Morphology of the nucleo-cytoplasmic interactions during the development ofAcetabularia cells

Protoplasma - An electron microscopic survey of nuclear events and changes in the perinuclear cytoplasm during the generative phase ofAcetabularia is presented with details on late stages in the...     

Competitive interactions between retinal ganglion cells during prenatal development

In the mammalian visual system, retinal ganglion cell axons terminate within the LGN in a series of alternating eye-specific layers. These layers are not present initially during development. In the cat they emerge secondarily following a prenatal period in which originally intermixed inputs from the two eyes gradually segregate from each other to give rise to the characteristic set of layers by birth. Many lines of evidence suggest that activity-dependent competitive interactions between ganglion cell axons from the two eyes for LGN neurons play an important role in the final patterning of retinogeniculate connections. Studies of the branching patterns of individual ganglion cell axons suggest that during the period when inputs from the two eyes are intermixed, axons from one eye send side branches into territory later occupied exclusively by axons from the other eye. Ultrastructural studies indicate that these branches in fact are sites of synaptic contacts, which are later eliminated since the side branches disappear as axons form their mature terminal arbors in appropriate territory. In vitro microelectrode recordings from LGN neurons indicate that they can receive convergent synaptic excitation from electrical stimulation of the optic nerves before but not after the eye-specific layers form, suggesting that at least some of the synaptic contacts seen at the ultrastructural level are functonal. Finally, experiments in which tetrodotoxin was infused intracranially during the two week period during which the eye-specific layers normally form demonstrate that it is possible to prevent, or at least delay, the formation of the layers. Accordingly, individual axons fail to develop their restricted terminal arbor branching pattern and instead branch widely throughout the LGN. These results indicate that all of the machinery necessary for synaptic function and competition is present during fetal life. Moreover, it is highly likely that neuronal activity is required for the formation of the eye-specific layers. If so, then activity would have to be present in the form of spontaneously generated action potentials, since vision is not possible at these early ages. Thus, the functioning of the retinogeniculate system many weeks before it is put to the use for which it is ultimately designed may contribute to the final patterning of connections present in the adult.     

Astrocyte-synapse interactions during brain development

Bidirectional communication between astrocytes and neurons is essential for proper brain development. Astrocytes, a major glial cell type, are morphologically complex cells that directly interact with neuronal synapses to regulate synapse formation, maturation, and function. Astrocyte-secreted factors bind neuronal receptors to induce synaptogenesis with regional and circuit-level precision. Cell adhesion molecules mediate the direct contact between astrocytes and neurons, which is required for both synaptogenesis and astrocyte morphogenesis. Neuron-derived signals also shape astrocyte development, function, and molecular identity. This review highlights recent findings on the topic of astrocyte-synapse interactions, and discusses the importance of these interactions for synapse and astrocyte development.     

Molecular interactions of syndecans during development

The syndecans, cell surface heparan sulfate proteoglycans (HSPGs), bind numerous ligands via their HS glycosaminoglycan chains. The response to this binding is flavored by the identity of the core protein that bears the HS chains. Each of the syndecan core proteins has a short cytoplasmic domain that binds cytosolic regulatory factors. The syndecans also contain highly conserved transmembrane domain and extracellular domains for which important activities are slowly emerging. These protein domains, which will be the focus of this review, localize the syndecan to sites at the cell surface during development where they collaborate with other receptors to regulate signaling and cytoskeletal organization.     

Morphology of epithelio-mesenchymal interaction during lung development of the mouse

Basement membrane gaps and epithelio-mesenchymal contacts could be shown in the lung of mouse embryos during the entire pregnancy period. Some of the contacts corresponded to gap junctions. The significance of these findings for the differentiation of epithelium and mesenchyme, as well as for the development of the epithelial tube system of the lung as a model for the epithelio-mesenchymal interaction, has been discussed taking into account the results of other investigators. It was concluded that direct epithelio-mesenchymal contacts are necessary for organ development.     

Division of the primary nucleus ofAcetabularia

Summary The division of the primary nucleus ofAcetabularia mediterranea, andAcetabularia cliftonii was studied by light microscopical observation of living cells. Nuclear and nucleolar volumes are reduced when the caps of the cells have reached their maximum diameter. When the nucleus has reached a size of about 30–50 m in diameter, condensed chromosomes are formed which are separated by an intranuclear spindle.     

Thyroid-thymus interactions during development and aging

A good body of experimental and clinical evidences suggests that bidirectional interactions do exist between the neuroendocrine system and the thymus activity. In particular, thymic endocrine activity seems to be strongly influenced by neuroendocrine signals. In this context, studies performed in hyper- and hypothyroid subjects and in the low triiodothyronine (T3) syndrome, which affects premature infants, have clearly shown that thyroid hormones and in particular T3 physiologically modulate thymic peptide secretion. In vitro experiments, with thymic whole-organ cultures, have demonstrated that thyroid hormones exert their action on the epithelial cells of the thymus deputed to synthesize and secrete thymic peptides and that such an effect does not seem to depend on the known permissive action of thyroid hormones.     

