Biomedical subjects

B Lom

Publications and source records attributed to B Lom.

6 recordsLinked to original sources

PubMed1999

Brain-derived neurotrophic factor differentially regulates retinal ganglion cell dendritic and axonal arborization in vivo.

Expression of the neurotrophin brain-derived neurotrophic factor (BDNF) and its receptor trkB in the ganglion cell layer of the Xenopus retina during retinal ganglion cell (RGC) dendritic arborization indicates that BDNF is spatially and temporally available to influence RGC morphological differentiation (; ). BDNF promotes RGC axon arborization in vivo by acting as a target-derived trophic factor (). To determine whether BDNF also acts locally to regulate RGC dendritic development in vivo, we altered retinal neurotrophin levels at the onset of dendritic arborization and assessed the resulting arbor morphologies of RGCs retrogradely labeled with fluorescent dextrans. Injecting neurotrophins or BDNF function-blocking antibodies coupled to microspheres provided local alterations of retinal neurotrophin levels. BDNF significantly decreased RGC dendritic arbor complexity, whereas neutralizing endogenous BDNF levels with function-blocking antibodies significantly increased dendritic arbor complexity. RGCs exposed to other neurotrophins, as well as RGCs in retinae treated with BDNF but in areas not directly exposed to the neurotrophin, developed dendritic arbors that were indistinguishable from controls, indicating that exogenous BDNF acts specifically and locally. In the tectum, where RGC axons arborize, BDNF had opposite effects. BDNF significantly increased RGC axon arbor complexity and anti-BDNF reduced RGC arborization. Thus, BDNF reduces RGC dendritic arborization within the retina and increases axon arborization in the tectum. These results indicate that BDNF can differentially modulate axonal and dendritic arborization within a single neuronal population in opposing manners and raise the possibility that differential modulation by a neurotrophic factor finely tunes the morphological differentiation program of a neuron.

Animals↗

PubMed1998

Fibroblast growth factor receptor signaling in Xenopus retinal axon extension.

Fibroblast growth factor receptors (FGFRs) and N-cadherin both regulate axon extension in developing Xenopus retinal ganglion cells (RGCs). Cultured cerebellar neurons have been shown to require FGFR activity for N-cadherin-stimulated neurite outgrowth, raising the possibility that N-cadherin is a FGFR ligand. To investigate this possibility in the developing visual system, retinal neurons were transfected with a dominant-negative FGFR (XFD) and plated on purified N-cadherin substrates. XFD-expressing neurons extended markedly shorter processes than control GFP-expressing neurons, implicating a role for FGFRs in N-cadherin-stimulated neurite outgrowth. To examine whether N-cadherin and FGFRs share the same pathway or use distinct second messenger pathways, specific inhibitors of implicated signaling molecules were added to neurons stimulated by N-cadherin, basic fibroblast growth factor (bFGF), or brain-derived nerve factor (BDNF) (which stimulates RGC outgrowth by a FGFR-independent mechanism). Diacylglycerol (DAG) lipase and Ca2+/calmodulin kinase II inhibitors both significantly reduced outgrowth stimulated by N-cadherin or bFGF but not by BDNF. Furthermore, we show that inhibiting DAG lipase activity in RGC axons extending in vivo toward the optic tectum reversibly slows axon extension without collapsing their growth cones. Thus, a common second-messenger signaling pathway mediating both N-cadherin- and bFGF-stimulated neurite extension is consistent with a model in which N-cadherin directly modulates the FGFR or a model whereby both FGFR and N-cadherin regulate the same second-messenger system.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1997

Is laminin-1 a guidance cue for cerebellar granule cell migration?

Laminin-1 is a glycoprotein found in the basement membrane of many tissues. In the cerebellum of rodents, it has also been localized along Bergmann glial fibers, where it is thought to be involved in promoting granule cell migration by enhancing adhesion and neurite outgrowth along these fibers. Recent reports, however, indicate that laminin-1 is not present on Bergmann fibers, but instead is associated with blood vessels and meninges. Furthermore, attempts to block granule cell migration using antibodies against laminin-1 have yielded conflicting results. In this report, we provide further evidence that laminin-1 is associated exclusively with blood vessels and meninges in the cerebellum of postnatal rats. In addition, we show that adhesion and neurite outgrowth of granule cells was impeded on laminin-coated surfaces. In fact, cerebellar cells dramatically and consistently avoided laminin-1 regions of patterned surfaces. Cells did adhere to laminin regions if it was coadsorbed with polylysine or tested in serum-containing medium. Avoidance of laminin-1 regions in culture was not, however, blocked by pretreatment with laminin-1 antibodies. By comparison, mouse neuroblastoma cells adhered preferentially to laminin-1 regions in serum-free medium, a response which was blocked by laminin-1 antibodies. These results indicate that laminin-1 is not involved in granule cell migration along Bergmann glial fibers. Instead, they suggest that laminin-1 may function as a repulsive guidance cue preventing granule cells from following inappropriate pathways during development.

