Poly(ADP-ribosylation) of atypical CS histone variants is required for the progression of S phase in early embryos of sea urchins.

The patterns of poly(ADP-ribosylation) in vivo of CS (cleavage stage) histone variants were compared in sea urchin zygotes at the entrance and the exit of S1 and S2 in the initial developmental cell cycles. This post-translational modification was detected by Western immunoblots with rabbit sera anti-poly(ADP-ribose) that was principally reactive against ADP-ribose polymers and slightly against ADP-ribose oligomers. The effect of 3 aminobenzamide (3-ABA), an inhibitor of the poly(ADP-ribose) synthetase, on S phase progression was determined in vivo by measuring the incorporation of 3H thymidine into DNA. The results obtained indicate that the CS histone variants are poly(ADP-ribosylated) in a cell cycle dependent manner. A significantly positive reaction of several CS variants with sera anti-poly(ADP-ribose) was found at the entrance into S phase, which decreases after its completion. The incubation of zygotes in 3-ABA inhibited the poly(ADP-ribosylation) of CS variants and prevented both the progression of the first S phase and the first cleavage division. These observations suggest that the poly(ADP-ribosylation) of atypical CS histone variants is relevant for initiation of sea urchin development and is required for embryonic DNA replication.     

Prenatal Stress Down-Regulates Reelin Expression by Methylation of Its Promoter and Induces Adult Behavioral Impairments in Rats

Prenatal stress causes predisposition to cognitive and emotional disturbances and is a risk factor towards the development of neuropsychiatric conditions like depression, bipolar disorders and schizophrenia. The extracellular protein Reelin, expressed by Cajal-Retzius cells during cortical development, plays critical roles on cortical lamination and synaptic maturation, and its deregulation has been associated with maladaptive conditions. In the present study, we address the effect of prenatal restraint stress (PNS) upon Reelin expression and signaling in pregnant rats during the last 10 days of pregnancy. Animals from one group, including control and PNS exposed fetuses, were sacrificed and analyzed using immunohistochemical, biochemical, cell biology and molecular biology approaches. We scored changes in the expression of Reelin, its signaling pathway and in the methylation of its promoter. A second group included control and PNS exposed animals maintained until young adulthood for behavioral studies. Using the optical dissector, we show decreased numbers of Reelin-positive neurons in cortical layer I of PNS exposed animals. In addition, neurons from PNS exposed animals display decreased Reelin expression that is paralleled by changes in components of the Reelin-signaling cascade, both in vivo and in vitro. Furthermore, PNS induced changes in the DNA methylation levels of the Reelin promoter in culture and in histological samples. PNS adult rats display excessive spontaneous locomotor activity, high anxiety levels and problems of learning and memory consolidation. No significant visuo-spatial memory impairment was detected on the Morris water maze. These results highlight the effects of prenatal stress on the Cajal-Retzius neuronal population, and the persistence of behavioral consequences using this treatment in adults, thereby supporting a relevant role of PNS in the genesis of neuropsychiatric diseases. We also propose an in vitro model that can yield new insights on the molecular mechanisms behind the effects of prenatal stress.     

Classical Xenopus laevis progesterone receptor associates to the plasma membrane through its ligand-binding domain

During the last decade, considerable evidence is accumulating that supports the view that the classic progesterone receptor (xPR-1) is mediating Xenopus laevis oocyte maturation through a non-genomic mechanism. Overexpression and depletion of oocyte xPR-1 have been shown to accelerate and to block progesterone-induced oocyte maturation, respectively. In addition, rapid inhibition of plasma membrane adenylyl cyclase (AC) by the steroid hormone, supports the idea that xPR-1 should be localized at the oocyte plasma membrane. To test this hypothesis, we transiently transfected xPR-1 cDNA into Cos-7 cells and analyzed its subcellular distribution. Through Western blot and immunofluorescence analysis, we were able to detect xPR-1 associated to the plasma membrane of transfected Cos-7 cells. Additionally, using Progesterone-BSA-FITC, we identified specific progesterone-binding sites at the cell surface of xPR-1 expressing cells. Finally, we found that the receptor ligand-binding domain displayed membrane localization, in contrast to the N-terminal domain, which expressed in similar levels, remained cytosolic. Overall, these results indicate that a fraction of xPR-1 expressed in Cos-7 cells, associates to the plasma membrane through its LBD.