Alter Cell Behavior Research Articles

The influence of elastin-coated 520-nm- and 20-nm-diameter nanoparticles on human fibroblasts in vitro

Magnetic nanoparticles have been used for biomedical purposes for several years. In recent years, nanotechnology has developed to a stage that makes it possible to engineer particles to provide opportunities for the site-specific delivery of drugs. To this end, a variety of iron oxide particles have been synthesized. The size and surface of the particles are crucial factors in the application of the particles. Therefore, this study involves the use of two types of magnetic nanoparticles derivatized with elastin and synthesized with differing diameters, compared with identical underivatized plain particles. This influence in vitro was assessed using human dermal fibroblasts and various techniques to observe cell-particle interaction, including light and fluorescence microscopy and scanning electron microscopy. The results indicate that derivatized particles induce alterations in cell behavior and morphology distinct from the plain particles, suggesting that cell response can be directed via specifically engineered particle surfaces. However, little difference was observed between the different diameters.

Molecular and genetic toxicology of 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP)

The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), formed when meat containing food is cooked, induces cancer of the colon, prostate and mammary gland of rats, tumours that are strongly associated with a Western diet. After consumption of a meat meal, PhIP is rapidly absorbed, metabolised and bioactivated to DNA damaging species. Thus, PhIP should be considered as a candidate etiological agent for human cancer. Studies in vitro in model mammalian cell culture systems, and in vivo in transgenic animals, have shown that mutation induced by PhIP is dose dependent and describes a mutational “fingerprint” that is characteristic of the chemical. This genetic toxicity is dependent upon CYP1 family metabolic activation and is detectable in these model systems at μM concentrations. At early time points, PhIP treated cells show subtle signs of toxicity that lead to altered growth and cycling. Using co-culture systems where one cell line bioactivates PhIP with a second cell line as target, we showed in human lymphoblastoid target cells that PhIP induced a dose- and time-dependent S-phase delay of the cell cycle. With time, the cell population became increasingly apoptotic with remaining survivors carrying a mutated gene set. Transcript profiling of treated cells indicated differential expression of genes involved in cell cycle regulation, stress response, receptors and tumour related genes. Prominent was elevation of p21 cip1/waf1 transcript and Western blot analysis confirmed induction of p21 cip1/waf1 and p53 proteins. The dose dependency and temporal aspects of these changes indicate that manipulation of the cell cycle and growth in response to PhIP is a precursor to mutant selection. Reduction of the PhIP dose allows dissection of a different battery of cellular responses that favour cell growth rather than inhibition. This pro-growth stimulus is oestrogen-like and encompasses altered gene expression, proliferation and cell behaviour. In human breast cell lines, these PhIP-mediated pro-oestrogenic responses are inhibited by the anti-oestrogen ICI 182,780. This range of molecular and genetic responses induced in cells by PhIP is quite remarkable. Its ability to activate S-phase cell cycle checkpoint, alter gene expression leading to apoptosis and an increased frequency of mutation are probably direct consequences of its genetic toxicity. In contrast, its pro-oestrogenic activity is likely to be a driver of clonal expansion. We suggest that these PhIP-induced genomic and cellular events contrive to manipulate cell cycle and survival. Understanding these molecular processes as well as the genetic toxicology of the chemical will help to define the involvement of PhIP in carcinogenesis and shed light upon its tissue specificity.

Interfaces between the detection, signaling, and repair of DNA damage.

Left unrepaired, the myriad types of damage that can occur in genomic DNA pose a serious threat to the faithful transmission of the correct complement of genetic material. Defects in DNA damage signaling and repair result in genomic instability, a hallmark of cancer, and often cause lethality, underlining the importance of these processes in the cell and whole organism. The past decade has seen huge advances in our understanding of how the signal transduction pathways triggered by DNA damage radically alter cell behavior. In contrast, it is still unclear how primary DNA damage is detected and how this interfaces with signal transduction and DNA repair proteins.