Aging↗

PubMed1996

Kinetics of bone cell organization and mineralization on materials with patterned surface chemistry.

Materials with spatially resolved chemistries (i.e. patterned surfaces) have been used to guide and organize the position of mammalian cells in vitro. A common theme in guiding the spatial distribution of cells has been the use of patterned alkylsiloxanes, where one region contains an aminosilane and the other an alkylsilane. The regions of the aminosilane served as preferential sites for cell attachment and spreading, presumably dependent on the association between cell surface proteoglycans the positively charged amine. In this study, experiments were conducted with patterns of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS) and dimethyldichlorosilane (DMS) to determine the kinetics of spatial organization of bone-derived cells, and whether initial attachment and spreading affected the rate of matrix mineralization (i.e. bone formation) in extended cultures. The bone cells required the presence of serum or preadsorption of serum proteins to the patterned EDS/DMS surface to organize according to the lithographically defined surface chemistry. Time-lapse video microscopy indicated that cells were randomly distributed over the EDS/DMS surface at the time of plating, but organized on the EDS regions within 30 min. When cultures were extended for 15 and 25 days, the matrix synthesized by the cells was preferentially mineralized on the EDS chemistry. These results demonstrate the ability of surface chemistry modifications to organize cells and form mineralized tissue in vitro. The methods employed should have general value to the engineering of tissues in vitro.

Animals↗

PubMed1993

Pathfinding by neuroblastoma cells in culture is directed by preferential adhesion to positively charged surfaces.

Pathfinding is a fundamental behavior of migrating neuroblasts and advancing growth cones. We have analyzed this behavior in culture using mouse neuroblastoma (N1E-115) cells grown on a chemically patterned surface. The patterned surface was defined photolithographically and consisted of intersection 10-micron-wide pathways. The pathways were coated with positively charged amines and separated by regions bound with uncharged alkanes. Cells and growth cones were guided along the pathways and made choices at intersections. Whereas migrating cells made random choices at intersections, growth cones displayed a preference for advancing straight ahead. Interference reflection microscopy (IRM) revealed that pathfinding by cells and growth cones was correlated with greater overall attachment to aminated regions, although cell bodies and appendages also attached to adjacent alkanated regions. Thus guidance was not simply due to contact inhibition by alkanes; rather, it was due to "preferential" adhesion to aminated surfaces. Gray level analysis of IRM images demonstrated that focal and close contacts were made on both surfaces, indicating that preferential adhesion was not the result of tighter attachment to aminated surfaces. Fluorescent labeling of F-actin and microtubules indicated that preferential adhesion was not due to compartmentalization of these cytoskeletal structures on aminated regions. We propose that preferential adhesion involved a signal transduction mechanism that discriminated between positively charged and uncharged molecules. Such a mechanism could contribute to pathfinding by neuroblasts and growth cones along extracellular matrix proteins in vivo.

Acid-Base Equilibrium↗

PubMed1993

A versatile technique for patterning biomolecules onto glass coverslips.

A fast, inexpensive, and versatile technique for patterning the surface of glass coverslips with molecules of biological interest is described. The technique combines photolithographic, silane-coupling, and protein adsorption procedures to pattern coverslips with amines, alkanes, and proteins with micrometer spatial resolution. The attachment of amines and alkanes was verified using contact angle and X-ray photoelectron spectroscopic (XPS) measurements. XPS results showed that amines and alkanes were attached in 1-4 nm thickness covering approximately 20% and 45%, respectively, of the surface. Patterns of amines were visualized using fluorescent staining, and patterns of proteins were detected immunochemically. Patterned coverslips were used to investigate adhesion and neurite outgrowth of mouse neuroblastoma (N1E-115) cells. Cells were examined on the following patterns: alkane-glass, protein-glass, amine-alkane, and amine-protein. Cell attachment and neurite outgrowth on patterned coverslips displayed the following preferences: laminin, fibronectin, or collagen IV > amine or glass > alkane or bovine serum albumin. This patterning method should be useful for studies of cell-surface interactions, cell migration, nerve regeneration, and the formation of neural networks in vitro.

Alkanes↗