Spore germination

Despite being relatively insensitive to environmental insult, the spore is responsive to low concentrations of chemical germinants, which induce germination. The process of bacterial spore germination involves membrane permeability changes, ion fluxes and the activation of enzymes that degrade the outer layers of the spore. A number of components in the spore that are required for the germination response have been identified, including a spore-specific family of receptor proteins (the GerA family), an ion transporter and cortex lytic enzymes. The germinant traverses the outer layers of the spore and interacts with its receptor in the inner membrane to initiate the cascade of germination events, but the molecular details of this signal transduction process remain to be identified.     

雷公藤红素缓解刀豆蛋白A诱导的小鼠急性肝损伤作用及其机制

将36只同一批次体重无明显差异的7周龄C57雄鼠随机分为6组,每组6只,即对照组,模型组,地塞米松(dexamethasone, DXM)组及雷公藤红素(celastrol, Cel)低、中、高剂量组(1.5、3、6 mg/kg),连续灌胃7 d后尾静脉注射20 mg/kg刀豆蛋白A(concanavalin A, ConA),地塞米松(0.5 mg/kg)于刀豆蛋白给药前1 h腹腔注射.注射8 h后处死小鼠,取其血清分别检测白介素-6(IL-6)、白介素-10(IL-10)、肿瘤坏死因子-α(tumor necrosis factor-α,TNF-α)和丙氨酸氨基转移酶(ALT)及天冬氨酸转移酶(AST)的含量.取小鼠肝脾称重计算脏器系数,苏木精-伊红(HE)染色观察肝组织病理改变,用实时定量PCR法(RT-qPCR法)检测肝组织中相关基因mRNA的表达水平,流式细胞术检测脾脏中巨噬细胞的极化方向,从而研究雷公藤红素对刀豆蛋白A诱导的小鼠急性肝损伤的保护作用及其机制.结果显示:相较于正常组,模型组小鼠的肝组织明显发生急性肝炎,其小叶结构紊乱,肝细胞结构破坏,汇管区炎症细胞浸润,雷公藤...     

Adaptive radiation of multituberculate mammals before the extinction of dinosaurs

The Cretaceous-Paleogene mass extinction approximately 66 million years ago is conventionally thought to have been a turning point in mammalian evolution. Prior to that event and for the first two-thirds of their evolutionary history, mammals were mostly confined to roles as generalized, small-bodied, nocturnal insectivores, presumably under selection pressures from dinosaurs. Release from these pressures, by extinction of non-avian dinosaurs at the Cretaceous-Paleogene boundary, triggered ecological diversification of mammals. Although recent individual fossil discoveries have shown that some mammalian lineages diversified ecologically during the Mesozoic era, comprehensive ecological analyses of mammalian groups crossing the Cretaceous-Paleogene boundary are lacking. Such analyses are needed because diversification analyses of living taxa allow only indirect inferences of past ecosystems. Here we show that in arguably the most evolutionarily successful clade of Mesozoic mammals, the Multituberculata, an adaptive radiation began at least 20 million years before the extinction of non-avian dinosaurs and continued across the Cretaceous-Paleogene boundary. Disparity in dental complexity, which relates to the range of diets, rose sharply in step with generic richness and disparity in body size. Moreover, maximum dental complexity and body size demonstrate an adaptive shift towards increased herbivory. This dietary expansion tracked the ecological rise of angiosperms and suggests that the resources that were available to multituberculates were relatively unaffected by the Cretaceous-Paleogene mass extinction. Taken together, our results indicate that mammals were able to take advantage of new ecological opportunities in the Mesozoic and that at least some of these opportunities persisted through the Cretaceous-Paleogene mass extinction. Similar broad-scale ecomorphological inventories of other radiations may help to constrain the possible causes of mass extinctions.