The regulation of GTP-binding proteins during fertilization and zygote differentiation in Dictyostelium discoideum.
The development changes in GTP-binding proteins and the regulation of their appearance by calcium ions were investigated during early sexual development in Dictyostelium discoideum. GTP gamma S strongly inhibited gamete cell fusion, while GDP beta S slightly augmented it, suggesting that G-proteins have a critical role in cell fusion. A 52-kDa protein recognized by an anti-GTP-binding site-specific immune serum, was abundant during calcium-dependent early sexual development but decreased in amount concomitant with cell fusion. This protein remained at high levels in Ca(2+)-deficient cultures, suggesting that its down-regulation is linked to the events of sexual development. Analysis of substrates for cholera and pertussis toxin-mediated [32P]ADP-ribosylation in D. discoideum extracts determined that the 52-kDa protein is a G-alpha subunit similar to mammalian Gs. The 52-kDa protein was also detected in vegetative, asexual amoebae, but diminished rapidly within the first 2 h of starvation. Together these data indicate that the 52-kDa protein functions during the growth phase and is lost upon entry into either the sexual or asexual developmental programs. The amounts of several lower molecular weight GTP-binding proteins, ranging from 21- to 28 kDa, increased during the stage of zygote differentiation and their increases were calcium dependent. These data provide the first analysis of G-proteins during sexual development of D. discoideum and lay the foundation for continued analysis of the signal transduction events mediating cell fusion and zygote differentiation.
Browning
D D
DD
Department of Zoology, Erindale College, University of Toronto, Mississauga, Ontario, Canada.
Poludnikiewicz
M B
MB
Proteau
G A
GA
O'Day
D H
DH
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002459:Cell Fusion; D004023:Dictyostelium / Q000378:metabolism*; D005306:Fertilization; D005656:Fungal Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D015398:Signal Transduction; D015053:Zygote / Q000378:metabolism
D005656:Fungal Proteins; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D002118:Calcium