Is there a hormonal network in Tetrahymena? A systematic investigation of hormonal effects on the hormone content

The effect of six hormones (histamine, serotonin, insulin, epidermal growth factor (EGF), oxytocin and gonadotropin) was studied on the hormone (histamine, serotonin, adrenocorticotropic hormone [ACTH], endorphin and triiodothyronine [T(3)]) content of Tetrahymena. The hormones were given in 10(-9) or 10(-12) M concentrations or as 0.1 and 0.001 I.U. ml(-1) (in the case of oxytocin and gonadotropin) for 1 h. The hormones in picomolar concentration, i.e. at levels which can be present also in natural conditions, influence the amount of other hormones inside the cell. Their effect is not a general one: it is individual, the level of one of the hormones was elevated, while that of the others diminished under the effect of the same hormonal stimulus. Insulin was the only hormone, which influenced the concentration of other hormones in one direction, elevating them. This effect could have a role in the life-saving property of this hormone in Tetrahymena, but the hormones were not studied from this point of view. Usually there is no difference between the effect of the two concentrations used, but there are situations when the effect of the two concentrations is opposite. This means that there is a possible concentration dependence and this could influence differently the cells which are far from or near to the secretor cell. Considering earlier observations, the duration of the treatment can also influence the result. The results give new data to the hormonal regulation at unicellular level (which can be the base of regulation at higher evolutionary levels) and point to the possibility of a hormonal network.     

The application of RAPD markers in stock discrimination of the four-wing flyingfish, Hirundichthys affinis in the central western Atlantic

The polymerase chain reaction–random amplified polymorphic DNA (PCR–RAPD) technique was used to examine genetic variability and population structuring in the four-wing flyingfish, Hirundichthys affinis within the central western Atlantic. Three random decamer primers and pairs of these primers were used to amplify nuclear DNA from 360 fish sampled from six populations (at five locations) across the region. A total of 58 polymorphic RAPD markers were identified, 20 of which were population-specific and six of which were subregional or stock-specific markers. Cluster analysis of similarity indices indicated the presence of three genetically distinct subregional stocks located in the eastern Caribbean, southern Netherlands Antilles and Brazil, respectively. Estimates of gene diversity (φ) and gene flow ( Nm ) are consistent with this three-stock hypothesis. Furthermore, partially restricted gene flow was apparent among spatially and temporally separate sampled populations within the eastern Caribbean subregional stock, indicating the possible presence of different spawning groups. These results are entirely consistent with those obtained from PCR–RFLP analysis of the mtDNA D-loop in the same fish, indicating the presence of barriers to dispersal and interbreeding in both sexes. We conclude that the PCR–RAPD technique is suitable for determining population stock structure in this species and that a three-stock approach to managing H. affinis within the central western Atlantic would be appropriate.     

Carbohydrate metabolism in the stick insect, Carausius morosus

Age-related changes in some parameters related to carbohydrate metabolism in the stick insect, Carausius morosus, were investigated during the 6th instar and up to day 37 of adult life. Total haemolymph carbohydrate concentration and the fat body glycogen content are low and may be related to the low activity of this insect. Trehalose constitutes about 75–80% of the total blood carbohydrate pool. During the moult, total blood carbohydrate, fat body glycogen and haemolymph volume, decrease while glycogen phosphorylase activity of the fat body is slightly activated. The effects are brought about mainly by reduced feeding activity, but may also be influenced by the shedding and replacement of the cuticle. During starvation, blood homeostasis is maintained at the expense of fat body glycogen via an activation of phosphorylase. During reproduction, although no dramatic changes in fat body glycogen levels occur, blood carbohydrates are maintained and fat body phosphorylase is slightly activated. The possibility is discussed that during moulting and reproduction, blood sugar homeostasis is maintained by a hormonal mechanism controlling glycogen phosphorylase. No circadian rhythm in any parameter investigated is observed.     

The role of chloride ions in the regulation of steroidogenesis in rat Leydig cells and adrenal cells

The role of chloride ions in the regulation of steroidogenesis in rat Leydig cells and adrenal cells has been investigated. It was found that the chloride channel blocker 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) inhibited LH but not dibutyryl cAMP (dbcAMP)-stimulated steroidogenesis in the Leydig cells. This was found to be via an inhibition of cAMP production, because both LH- and forskolin-stimulated cAMP productions were inhibited by DIDS. The exclusion of chloride ions enhanced steroidogenesis during incubation of Leydig cells and adrenal cells with dbcAMP. The adrenal cells were found to be more sensitive to dbcAMP than Leydig cells and the enhancing effects of chloride removal were higher. In the presence of chloride ions, near maximum steroidogenesis was achieved with approximately 60 μM and 1 mM dbcAMP in the adrenal and Leydig cells, respectively. In the absence of chloride ions the concentrations required decreased approximately 50-fold and 10-fold, respectively. It is concluded that although LH may regulate DIDS sensitive chloride channels, the enhanced stimulation of cAMP-mediated steroidogenesis by chloride exclusion is not mediated via these channels. We propose a model based on the present and previous studies [1] with Leydig tumour (MA10) cells i.e. that intracellular chloride ion depletion enhances the action of cAMP on protein synthesis which results in increased synthesis of the Steroidogenic Acute Regulator (StAR) protein and consequently increased steroidogenesis.     

