Pertussis toxin-sensitive G protein participating in starfish oocyte maturation induced by 1-methyladenine

Isolation of candidate genes for apomixis in Poa pratensis L

The essential feature of apomixis is that an embryo is formed autonomously by parthenogenesis from an unreduced egg of an embryo sac generated through apomeiosis. The genetic constitution of the offspring is, therefore, usually identical to the maternal parent, a trait of great interest to plant breeders. If apomixis were well understood and harnessed, it could be exploited to indefinitely propagate superior hybrids or specific genotypes bearing complex gene sets. A fundamental contribution to the understanding of the genetic control of the apomictic pathway could be provided by a deep knowledge of molecular mechanisms that regulate the reproductive events. In Poa pratensis the cDNA-AFLP method of mRNA profiling allowed us to visualize a total of 2248 transcript-derived fragments and to isolate 179 sequences that differed qualitatively or quantitatively between apomictic and sexual genotypes at the time of flowering when the primary stages of apomixis occur. Three ESTs were chosen for further molecular characterization because of their cDNA-AFLP expression pattern and BLAST information retrieval. The full-lengths of the newly isolated genes were recovered by RACE and their temporal expression patterns were assessed by RT-PCR. Their putative role in cell signaling transduction cascades and trafficking events required during sporogenesis, gametogenesis and embryogenesis in plants is reported and discussed.

Separate activation of the cytoplasmic and nuclear calcium pools in maturing starfish oocytes

The dynamics of the cytoplasmic and nuclear Ca2+ pools in starfish oocytes arrested at the prophase of the first meiotic division or after induction of meiosis by 1-methyladenine (1-MA) have been studied by confocal microscopy. A 70 kDa fluorescent Ca2+ indicator has been injected in either the cytoplasm or the nucleus, and shown to remain restricted to the compartment of injection. 1-MA induced a first Ca2+ transient in the cytosol, followed by a nuclear transient, and eventually by a second cytosolic transient. The latter failed to occur if the nuclear peak was suppressed. This required the nuclear injection of antagonists of the inositol 1,4,5-trisphosphate (InsP3) and cyclic-ADPribose (cADPr) Ca2+ channels, showing that both channel types were active in the inner envelope membrane. The nuclear injection of the Ca2+ channel antagonists affected the process of meiosis reinitiation: in about one third of the injected oocytes no breakdown of the nuclear envelope (GVBD) was observed. In the others, even if GVBD eventually occurred, the intermixing of the nucleoplasm and cytoplasm was inhibited.

In vivo and in vitro induction of germinal vesicle breakdown in a freshwater bivalve, the zebra mussel Dreissena polymorpha (Pallas)

Oocyte maturation and germinal vesicle breakdown (GVBD) was induced in zebra mussel (Dreissena polymorpha) oocytes by in vivo and in vitro application of serotonin (5-hydroxytryptamine, 5-HT), and in vitro application of 8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT, a 5-HT1A receptor agonist). Oocytes initiated GVBD approximately 30 minutes after exposure to 5-HT (10(-3) M) at 23 degrees C, and by 40-50 minutes after exposure, most oocytes lacked a germinal vesicle. An exposure time to 5-HT as brief as five to ten minutes was required to trigger the maturation process, which terminates in spawning of fertilizable oocytes in nearly all mussels. But, with an exposure time of less than five minutes, spawning was reduced by application of 10(-4) M methiothepin (a potent blocker of 5-HT-induced spawning in zebra mussels). Thus, the sequence of oocyte maturation events in zebra mussels was determined. Oocytes are arrested at the germinal vesicle stage (prophase I) within the ovary. 5-HT reinitiates the maturation process, including GVBD and spawning of metaphase I oocytes, which are further arrested until fertilization. To our knowledge this is the first demonstration of oocyte maturation induction by serotonergic ligands in a freshwater bivalve.