Human fibronectin and MMP-2 collagen binding domains compete for collagen binding sites and modify cellular activation of MMP-2.

The region of fibronectin (FN) surrounding the two type II modules of FN binds type I collagen. However, little is known about interactions of this collagen binding domain with other collagen types or extracellular matrix molecules. Among several expressed recombinant (r) human FN fragments from the collagen binding region of FN, only rI6-I7, which included the two type II modules and both flanking type I modules, bound any of several tested collagens. The rI6-I7 interacted specifically with both native and denatured forms of types I and III collagen as well as denatured types II, IV, V and X collagen with apparent K(d) values of 0.2-3.7 x 10(-7) M. Reduction with DTT disrupted the binding to gelatin verifying the functional requirement for intact disulfide bonds. The FN fragments showed a weak, but not physiologically important, binding to heparin, and did not bind elastin or laminin. The broad, but selective range of ligand interactions by rI6-I7 mirrored our prior observations for the collagen binding domain (rCBD) from matrix metalloproteinase-2 (MMP-2) [J. Biol. Chem. 270 (1995) 11555]. Subsequent experiments showed competition between rI6-I7 and rCBD for binding to gelatin indicating that their binding sites on this extracellular matrix molecule are identical or closely positioned. Two collagen binding domain fragments supported cell attachment by a beta1-integrin-dependent mechanism although neither protein contains an Arg-Gly-Asp recognition sequence. Furthermore, activation of MMP-2 and MMP-9 was greatly reduced for HT1080 fibrosarcoma cells cultured on either of the fibronectin fragments compared to full-length FN. These observations imply that the biological activities of FN in the extracellular matrix may involve interactions with a broad range of collagen types, and that exposure to pathologically-generated FN fragments may substantially alter cell behavior and regulation.

Increased Tie2 Expression, Enhanced Response to Angiopoietin-1, and Dysregulated Angiopoietin-2 Expression in Hemangioma-Derived Endothelial Cells

Infantile hemangiomas are endothelial tumors that grow rapidly in the first year of life and regress slowly during early childhood. Although hemangiomas are well-known vascular lesions, little is known about the mechanisms that cause the excessive endothelial cell proliferation in these most common tumors of infancy. To investigate the molecular basis of hemangioma, we isolated endothelial cells from several proliferative-phase lesions and showed that these cells are clonal and exhibit abnormal properties in vitro (E. Boye, Y. Yu, G. Paranya, J. B. Mulliken, B. R. Olsen, J. Bischoff: Clonality and altered behavior of endothelial cells from hemangiomas. J Clin Invest 2001, 107:745-752). Here, we analyzed mRNA expression patterns of genes required for angiogenesis, including members of the vascular endothelial growth factor (VEGF)/VEGF receptor family and the angiopoietin/Tie family, in hemangioma-derived and normal endothelial cells. KDR, Flt-1, Tie1, Tie2, and angiopoietin-2 (Ang2) were strongly expressed in cultured hemangioma-derived endothelial cells and in hemangioma tissue. In contrast, there was little expression of angiopoietin-1 (Ang1) or VEGF. We found Tie2 mRNA and protein up-regulated with a concomitant increase in cellular responsiveness to Ang1 in most hemangioma-derived endothelial cells. Ang2 mRNA was down-regulated in response to serum in hemangioma-derived endothelial cells, but not in normal endothelial cells, suggesting altered regulation. These findings implicate Tie2 and its ligands Ang1 and Ang2 in the pathogenesis of hemangioma.

Activation of PKC-beta(I) in glomerular mesangial cells is associated with specific NF-kappaB subunit translocation.

