Elżbieta BEDNARSKA, Marta LENARTOWSKA

Role of calcium signalling in the pollen tube growth regulation

Summary: Angiosperm pollen tube growth is recognised as an important model for studies of signal transduction in plants. In the past 10 years this field of research has expanded significantly. Recent studies has been focused on the molecular evens involving calcium ions in mechanisms of the pollen tube growth and orientation. Important results on the biochemical and physiological aspects of the molecular regulation of these processes have been reported. The following review attempts to cover these issues. The aim of this paper is to present a general overview of the calcium homeostasis regulation in developing pollen tube, the involvement of the phosphatidylinositide signal transduction pathway during pollen tube growth and the signaling role for cytosolic free Ca2+ in the tube reorientation. 

Key words: signal transduction, calcium ions, pollen tube, orientation of pollen tube tip growth

[Postepy Biologii Komorki 2000; 27: 467�480]

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Lidia CISZAK, Dariusz WOŁOWIEC, Agata KOSMACZEWSKA, Dorota BOĆKO, Irena FRYDECKA

Cyclin-dependent kinase inhibitor p27: structure, role in cell physiology and in malignancies

Summary: P27 protein, which belongs to CIP/KIP family of cyclin-dependent kinase inhibitors, is the subject of a large number of studies from the sphere of cell biology and pathogenesis of neoplastic proliferation, because it controls not only cell cycle by regulating activity of cyclin-CDK complexes, but it is also involved in apoptosis. P27 protein regulates the activity of cyclin-CDK complexes in two distinct ways. First, it inhibits the activity of the cyclin-CDK complexes. The crystal structure of N-terminal portion of p27, CDK2 and cyclin A complex reveals, that p27 binding causes large conformational changes in and around the catalytic cleft of enzyme, which eliminate any potential for ATP binding. These structural changes are likely to be determinants of inhibition. Second, p27 promotes assembly of stable CDK4-cyclin D1 complexes. It increases the affinity of kinase CDK4 to cyclin D1, influences D-type cyclin levels and cyclin D1 stability. P27 protein facilitates nuclear accumulation of cyclin D1 and CDK4 kinase, too. Recent studies indicated, that the interaction between p27 and cyclin-CDK complexes is more complicated than it had been supposed before. On the one hand p27 protein can be regulator of CDK-cyclin complexes and on the other hand the level of p27 protein in the cell is directly controlled by CDK2-cyclin E complex, which causes phosphorylation of p27 on treonine 187. This phosphorylation is a signal to p27 degradation by ubiquitin-proteasome pathway.
Little information is available on the role of p27 protein in apoptosis. We don�t know the finally answer on the question when p27 induces programmed cell death and when it inhibits apoptosis. 
Because p27 protein plays an important role in regulation of cell proliferation and in apoptosis, a special attention of a large number of studies has be given how the disturbances in the level of this protein affect malignant transformation. The expression of p27 protein in human tumor cells most frequently is diminished comparatively to their normal counterparts, and, in some instances, may have prognostic importance. This information could have clinial application. 

Key words: cyclin-dependent kinase inhibitors, the CIP/KIP protein family, p27, malignancy  

[Postepy Biologii Komorki 2000; 27: 481–504]

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Krzysztof BRYNIARSKI

Testicular macrophages

Summary: Testicular macrophages represent the population of non-inflammatory tissue macrophages. They are located in the testicular interstitial tissue, where they are able to proliferate, but physiologically they do not appear in the seminiferous tubules. Testicular macrophages and Sertoli cells are involved in the mechanism of blood-testis barrier, which makes testis an immunologically privileged organ. Testicular macrophages acting paracrinally, directly or indirectly, regulate the endocrinal activity of Leydig cells and spermatogenesis. Mutual relations between testicular macrophages, Leydig cells and Sertoli cells confirm their strong functional dependance as well as cooperation of immune and endocrine systems. Testicular cells relations, which take part in the formation of testis immune independance are still explored.

Key words: testicular macrophages (TMf), Sertoli cells, Leydig cells, monokines, blood-testis barrier, immune-privilege organs

 
[Postepy Biologii Komorki 2000; 27: 505–526]

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Dorota SULEJCZAK

Apoptosis and methods of identification of this phenomenon

Summary: Two alternative modes of cell death are distinguished in the recent literature. The first one is an accidental cell death, generally defined as necrosis and the second one is programmed cell death (PCD), called apoptosis. In some situations, for example in many pathologies, both types of cell death can occur simultaneously. It is very important to know which type of cell death is dominant in case of particular disease, because it determines effective therapy. Numerous methods have been employed to identify apoptotic and necrotic cells. The methods enable to detect endonucleolytic DNA degradation, changes in cell morphology and presence of particular proteins activated. The present study shows and discusses multiple methods that should be used for a proper characterisation of cell death.

Key words: apoptosis, necrosis, DNA fragmentation, TUNEL, ISNT, histochemistry

[Postepy Biologii Komorki 2000; 27: 527–568]

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Jacek Z. KUBIAK

Cell cycle � two conferences for 30th anniversary of studies

Summary: This article renders account of two international scientific conferences on the control of the cell cycle: 237 symposium of the Novartis Foundation. "The Cell Cycle & Development" which took place in London, Great Britain in April 2000 and Jacques Monod Conference "The Cell Division Cycle, in Honour of Yoshio Masui" which took place in Roscoff, France in May 2000.

