Effect of TNF-a on Fatty Tissue Metabolism

Summary: TNF-a plays a key role in regulating energy metabolism under both physiological and pathological states. Current opinions of TNF-a actions on lipid metabolism were presented. The influence of TNF-aon both leptin and PAI-1 biosynthesis was underlined. The role of the cytokine as an essential factor in development of insulin resistance was pointed out.

Key words: tumor necrosis factor-a (TNF-a), adipose tissue, lipid metabolism.

Molecular Basis of Alagille Syndrome

Summary: Alagille syndrome (AGS) is a congenital disorder with autosomal dominant inheritance. It occurs with a frequency 1 : 70 000 births. The JAG1 gene, responsible for AGS, codes a ligand for a Notch receptor involved in a highly conserved process of signal transmission between cells. Up to now 193 different mutations (deletions, insertions, transitions and transversions) have been identified in the JAG1 gene. Probably the haploinsufficiency and/or the dominat negative effect are mechanisms involved in AGS pathogenesis. There is no significant correlation between genotype and phenotype of AGS patients.

Key words: Alagille syndrome, AGS, JAG1 gene, JAG1 protein, mutations, Notch signaling.

Strategies of Symbiotic Rhizobia in Overcoming of Defense Reactions in Legumes

Summary: The review discusses the specific interactions between endosymbiotic rhizobia and their plant hosts during the development of symbiosis. Plant defense reactions (local and systemic) activated in the response to the infection and the penetration of plant tissues by rhizobia are characterized. Several bacterial strategies that permit to overcome or suppress the plant defense reactions are presented. Moreover, the plant factors are characterized that support bacterial invasion and the development of effective symbiosis of rhizobia with legume plants.

Key words: plant defense mechanisms, Rhizobium-legume symbiosis

Jasmonides in Breaking Dormancy and Seed Germination

Summary: Jasmonic acid (JA) and its methyl ester (JA-Me) is the most known representative of the new plant growth regulators called jasmonides. Occurrence of these compounds was detected in the seeds of many plant species, most of them from Leguminosae family. The content of jasmonides in the seeds varies in the range of 10–100 ng ˇ g–1 fresh weight. The influence of jasmonides on seed germi nation is dependent on physiological status of seeds. They stimulate dormant and inhibit non-dormant seed germination. Changes in the content of these regulators during stratification of primary dormant oily  seeds suggest jasmonates involvement in the regulation in these seeds’ of primary dormancy breaking. Obtained data indicate that this effect is involved with stimulation of acid and alkaline lipase activity, enzymes hydrolysing storage oil materials necessary in the embryo growth. The knowledge about jasmonates involvement in the regulation of non-dormant seeds germination is based only on determination of exogenous JA-Me significance in the control of this process. Inhibitory effect of JA-Me on Amaranthus caudatus seed germination is reversed by exogenous ethylene, gibberellins and cytokinins. Gibberellins and cytokinins need ethylene action for reversing JA-Me inhibition. The influence of JA-Me on Amaranthus caudatus and Xanthium pennsylvanicum seed germination involves ethylene biosynthesis control: the inhibition of ACC synthase activity and/or synthesis as well as activity of ACC oxidase. Probably JA-Me also is involved in the control of other metabolical processes during seed germination i.e. respiration or mobilisation of carbohydrate storage materials. Current data on this topic are presented in this paper.

Key words: jasmonic acid (JA), methyl jasmonate (JA-Me), breaking dormancy, seed germination

Estrogens and their Role in the Regulation of Spermatogenesis

Summary: In this review the site of aromatization as well as new biochemical and molecular aspects of the action of estrogens are presented. In the male gonad, estrogens are synthesized by Leydig cells, Sertoli cells, and germ cells. Estrogen receptors are expressed in the testis, efferent ductules, epididymis, and prostate. In males, estrogens are clearly involved in the negative feedback effects of testosterone on the brain to control pituitary gonadotropin release. Recent evidence suggests that estrogens may also exert paracrine actions within the testis itself. These hormones play an important role in proliferation and differentiation of Sertoli and Leydig cells as well as they are implicated in the regulation of germ cell develpoment. Recent studies on the spermatogenic phenotypes in knockout mice lacking functional estrogen receptors and aromatase provide clear evidence that estrogens and their receptors are required for induction and/or maintenance of spermatogenesis. However, precise, physiological functions of estrogens and their mechanisms of action in the male reproductive tract are still not fully understood.

