Introduction to the Symposium and Studies on the Surfaces of Separated and Synchronized Tumor and Embryonic Cell Populations

Tumor and embryonic cell surfaces are examined in this symposiumwith respect to their roles in cell-cell interactions and inearly development and malignancy. Three sets of studies havebeen recently performed in my laboratory to help elucidate thenature of tumor and embryonic cell surfaces and the means bywhich these cells adhere to each other. We separated an in vivo129/J ascites mouse teratoma into specific subpopuladons ofcells by velocity sedimentation in shallow density gradients.The teratoma consistently separated into two major populations:"large" and "small" cells. Only the large cells displayed "malignant-like"surface characteristics in terms of their agglutinability withcarbohydrate binding lectins. The teratoma cells were also synchronizedin culture with thymidine plus colcemid. In these synchronizedcultures, cellular adhesiveness and glutamine synthetase specificactivity displayed oscillatory patterns with peaks of glutaminesynthetase specific activity occurring just prior to peaks ofadhesivenesss. Also, both glutamine synthetase specific activityand cellular adhesiveness were enhanced by two compounds: actinomycinD and hydrocortisone. Based upon previous work that implicatesL-glutamine in intercellular adhesion, it is not unreasonableto speculate that glutamine synthetase specific activity andcellular adhesiveness may be causally related. The problem ofaltered tumor cell adhesiveness is important because it seems,in part, to be responsible for tumor spread. Finally, the seaurchin embryo system was utilized to identify specific cellsurface carbohydrates that may be involved in intercellularadhesion. In 15 separate experiments with each sugar and with15 different saccharides, D-galactose and N-acetyl-D-galactosaminewere the best inhibitors of rotation-medicated reaggregationof 24-hr sea urchin embryo cells dissociated by removal of divalentcations. ß-galactosidase also inhibited reaggregationof these cells. These results implicate galactopyranosyl-likeresidues in the adhesion of 24-hr sea urchin embryo cells witheach other.     

Global assessment of coral bleaching and required rates of adaptation under climate change

Elevated ocean temperatures can cause coral bleaching, the loss of colour from reef‐building corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long‐term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere–ocean general circulation models (GCMs) to the local conditions around representative coral reefs. Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral Reef Watch bleaching prediction method to the output of a low‐ and high‐climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM‐resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985–2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios. The results indicate that bleaching could become an annual or biannual event for the vast majority of the world's coral reefs in the next 30–50 years without an increase in thermal tolerance of 0.2–1.0°C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.     

Cells and Organizers

This article evaluates historically some of the factors otherthan the new "cell biology" that have influenced embryologiststo think in terms of cells rather than supracellular agencies.Evidence of Spemann's emphasis on organizers as supracellularphenomena is presented, but it is pointed out that Spemann raisedsome cellular questions that were by-passed at the time. Vogtand others who studied morphogenetic movements in the 1920'salso considered these as supracellular processes, although Vogtpreviously (1913) had studied the movements of individual amphibianembryonic cells isolated in vitro. It is pointed out that the number of investigators who studiedisolated cells in vitro before the development of tissue culturewas considerable, including Remak (1855), Stricker (1864), andHis (1899), among others. Holtfreter observed the actions ofisolated cells from 1931 on, in part, at first, because thecells isolated themselves from cell groups in vitro. His studiesof explants, in the 1930's, 1940's, and 1950's, emphasized thatsupracellular phenomena must be explained in terms of cell properties,including membrane properties. In addition, the dramatic resultsof his experiments demonstrating affinity drew attention tocells as organized individuals, just as Spemann's experimentshad done earlier to demonstrate the integrative qualities ofembryos-as-wholes.