Key words: -
 

[Postepy Biologii Komorki 2000; 27: 569–582]

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Piotr WIDŁAK

Mechanisms of DNA fragmentation and chromatin condensation in cells undergoing apoptosis

Summary: Sequential cleavage of genomic DNA into large-scale DNA fragments of 50-kb, followed by formation of mono- and oligonucleosomal DNA fragments, is a biochemical hallmark of apoptosis. Chromatin condensation is correlated with apoptotic DNA fragmentation. One of the nucleases primarily responsible for DNA cleavage is called DFF40/CAD. DFF40/CAD is activated by caspase-3 that cuts the nuclease inhibitor DFF45/ICAD. Other nucleases (e.g. NUC18, DNase g and DNase II) have been also postulated to be involved in apoptosis. Formation of large-scale DNA fragments is potentially mediated by DNA topoisomerase II.

Key words: apoptosis, nucleases, caspases, chromatin
 

[Postepy Biologii Komorki 2000; 27: 583–598]

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Jan ŻEROMSKI

Place and role of CD56/NCAM molecule in biology and medicine

Summary: The actual state of study on 140 kD isoform of neural cell adhesion molecule (CD56/NCAM) was presented. Its biosynthesis, structure and putative functions were shortly delineated. Complexity of CD56 structure is the result not only of posttranscriptional alterations of mRNA, but also posttranslational modifications due to binding of various chemical groups. Its distribution both in normal and pathological tissues was described, the latter predominantly within malignant tumors. In normal tissues apart from nervous system an important localization of CD56 appears to be on cells of endocrine glands. Among malignant tumors apart from neoplasms of neuroectodermal origin, CD56 is expressed on cells of several tumors of hemopoetic system, rhabdomyosarcomas but also on some carcinomas. The attention was paid to the possible value of the determination of CD56 in clinical medicine.

Key words: adhesion cells, CD56/NCAM, neural system, malignant tumors

[Postepy Biologii Komorki 2000; 27: 599�608]

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Szczepan JÓZEFOWSKI

Signal detection and transduction involved in plant disease resistance.

I. Recognition and early signal transduction pathways

Summary: Plants use diverse mechanisms to defend themselves from pathogens that include the generation of reactive oxygen species, cell wall modifications, localized cells death, production of phytoalexins and pathogenesis-related proteins (PR). Specific compounds released during host-pathogen interaction which are directly responsible for triggering of defense responses, are called elicitors. They may be either race-specific or shared by several different pathogens. In the case of race-specific recognition, plant disease resistance (R) genes confer an ability to resist infection by pathogens expressing specific corresponding avirulence (Avr) genes. Multiple, still poorly-defined, signaling pathways are set in motion by R gene products. In the first part of this review the current state of knowledge concerning recognition mechanisms and early signal transduction pathways in plant defense against infection is presented, and discussed in the context of signal transduction mechanisms functioning in other organisms.

Key words: defense responses, plants, signal transduction, respiratory burst, SAR, HR

[Postepy Biologii Komorki 2000; 27: 609�622]

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Szczepan JÓZEFOWSKI

Signal detection and transduction involved in plant disease resistance.

II. Defense gene activation

Summary: Both the localized, programmed host cell death, so-called hypersensitive response (HR), and the subsequent development of long-lasting, broad-spectrum resistance throughout the plant known as systemic acquired resistance (SAR) � the phenomena characteristic of plant defense response � depend on new gene expression. The second part of this review concerns signal transduction pathways that link specific receptors with defense gene activation. Among others, the structure and functions of disease resistance (R) gene products, which confer on plants an ability to resist infection by pathogens expressing specific corresponding avirulence (Avr) genes, are discussed.

Key words: defense responses, plants, signal transduction, MAP kinases, SAR, HR

[Postepy Biologii Komorki 2000; 27: 623�632]

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Anna JAKUBOWSKA, Stanisław KOWALCZYK

Abscisic acid � Perception and signal transduction

Summary: Abscisic acid (ABA) is involved in many developmental processes throughout the life cycle of plants, as well as in plant adaptation to environmental stresses. Guard cells are an excellent system for the studying of ABA perception and signal transduction. Studies of the stomatal responses to ABA have provided evidence for both the plasma membrane and in cytoplasm ABA perception sites. However, the receptor proteins have not been identified as yet. Lately, significant progress has been made in the identification of some elements of the ABA signaling pathway in guard cells. So far, Ca2+, cytosolic pH, 1,4,5-inositol triphosphate, cyclic ADP ribose and protein phosphorylation have been identified. Genetic studies on ABA-insensitive mutants in maize and Arabidopsis thaliana have also led to identification of several components involved in the signaling pathway responsible for regulating of seed development. A cis-acting ABA response element (ABRE) was identified as the promoter sequence motif conserved between several ABA-induced genes. The corresponding nuclear regulator proteins that specifically bind to the ABRE have been cloned. Most of them belong to the bZIP protein family of transcription factors.

Key words: abscisic acid (ABA), receptor, signal transduction, gene expression, guard cells

[Postepy Biologii Komorki 2000; 27: 633�656]

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