Elsevier

Developmental Biology

Volume 193, Issue 2, 15 January 1998, Pages 146-155
Developmental Biology

Regular Article
Signal Transduction Pathways Leading to Spore Differentiation inDictyostelium discoideum

https://doi.org/10.1006/dbio.1997.8804Get rights and content
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Abstract

Cells that overexpress PKA as a consequence of carrying multiple copies of the gene encoding the catalytic subunit can be induced to sporulate when developing as single cells. A peptide phosphorylated by PKA, termed SDF-1, has recently been shown to stimulate this process (Anjardet al.,1997). Several genes have been implicated in a signal transduction pathway by which prestalk cells induce encapsulation of prespore cells during terminal differentiation including a prestalk-specific putative membrane protease (TagC) and a two-component system consisting of a receptor-histidine kinase (DhkA) and a response regulator with cAMP phosphodiesterase activity (RegA). To determine whether SDF-1 uses this pathway, strains carrying null mutations in the pertinent genes were transformed with apkaCplasmid such that they can overexpress PKA. Since these mutant strains all sporulated efficiently when SDF-1 was added, it appears that other gene products mediate the response. However, we found thatregAmutant cells release a distinct factor, SDF-2, that rapidly induces encapsulation of test cells overexpressingpkaC.Since cells in whichtagCis disrupted do not form SDF-2 and cells in whichdhkAis disrupted do not respond to SDF-2, this peptide appears to use the two-component system that regulates PKA activity. SDF-2 is a small peptide released by prestalk cells in a manner dependent on TagC. It appears to act on prespore cells through the DhkA receptor to inhibit the cAMP phosphodiesterase of RegA, thereby activating PKA via cAMP. The process of induction by SDF-2 can be shown to be distinct from that by SDF-1. SDF-2 appears to stimulate prestalk cells to release additional SDF-2 by acting through a signal transduction pathway that also involves DhkA, RegA, and PKA. Based on these results we present a model for the signal transduction cascade regulating spore differentiation.

Keywords

Dictyostelium
spore differentiation
PKA
peptide
signal transduction

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