Two-stage dependence for 1-methyladenine induced reinitiation of meiotic maturation in starfish oocytes.
The maturation hormone 1-methyladenine (1-MA) causes meiotic resumption of prophase arrested immature starfish oocytes. Continuous exposure to > or = 0.5 microM 1-MA causes germinal vesicle breakdown (GVBD) in approximately 20 min, but oocytes pretreated for > 30 min with a subthreshold dose of 1-MA undergo GVBD much faster (approximately 10 min) when they are exposed to 1 microM 1-MA. Furthermore, a very low subthreshold 1-MA suffices to start the maturation process: oocytes exposed to 0.005 microM 1-MA for up to 10 min followed by 1 microM 1-MA is equivalent to continuous exposure to 1 microM 1-MA. These dose and timing relationships indicate that there is a two-stage dependence on 1-MA. A possible explanation for this dependence is that there are two processes involved: an initial process that is triggered by a low dose of 1-MA, and a second process that cannot start until the first process is completed and is stimulated by a higher dose of 1-MA. These subthreshold 1-MA effects on GVBD timing are not directly coupled to changes in calcium physiology that also occur during maturation. Subthreshold 1-MA was found to cause a transient accumulation of Cdc2/cyclin B into the nucleus. The two-stage dependence indicates that there are unsuspected features in this well-studied pathway leading to GVBD. In the animal, this hormone dependence may help to synchronize maturation throughout all parts of the ovary.
Terasaki
Mark
M
Department of Cell Biology, University of Connecticut Health Center, Farmington, CT 06032, USA. terasaki@uchc.edu
Runft
Linda
L
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D008540:Meiosis / Q000187:drug effects* / Q000502:physiology*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D013215:Starfish / Q000187:drug effects* / Q000378:metabolism*
D019926:Cyclin B; C008407:1-methyladenine; D016203:CDC2 Protein Kinase; D000225:Adenine; D002118:Calcium