Nuclear and chromatin structure in rat spermatozoa

The nuclei of mature mammalian spermatozoa contain a highly ordered, lamellar substructure, presumably constituting the nucleoprotein of the haploid chromosomal complement. With a view toward constructing a plausible model of chromatin packing in sperm, we have determined some of the quantitative parameters associated with these “nuclear lamellae” in rat spermatozoa. Epididymal sperm from white, Sprague-Dawley rats were examined by conventional sectioning methods, freeze fracture of fixed and unfixed specimens, and by whole mount replica techniques. Fixation and glycerolation did not significantly alter nuclear structure as seen by freeze fracture. Numerical data obtained from cross fractures of sperm heads indicate that the number of lamellae are quite constant at 10.4 ± 1.8 and that the linear measure of the lamellae is 7.2 ± 2.3 μm per cross fracture. The total area of cross fracture, assuming an elliptical profile is 2.3 k 0.7 μm² and the thickness of the lamellae is 18.2 ± 3.5 nm with a range of 13.5 to 25.5 nm. An estimate of the total surface area of the nuclear lamellae could be made from measurements of projected nuclear area (from replicas and sections) as 173 ± 15 μm². From these data and the known amount of DNA in the rat sperm nucleus, a model can be proposed for the organization of the nucleoprotein in these lamellar sheets. It is suggested that the chromatin is arranged in a coiled-coil configuration closely associated together in a side-by-side fashion and continuous in extent. Approximate calculations based on this simple model are within a factor of 2 or 3 of predicting the correct amount of DNA in the sperm nucleus.     

Activity-dependent and hormonal regulation of neurotrophin mRNA levels in brain–implications for neuronal plasticity

The neurotrophins exhibit neurotrophic effects on specific, partially overlapping populations of neurons both in the peripheral and the central nervous system (CNS). In the periphery, they are synthesized by a variety of nonneuronal cells, and their synthesis seems to be independent of the neuronal input. In contrast, in the CNS all neurotrophins are expressed under physiological conditions primarily by neurons. The production of NGF and BDNF is controlled by neuronal activity: up-regulation by glutamate and acetylcholine, down-regulation by gamma-aminobutyric acid. In contrast, NT-3 regulation is independent of neuronal activity, but it is up-regulated by thyroid hormones and BDNF. The latter observation suggests that NT-3 might be controlled indirectly by neuronal activity via BDNF. In peripheral nonneuronal tissues, glucocorticoid hormones down-regulate NGF mRNA levels both in vitro and in vivo. In contrast, in the CNS, neuronal production of NGF is enhanced by glucocorticoids. The rapid regulation of NGF and BDNF by subtle physiological stimuli together with the recent demonstration that the neurotrophin release neurotransmitters such as acetylcholine opens up interesting perspectives for the function of neurotrophins as mediators of neuronal plasticity. 1994 John Wiley & Sons, Inc.     

PML is critical for ND10 formation and recruits the PML-interacting protein daxx to this nuclear structure when modified by SUMO-1.

Nuclear domain 10 (ND10), also referred to as nuclear bodies, are discrete interchromosomal accumulations of several proteins including promyelocytic leukemia protein (PML) and Sp100. In this study, we investigated the mechanism of ND10 assembly by identifying proteins that are essential for this process using cells lines that lack individual ND10-associated proteins. We identified the adapter protein Daxx and BML, the RecQ helicase missing in Bloom syndrome, as new ND10-associated proteins. PML, but not BLM or Sp100, was found to be responsible for the proper localization of all other ND10-associated proteins since they are dispersed in PML-/- cells. Introducing PML into this cell line by transient expression or fusion with PML-producing cells recruited ND10-associated proteins into de novo formed ND10 attesting to PMLs essential nature in ND10 formation. In the absence of PML, Daxx is highly enriched in condensed chromatin. Its recruitment to ND10 from condensed chromatin requires a small ubiquitin-related modifier (SUMO-1) modification of PML and reflects the interaction between the COOH-terminal domain of Daxx and PML. The segregation of Daxx from condensed chromatin in the absence of PML to ND10 by increased accumulation of SUMO-1-modified PML suggests the presence of a variable equilibrium between these two nuclear sites. Our findings identify the basic requirements for ND10 formation and suggest a dynamic mechanism for protein recruitment to these nuclear domains controlled by the SUMO-1 modification state of PML.     

中国山杨遗传多样性及遗传结构分析

利用6个单拷贝核基因标记,对中国山杨(Populus davidiana Dode)14个自然居群的遗传多样性和遗传分化水平进行了研究。结果表明,中国山杨表现出较高的遗传多样性水平,各居群间基因流(Nm)为0.66;居群内的变异占总变异的百分比(71.82%)大于居群间(28.18%)。Mantel test检验结果显示居群遗传距离和地理距离间没有相关性。失配分布检测显示中国山杨历史上曾经历过种群的扩张。复杂的种群历史动态、高度异交和较高的碱基突变速率是中国山杨遗传多样性水平较高的原因;而较强的花粉和种子扩散能力及中国山杨的连续分布可能是其居群间遗传分化较小的原因。     

生长素对拟南芥叶片发育调控的研究进展

叶片（包括子叶）是茎端分生组织产生的第一类侧生器官,在植物发育中具有重要地位。早期叶片发育包括三个主要过程：叶原基的起始,叶片腹背性的建立和叶片的延展。大量证据表明叶片发育受到体内遗传机制和体外环境因子的双重调节。植物激素,尤其是生长素在协调体内外调节机制中起着不可或缺的作用。生长素的稳态调控、极性运输和信号转导影响叶片发育的全过程。本文着重介绍生长素在叶片生长发育和形态建成中的调控作用,试图了解复杂叶片发育调控网络。