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Biomedical subjects

D C Lo

Publications and source records attributed to D C Lo.

30 records · Page 2Linked to original sources
PubMed1995

Neurotrophins regulate dendritic growth in developing visual cortex.

Although dendritic growth and differentiation are critical for the proper development and function of neocortex, the molecular signals that regulate these processes are largely unknown. The potential role of neurotrophins was tested by treating slices of developing visual cortex with NGF, BDNF, NT-3, or NT-4 and by subsequently visualizing the dendrites of pyramidal neurons using particle-mediated gene transfer. Specific neurotrophins increased the length and complexity of dendrites of defined cell populations. Basal dendrites of neurons in each cortical layer responded most strongly to a single neurotrophin: neurons in layer 4 to BDNF and neurons in layers 5 and 6 to NT-4. In contrast, apical dendrites responded to a range of neurotrophins. On both apical and basal dendrites, the effects of the TrkB receptor ligands, BDNF and NT-4, were distinct. The spectrum of neurotrophic actions and the laminar specificity of these actions implicate endogenous neurotrophins as regulatory signals in the development of specific dendritic patterns in mammalian neocortex.

Animals↗
PubMed1995

Regulation of voltage-gated ion channels by NGF and ciliary neurotrophic factor in SK-N-SH neuroblastoma cells.

Neurotrophic factors have powerful effects on neuronal differentiation and the maintenance of neuronal phenotype, but understanding of their regulation of one important aspect of neuronal function, excitability, remains limited. We have examined the regulation of voltage-gated ion channels by two unrelated neurotrophic factors, NGF and ciliary neurotrophic factor (CNTF), in the SK-N-SH neuroblastoma cell line that is responsive to both factors. NGF and CNTF have strikingly different neuronal specificities and distributions in the nervous system, and might be expected to have significantly different effects on neuronal function. Using whole-cell, perforated-patch, and single-channel recording, we found that treatment with NGF increased levels of voltage-gated sodium, calcium, and potassium currents. In contrast, CNTF treatment increased levels of potassium currents only. NGF and CNTF appeared to regulate the same delayed-rectifier potassium current; in addition, NGF treatment resulted in increased levels of a second potassium current component. Such differential effects of neurotrophic factors on the expression of voltage-gated ion channels would have profound effects on the excitability of target neurons in vivo.

Calcium↗
PubMed1994

Neuronal transfection in brain slices using particle-mediated gene transfer.

Difficulties in neuronal transfection continue to restrict the applicability of molecular approaches to neurobiology. Conventional transfection techniques have been of limited effectiveness, particularly in intact neural tissues. Viral vectors effectively transfect neurons both in vitro and in vivo but are labor intensive to construct, difficult to control, and often compromise cell viability. We describe here an alternative strategy using particle-mediated gene transfer for the transfection of neurons and glia in intact brain slices. This approach is efficient, reliable, and does not require advanced molecular biological facilities for its application.

Animals↗
PubMed1994

Reversibility of the mononucleate-to-multinucleate myogenic transition during amphibian limb regeneration.

Muscle differentiation involves the fusion of mononucleate myoblasts to form multinucleate syncytial myotubes. In order to assess reversibility of the mononucleate-to-multinucleate transition in urodele limb regeneration, myotube formation was induced in cultured newt limb blastemal cells. Myotubes were purified, replated at low density and injected with a cytoplasmic lineage tracer. In some cases nuclei of myotubes were labelled by incorporation of tritiated thymidine. Labelled myotubes were stable in culture for 6-8 weeks and no transfer to mononucleate cells was observed. The myotubes were implanted under the wound epidermis of a hindlimb blastema. Labelled mononucleate cells were observed 1 week after implantation and such cells could derive both the cytoplasmic lineage tracer and the nuclear marker. The number of such cells increased by 2-3 weeks after implantation. These results provide strong support for the reversibility of muscle differentiation during urodele limb regeneration, and raise questions about the mechanism of such a reversal.

Animals↗
PubMed1994

Isoform-specific induction of a retinoid-responsive antigen after biolistic transfection of chimaeric retinoic acid/thyroid hormone receptors into a regenerating limb.

