯化可培养的粘细菌,分析其抗菌活性并从中筛选对马铃薯晚疫病菌具有拮抗作用的菌株。【方法】通过变性梯度凝胶电泳(DGGE)技术对从大兴安岭地区采集的15个土样中粘细菌资源的多样性进行分析,利用兔粪诱导、大肠杆菌划线诱导和滤纸诱导3种方法从土样中分离可培养的粘细菌,结合形态观察、生理生化特征和16S rRNA基因序列分析确定这些菌株的分类地位,通过平板对峙法对其进行抗菌活性分析。【结果】DGGE的分析结果显示,15个土样中共鉴定到13个属的粘细菌,基本覆盖了大部分已知的粘细菌种属以及部分未分类的粘细菌,表现出了丰富的多样性。共分离得到88株菌,从中得到22株纯菌,经鉴定属于2个属(粘球菌属与珊瑚球菌属)8个种(黄色粘球菌、橙色粘球菌、变绿粘球菌、珊瑚粘球菌、具枝粘球菌、大孢珊瑚球菌、弱小珊瑚球菌和珊瑚状珊瑚球菌)。抗菌结果显示:22株纯菌均表现出可以对一种甚至多种指示菌产生抗性,其中19株抑制大肠杆菌的生长,14株抑制马铃薯晚疫病菌的生长,8株抑制金黄色葡萄球菌的生长,13株抑制酿酒酵母菌的生长,7株抑制枯草芽孢杆菌的生长。【结论】内蒙古大兴安岭地区蕴藏着丰富的粘细菌资源,粘球菌属及珊瑚球菌属可能为该地区粘细菌菌群中的优势菌。分离纯化出的粘细菌菌株均表现出抑制一种甚至多种指示菌生长的活性,其中64%的纯菌对马铃薯晚疫病菌产生抗性,具有进一步研究的潜在价值。     

Design,synthesis and biological evaluation of novel diosgenin–benzoic acid mustard hybrids with potential anti-proliferative activities in human hepatoma HepG2 cells

To discover new lead compounds with anti-tumour activities, in the present study, natural diosgenin was hybridised with the reported benzoic acid mustard pharmacophore. The in vitro cytotoxicity of the resulting newly synthesised hybrids (8–10, 14a–14f, and 15a–15f) was then evaluated in three tumour cells (HepG2, MCF-7, and HeLa) as well as normal GES-1 cells. Among them, 14f possessed the most potential anti-proliferative activity against HepG2 cells, with an IC₅₀ value of 2.26 µM, which was 14.4-fold higher than that of diosgenin (IC₅₀ = 32.63 µM). Furthermore, it showed weak cytotoxicity against GES-1 cells (IC₅₀ > 100 µM), thus exhibiting good antiproliferative selectivity between normal and tumour cells. Moreover, 14f could induce G0/G1 arrest and apoptosis of HepG2 cells. From a mechanistic perspective, 14f regulated cell cycle-related proteins (CDK2, CDK4, CDK6, cyclin D1 and cyclin E1) as well mitochondrial apoptosis pathway-related proteins (Bax, Bcl-2, caspase 9, and caspase 3). These findings suggested that hybrid 14f serves as a promising anti-hepatoma lead compound that deserves further research.     

mTORC1-independent translation control in mammalian cells by methionine adenosyltransferase 2A and S-adenosylmethionine

Methionine adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylmethionine (SAM). As the sole methyl-donor for methylation of DNA, RNA, and proteins, SAM levels affect gene expression by changing methylation patterns. Expression of MAT2A, the catalytic subunit of isozyme MAT2, is positively correlated with proliferation of cancer cells; however, how MAT2A promotes cell proliferation is largely unknown. Given that the protein synthesis is induced in proliferating cells and that RNA and protein components of translation machinery are methylated, we tested here whether MAT2 and SAM are coupled with protein synthesis. By measuring ongoing protein translation via puromycin labeling, we revealed that MAT2A depletion or chemical inhibition reduced protein synthesis in HeLa and Hepa1 cells. Furthermore, overexpression of MAT2A enhanced protein synthesis, indicating that SAM is limiting under normal culture conditions. In addition, MAT2 inhibition did not accompany reduction in mechanistic target of rapamycin complex 1 activity but nevertheless reduced polysome formation. Polysome-bound RNA sequencing revealed that MAT2 inhibition decreased translation efficiency of some fraction of mRNAs. MAT2A was also found to interact with the proteins involved in rRNA processing and ribosome biogenesis; depletion or inhibition of MAT2 reduced 18S rRNA processing. Finally, quantitative mass spectrometry revealed that some translation factors were dynamically methylated in response to the activity of MAT2A. These observations suggest that cells possess an mTOR-independent regulatory mechanism that tunes translation in response to the levels of SAM. Such a system may acclimate cells for survival when SAM synthesis is reduced, whereas it may support proliferation when SAM is sufficient.