Aspects of trace element interactions during development

The origins of nutritional trace element deficiencies are summarized. Inadequate intake results in primary deficiency, whereas secondary or conditioned deficiencies can arise in several ways including trace element interactions. Evidence is presented and discussed for interactions of essential trace elements during prenatal and early postnatal development. Diets of widely different zinc and copper concentrations and ratios were fed to pregnant rats. Analysis of fetal outcome and copper and zinc concentrations of maternal and fetal livers showed that although there is an interaction between these metals it occurs only at levels of dietary copper deficiency. Iron and manganese interact so that high levels of one depress absorption of the other. Mice fed iron-supplemented diets had liver manganese concentrations lower than those of unsupplemented mice. Iron supplements at high but not low levels also depressed absorption of zinc. Conversely, zinc deficiency in pregnant rats caused higher than normal concentrations of iron in maternal and fetal liver. Trace element analyses of proprietary infant formulas indicate that in some, concentrations and ratios of these trace elements may be incorrect. The effects of essential trace element interactions during development should be further investigated. Caution is urged in considering levels of trace element supplements during pregnancy, lactation, or early childhood.     

Observations on the sterile whorls ofAcetabularia

Summary The sterile whorls ofAcetabularia increase greatly the surface area of the cell. These structures function in the uptake of solutes from the environment. The development of the whorls is controlled by light and also by the availability of nutrients.     

Lipid composition ofAcetabularia mediterranea (Lamour.) Variations during cap morphogenesis

Summary YoungAcetabularia mediterranea cells without cap have a fatty acid composition different from other green algae currently used for biological research. They contain important quantities of palmitic and oleic acid, but are very poor in polyunsaturated fatty acids such as linoleic and linolenic acid. (These polyunsaturated fatty acids are predominant in higher plants and many green algae.)     

盘基网柄菌细胞分化和凋亡的形态特征

本文用透射电镜和DAPI荧光染色法研究了盘基网柄菌(Dictyosteliumdiscoideum)细胞分化和柄细胞的凋亡特征,结果显示:细胞丘中绝大部分细胞的线粒体内出现一小空泡,随着发育进程,空泡逐渐增大,线粒体的嵴随之变少,直至线粒体完全空泡化,最后形成单层膜的空泡。据此我们推测前孢子细胞特有的空泡来源于线粒体,并且这种细胞器水平上的内自噬现象与前孢子细胞分化密切相关。在前柄细胞分化阶段,前柄细胞中出现数个自噬泡,最初吞噬的线粒体嵴结构完整;随着前柄细胞进一步分化,部分线粒体内出现类似于前孢子细胞中的内自噬现象,并且自噬泡只吞噬这种线粒体。在凋亡后期,细胞核内核仁消失,染色体固缩形成高电子密度斑块,自噬泡采用与细胞核膜融合的方式来完成核的清除,最后柄细胞完全空泡化且包被一层纤维素壁。作者认为前柄细胞凋亡过程实质上是一种分化过程,所以有其鲜明特点:细胞出现自噬泡,标志着凋亡开始,用自噬而不是凋亡小体来清除胞内各种细胞器,直到分化最后阶段才清除细胞核和形成纤维素壁。这些特点不仅是前柄细胞凋亡的形态学指标,也和细胞发育和分化相关。     

Neuronal--glial interactions during development and aging.

Integration of the central nervous system is an expression of cerebral homeostasis that is essential for the internal ability of the organism to adapt to its changing environment throughout life. It is generally accepted that neurons undergo no further division after differentiation, whereas glial cells continue to proliferate throughout life. The increase in glial cells with advanced age may reflect a compensatory process of the brain to overcome neuronal loss or neuronal functional changes that may occur with age. Therefore, these neuronal-glial interactions during development and aging may play a key role in the integrative capacity of the brain. One of the mechanisms contributing to brain stability is the blood-brain barrier, which regulates the neuronal-glial microenvironment in the mature organism. Neuronal intercommunication is mediated via neurotransmitter substances and a shift may occur from excitation to inhibition and vice versa in some CNS areas with aging. Studies of some aspects of cholinergic, monoaminergic and amino acid neurotransmission show that their maturational patterns are CNS-area specific and that some neurotransmitter processes decline with advanced age. Glial cells, besides participating in the regulation of extraneuronal environment, are also proposed to be involved in neurotransmission mechanisms in the adult and aging CNS and since they are the major CNS cellular compartment that changes with age they may thus contribute significantly to the maintenance of CNS integrative ability and adaptation with age.     

Translocation biosensors to study signal-specific nucleo-cytoplasmic transport, protease activity and protein-protein interactions

Regulated nucleo-cytoplasmic transport is crucial for cellular homeostasis and relies on protein interaction networks. In addition, the spatial division into the nucleus and the cytoplasm marks two intracellular compartments that can easily be distinguished by microscopy. Consequently, combining the rules for regulated nucleo-cytoplasmic transport with autofluorescent proteins, we developed novel cellular biosensors composed of glutathione S-transferase, mutants of green fluorescent protein and rational combinations of nuclear import and export signals. Addition of regulatory sequences resulted in three classes of biosensors applicable for the identification of signal-specific nuclear export and import inhibitors, small molecules that interfere with protease activity and compounds that prevent specific protein-protein interactions in living cells. As a unique feature, our system exploits nuclear accumulation of the cytoplasmic biosensors as the reliable readout for all assays. Efficacy of the biosensors was systematically investigated and also demonstrated by using a fully automated platform for high throughput screening (HTS) microscopy and assay analysis. The introduced modular biosensors not only have the potential to further dissect nucleo-cytoplasmic transport pathways but also to be employed in numerous screening applications for the early stage evaluation of potential drug candidates.