Diverse forms of clathrin coated vesicles in receptor mediated transport and segregation of macromolecules

Summary: In mammalian cells the clathrin coated vesicles participate in receptor mediated internalization, transport and sorting of macromolecules from the trans Golgi network to the endocytic pathway as well as from the plasma membrane to endosomes and lysosomes. The complex protein machinery controlling vesicle budding, transport and fusion are significantly conserved between the endocytic and sorting pathways. The internalization and intracellular transport are based respectively on tyrosine (YXXĆ) and dileucine (LL) signals. The overall processes include: interaction between the ligand and the membrane receptor, association of the ligand-receptor complex with appropriate adaptor protein (AP-1, AP-2, AP-3, AP-4), coating with clathrin or clathrin-like proteins, budding of the vesicle, sorting and interaction with the target membrane. Advances in understanding the molecular mechanisms of the receptor mediated endocytosis and sorting processes, especially those connected with AP-1 i AP-2 adaptor complexes are described in this paper.

Key words: endocytosis, transcytosis, clathrin, adaptor proteins

What is a plant cell? Position of plant cell walls

Summary: Plant cell walls are integral components of living cells, undergoing dynamic changes in response to internal as well as external stimuli. The revival of studies on plant walls has led to the situation where re-definition of a concept of „plant cell� is necessary. In this paper the current knowledge on plant walls is presented and differentiated understanding of the position of cell walls in plant cells is revealed. Starting from the analysis of basic tenets and corollaries of cell and organismal theories describing organisation of biological systems, an organismal model for interpretation of plant cell concept is proposed. On that basis an integral presence of cell walls in the architecture of plants and plant cells is indicated.

Key words: cellular theory; cell walls; exocellular matrix (ECM); extracellular matrix (ECM); organismal theory; plant cell (definition); protoplast   

Do animals with targeted genomic modification provide reliable research model. Lessons from neurobiology

Summary: This article is focused on problems related to application of mice knock-outs used in neurobiology. Diverse genetical background, genotype of mouse strain 129 (the main source of embryonic stem cells), developmental defects, pleiotropy and compensation make the interpretation of results from knock-out models difficult. The use of time- and space-specific "knock-outs of second generation", introduction of transgenes that reverse the effect of gene knock-outs, blocking of genes by antisense mRNA or point mutations may aid in eliminating some of these problems.

Key words: knock-out mice

The role of mast cells in angioneogenesis

Summary: The function of mast cells in angioneogenesis is not completely known. Their role in the processes of the stimulation, inhibition and regulation of the angiogenesis is connected with mediators of angiogenesis produced by mast cells, e.g. heparin, histamin, bFGF, VEGF, chymase, tryptase and hydrolases. The enzymatical actions of mast cells on extracellular matrix, mostly by proteases, change its structure and facilitate creation of three-dimensional vascular system. In this paper the literature data was discussed, proving direct and indirect role of mastocytes in neovascularization processes in malignant tumor. The interactions of the cells of extracellular matrix, mostly endothelial cells, mastocytes and fibroblasts, and role of mastocytes in metabolic regulation of angioneogenesis were described. The methods of studies on mast cells and angiogenesis were presented.

Key words: mast cell, angioneogenesis, extracellular matrix

Uniparental disomy (UPD) in man. The origin and clinical consequences

Summary: Summary. Uniparental disomy (UPD) is the presence, in a diploid individual, of a chromosome pair that derives from only one parent. In general the mechanism of formation of UPD is based on the correction of aneuplody derived from meiotic or mitotic errors. UPD almost all chromosmes have been documented but preponderance of maternal versus paternal disomy (3:1) have been observed. This difference can be explained with the frequency of aneuploidy in the female gametogenesis. After over 20 years of studies since the concept of UPD was introduced unusual and unexplained observations on the clinical expression some of genetic disorders are now clear. The phenotype in such disorders is determined by genomic imprinting disturbances and nonmendelian inheritance of monogenic recesive traits due to the loss of heterosigosity in UPD cases. Undetected mosaicism may also reflect an abnormal phenotype. The mechanisms of UPD formation, present knowledge on the frequency, risk factors and clinical consequences of uniparental disomy are presented.

Key words: uniparental disomy, aneuploidy, risk factors, clinical consequences
 

Non-proteinaceous inhibitors of the cyclin-dependent kinases

Summary: The cell cycle is regulated by the activity of cyclin dependent kinases (CDKs) associated with cyclins. Their activity is opposed by various CDK inhibitory proteins. Disregulation of the cell cycle occurs in various pathological conditions - the most important of them being cancer. Therefore, there is a continuous effort to search for chemical CDK inhibitors, which may be used as antiproliferative drugs. Various compounds have been already isolated and synthesized (e.g. olomoucin, roscovitine, flavopiridol and indirrubin). All known CDK inhibitors compete with ATP in the binding with CDKs. Chemical CDK inhibitors show antitumor activity in various in vitro assays and on experimental animals. Flavopiridol is already being tested in phase II clinical trials.

Key words: cell cycle, CDK inhibitors, cancer, cell proliferation
 

Gibberellins � signal perception and transduction

Summary: Isolated aleurone cells and protoplasts of cereal grains are particularly useful model system for studying of gibberellin signaling. Up to now, the identity of the receptor protein is unknown, but its activity in cereal aleurone has been localized to the plasma membrane. The gibberellin-signaling pathways identified in aleurone cells involve heterotrimeric G proteins, 1,4,5-inositol triphosphate, Ca2+, calmodulin, cGMP, cytosolic pH, protein phosphorylation, and transcription factors. The promoters of gibberellin-inducible a-amylase genes have been sequenced and motifs essential for hormone-stimulated transcription have been determined. Barley transcription regulators (Myb, HRT, ABF) that are important trans acting elements of gibberellin-inducible a-amylase genes were identified. In Arabidopsis thaliana four gibberellin-signaling mutants (gai, grs/rga, spy, shi) have been selected. The GAI, GRS/RGA and SHI proteins function as negative regulators of gibberellin-induced growth responses. Supposedly, the product of SPY gene is O-GlcNAc transferase that modifies proteins by glycosylation.

Key words: llin, gibberellin binding proteins, gibberellin signal transduction pathway, gibberellin mutants of Arabidopsis thaliana

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Hanna FABCZAK, Stanisław FABCZAK

Mechanism of photophobic response in ciliate Stentor coeruleus and related Blepharisma japonicum

Summary: Stentor and Blepharisma possess photoreceptor systems that render the cells capable of avoiding light. The observed photobehaviour is largely the result of a step-up photophobic response displayed by both ciliates. The photophobic response caused by a sudden increase in light intensity starts with a cessation of ciliary beating, then a period of ciliary reversal followed by renewed forward movement. Ciliary reversal correlates with the generation of an action potential, which is elicited by a photoreceptor potential as a result of light absorption by cellular pigments. The photochemical processes within the pigments lead in the case of Stentor, to internal cyclic GMP level changes that possibly result in changes of ionic conductance of cation channels gated by this cyclic nucleotide. In related Blepharisma cells, however, InsP3 seems to be responsible for the alterations in membrane potentials and induction of light avoiding response. This supposition is proved by a measured increase in the InsP3 levels in cells exposed to light and an identification of InsP3 receptor-like protein exclusively localized within the Blepharisma cell cortex.

Key words: photoreceptor system, G-protein, cGMP, InsP3, cGMP-dependent ion channels, electrical membrane potentials, photophobic response, ciliates, Blepharisma japonicum, Stentor coeruleus, phototransduction

[Postepy Biologii Komorki 2000; 27: 425�440]