Key words: estrogens, estrogen receptors, aromatase, spermatogenesis, testis, transgenic mice.

Mechanisms of Zinc and Cadmium Hyperaccumulation in Plants

Summary:  Among plant species that accumulate a large amount of zinc and cadmium Thlaspi caerulescens J. & C. Presl and Arabidopsis halleri (L.) O'Kane & Al.-Shehbaz have recently received considerable attention in studies examining the mechanisms of metal hyperaccumulation. They are characterized by higher rate of Zn and Cd uptake from a substrate, higher transport rate of the metals from root to shoot and higher tolerance to Zn and Cd in comparison with non-hyperaccumulating species. It was shown that in T. caerulescens Zn is taken up via ZNT1 a high-affinity Zn transport system. It was found that higher uptake rate of Zn in T. caerulescens is caused by increased expression of ZNT1 transporter in the root and shoot. Similar mechanisms may be expected to be operating in A. halleri. Cadmium may be transported into T. caerulescens cells by ZNT1 transporter, which mediate low-affinity Cd uptake, or by high-affinity Fe transporter IRT1, which mediate high-affinity Cd uptake. There are not data whether Cd enter plant cells in hyperaccumulators by other cation transporters (LCT1, members of Nramp family), which mediate low-affinity Cd uptake in non-hyperaccumulator plant species.It was proved that in T. caerulescens Zn was mainly localized in the vacuoles of epidermal leaf cells and was almost absent from the vacuoles of the cells from the stomatal complex. In A. halleri leaves, the trichomes had the largest concentrations of Zn and Cd. The epidermal cells other than trichomes contained lower concentrations of Zn and Cd than mesophyll cells. Probably it is connected with small size of epidermal cells and their vacuoles. This indicates that the mesophyll cells in the leaves of A. halleri are the major storage sites for Zn and Cd in contrast to T. caerulescens. In both plant species most of Zn and Cd accumulated in shoots was water-soluble. It was proposed that vacuoles and trichomes of leaves cells play an important role in hyperaccumulation and tolerance to Zn and Cd in A. halleri and T. caerulescens. Accumulation of Cd in the vacuoles of T. caerulescens is not connected with synthesis and level of phytochelatins, as it was observed in most investigated nonaccumulator plant species.

Key words: hyperaccumulators, zinc, cadmium, mechanisms of uptake, localization of metals.

IRP1, Protein Controling Iron Homeostasis in Mammalian Cells: Regulation of its Activities by Iron and Nitric

Summary: IRP1 posttranscriptionally regulates the expression of proteins involved in iron metabolism in mammals. IRP1 is a cytosolic bifunctional protein, which exhibits aconitase activity when it contains a catalytic [4Fe-4S] center (holo-IRP1) or trans-regulatory activity when it lacks this center (apo-IRP1). These activities are mutually exclusive and are conversely regulated by iron in the labile iron pool (LIP). In iron deficiency apo-IRP1 predominates in the cells and binds iron responsive elements (IREs) present in mRNAs encoding ferritin (Ft) subunits and transferrin receptor (TfR). The interaction of IRP1 with IRE located in the 5’UTR of Ft mRNA causes the inhibition of its translation and Ft synthesis. Binding of IRP1 to IRE located in the 3’UTR of TfR mRNA increases its stability and consequently increases TfR synthesis. The converse regulation of Ft and TfR synthesis resulting from the lack of binding of holo-IRP1 to IRE occurs in cells with high LIP level. In both, iron deficiency and excess IRP1-mediated regulation rapidly restores physiological LIP level. Apart from the regulation mediated by iron, nitric oxide (NO) was the first biological factor found to be able to regulate IRP1 activities. Similarly to iron chelators, NO inhibits aconitase activity of IRP1 and induces its IRE-binding activity. However, in contrast to iron deprivation, quick appearance of apo-IRP1 in cells exposed to NO results from the interaction of NO with [4Fe-4S] cluster of IRP1, its disassembly and removal from IRP1 molecule. Besides the modulation of IRP1 activities NO has been shown to down-regulate IRP1 level in the cells.

Key words: IRP1, aconitase, IRE, [4Fe-4S] center,  iron metabolism,  ferritin,  transferrin receptor, Fenton reaction, nitric. oxide, NOS.
 