Changes in expression and activity of protein kinase C (PKC) isoforms and early transcription factors may account for alterations in cell behavior seen in diabetes. We studied the expression of PKC-beta(I) in rat glomerular mesangial cells (MCs) cultured in normal or high glucose and compared it with the temporal and spatial expression of dimeric transcription factor (NF-kappaB) p50 and p65. The results show that in unstimulated cells PKC-beta(I) and NF-kappaB p50 are distributed in the cytosol and, on stimulation, their distribution is perinuclear and they are localized to the membrane. Serum-starved MCs cultured in high-glucose medium exhibit a predominantly cytosolic localization of PKC-beta(I) and both p50 and p65 NF-kappaB. However, phorbol 12-myristate 13-acetate (PMA) stimulation of cells grown in the presence of high glucose resulted in membrane translocation of PKC-beta(I) that was associated with nuclear translocation of NF-kappaB p65, but not NF-kappaB p50. Moreover, the translocation to the nucleus for NF-kappaB p65 was significantly higher in MCs exposed to high glucose compared with those exposed to normal glucose. These observations indicate that the NF-kappaB p65, but not NF-kappaB p50, expression and translocation pattern mirrors that of PKC-beta(I), which may be one important pathway by which signaling is enhanced in the high-glucose state.

Effects of protein kinase inhibitor, HA1077, on intraocular pressure and outflow facility in rabbit eyes.

To elucidate the roles of protein kinase in regulating the intraocular pressure (IOP) and outflow facility in rabbit eyes. A protein kinase inhibitor, 1-(5-isoquinolinesulfonyl)-homopiperazine (HA1077), was used. The IOP and the outflow facility were measured before and after topical, intracameral, or intravitreal administration of HA1077 in rabbits. Western blot analysis was performed to detect the 20-kd light chain of myosin in human trabecular meshwork (TM) cells and bovine ciliary muscle (CM) tissues. The cell morphologic condition and distribution of actin filaments and vinculin in TM cells were studied using cell biology techniques. Carbachol-induced contraction of isolated bovine CM strips following administration of HA1077 was examined in a perfusion chamber. In rabbit eyes, the administration of HA1077 resulted in a significant decrease in IOP in a dose-dependent manner. An increased outflow facility was also observed. Western blot analysis revealed the presence of 20-kd light chain of myosin in human TM cells and bovine CM tissues. In cultured human TM cells, exposure to HA1077 disrupted actin bundles and impaired focal adhesion formation. In addition HA1077 showed relaxation of bovine CM strips. Use of HA1077 caused a reduction in IOP and an increase in the outflow facility. The results of in vitro experiments suggest that the IOP-lowering effects of HA1077 may be related to the altered cellular behavior of TM cells and relaxation of CM contraction. The results of these studies suggested that protein kinase inhibitors have the potential to be developed into a treatment modality for glaucoma.

Proteases in invasion: matrix metalloproteinases

The role of proteases in general, and the matrix metalloproteinases in particular, in tumor invasion and metastasis is well established. However, the classic view that these enzymes simply provide a mechanism for the breakdown of connective tissue barriers has been challenged. This overview summarizes recent evidence to support the changing view of the role of matrix metalloproteinases in cancer progression. First we briefly review the central role of cell invasion in cancer progression and also the matrix metalloproteinase family members. We then focus on the emerging roles for these enzymes in cancer progression, including the role of matrix metalloproteinases in cell proliferation and release of growth factors, cell migration and in modification of the extracellular matrix to reveal cryptic sites that alter cell behaviour.

Clonality and altered behavior of endothelial cells from hemangiomas.

Hemangioma, the most common tumor of infancy, is a benign vascular neoplasm of unknown etiology. We show, for the first time to our knowledge, that endothelial cells from proliferating hemangioma are clonal, and we demonstrate that these hemangioma-derived cells differ from normal endothelial cells in their rates of proliferation and migration in vitro. Furthermore, migration of hemangioma endothelial cells is stimulated by the angiogenesis inhibitor endostatin, unlike the inhibition seen with normal endothelial cells. We conclude that hemangiomas constitute clonal expansions of endothelial cells. This is consistent with the possibility that these tumors are caused by somatic mutations in one or more genes regulating endothelial cell proliferation.

Three-dimensional structural analysis of fibronectin heparin-binding domain mutations.