Retinoic acid (RA) induces secretory differentiation in the wound epidermis of a regenerating amphibian limb. We investigated the role of individual RA receptor (RAR) types in the newt wound epidermis by introducing chimaeric RA/thyroid hormone (T3) receptors (chi alpha 1 and chi delta 1) that can be activated by T3. A biolistic particle delivery system was employed to transfect cells in the wound epidermis of a regenerating limb and approximately 10% of the cells in targeted surface areas expressed marker genes. Both chi alpha 1 and chi delta 1 were comparable in their ability to stimulate transcription of a synthetic reporter construct through a RA response element after activation with T3 in situ. This activation was also comparable to that obtained by the endogenous complement of RARs in the RA-treated, transfected wound epidermis. The RA-inducible WE3 antigen, a marker for secretory differentiation, which distinguishes the wound epidermis from normal skin (Tassava, R. A., Johnson-Wint, B. and Gross, J. 1986, J. Exp. Zool. 239, 229-240), was used to assess the functional role of chi alpha 1 and chi delta 1. Chimaeric receptors were transfected with an alkaline phosphatase marker gene, activated with T3, and the expression of both the marker and WE3 was analyzed by double-label immunofluorescence. Newt limbs transfected with chi delta 1 showed many double-labelled cells dependent on the presence of T3, whereas contralateral limbs transfected with an alkaline phosphatase marker lacking chimaeric receptor sequences did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Reversal of muscle differentiation during urodele limb regeneration.

Recent studies suggest that maintenance of the differentiated state requires continuous regulation. Limb regeneration in urodele amphibians provides a context in which to address this issue, as limb regeneration may involve the dedifferentiation of multinucleate myotubes to yield mononucleate blastemal cells, which then proliferate and contribute to regenerate tissues. To evaluate this possibility, cultured newt limb myotubes were selectively microinjected with the lineage tracer rhodamine-dextran and introduced into regenerating limbs. In culture, such labeled myotubes were stable after 6-8 weeks, and transfer of the tracer to mononucleate cells was not observed. In contrast, after implantation of labeled myotubes under the wound epidermis of limb blastemas, strongly labeled mononucleate cells were observed after 1 week. These cells could be double-labeled with the cytoplasmic lineage tracer and [3H]thymidine that had been incorporated into the nuclei of implanted myotubes. The number of labeled mononucleate cells increased significantly by 2-3 weeks after implantation, indicating that these cells proliferated. Although the fate of these cells at later times was uncertain, we provide evidence consistent with their subsequent differentiation. These results demonstrate reversal in the mononucleate-to-multinucleate transition of vertebrate myogenesis.

Animals↗
PubMed1992

Signal transduction and regulation of neurotrophins.

Our understanding of the molecular nature of neurotrophic interactions has been greatly enhanced by the recent isolation and characterization of several new neurotrophic factors and their receptors. Neurotrophic factors have been found to be regulated by neuronal activity in the central nervous system, and may be involved in activity-dependent processes throughout development and maturity.

Animals↗
PubMed1992

NGF takes shape.

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Journal Article↗
PubMed1991

Role of a key cysteine residue in the gating of the acetylcholine receptor.

We have examined changes in single-channel behavior that result from conservative amino acid substitutions at the Cys230 residue in the putative first transmembrane region (M1) of the murine nicotinic acetylcholine receptor. Mutations made in the gamma subunit altered the energy barrier for a single closing rate constant in proportion to the size of the substituted side chain. One of these substitutions, when made in the alpha subunits, had no effect on gating. No mutations altered permeation. We conclude that the region surrounding the M1 Cys is involved in the gating of the nicotinic acetylcholine receptor and that the gamma subunit contributes significantly to the control of channel closure.

Animals↗
PubMed1990

Influence of the gamma subunit and expression system on acetylcholine receptor gating.

We have developed a partial kinetic theory for the gating of murine nicotinic acetylcholine receptors (AChRs) expressed in Xenopus oocytes and have used this theory to characterize the role of the gamma subunit in single-channel behavior. Permeation and gating were found to be largely unaffected in AChRs produced in oocytes when the gamma subunit transcript was omitted from microinjections of AChR subunit RNAs. In contrast, marked changes in gating kinetics resulted when even very conservative single amino acid substitutions were introduced into the gamma subunit, indicating that the gamma subunit can have a large effect on AChR gating. We also found that channel openings were much prolonged when murine AChRs were expressed in BC3H-1 cells.

Animals↗