ABSTRACT
Germ cells divide and differentiate in a unique local microenvironment under the control of somatic cells. Signals released in this niche instruct oocyte reentry into the meiotic cell cycle. Once initiated, the progression through meiosis and the associated programme of maternal messenger RNA translation are thought to be cell autonomous. Here we show that translation of a subset of maternal mRNAs critical for embryo development is under the control of somatic cell inputs. Translation of specific maternal transcripts increases in oocytes cultured in association with somatic cells and is sensitive to EGF-like growth factors that act only on the somatic compartment. In mice deficient in amphiregulin, decreased fecundity and oocyte developmental competence is associated with defective translation of a subset of maternal mRNAs. These somatic cell signals that affect translation require activation of the PI(3)K-AKT-mTOR pathway. Thus, mRNA translation depends on somatic cell cues that are essential to reprogramme the oocyte for embryo development.
Subject(s)
Gene Expression Regulation , Oocytes/physiology , Protein Biosynthesis , RNA, Messenger, Stored/genetics , Amphiregulin , Animals , Cell Cycle Proteins , Cells, Cultured , Cumulus Cells/physiology , EGF Family of Proteins , Female , Glycoproteins/genetics , Glycoproteins/metabolism , Intercellular Signaling Peptides and Proteins/genetics , Intercellular Signaling Peptides and Proteins/metabolism , Meiosis , Mice , Mice, 129 Strain , Mice, Inbred C57BL , Microtubule-Associated Proteins , Nuclear Proteins , Oogenesis , Phosphatidylinositol 3-Kinases/metabolism , Proto-Oncogene Proteins c-akt/metabolism , RNA, Messenger, Stored/metabolism , Signal Transduction , TOR Serine-Threonine Kinases/metabolismABSTRACT
BACKGROUND: A reduced number of progressively motile sperm (as may occur in cases of asthenozoospermia or when cryopreserved spermatozoa are used for fertilization) limits the possibility of applying various assisted reproductive techniques (ARTs). We previously showed that incubation of sperm with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 increases sperm progressive motility and enhances the number of sperm recovered by capacitation protocols used in ART. METHODS AND RESULTS: In the present study, we investigate the motility-enhancing effects of this compound in epididymal mouse sperm, and examine the use of the mouse system to investigate the effect of LY294002 on oocyte fertilization and preimplantation embryo development. Our results show that neither pre-incubation of mouse spermatozoa with the inhibitor during in vitro capacitation nor the direct addition of LY294002 to the sperm-oocyte mixture significantly affects the process of fertilization and preimplantation development of embryos produced even when they developed in the presence of LY294002. CONCLUSIONS: The present data encourage the design of new drugs based on the molecular structure of LY294002, which may open up new options for the in vitro treatment of human/animal asthenozoospermia.
Subject(s)
Blastocyst/drug effects , Chromones/pharmacology , Enzyme Inhibitors/pharmacology , Morpholines/pharmacology , Phosphoinositide-3 Kinase Inhibitors , Sperm Motility/drug effects , Animals , Blastocyst/cytology , Blotting, Western , Cryopreservation , Electrophoresis, Polyacrylamide Gel , Embryo, Mammalian/metabolism , Embryo, Mammalian/pathology , Embryonic Development , Epididymis/pathology , Female , Fertilization , Humans , Ice , Male , Mice , Oocytes/cytology , Oocytes/metabolism , Phosphorylation , Sperm Capacitation , Spermatozoa/metabolism , Spermatozoa/pathology , Time FactorsABSTRACT
In fertilized mouse eggs, de novo transcription of embryonic genes is first observed during the S phase of the one-cell stage. This transcription, however, is mostly limited to the male pronucleus and possibly uncoupled from translation, making the functional meaning obscure. We found that one-cell mouse embryos respond to the osmotic shock of in vitro isolation with migration of HSF1, the canonical stress activator of mammalian heat shock genes, to pronuclei and by transient transcription of the hsp70.1, but not hsp70.3 and hsp90, heat shock genes. Isolated growing dictyate oocytes also display a nuclear HSF1 localization, but, in contrast with embryos, they transcribe both hsp70.1 and hsp70.3 genes only after heat shock. Intranuclear injection of double-stranded oligodeoxyribonucleotides containing HSE, GAGA box or GC box consensus sequences, and antibodies raised to transcription factors HSF1, HSF2, Drosophila melanogaster GAGA factor, or Sp1 demonstrated that hsp70.1 transcription depends on HSF1 in both oocytes and embryos and that Sp1 is dispensable in oocytes and inhibitory in the embryos. Hsp70.1 thus represents the first endogenous gene so far identified to be physiologically activated and tightly regulated after fertilization in mammals.
