Cellular and molecular mechanisms of memory: the LTP connection.

Studies of the cellular and molecular mechanisms of memory formation have focused on the role of long-lasting forms of synaptic plasticity such as long-term potentiation (LTP). A combination of genetic, electrophysiological and behavioral techniques have been used to examine the possibility that LTP is a cellular mechanism of memory storage in the mammalian brain. Although a definitive answer remains elusive, it is clear that in many cases manipulations that alter LTP alter memory, and training regimens that produce memory can produce LTP-like potentiation of synaptic transmission.     

肝纤维化的细胞和分子机制

肝脏纤维化(hepatic fibrosis)是多种慢性肝病的共同病理基础,是进一步向肝硬化发展的中心环节。肝脏内一些免疫细胞如枯否细胞(Kupffer cell,KC)、树突状细胞(dendritic cell,DC)、T淋巴细胞、NK细胞(nature killer cell,NK cell)、B细胞等在多种致病因素刺激下激活,释放多种细胞因子和趋化因子,引起一系列病理变化,共同参与肝纤维化的发生和发展过程。本文主要从肝脏内各类免疫细胞以及分泌的细胞因子方面,对肝纤维化形成机制的最新研究进展进行综述。     

Cellular and molecular mechanisms of muscle atrophy

Skeletal muscle is a plastic organ that is maintained by multiple pathways regulating cell and protein turnover. During muscle atrophy, proteolytic systems are activated, and contractile proteins and organelles are removed, resulting in the shrinkage of muscle fibers. Excessive loss of muscle mass is associated with poor prognosis in several diseases, including myopathies and muscular dystrophies, as well as in systemic disorders such as cancer, diabetes, sepsis and heart failure. Muscle loss also occurs during aging. In this paper, we review the key mechanisms that regulate the turnover of contractile proteins and organelles in muscle tissue, and discuss how impairments in these mechanisms can contribute to muscle atrophy. We also discuss how protein synthesis and degradation are coordinately regulated by signaling pathways that are influenced by mechanical stress, physical activity, and the availability of nutrients and growth factors. Understanding how these pathways regulate muscle mass will provide new therapeutic targets for the prevention and treatment of muscle atrophy in metabolic and neuromuscular diseases.     

飞蝗嗅觉的细胞与分子机制研究进展

生命的进化依赖于其周边的化学环境,通过对这些化学物质的感受,适应环境,生命得以繁衍。直到现在,各种有机体仍然保留着这种古老而有效的感知方式。飞蝗是世界性的农业大害虫,其很多行为如远距离迁飞、聚集、取食、产卵等是其造成灾害的重要生物学因素,而这些行为都与其感受化学信息相关。深入研究飞蝗感受化学信息的机制对于揭示生物感受化学信息的分子和细胞机制的多样性,设计出可以激发或钝化这些蛋白质的引诱剂或忌避剂,进而防治害虫等具有重要意义。该文主要介绍了该课题组在东亚飞蝗(Locusta migratoria manilesis)感受化学信息机制方面的一些进展。通过超微结构研究发现在飞蝗触角上至少有毛形、锥形、腔锥形和刺形4种类型的化学感受器,明确了各种感受器的超微结构特征,其中毛形和锥形是重要的嗅觉感受器。以此为基础,单感受器电位记录试验结果表明飞蝗触角上的毛形感受器至少有7种功能亚型,其中5种亚型每个感受器含有2个神经原,2种亚型每个感受器含有3种神经原。初步明确了飞蝗毛形感受器神经原对一些化学信息的编码特征。在飞蝗的触角中鉴定出了飞蝗气味分子结合蛋白(LmigOBP1),通过免疫细胞化学定位实验证明该蛋白特异表达在飞蝗毛形和锥形感受器的淋巴液中,而且在胚胎即将孵化前就开始表达,此后在各个胚后发育时期都表达,说明该蛋白可能参与飞蝗胚后发育的所有阶段的嗅觉活动。采用荧光竞争结合实验方法,明确了LmigOBP1对有15～17个碳原子的直链的脂肪族醇、酯或醛有很强的亲和力,说明该蛋白有结合特异性。采用生物信息学技术模拟出了更为合理的LmigOBP1的三维结构,通过对接实验,提出了飞蝗气味分子结合蛋白结合腔中可能参与结合十五醇的氨基酸残基。之后通过定点氨基酸突变将59位的丝氨酸、74位的天冬酰氨和87位的缬氨酸分别用丙氨酸替代获得三个突变体蛋白(S59A、N74A、V87A),通过与野生型蛋白荧光竞争结合实验结果的比较,发现突变体S59A的结合模式与野生型相同,N74A几乎丧失了全部结合能力,而V87A则对有些气味分子的结合能力有较大改变。因此,位于结合腔开口处的74位天冬酰氨是该蛋白的重要结合位点,而位于结合腔底部的87位缬氨酸也是结合位点。结合前人的结果,我们首次提出了昆虫气味分子结合蛋白依赖位于结合腔开口处的亲水性氨基酸实现对气味分子的初始识别的假说。文章最后对今后研究的一些重点进行了讨论。     