Secretory Organelles of Toxoplasma Gondii – their Role in Host Cell Invasion

Summary: Toxoplasma gondii is an obligate, intracellular parasite that can infect nearly any vertebrate cell type. T. gondii invades host cell by an active process driven by the parasite. The invasion is associated with secretion of proteins from three sets of secretory organelles: the micronemes, rhoptries and dense granules. Microneme proteins are responsible for attachment to the host cell; rhoptry content participates in the formation of parasitophorous vacuole. Dense granule proteins are secreted continuosly during intracellular development of the parasite and they play an important role in nutrient acquisition. This assay presents all known facts about secretory organelles of T. gondii and their role in host cell invasion.

Keywords: Toxoplasma gondii, secretory organelles, secretory proteins

PACAP and VIP Peptides: Localization, Receptors, and Physiological Function

Summary: Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) belong to a superfamily of polypeptide hormones which also includes glucagon, secretin and growth hormone-releasing hormone. PACAP and VIP are widely distributed both in the central ner-vous system and peripherial organs of various vertebrates. PACAP exists in two biologically active forms: a dominant 38-amino acid form (PACAP38) and  a shorter 27-amino acid form (PACAP27). PACAP27 shows 68% sequence identity with VIP (a 28-amino acid polypeptide). The sequence of  both PACAP and VIP has been remarkably well conserved in the course of evolution. Both peptides exert their actions via common receptors: VPAC1 and VPAC2, which bind VIP and PACAP with similar affinity. Additionally, PACAP also stimulates PAC1 type receptors, which bind PACAP with much higher affinity than VIP. PACAP and VIP act as neuroregulatory agents, neurotransmitters, as well as neurotrophic and neuroprotective factors.

Key words: pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), PAC1, VPAC1, VPAC2 receptors, adenylate cyclase, cAMP, protein kinase A, phospholipase C, inositol trisphosphate, diacylglycerol, Ca2+, neuroprotection.

Suppressory Antigen CTLA-4 Gene Polymorphism – Risk of Autoimmunity

Summary: The actual state of study on the association between the most frequently reported the CTLA-4 gene exon 1 G49A polymorphism with autoimmune diseases was described. The mechanizm of the role of CTLA-4 (CD152) in negative regulation of immune response was briefly described. CTLA-4 gene structure was presented. Critical evaluation of CTLA-4 gene polymorphism in Addison’s disease, insulin-dependent diabetes mellitus, Graves’ disease, Hashimoto’s thyroiditis and multiple sclerosis was described.

Key words: CTLA-4, CD152, T lymphocytes, autoimmune diseases, polymorphism.

Synthesis and Hydrolysis of Plant Hormone Conjugates in Regulation of Active Hormone Levels

Summary: Plant hormones are important in all aspects of plant growth and development, but our understanding of hormonal homeostasis is far from complete. Phytohormone conjugation is considered as a part of the mechanism to control cellular levels of these compounds. This is a ubiquitous process in plants that responds to environmental and physiological factors. While numerous conjugates have been identified in higher plants, their location within cells and tissues, the enzymes and genes involved in their metabolism, and the biological functions, are not clearly understood. Some conjugates of auxin, gibberellins and cytokinins are thought to be temporary storage forms, from which free active hormones can be released after hydrolysis. It is also believed that conjugates serve functions such as irreversible inactivation, transport, compartmentalization and protection against oxidative degradation. In this paper previous results, and recent advances in studies on some phytohormone conjugation, involving biochemical and molecular biology approaches, in connection with their possible physiological functions, are reported.

Key words:  plant hormone, conjugation, auxins, cytokinins, gibberellins, abscisic acid, ethylene.

Follicular Dendritic Cells – Development and Function

Summary: Summary: Follicular dendritic cells (FDC) are distinct antigen presenting cells, that differ from myeloid dendritic cells in orgin, function and cell surface markers. FDC reside within B-cell follicles  of secondary lymphoid tissue and play an essential role in germinal center formation. The hallmark of FDC is ability to trap antigen-antibody complexes and retain  their on the surface for long periods of time (from months to years). Their long dendritic processes form a weblike network, which intimately associates with neighboring B cells. The intimate contact between these two cells is belived to be necessary for such important events, as: somatic mutation, affinity maturation, class switching and development of memory B cells.

Key words: follicular dendritic cells,  germinal center, B cell growth.