Regulation of DdrasG gene expression during Dictyostelium development.

Abstract

DdrasG gene expression during the early development of Dictyostelium discoideum has been examined in detail. The amount of DdrasG-specific mRNA increased approximately twofold during the first 2 to 3 h of development and then declined rapidly, reaching negligible levels by the aggregation stage. The increase in mRNA levels that occurred during the first 2 to 3 h of development also occurred during differentiation in cell suspensions and was enhanced when cells were shaken rapidly. This initial increase was unaffected by cell density. When cells were set up to differentiate on filters, the addition of a glucose-amino acid mixture slightly delayed differentiation and had a similar effect on the expression of the gene. The decline in DdrasG expression during development did not occur when cells were treated with cycloheximide, suggesting that the expression of a developmentally regulated gene product is essential for the reduction of DdrasG gene mRNA. There was no decrease in DdrasG mRNA level during differentiation in shake suspension, but the decrease did occur upon application of pulses of cyclic AMP to shaking cultures. The application of a continuously high level of cyclic AMP delayed the increase in expression of the gene and did not result in the subsequent decline. These results suggest that the induction of a functional cyclic AMP relay system is important in reducing DdrasG gene mRNA levels.

IQGAP-related protein IqgC suppresses Ras signaling during large-scale endocytosis

“…First, the temporal profile of the IqgC response to both chemoattractants corresponds to the response of the active Ras pan-probe (24,53,54). Second, the response to folic acid is more prominent than the response to cAMP, consistent with the temporal expression profile of RasG (72). Third, based on the similarity of the reduced ERK2 phosphorylation response to both chemoattractants in cells expressing constitutively active RasG, it was suggested that RasG is involved in the regulation of signaling pathways initiated by both folic acid and cAMP receptors (73).…”

Overexpression of an Activated rasG Gene during Growth Blocks the Initiation of Dictyostelium Development

“…The previously reported expression pattern for rasG suggested that the gene product was important for growth and early differentiation (21,35). To understand its possible role in these processes, attempts were made to overexpress the gene.…”

Ras proteins in the control of the cell cycle and cell differentiation

“…rasD and rasG products are closely related to mammalian Ras proteins, whereas rasB, rasC, and rasS are more divergent. rasD is induced by cAMP and expressed after aggregation, while rasG is expressed prior to germination and during vegetative growth [316][317][318][319]. Thus, Dictyostelium is the only organism expressing different ras genes at different stages of development.…”