title: Differing mechanisms of cAMP- versus seawater-induced oocyte maturation in marine nemertean worms I. The roles of serine/threonine kinases and phosphatases.
abstract: Unlike in most animals, oocytes of marine nemertean worms initiate maturation (=germinal vesicle breakdown, GVBD) following an increase, rather than a decrease, in intraoocytic cAMP. To analyze how serine/threonine (Ser/Thr) kinase cascades involving mitogen-activated protein kinase (MAPK), maturation-promoting factor (MPF), cAMP-dependent protein kinase (PKA), and phosphatidylinositol 3-kinase (PI3K) regulate nemertean GVBD, oocytes of Cerebratulus sp. were treated with pharmacological modulators and stimulated with cAMP-elevating drugs or seawater (SW) alone. Both cAMP elevators and SW triggered GVBD while activating MAPK, its target p90Rsk, and MPF. Similarly, neither cAMP- nor SW-induced GVBD was affected by several Ser/Thr phosphatase inhibitors, and both stimuli apparently accelerated GVBD via a MAPK-independent, PI3K-dependent mechanism. However, inhibitors of Raf-1, a kinase that activates MAPK kinase, blocked GVBD and MAPK activation during SW-, but not cAMP-induced maturation. In addition, MPF blockers more effectively reduced GVBD and MAPK activity in SW versus in cAMP-elevating treatments. Moreover, the two maturation-inducing stimuli yielded disparate patterns of PKA-related MAPK activations and phosphorylations of putative PKA substrates. Collectively, such findings suggest that in maturing oocytes of Cerebratulus sp., Ser/Thr kinase cascades differ during cAMP- versus SW-induced GVBD in several ways, including MAPK activation modes, MPF-feedback loops, and PKA-related signaling pathways. Additional differences in cAMP- versus SW-induced oocyte maturation are also described in the accompanying study that deals with the roles of tyrosine kinase signaling during GVBD.
authors.affiliation: Department of Biology, University of New Mexcio, Albuquerque, 87131, USA. sstr@unm.edu
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Stricker
authors.forename: Toni L
authors.initials: TL
authors.lastname: Smythe
mesh_terms: D000730:Androstadienes / Q000493:pharmacokinetics; D000818:Animals; D000845:Annelida / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D016200:Maturation-Promoting Factor / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D012623:Seawater; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D019908:Proto-Oncogene Proteins c-raf; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D017868:Cyclic AMP-Dependent Protein Kinases; D016200:Maturation-Promoting Factor; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D017027:Protein Tyrosine Phosphatases; D000077191:Wortmannin