Using recombinant fibronectin proteins containing the V region and two point mutations in the high-affinity heparin-binding domain, we previously showed that these domains modulate tumor cell invasion as well as proteinase expression and apoptosis in human fibroblasts. Structurally, the wildtype counterparts to these two point mutations, together with four other discontinuous, positively charged residues, form a cationic cradle in domain III-13 of fibronectin that binds heparin. We constructed a three-dimensional model of this cationic cradle and determined whether the two engineered point mutations in the heparin-binding domain would alter this cradle conformation, thus explaining the altered cell behavior. Our model of fibronectin domain III-13 was generated from a template of the three-dimensional structure of a homologous (25% identity) domain, III-3, from tenascin. The amino acid sequences of III-13 that differed from tenascin III-3 were replaced, and side chains for positively charged arginines 6 and 7 were substituted with uncharged threonines. The model revealed that the two mutated threonine residues were solvent accessible, readily accommodated as part of an antiparallel beta strand, and remained part of the three-dimensional cradle. These models suggest that the two point mutations in the heparin-binding domain of fibronectin III-13 alter cell function probably through changes in charge and not through changes in the conformational structure of the cationic cradle. J. Cell. Biochem. Suppl. 36: 156-161, 2001.

Memory of Past Exposure to the Chemokine IL-8 Inhibits the Contraction of Fibroblast-Populated Collagen Lattices

The inflammatory cytokine makeup of healing wounds helps delineate the phases of the repair process. As an example, during the lag phase (inflammatory phase) of repair, elevated levels of IL-8, a chemokine, participate in the activation and chemotaxis of neutrophils. During the normal proliferative and remodeling phases of repair, IL-8 levels are minimal. Healing burn wounds often have small, open, slow-to-heal areas, which have been shown to contain elevated levels of IL-8. Does a limited exposure of IL-8 to fibroblasts in vitro at the concentrations measured in these unhealed sites cause altered cell behavior? To study this possibility the fibroblast-populated collagen lattice (FPCL) model, an in vitro model of wound contraction, was used to investigate fibroblast response to IL-8. As previously reported, the chronic exposure of fibroblasts to IL-8 at 30 ng/ml within FPCLs significantly inhibited FPCL contraction. Fibroblasts in monolayer culture were incubated with IL-8 for 3 days. In the absence of IL-8, FPCLs were manufactured with these preexposed cells and it was found that FPCL contraction was inhibited. Fibroblasts retained their reduced capacity of reorganizing collagen fibrils when previously exposed to IL-8. Treating fibroblasts in monolayer with IL-8 for only 1 h prior to their incorporation into collagen lattices caused inhibition of FPCL contraction. The speculation is that in vivo open areas in reepithelialized healed burns are the consequence of the local population of fibroblasts having been exposed to elevated levels of IL-8. Such an earlier exposure triggers a memory in this population of fibroblasts that alters their capacity to lay down an extracellular matrix that optimizes the migration of epidermal cells.

Lysophosphatidylcholine-induced cellular injury in cultured fibroblasts involves oxidative events

Lysophosphatidylcholine (lysoPC), formed during LDL oxidation and located within atherosclerotic plaques, induces numerous cellular responses, but via unknown mechanisms. Cellular events involved in sublethal lysoPC-induced injury were examined because these are relevant to mechanisms by which lysoPC alters cell behavior. LysoPC evoked transient membrane permeabilization in fibroblasts within 10 min. Cells underwent reversible rounding within 2 h, returning 3 h later to grossly normal appearance and a normal response to growth stimulation. We asked whether this sublethal permeabilization resulted from physical perturbation of the plasma membrane or if it required cellular events. LysoPC induced leakage of fluorescent dye from unilamellar phospholipid vesicles, suggesting physical membrane perturbation was a significant contributor. To characterize this further we increased the cholesterol content of cells and vesicles to stabilize membranes, and found decreased lysoPC-induced permeabilization in both cell and cell-free systems as cholesterol levels increased. Interestingly, vitamin E, a known antioxidant, blunted lysoPC-induced permeabilization and morphological changes in cells. Thus, lysoPC appeared to cause an unexpected oxidant stress-dependent enhancement of cell injury. To confirm this, several structurally distinct antioxidants, including N, N'-diphenyl-1,4-phenylenediamine, Desferal, Tiron, and 4-hydroxy TEMPO, were applied and these also were inhibitory. Oxidant stress was observed by a lysoPC-induced increase in fluorescence of 5- and 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, an intracellular marker of reactive oxygen species. Lysophosphatidylethanolamine (lysoPE) caused qualitatively similar morphological changes to cells and induced permeabilization, but injury by lysoPE was not inhibited by antioxidants. These data suggest that generation of intracellular reactive oxygen species follows lysoPC-induced plasma membrane destabilization and that this lysoPC-specific oxidant stress enhances cell injury. This intracellular oxidant stress in response to lysoPC may be an integral part of the multiple influences lysoPC has on gene expression and cell function.

