Tissue- and development-specific distributions of cytoskeletal elements in growing cells of the maize root apex

ABSTRACT

Indirect immunofluorescence performed using sections of actively growing maize root apices fixed and then embedded in low-melting-point Steedman's wax has proved efficient in revealing the arrangements and reorganizations of motility-related cytoskeletal elements which are associated with root cell development and tissue differentiation. This powerful, yet relatively simple, technique shows that specific rearrangements of both microtubular (MT) and actin microfilament (MF) arrays occur in cells as they leave the meristem and traverse the transitional region interpolated between meristem and elongation region. Cytoskeletal and growth analyses have identified the transition zone as critical for both cell and root development; it is in this zone that cell growth is channelled, by the cytoskeleton, into a strictly polarized mode which enables root tips to extend rapidly through the soil in search of water and nutrients. An integrated cytoskeletal network is crucial for both the cytomorphogenesis of individual cells and the overall morphogenesis of the plant body. The latter process can be viewed as a reflection of the tight control which cytoskeletal networks exert not only over cell division planes in the cells within meristematic apices but also over the orientation of cell growth in the meristem and elsewhere. Endoplasmic MTs interconnecting the plasma membrane with the nucleus are suggested to be involved in cell division control; they may also act as a two-way cytoskeletal communication channel for signals passing to and fro between the extracellular environment and the genome. Moreover, the dynamism of endoplasmic MTs exerts direct effects on chromatin structure and the accompanying nuclear architecture and hence can help exert a cellular level of control over cell growth and cell cycle progression. Because the inherent dynamic instability of MTs depends on the concentration of tubulin dimers within the cytoplasm, we propose that when asymmetric cell division occurs, it will result in two daughter cells which differ in the turnover rates of their MTs. This phenomenon could be responsible for different cell fates of daughter plant cells produced by such cell divisions.     

Activation of complement by tetrathyridia of Mesocestoides corti: enhancement by antibodies from infected mice and lack of effect on parasite viability

Tetrathyridia of the cestode Mesocestoides corti were isolated from the peritoneal cavity of infected mice. The parasites activated guinea pig and mouse complement (C) in vitro by both the classical and alternative pathways as shown by quantitative C fixation and crossed immunoelectrophoresis. The ability of tetrathyridia to activate mouse C was enhanced by preincubating the parasites in serum obtained from mice infected with M. corti. Antibodies of the IgG1 class, an immunoglobulin found in profoundly increased amounts in mice infected with M. corti, as well as IgM and IgG2 antibodies, bound to cultured tetrathyridia and facilitated deposition of the third component of C (C3) from dilute mouse serum, presumably via classical pathway activation. The results demonstrate that mouse IgG1 antibodies do not prevent the activation of C by the tetrathyridia or by C-fixing antibodies of other classes which become attached to the tetrathyridia. The activation of C in vitro by tetrathyridia did not affect their ability to grow in mice, even though C3-derived polypeptides could be detected by immunofluorescence on the surface of the parasites.     

Glycogen Metabolism in Chlamydia-Infected HeLa-Cells

A difference in glycogen metabolism between two strains of Chlamydia agents was observed which can serve as a taxonomic marker to distinguish C. psittaci from C. trachomatis.     

Endocannabinoids and the renal proximal tubule: An emerging role in diabetic nephropathy

Diabetic nephropathy is a leading cause for the development of end-stage renal disease. In diabetes mellitus, a number of structural changes occur within the kidney which leads to a decline in renal function. Damage to the renal proximal tubule cells (PTCs) in diabetic nephropathy includes thickening of the basement membrane, tubular fibrosis, tubular lesions and hypertrophy. A clearer understanding of the molecular mechanisms involved in the development of diabetic kidney disease is essential for the understanding of the role cellular pathways play in its pathophysiology. The endocannabinoid system is an endogenous lipid signalling system which is involved in lipogenesis, adipogenesis, inflammation and glucose metabolism. Recent studies have demonstrated that in diabetic nephropathy, there is altered expression of the endocannabinoid system. Future investigations should clarify the role of the endocannabinoid system in the development of diabetic nephropathy and within this system, identify potential therapeutics to reduce the burden of this disease.