Induction of meiotic maturation in mouse oocytes by adenosine analogs

In this study we have examined the meiosis-inducing influence of adenosine analogs in mouse oocytes. When a varied group of nucleosides and nucleotides were tested on overnight cultures of hypoxanthine-arrested, cumulus cell-enclosed oocytes (CEO), halogenated adenosine nucleosides, but not native adenosine, exhibited a significant meiosis-inducing capability. When tested under a variety of conditions, meiotic induction by 8-bromo-adenosine (8-Br-Ado) and a second adenosine analog, methylmercaptopurine riboside (MMPR), was especially potent in denuded oocytes (DO) compared to CEO and was not dependent on the type of inhibitor chosen to maintain meiotic arrest. Germinal vesicle breakdown (GVB) was stimulated with rapid kinetics and was preceded by an increase in AMP-activated protein kinase (AMPK) activity. Moreover, compound C, an inhibitor of AMPK, blocked the meiosis-inducing activities of both adenosine analogs. When tested for an effect on meiotic progression to metaphase II (MII) in spontaneously maturing CEO, 8-Br-Ado and the AMPK activator, 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR), increased the percentage of MII-stage oocytes, but MMPR decreased this number. Adenosine and inhibitors of de novo purine synthesis had no effect on the completion of maturation, while compound C suppressed this process. These results support the proposition that oocyte AMPK mediates the positive influence of AICAR and 8-Br-Ado on both the initiation and completion of meiotic maturation. The role of AMPK in MMPR action is less clear.     

The PKC pathway and in particular its beta1 isoform is clearly involved in meiotic arrest maintenance but poorly in FSH-induced meiosis resumption of the mouse cumulus cell enclosed oocyte

PKC modulators were used to investigate the role of the PKC pathway either on the maintenance of meiotic arrest or on FSH-induced maturation of mouse cumulus cell enclosed oocytes (CEOs). (1) Whereas PKC activation (PMA 8 microM) overcomed clearly the HX-maintained meiotic arrest (83.7 +/- 3.6% vs. 16.1 +/- 10.6% GVBD oocytes), PKC inhibition (Calphostin C 100 nM) did not. On the contrary, it better maintained the meiotic arrest than HX alone. (2) No significant effect of PKC activation or inhibition was observed. (3) HX alone maintained PKCbeta1 in the cytoplasm, whereas FSH and PKC activation induced partly its translocation into the nucleus. The results show that whereas the PKC pathway is clearly involved in maintenance of the meiotic arrest through PKCbeta1, it is not involved in FSH-induced meiosis of CEOs.     

In vitro culture of secondary follicles and prematuration of cumulus–oocyte complexes from antral follicles increase the levels of maturation‐related transcripts in bovine oocytes

This study evaluates the levels of messenger RNA (mRNA) for eIF4E, PARN, H1FOO, cMOS, GDF9, and CCNB1 in oocytes from secondary and antral follicles at different stages of development. The effects of in vitro culture, in vitro prematuration, and in vitro maturation on the expression of these genes on oocytes were also analyzed. The results showed that mRNA levels for H1FOO, GDF9, and PARN were higher in oocytes from small, medium, and large antral follicles, respectively, than those seen in secondary follicles. Oocytes from small, medium, and large antral follicles had higher levels of CCNB1 than oocytes from secondary follicles. Oocytes from cultured secondary follicles had higher levels of GDF9, CMOS, PARN, eIF4E, CCNB1, and H1FOO than before culture. Prematured oocytes from small antral follicles had higher levels of mRNA for GDF9, PARN, and eIF4E than before culture. In addition, higher levels of cMOS and H1FOO were identified in prematured oocytes from medium antral follicles. In conclusion, follicular growth is associated with an increase in the expression of H1FOO, GDF9, CCNB1, and PARN. The culture of secondary follicles, prematuration, and maturation of oocytes from antral follicles increase the expression of eIF4E, PARN, H1FOO, cMOS, GDF9, and CCNB1.     