GENITOURINARY RHABDOMYOSARCOMA: Treatment Options

Dramatic improvements have occurred in the treatment and prognosis of the child with rhabdomyosarcoma over the past 2 decades. Increased understanding of tumor behavior has improved survival and focused attention on important quality of life issues. Future therapeutic advances will depend largely on an improved molecular understanding of altered cell behavior and the continued efforts of multi-institutional studies.

Distribution of spontaneous currents along the somato-dendritic axis of rat hippocampal CA1 pyramidal neurons

Excitatory and inhibitory pathways have specific patterns of innervation along the somato-dendritic axis of neurons. We have investigated whether this morphological diversity was associated with variations in the frequencies of spontaneous and miniature GABAergic and glutamatergic synaptic currents along the somato-dendritic axis of rat hippocampal CA1 pyramidal neurons. Using in vitro whole cell recordings from somata, apical dendrites and basal dendrites (for which we provide the first recordings) of CA1 pyramidal neurons, we report that over 90% of the spontaneous currents were GABAergic, <10% being glutamatergic. The frequency of spontaneous GABAergic currents was comparable in the soma and in the dendrites. In both somata and dendrites, the Na + channel blocker tetrodotoxin abolished more than 80% of the spontaneous glutamatergic currents. In contrast, tetrodotoxin abolished most dendritic (>90%) but not somatic (<40%) spontaneous GABAergic currents. Computer simulations suggest that in our experimental conditions, events below 40 pA are electrotonically filtered to such a degree that they are lost in the recording noise. We conclude that, in vitro, inhibition is massively predominant over excitation and quantitatively evenly distributed throughout the cell. However, inhibition appears to be mainly activity-dependent in the dendrites whereas it can occur in the absence of interneuron firing in the soma. These results can be used as a benchmark to compare values obtained in pathological tissue, such as epilepsies, where changes in the balance between excitation and inhibition would dramatically alter cell behaviour.

High glucose induces the activity and expression of Na(+)/H(+) exchange in glomerular mesangial cells.

Changes in activity or expression of transporters may account for alterations in cell behavior in diabetes. We sought to ascertain if mesangial cells (MC) grown in different glucose concentrations exhibit changes in activity and expression of acid-extruding transporters, the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger. pH(i) was determined by the use of the fluorescent pH-sensitive dye BCECF. In MCs grown in 5 mM glucose (control), the Na(+)/H(+) exchanger was responsible for 31.8 +/- 5.1% of steady-state pH(i), whereas Na(+)-dependent Cl(-)/HCO(-)(3) contributed 62.9 +/- 4.0% (n = 11). In MCs grown in high glucose for 2 wk, Na(+)/H(+) exchange contribution to acid-extrusion increased as follows: 42.3 +/- 4.6% [n = 8, 10 mM, not significant (NS)], 51.1 +/- 5.1% (n = 8, 20 mM, P < 0.01), and 64.8 +/- 5.5% (n = 7, 30 mM, P < 0.001). The Na(+)-dependent Cl(-)/HCO(-)(3) exchanger contributed less [47.0 +/- 4.6, 38.6 +/- 5.8, and 21.1 +/- 3.8%, for 10, 20, and 30 mM glucose, respectively (n > 7)]. We sought to ascertain if the magnitude of the acute stimulated response to ANG II by the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger is changed. Na(+)/H(+) exchanger (1.89-fold increase in 30 vs. 5 mM, P < 0.002), but not Na(+)-dependent Cl(-)/HCO(-)(3) exchange (0. 17-fold, NS), exhibited an enhanced response to ANG II (1 microM). Na(+)/H(+) exchange (NHE1) expression was significantly different (1. 72-fold) after prolonged exposure to high glucose. These results suggest that the Na(+)/H(+) exchanger, but not Na(+)-dependent Cl(-)/HCO(-)(3) exchanger, may play an early role in the response to hyperglycemia in the diabetic state.

