High cAMP in spores of Dictyostelium discoideum: association with spore dormancy and inhibition of germination.
Signalling mechanisms involving cAMP have a well-documented role in the coordination of multicellular development and differentiation leading to spore formation in the social amoeba, Dictyostelium discoideum. The involvement of cAMP in the poorly understood developmental stages of spore dormancy and germination have been investigated in this study. Dormant spores contained up to 11-fold more cAMP than nascent amoebae. The spore cAMP levels were not constant, but typically underwent a surge at 14-18 d when spores acquired the ability to germinate spontaneously. The high cAMP levels decreased only during successful spore germination, i.e. emergence of nascent amoebae. The temporal pattern of cAMP decrease was complex and unique to the method of spore activation, supporting our hypothesis that exogenously (e.g. heat) activated and autoactivated spores germinate by different mechanisms. During heat-induced activation, transcription of acg (a gene encoding adenylyl cyclase associated with germination) correlated well with spore cAMP content. Young wild-type spores, incapable of spontaneous germination, maintained a uniformly high cAMP level, and spore cAMP levels also remained high if germination was inhibited. When activated spores were deactivated by applying increased osmotic pressure, cAMP concentrations rose and ultimately levelled off at the high levels typical of dormant spores. The correlation between high cAMP and failure to germinate was also evident when autoactivation was inhibited by the cAMP analogue, 8-bromo-cAMP. Also, spores from a strain (HTY217) with unrestrained protein kinase A activity were incapable of spontaneous germination. Overall, our experiments provide evidence for continued cAMP signalling in spores up to 18 d after sporulation and for linkages between elevated cAMP, spore deactivation and inhibition of spontaneous germination.
Virdy
Kiran J
KJ
Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4.
Sands
Todd W
TW
Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4.
Kopko
Susan H
SH
Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4.
van Es
Saskia
S
Institute of Molecular Plant Sciences, Cell Biology Section, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, Netherlands.
Meima
Marcel
M
Institute of Molecular Plant Sciences, Cell Biology Section, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, Netherlands.
Schaap
Pauline
P
Institute of Molecular Plant Sciences, Cell Biology Section, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, Netherlands.
Cotter
David A
DA
Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D018869:Heat-Shock Response; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016053:RNA, Protozoan / Q000235:genetics / Q000378:metabolism; D013170:Spores / Q000378:metabolism / Q000502:physiology; D014158:Transcription, Genetic
D012333:RNA, Messenger; D016053:RNA, Protozoan; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D000262:Adenylyl Cyclases