Plague studies in California: a review of long‐term disease activity,flea‐host relationships and plague ecology in the coniferous forests of the Southern Cascades and northern Sierra Nevada mountains

We review 28 years of long‐term surveillance (1970–1997) for plague activity among wild rodents from ten locations within three coniferous forest habitat types in the northern Sierra Nevada and the Southern Cascade mountains of northeastern California. We identify rodent hosts and their fleas and document long‐term plague activity in each habitat type. The highest seroprevalence for Yersinia pestis occurred in the chipmunks, Tamias senex and T. quadrimaculatus, and the pine squirrel, Tamiasciurus douglasii. The most commonly infected fleas were Ceratophyllus ciliatus and Eumolpianus eumolpi from chipmunks and Oropsylla montana and O. idahoensis from ground squirrels. Serological surveillance demonstrated that populations of T. senex, T. quadrimaculatus and T. douglasii are moderately resistant to plague, survive infection, and are, therefore, good sentinels for plague activity. Recaptured T. senex and T. quadrimaculatus showed persistence of plague antibodies and evidence of re‐infection over a two year period. These rodent species, their fleas, and the ecological factors common to the coniferous forest habitats likely promote the maintenance of plague foci in northeastern California.     

The combined effects of a long‐term experimental drought and an extreme drought on the use of plant‐water sources in a Mediterranean forest

Vegetation in water‐limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species‐specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long‐term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long‐term experimental drought shifted water uptake toward deeper (10–35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought‐affected plants. This study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions.     

Lipid peroxidation and apoptotic response in rat brain areas induced by long‐term administration of nandrolone: the mutual crosstalk between ROS and NF‐kB

The aim of this study was to evaluate the played by oxidative stress in the apoptotic response in different brain areas of rats chronically treated with supra‐physiological doses of nandrolone decanoate (ND). Immunohistochemical study and Western blot analysis were performed to evaluate cells' apoptosis and to measure the effects of expression of specific mediators, such as NF‐κB (nuclear factor kappa‐light‐chain‐enhancer of activated B cells), Bcl‐2 (B‐cell lymphoma 2), SMAC/DIABLO (second mitochondria‐derived activator of caspases/direct IAP‐binding protein with low PI) and VMAT2 (vesicular monoamine transporter 2) on apoptosis. The results of the present study indicate that a long‐term administration of ND promotes oxidative injury in rat brain specific areas. A link between oxidative stress and NF‐κB signalling pathways is supported by our results. In addition to high levels of oxidative stress, we consistently observed a strong immunopositivity to NF‐κB. It has been argued that one of the pathways leading to the activation of NF‐κB could be under reactive oxygen species (ROS)‐mediated control. In fact, growing evidence suggests that although in limited doses, endogenous ROS may play an activating role in NF‐κB signalling, while above a certain threshold, they may negatively impact upon this signalling. However, a mutual crosstalk between ROS and NF‐κB exists and recent studies have shown that ROS activity is subject to negative feedback regulation by NF‐κB, and that this negative regulation of ROS is the means through which NF‐κB counters programmed cells.     

Age‐related loss of neuronal nicotinic receptor expression in the aging mouse hippocampus corresponds with cyclooxygenase‐2 and PPARγ expression and is altered by long‐term NS398 administration

Age‐related changes in the mammalian dorsal hippocampus are associated with diminished expression of neuronal nicotinic acetylcholine receptors (nAChR), which is particularly severe in pathologies such as those associated with dementias, including Alzheimer's disease. Because the mouse is a useful model for age‐related decline in nAChR expression in the basal forebrain and limbic system, we used immunohistochemistry to examine the influence of long‐term (12‐month) oral administration of nicotine and/or the cyclooxygenase‐2 (COX‐2) preferring non‐steroidal anti‐inflammatory drug (NSAID) NS398 on nAChRα4, α5, α7, and β4 expression in the C57BL/6 mouse. Inhibitory neurons of the dorsal hippocampus that express nAChRs also constitutively express COX‐2 and the peroxisome proliferator‐antagonist receptor subtype gamma‐2 (PPARγ2) which is also a target of NS398. Administration of NS398 correlated with retention of nAChRα4 and to a lesser extent nAChRβ4, but not nAChRα5 or α7, but nicotine exhibited no similar effect. Nicotine and NS398 co‐administration abolished the NS398‐related effect on nAChRα4 retention. These results provide evidence that the interaction during aging between oral administration of nicotine and NSAIDs are not straightforward and could even be antagonistic when combined. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2005