Lectins: Sources, Activities, and Applications

ABSTRACT: Lectins are glycoproteins or oligomeric proteins with one or more sugar-binding site(s) per subunit. These molecules are of nonimmune origin and bind reversibly with specific sugars and precipitate polysaccharides, glycoproteins, and glycolipids bearing specific sugars, thus acting as cell recognizers. They play a key role during the initiation of infections in the altered behavior of cells during metastasis and in protection of neonates against environmental antigens. The specificity of lectins for certain sugars has been used as probes to detect cell surface sugars, enzymes, immunoglo-bulins, and to identify tumorogenic cells. Lectin-liposome conjugates have also found applications for targeted drug delivery. In addition, they have been used for flocculation of bacterial suspensions in the industry. This review discusses various sources of lectins and the mechanism behind their potential role in diverse fields of biological interest.

Preeclampsia: The Endothelium, Circulating Factor(s) and Vascular Endothelial Growth Factor

It has been proposed that endothelial cell activation is the primary event in the multisystem disorder of preeclampsia. Evidence for endothelial involvement in this condition abounds. The best-characterized morphologic abnormality of this syndrome, glomerular endotheliosis, involves endothelial cells. Also associated with preeclampsia is a loss of endothelial cell integrity, with the consequent increase in vascular permeability, and an increase in the circulating levels of the endothelial cell markers, fibronectin, von Willebrand factor, tissue plasminogen activator, and plasminogen activator inhibitor-1. It is now well documented that endothelial activation contributes to the coagulation abnormalities observed in this disease. There is much evidence that the endothelial alterations in preeclampsia result from one or more circulating factors. The incubation of cultured endothelial cells with serum or plasma samples, taken from normal pregnant women and women with preeclampsia, results in marked alterations in cell behavior and metabolic processes. More recently, experiments employing myographic techniques have demonstrated convincingly the effects of a circulating factor(s) on the function of endothelial cells of resistance arteries. Vascular endothelial growth factor (VEGF) possesses many of the characteristics required of a candidate circulating factor. It contains a hydrophobic secretory signal sequence, exerts in vitro effects specific to vascular endothelial cell, and promotes endothelial expression of procoagulant activity. Circulating VEGF concentrations are elevated in women with preeclampsia, and VEGF increases microvascular endothelial cell prostacyclin production in a dose-dependent manner, analogous to the acute effects of plasma from patients with preeclampsia. Similarly, in myographic studies, when myometrial resistance arteries are incubated with VEGF, there are dose-dependent alterations in endothelium-dependent behavior, mirroring those found after incubation with plasma from patients with preeclampsia.

Development of pH regulatory transport in glomerular mesangial cells.

