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1.
DeDe宝
(2024-09-12 14:24):
#paper, DOI: 10.1073/pnas.0805414105 ,Neural basis of the cognitive map: Path integration does not require hippocampus or entorhinal cortex. 研究主要探讨了海马体和内嗅皮层在记忆功能和空间认知中的作用，尤其是它们在路径整合能力中的作用。路径整合是指利用自身运动线索来跟踪参考位置的能力。当被试被要求蒙上眼睛导航并指向起点位置，海马体或内嗅皮层受损的被试表现与对照组相似。在距离估计任务中，受损组和对照组的估计也相似。只有在延迟和分心条件下，受损组表现不如对照组，显示了他们在长期记忆任务上的困难。上述结果表明，虽然海马体和内嗅皮层对于长期记忆至关重要，但它们对于路径整合的空间计算并不是必需的。
Proceedings of the National Academy of Sciences,
2008-8-19.
DOI: 10.1073/pnas.0805414105
Abstract:
The hippocampus and entorhinal cortex have been linked to both memory functions and to spatial cognition, but it has been unclear how these ideas relate to each other. An important …
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The hippocampus and entorhinal cortex have been linked to both memory functions and to spatial cognition, but it has been unclear how these ideas relate to each other. An important part of spatial cognition is the ability to keep track of a reference location using self-motion cues (sometimes referred to as path integration), and it has been suggested that the hippocampus or entorhinal cortex is essential for this ability. Patients with hippocampal lesions or larger lesions that also included entorhinal cortex were led on paths while blindfolded (up to 15 m in length) and were asked to actively maintain the path in mind. Patients pointed to and estimated their distance from the start location as accurately as controls. A rotation condition confirmed that performance was based on self-motion cues. When demands on long-term memory were increased, patients were impaired. Thus, in humans, the hippocampus and entorhinal cortex are not essential for path integration.
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2.
钟鸣
(2022-07-18 02:00):
#paper doi:10.1073/pnas.0404172101 Proc Natl Acad Sci U S A, 2004, Genomic analysis of Bacteroides fragilis reveals extensive DNA inversions regulating cell surface adaptation 脆弱拟杆菌(BF)和多形拟杆菌（BT）都是人体肠道内的细菌，但生态位以及致病性不同：BF附着于黏膜表面，具有致病，是致病力最强的拟杆菌；BT存在于结肠内，无致病性。这里，作者比较了二者的基因组，侧重于基因组倒位。
作者首先比较了荚膜基因座，因为荚膜是BF的主要毒力因子。比较发现，BF中有9个荚膜基因座，BT中则是7个。拟杆菌的荚膜基因座前的启动子序列两侧有IR（反转重复序列），IR的存在使得启动子在某些情况下发生翻转，翻转后的启动子序列随即失效，进而导致下游基因不被转录和表达，拟杆菌借此机制产生不同类型的荚膜（相变），以逃避宿主的免疫杀伤。对BT和BF荚膜基因座的启动子分析表明，BF的9个荚膜基因座都是可以翻转的，且翻转都是由丝氨酸型重组酶mpi介导的，这表明BF的9个荚膜基因座的翻转是全局调控的。而BT的7个荚膜基因座中只有4个是可翻转的，而且是分别被4个不同的酪氨酸型重组酶介导的，这与BF形成鲜明对比。
BF的荚膜多糖可以诱导形成脓肿，这种毒性离不开荚膜多糖重复单元中带正电荷的游离氨基和负电荷基团的存在。分析发现BF中有4种荚膜基因座可以产生同时带有游离氨基和负电荷集团的荚膜多糖，而BT中只有1种，这种差异可能与BF具有更高的毒力有关。
作者还预测了荚膜基因座之外的区域的翻转事件，在BF中鉴定了31个可翻转的区域并通过PCR证实了。其中代表性的是SusC/SusD（同源）基因，其产物定位于细菌表面，将环境中的淀粉多糖分解成单糖并转运到细菌内部提供营养。SusC/SusD（同源）基因的可变表达受7种倒位机制调节，这是已鉴定的全部倒位调节机制类型。作者使用图示简洁形象的解释了这7种调节机制，十分复杂且有趣。
总而言之，BF中广泛存在的DNA倒位调节了细菌的毒力调控和营养利用系统等生物功能的调控，且不同致病性物种间的机制有异同。
Abstract:
Bacteroides are predominant human colonic commensals, but the principal pathogenic species, Bacteroides fragilis (BF), lives closely associated with the mucosal surface, whereas a second major species, Bacteroides thetaiotaomicron (BT), concentrates …
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Bacteroides are predominant human colonic commensals, but the principal pathogenic species, Bacteroides fragilis (BF), lives closely associated with the mucosal surface, whereas a second major species, Bacteroides thetaiotaomicron (BT), concentrates within the colon. We find corresponding differences in their genomes, based on determination of the genome sequence of BF and comparative analysis with BT. Both species have acquired two mechanisms that contribute to their dominance among the colonic microbiota: an exceptional capability to use a wide range of dietary polysaccharides by gene amplification and the capacity to create variable surface antigenicities by multiple DNA inversion systems. However, the gene amplification for polysaccharide assimilation is more developed in BT, in keeping with its internal localization. In contrast, external antigenic structures can be changed more systematically in BF. Thereby, at the mucosal surface, where microbes encounter continuous attack by host defenses, BF evasion of the immune system is favored, and its colonization and infectious potential are increased.
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