We have analyzed the effect of extracellular stimuli on the differentiation state of the CA77 thyroid C-cell line as a model to understand the control of neural crest cell differentiation. In contrast to the endocrine C-cell phenotype, we found that CA77 cells have a neuronal phenotype characterized by laminin-induced neurites, neuronal antigens, and calcitonin gene-related peptide (CGRP) mRNA expression. Treatment with dexamethasone and retinoic acid reversibly repressed some of these neuronal characteristics to induce features more characteristic of the parental C-cells. In the case of dexamethasone treatment, there was a partial retraction and thinning of neurites, an increased number of secretory vesicles in the cell bodies, and about a 10-fold decrease in DNA synthesis. Treatment with retinoic acid alone or in combination with dexamethasone caused decreased cell adhesion and an even more extensive retraction of the neurites. Dexamethasone also biased the steady state levels of the alternatively spliced transcripts from the calcitonin/CGRP gene to favor calcitonin relative to CGRP mRNA. While retinoic acid treatment decreased both calcitonin and CGRP mRNA levels, the combination of dexamethasone and retinoic acid still yielded the increase in calcitonin relative to CGRP mRNA. These results suggest that glucocorticoids and retinoic acid may contribute to a late and reversible differentiation of thyroid C-cells by partly repressing neuronal properties.
The appearance of a new rail car technology, combining the features of the latest in low-floor streetcar design with those of diesel freight railways, makes it possible to consider rail service for passenger flows much lower than generally have been found feasible until now. With the introduction of any new technology comes the question, What is its role? It is concluded that the provision of short-haul services—within inner and outer suburbs, and between such places and downtowns—is where the greatest potential lies. Additional applications are ( a) similar services extending beyond the commutershed into the trading hinterland of a city, ( b) those catering to cross-radial travel within a central city or region that is not oriented to downtown, and ( c) those that may sometimes involve a nonurban region or tourism. This could be a significant development, as much of the U.S. and Canadian population lives in low-density suburbs or semirural counties, both of which can be expected to continue their dominance of the growth agenda. One of the advantages of this new family of diesel light rail technology arises from its ability to use existing pathways through cities and towns. This keeps costs low and avoids the dislocation and environmental problems associated with the taking of large swaths of land required by many solutions. One way to do this is by using existing railway tracks or rights of way. Another is to share right-of-way space with a road, either in a streetcar format or on a separate strip. The results have proven useful in an assessment of freight railway lines in Calgary and Edmonton with respect to their potential for diesel light rail services.
The transit system serving Greater Vancouver has high ridership and a high rate of growth. Using as a base the well-designed, well-patronized trolleybus grid in the City of Vancouver, an inter-connected suburban bus network has been created, with radial, cross-radial, and local routes meeting on a timed connection basis at suburban shopping centres and other foci. Planners' thoughts for the future include greater emphasis on the micro and macro aspects of land use and relations to transit; the use of capital intensive modes for heavy trunk routes; and the use of various forms of para-transit for low-density and certain feeder applications.
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