Autophagy pathway: Cellular and molecular mechanisms

Macroautophagy/autophagy is an essential, conserved self-eating process that cells perform to allow degradation of intracellular components, including soluble proteins, aggregated proteins, organelles, macromolecular complexes, and foreign bodies. The process requires formation of a double-membrane structure containing the sequestered cytoplasmic material, the autophagosome, that ultimately fuses with the lysosome. This review will define this process and the cellular pathways required, from the formation of the double membrane to the fusion with lysosomes in molecular terms, and in particular highlight the recent progress in our understanding of this complex process.     

Cellular and molecular mechanisms in focal epileptogenesis

In the review, it is presented an analysis of experimental data about cellular and molecular mechanisms of focal epileptogenesis. Basic principals of synchronized burst activity development in epileptogenic focus are considered. The roles of synaptic activities and extrasynaptic membrane excitability for epileptiform activity development are discussed. The various pathways of Ca2+ entry into neurones as well as an involvement of Ca2+/calmodulin-dependent protein phosphorylation in mechanisms of epileptogenesis are analyzed. In vitro and in vivo experimental models of epileptogenesis (especially, kindling and audiogenic seizures) allowing to study the predisposition of neuronal circuit to epileptiform activity development are discussed.     

Cellular and molecular mechanisms of regeneration in Xenopus

We have employed transgenic methods combined with embryonic grafting to analyse the mechanisms of regeneration in Xenopus tadpoles. The Xenopus tadpole tail contains a spinal cord, notochord and segmented muscles, and all tissues are replaced when the tail regenerates after amputation. We show that there is a refractory period of very low regenerative ability in the early tadpole stage. Tracing of cell lineage with the use of single tissue transgenic grafts labelled with green fluorescent protein (GFP) shows that there is no de-differentiation and no metaplasia during regeneration. The spinal cord, notochord and muscle all regenerate from the corresponding tissue in the stump; in the case of the muscle the satellite cells provide the material for regeneration. By using constitutive or dominant negative gene products, induced under the control of a heat shock promoter, we show that the bone morphogenetic protein (BMP) and Notch signalling pathways are both essential for regeneration. BMP is upstream of Notch and has an independent effect on regeneration of muscle. The Xenopus limb bud will regenerate completely at the early stages but regenerative ability falls during digit differentiation. We have developed a procedure for making tadpoles in which one hindlimb is transgenic and the remainder wild-type. This has been used to introduce various gene products expected to prolong the period of regenerative capacity, but none has so far been successful.     

Cellular and molecular mechanisms underlying LPS-associated myocyte impairment

Recently we reported that Toll-like receptor 4 (TLR4)-positive immune cells of unknown identity were responsible for the LPS-induced depression of cardiac myocyte shortening. The aim of this study is to identify the TLR4-positive cell type that is responsible for the LPS-induced cardiac dysfunction. Neither neutrophil depletion alone nor mast cell deficiency had any impact on the impairment of myocyte shortening during LPS treatment. In contrast, LPS-treated, macrophage-deficient mice demonstrated a partial reduction in shortening compared with saline-treated, macrophage-deficient mice. Because the removal of macrophages could only partially restore myocyte shortening, we also investigated the effects of removing both neutrophils and macrophages on myocyte shortening. Interestingly, endotoxemic, neutrophil-depleted, and macrophage-deficient mice had completely restored myocyte shortening. Because both macrophages and neutrophils can produce nitric oxide (NO) and TNF-alpha, we examined LPS-treated inducible NO synthase knockout (iNOSKO) mice and TNF receptor (TNFR)-deficient mice. Eliminating both TNFR1 and TNFR2 was required to restore myocyte shortening during LPS treatment, whereas iNOS deficiency had no effect. These data suggest that macrophages and to a lesser degree neutrophils cause cardiac impairment, presumably via TNF-alpha.     

