The Effect Of Gp150 On Membrane Proteins And Protein Kinases During Dictyostelium Discoideum Development

In Dictyostelium amoebae, cell-type differentiation, spatial patterning, and morphogenesis are controlled by a combination of cell- autonomous mechanisms and intercellular signaling. A chemotactic aggregation of ~ 10~5 cells leads to the formation of a multicellular organism. Cell-type differentiation and sorting result in a small number of defined cell types organized along an anteroposterior axis. Finally a mature fruiting body is created by the terminal differentiation of stalk and spore cells. During development, membrane proteins play an important role in cell-type differentiation, including spatial patterning, and morphogenesis. The membrane glycoprotein gpl50 is encoded by the lagC gene and mediates cell-cell adhesion by heterophilic binding during Dictyostelium discoideum development. In experiment, we take KAX-3(wild type) cell and AK127(lagC-null) as experiment material. To study the function of gpl50, we have examined the effect of gpl50 on morphogenesis, membrane proteins and protein kinases during Dictyostelium discoideum development1) The KAX-3 cells can complete development, and form a mature fruiting body finally. The AK127 cells fail to establish tight mound and the loose mound disaggregates before the cells eventually die.2) The absence of gpl50 change the expression of many membrane proteins.The membrane proteins which change apparently include 68kD, 65kD, 60kD, 50kD, 45kD, 37kD, 34kD, 31kD, 17kD. One of the most interesting changes is about protein of 17kD. In mound stage, The content of 17kD increases distinctly, and it suggests that the protein of 17kD is important during Dictyostlium multicellular development. The protein of 17kD is an histidine rich actin binding protein from Dictyostelium discoideum. The structure of the protein is similar to interleukin and the fibroblast growth factor. It indicates that gpl50 may function in other signal transduction pathways and may affect on the expression of the membrane proteins.3) At aggregation stage during Dictyostlium multicellular development, the activity of PKA changes alike in both KAX-3 cells and AK127 cells. It suggest gpl50 does not influence the activity of PKA at aggregation stage. At slug stage, the activity of PKA in KAX-3 cells functions in the form of oscillatory waves, and has a large amplitude at the end of this stage, which could prepare for terminal differentiation. While AK127 cells have the same oscillatory waves at the beginning of slug stage, then the activity of PKA reach the level of the aggregation stage. It suggests that thegpl50 plays a role to keep the activity of PKA in appropriate range as well as time. 4) At aggregation stage during Dictyostlium multicellular development, the activity of PKC changes alike in both KAX-3 cells and AK127 cells. It suggest gpl50 does not influence the activity of PKC at aggregation stage. In mound and slug stage, the activity of PKC functions in the form of oscillatory waves in both KAX-3 cells and AK127 cells, but mutant cells have oscillatory waves with large amplitude. It indicates that gpl50 and other signal molecules keep the activity of PKC in appropriate range. The regulation of PKC activity was not accurately mediated, if no gpl50 protein.These studies indicate that gpl50 functions not only as cell adhesion molecule, but as signal molecule mediating signal transduction pathways.