Developmental changes in activity or expression of transporters may account for alterations in cell behavior as the nonpolarized cell matures. We sought to ascertain whether there is a maturational change in each of the major acid-base transporters in the developing mesangial cell (MC), the Na/H exchanger, Na-dependent Cl/HCO3 exchanger, and the Cl/HCO3 exchanger. Intracellular pH (pHi) was determined by the use of the fluorescent pH-sensitive dye, 2',7'-bis(2- carboxyethyl)-5(6)-carboxyfluorescein (BCECF). We assessed transporter activity by studying recovery from an acid load (NH4/NH3) in CO2/HCO3. In adult MCs, Na/H exchanger was responsible for 35.2 +/- 4.3% of steady-state pHi, whereas the Na-dependent Cl/HCO3 exchanger contributed 58.7 +/- 6.1 (n = 14). In term MCs (tMCs), from days 1-3 after birth, the Na/H exchanger contributes 62.9 +/- 7.8% (n = 11, P < 0.001 vs. adult), whereas the Na-dependent Cl/HCO3 exchanger contributes 34.0 +/- 5.7% (n = 12, P < 0.001 vs. adult), to the rate of recovery from an acid load in these cells. However, in tMCs (days 4-6), the Na/H contributes 47.2 +/- 5.9% (n = 8, P < 0.05 vs. adult), whereas the Na-dependent Cl/HCO3 exchanger contributes 48.7 +/- 7.3% (n = 13, P < 0.05 vs. adult), to the rate of recovery. tMCs (days 6-12) yielded transporter activity that was not statistically different than adult MCs (37.8 +/- 4.9 and 54.3 +/- 10.2% for Na/H and Na-dependent Cl/HCO3, respectively). The magnitude of the stimulated response to angiotensin II by Na/H and Na-dependent Cl/HCO3 exchanger in adult and tMCs is unchanged throughout development. The Na/H exchanger appears to play a greater role in pHi homeostasis earlier on in development, and this may reflect developmental needs of the maturing cell.

Role of nonrandomly oriented cell division in shaping and bending of the neural plate

Neural plate shaping and bending are crucial to the process of neural tube formation. Shaping requires intrinsic forces generated by alterations in neuroepithelial cell behavior, whereas bending requires similar intrinsic forces and extrinsic forces generated by alterations in cell behaviors outside the neural plate. This study evaluates the role of nonrandomly oriented cell division in neural plate shaping and epidermal ectoderm expansion during bending by examining mitotic spindle orientation in the neuroepithelium and epidermal ectoderm throughout neurulation. Neuroepithelial mitotic spindles are oriented preferentially in the rostrocaudal plane, suggesting a role for nonrandomly oriented (i.e., rostrocaudal) neuroepithelial cell division in longitudinal lengthening of the neural plate during shaping. Epidermal ectoderm mitotic spindles are oriented preferentially in both rostrocaudal and mediolateral planes, suggesting a role for nonrandomly oriented cell division in epidermal ectoderm elongation and expansion. In neural plate and epidermal ectoderm isolates separated prior to shaping and bending, mitotic spindles continued to be oriented preferentially in the rostrocaudal plane; however, a preferential mediolateral mitotic spindle orientation could not be demonstrated in the epidermal ectoderm isolates. We conclude that the nonrandom rostrocaudal orientation of cell division in the neuroepithelium and epidermal ectoderm is an autonomous process, occurring in the absence of forces from adjacent tissues, whereas the nonrandom mediolateral orientation of cell division in the epidermal ectoderm is dependent upon interactions with the neural plate.

Adhesion molecules in the glomerular mesangium

Experimental evidence indicates that extensive "cross-talk" exists between glomerular cells, extracellular matrix molecules and soluble mediator substances affecting the proliferative and secretory phenotype of glomerular mesangial cells. Both matrix and cytokines regulate mesangial cell behavior in vitro and in vivo after binding to specific cell surface receptors. It appears as if the concerted action of insoluble and soluble ligands on mesangial cells involves a reciprocal regulation of matrix molecules and cytokines as well as expression and affinity of their respective receptors. Elucidation of the potential biologic and clinical relevance of cell-matrix interactions in the glomerular mesangium represents a challenging goal in current kidney research. This brief review summarizes recent investigations concerning regulation of expression and function of adhesion molecules and matrix receptors in the mesangium. In addition to results from cell culture studies, descriptive findings on expression and regulation of adhesion molecules and their potential role for altered mesangial cell behavior in glomerular disease is considered.