Cellular and molecular mechanisms of cerebellar granule cell migration

The real-time observation of cell movement in brain slice preparations reveals that in the developing brain, postmitotic neurons alter their shape concomitantly with changes in the mode, direction, tempo, and rate of migration as they traverse different cortical layers. Although it has been hypothesized that orchestrated activities of multiple external cues and cell-cell contact are essential for controlling the cortical-layer-specific changes in cell migration, signaling mechanisms and external guidance cues related to the alteration of neuronal cell migration remain to be determined. In this article, we will first review recent studies on position-specific changes in granule cell behavior through different migratory terrains of the developing cerebellar cortex. We will then present possible roles for the coordinated activity of Ca²⁺ channels, NMDA type of glutamate receptors, and intracellular Ca²⁺ fluctuations in controlling cerebellar granule cell movement. Furthermore, we will discuss the crucial roles of brain-derived neurotrophic factor (BDNF), neuregulin (NRG), stromal cell-derived factor 1α (SDF-1α), ephrin-B2, and EphB2 receptor in providing directional cues promoting granule cell migration from the external granular layer (EGL) to the internal granular layer (IGL). Finally, we will demonstrate that endogenous somatostatin controls the migration of granule cells in a cortical layer-specific manner: Endogenous somatostatin accelerates granule cell movement near the birthplace within the EGL, but significantly slows down the movement near their final destination within the IGL.     

Cellular and molecular mechanisms of cerebellar granule cell migration

The real-time observation of cell movement in brain slice preparations reveals that in the developing brain, postmitotic neurons alter their shape concomitantly with changes in the mode, direction, tempo, and rate of migration as they traverse different cortical layers. Although it has been hypothesized that orchestrated activities of multiple external cues and cell-cell contact are essential for controlling the cortical-layer-specific changes in cell migration, signaling mechanisms and external guidance cues related to the alteration of neuronal cell migration remain to be determined. In this article, we will first review recent studies on position-specific changes in granule cell behavior through different migratory terrains of the developing cerebellar cortex. We will then present possible roles for the coordinated activity of Ca2+ channels, NMDA type of glutamate receptors, and intracellular Ca2+ fluctuations in controlling cerebellar granule cell movement. Furthermore, we will discuss the crucial roles of brain-derived neurotrophic factor (BDNF), neuregulin (NRG), stromal cell-derived factor 1alpha (SDF-1alpha), ephrin-B2, and EphB2 receptor in providing directional cues promoting granule cell migration from the external granular layer (EGL) to the internal granular layer (IGL). Finally, we will demonstrate that endogenous somatostatin controls the migration of granule cells in a cortical layer-specific manner: Endogenous somatostatin accelerates granule cell movement near the birthplace within the EGL, but significantly slows down the movement near their final destination within the IGL.     

Common molecular mechanisms in explicit and implicit memory

Cellular and molecular studies of both implicit and explicit memory suggest that experience-dependent modulation of synaptic strength and structure is a fundamental mechanism by which these memories are encoded and stored within the brain. In this review, we focus on recent advances in our understanding of two types of memory storage: (i) sensitization in Aplysia, a simple form of implicit memory, and (ii) formation of explicit spatial memories in the mouse hippocampus. These two processes share common molecular mechanisms that have been highly conserved through evolution.     

