Epidermal Growth Factor Signaling and Mitogenesis in Plcg1 Null Mouse Embryonic Fibroblasts

Gene targeting techniques and early mouse embryos have been used to produce immortalized fibroblasts genetically deficient in phospholipase C (PLC)-γ1, a ubiquitous tyrosine kinase substrate. Plcg1−/− embryos die at embryonic day 9; however, cells derived from these embryos proliferate as well as cells from Plcg1+/+ embryos. The null cells do grow to a higher saturation density in serum-containing media, as their capacity to spread out is decreased compared with that of wild-type cells. In terms of epidermal growth factor receptor activation and internalization, or growth factor induction of mitogen-activated protein kinase, c-fos, or DNA synthesis in quiescent cells, PLcg1−/− cells respond equivalently to PLcg1+/+ cells. Also, null cells are able to migrate effectively in a wounded monolayer. Therefore, immortalized fibroblasts do not require PLC-γ1 for many responses to growth factors.

Farnesyltransferase inhibitors induce dramatic morphological changes of KNRK cells that are blocked by microtubule interfering agents

Farnesyltransferase inhibitors (FTIs) exhibit the remarkable ability to inhibit transformed phenotypes of a variety of human cancer cell lines and to block the growth of cancer cells in a number of animal model systems. In this paper, we report that the addition of FTI to v-K-ras- transformed NRK cells (KNRK) results in dramatic morphological changes. Within 24 h after the addition of FTI, the round morphology of KNRK cells was changed to an elongated (flattened and spread out) morphology resembling those of untransformed NRK cells. No morphological effects were seen when similar concentrations of FTI were added to NRK cells. Phalloidin staining showed that FTI treatment did not restore the disrupted actin cytoskeleton in KNRK cells. In contrast, FTI addition resulted in the appearance of extensive microtubule networks in KNRK cells. The addition of a low concentration (1.2 nM) of vincristine or vinblastine, agents that interfere with microtubule dynamics, blocked the FTI-induced morphological changes in KNRK cells. In contrast, cytochalasin B, which interferes with actin polymerization, did not block the morphological changes. The FTI-induced morphological changes were associated with a decrease in the percentage of cells in S-phase, and the addition of 1.2 nM vincristine did not have additional effects on cell cycle progression. A higher concentration (12 nM) of vincristine caused synergistic effect with FTI to enrich dramatically KNRK cells in G2/M phase. These results suggest that FTI affects cell morphology and that microtubule dynamics are involved in these processes.

Toward a new synthesis: Major evolutionary trends in the angiosperm fossil record

Angiosperm paleobotany has widened its horizons, incorporated new techniques, developed new databases, and accepted new questions that can now focus on the evolution of the group. The fossil record of early flowering plants is now playing an active role in addressing questions of angiosperm phylogeny, angiosperm origins, and angiosperm radiations. Three basic nodes of angiosperm radiations are identified: (i) the closed carpel and showy radially symmetrical flower, (ii) the bilateral flower, and (iii) fleshy fruits and nutritious nuts and seeds. These are all coevolutionary events and spread out through time during angiosperm evolution. The proposal is made that the genetics of the angiosperms pressured the evolution of the group toward reproductive systems that favored outcrossing. This resulted in the strongest selection in the angiosperms being directed toward the flower, fruits, and seeds. That is why these organs often provide the best systematic characters for the group.