Signal transduction - Our current model

Our current view of the GDT:
The only known gene product presumably involved PSF secretion is ACR (adenylylcyclase): an ACR knock-out strain appears to overproduce PSF (Riemann and Nellen, unpublished). PSF then stimulates the PSF receptor which transduces the signal to the PSF regulated YakA, YakA is an inhibitor of PufA which in turn inhibits translation of PKA (see Souza et al., Development. 1999;126:3263, Souza et al., Development. 1998; 125:2291). Mutant analysis shows, however, that PSF does not only stimulate the YakA pathway. The unknown receptor X-R senses another signal which is most likely transferred in a Ga2 dependent way to CRAC and finally activates PKA. AdenylylcyclaseA (ACA) is not required for this pathway. gdt1 is a transmembrane protein and a negative regulator of the GDT. The C-terminal domain of gdt1p has homology to protein kinases but activity has not yet been shown. gdt1p may inhibit a newly identified gene product gdt2p which is a positive regulator of the GDT. The position in the signalling chain of another newly identified positive regulator, gdt3p, is not yet known. gdt1p is phosphorylated in vitro by PKA. We suggest that at high cell densities, residual gdt1p is rapidly inactivated by phosphorylation. The negative pathway to inhibit discoidin expression in later development is, at least in part, mediated by cAMP and the receptor cARI. Surprisingly, G-proteins appear not to be required for transducing the signal. Among other responses, cARI triggers Ca2+ influx which finally results in discoidin downregulation.