Cellular and molecular mechanisms of development of the external genitalia

The limb and external genitalia are appendages of the body wall. Development of these structures differs fundamentally in that masculine development of the external genitalia is androgen dependent, whereas development of the limb is not. Despite this fundamental difference in developmental regulation, epithelial-mesenchymal interactions play key roles in the development of both structures, and similar regulatory molecules are utilized as mediators of morphogenetic cell-cell interactions during development of both the limb and external genitalia. Given the relatively high incidence of hypospadias, a malformation of penile development, it is appropriate and timely to review the morphological, endocrine, and molecular mechanisms of development of the genital tubercle (GT), the precursor of the penis in males and the clitoris in females. Morphological observations comparing development of the GT in humans and mouse emphasize the validity of the mouse as an animal model of GT development and validate the results of experimental studies. Accordingly, the use of mutant mice provides important insights into the roles of specific regulatory molecules in development of the external genitalia. While our current understanding of the morphological and molecular mechanisms of mammalian external genitalia development is still rudimentary, this review summarizes the current state of our knowledge and whenever possible draws from the rich experimental embryology literature on other relevant organs such as the developing limb. Future research on the hormonal and molecular mechanisms of GT development may yield strategies to prevent or reduce the incidence of hypospadias and to elucidate the molecular genetic mechanisms of GT morphogenesis, especially in relation to common organogenetic pathways utilized in other organ systems.     

Cellular and molecular mechanisms of vitamin D in food allergy

Food allergies are becoming increasingly prevalent, especially in young children. Epidemiological evidence from the past decade suggests a role of vitamin D in food allergy pathogenesis. Links have been made between variations in sunlight exposure, latitude, birth season and vitamin D status with food allergy risk. Despite the heightened interest in vitamin D in food allergies, it remains unclear by which exact mechanism(s) it acts. An understanding of the roles vitamin D plays within the immune system at the cellular and genetic levels, as well as the interplay between the microbiome and vitamin D, will provide insight into the importance of the vitamin in food allergies. Here, we discuss the effect of vitamin D on immune cell maturation, differentiation and function; microbiome; genetic and epigenetic regulation (eg DNA methylation); and how these processes are implicated in food allergies.     

Cellular and molecular mechanisms of neuronal migration in neocortical development

The complicated mammalian brain structure arises from accurate movements of neurons from their birthplace to their final locations. Detailed observation of this migration process by various methods revealed that neuronal migration is highly motile and that there are different modes of migration. Moreover, mouse mutants or human disorders that disrupt normal migration have provided significant insights into molecular pathways that control the neuronal migration. Although our knowledge is still fragmentary, it is becoming clear that various molecules are participating in this process. In this review, we outline about the cellular and molecular mechanisms of neuronal migration in the cerebral cortex.     

Cellular and molecular mechanisms of vaccine-induced protection against retroviral infections

More than 15 years after the discovery of human immunodeficiency virus (HIV), researchers are still struggling to design a protective AIDS vaccine. A remaining problem is a lack of basic knowledge about the immunological requirements for protection against retroviruses. Infection of macaque monkeys with simian immunodeficiency virus is still the best model for HIV vaccine research. However, in this model it remains difficult to determine protective immunological mechanisms because of limited numbers of experimental animals and their genetic heterogeneity. Thus, fundamental concepts in retroviral immunology have to be defined in other ways such as mouse models. This minireview summarizes new findings on cellular and molecular mechanisms in protection of mice against Friend murine retrovirus infection. It has been shown that complex immune responses, including B and T cell responses, are required for efficient protection in this model. Multiple viral antigens are necessary to elicit such broad immune reactivity. Efficacious vaccines must protect not only against acute disease, but also against the establishment of persistent infections or the host is at serious risk of virus reactivation. The minireview closes with a discussion on the relevance of findings from the mouse model on the design of a protective vaccine against HIV.     

Cellular and molecular mechanisms of aging: a review]

Since the beginning of this century, a large body of experimental data and observations accumulated concerning experimental and clinical gerontology. These data can be classified and analyzed according to the level of experimentation or observation as concerning aging at the molecular, cellular level or at higher levels of hierarchical organisation such as tissues, organs or the whole organism. Observations of these higher levels are mostly derived from epidemiological studies of human aging, horizontal studies or preferably vertical studies. The relative coherence of data collected at the molecular and cellular levels renders plausible a tentative of interpretation of aging phenomena at higher levels or hierarchical organisations from the tissues to the whole organism by using the data obtained at the molecular and cellular levels. The present article is a tentative for this kind or integrative interpretation of aging.