We studied the temporal and spatial pattern of lipid transfer protein (LTP) gene expression, as well as the localization of this protein, in maize. Using an LTP gene, we observed an accumulation of LTP mRNA in embryos and endosperms during seed maturation. LTP gene expression was also investigated in young seedlings. After germination, the leve1 of LTP mRNA in the coleoptile increased, with a maximum at 7 days, whereas LTP mRNA levels were low in the scutellum and negligible in roots. The high levels of LTP mRNA found in coleoptiles and embryos were confirmed by in situ hybridization. Moreover, LTP gene expression appeared to be localized in the externa1 cellular layers and around the leaf veins. Using immunogold methods, we also observed that LTP was distributed heterogeneously in the different cells of coleoptiles and leaves. The highest concentrations of LTP were found in the outer epidermis of the coleoptiles as well as in the leaf veins. Together, our observations indicate that LTP gene expression is not only organ specific and time specific but also cell specific.
We have produced transgenic mice using the mouse placental lactogen type II promoter to force and restrict the expression of the mouse major histocompatibility complex (MHC) class I molecule, H-2K(b), to the placenta. We show that the transgenic MHC antigen H-2K(b) is expressed exclusively in trophoblast giant cells from Day 10.5 until the end of gestation. This expression affects neither the fetal development nor the maternal tolerance to the fetus in histoincompatible mothers. We have used the 3.83 B cell receptor (BcR) transgenic mouse line to follow the fate of H-2K(b)-specific maternal B cells in mothers bearing H-2K(b)-positive placentas. Our results suggest that transgenic H-2K(b) molecules on trophoblast giant cells are recognized by 3.83 BcR-transgenic B cells in the bone marrow of pregnant females. This antigen recognition triggers the deletion of a bone marrow B cell subpopulation, including immature and transitional B cells. Their percentage decreases during the second half of gestation and is down to 8% on Day 17.5, compared to 22% in the (3.83 Tg female x Fvb) control group. This deletion might contribute to the process of maternal tolerance of the conceptus.
p53 is a nuclear protein that acts like a tumor suppressor and is involved in regulation of cellular growth. In Xenopus, the p53 protein is highly expressed during oogenesis and is strictly cytoplasmic in the oocyte. We have analysed its participation in DNA replication and transcription during early development, using the egg and oocyte as model-systems. The injection of sperm nuclei into Xenopus eggs is followed by DNA replication and mitotic events. We show that the endogenous p53 enters the nuclei and moves through a series of discrete subnuclear loci whose distribution is S-phase speci®c. A speci®c peripheral nuclear localization of p53 is observed before entry into S-phase, followed by an internal localization which is strictly dependent on ongoing DNA synthesis. At no stage in the cell cycle, however, did we observe any co-localization with RPA or PCNA, which were used as initiation or elongation markers for DNA replication. We also show that injection into the nucleus of the oocyte of small amounts of either Xenopus or human p53 ± less than 10% of the cytoplasmic storage ± is su cient to block RNA polymerase IIdependent transcription from a coinjected TATA-boxcontaining reporter plasmid. Transcription is rescued by microinjection of the TATA-box binding protein (TBP), suggesting that nuclear exclusion of p53 during oogenesis may be necessary for transcription of maternal genes. These characteristics are discussed in relation to the regulation of nuclear activities during early embryogenesis.
The remarkable stabthty of c-myc durmg oogenesrs contrasts wrth Its dcgradatron durmg the early dcvclopmental period m Xenopus lucv~s Three evolutionary conserved mottfs found m the 3'-untranslated region of Xenopus c-myc RNAs have been analyzed for a possible pole m c-myc RN.4 degradatton No specrfic degradatron was observed when these sequences were cloned downstream of a mportcr gene and the corrcspondmg RNAs were InJected mto fertthzed eggs The relatron between polyadenylatton and degrddatton of c-myc mRNA has been exammed durmg early development c-myc IS adenylated durmg early oogenesis, and a drdmattc de-adenylation occurs m full grown oocytes Consequently, the de-adenylatton of c-myc mRNA that OLCUPS m eggs mrght be a rcqutrement for Its degradation after fertthxatton, but IS not suffictent to trtgger tts degradation C-myc. mRNA stabthty, Polyadenytatton, Xenopas laevrs
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