Regulation and execution of molecular disassembly and catabolism during senescence

Senescence is a highly orchestrated developmental stage in the life cycle of plants. The onset of senescence is tightly controlled by signaling cascades that initiate changes in gene expression and the synthesis of new proteins. This complement of new proteins includes hydrolytic enzymes capable of executing catabolism of macromolecules, which in turn sets in motion disassembly of membrane molecular matrices, leading to loss of cell function and, ultimately, complete breakdown of cellular ultrastructure. A distinguishing feature of senescence that sets it apart from other types of programmed cell death is the recovery of carbon and nitrogen from the dying tissue and their translocation to growing parts of the plant such as developing seeds. For this to be accomplished, the initiation of senescence and its execution have to be meticulously regulated. For example, the initiation of membrane disassembly has to be intricately linked with the recruitment of nutrients because their ensuing translocation out of the senescing tissue requires functional membranes. Molecular mechanisms underlying this linkage and its integration with the catabolism of macromolecules in senescing tissues are addressed.     

Solution structure of NOD1 CARD and mutational analysis of its interaction with the CARD of downstream kinase RICK

NOD1 is a cytosolic signalling host pattern-recognition receptor composed of a caspase-activating and recruitment domain (CARD), a nucleotide-binding and oligomerization domain (NOD) and leucine-rich repeats. It plays a crucial role in innate immunity by activating the NF-kappaB pathway via its downstream effector the kinase RICK (RIP2) following the recognition of a specific bacterial ligand. RICK is recruited by NOD1 through interaction of their respective CARDs. Here we present the high resolution NMR structure of the NOD1 CARD. It is generally similar to other CARDs of known structure, consisting of six tightly packed helices, although the length and orientation of the last helix is unusual. Mutations in both the NOD1 and RICK CARD domains were assayed by immuno-precipitation of cell lysates and in vivo NF-kappaB activation in order to define residues important for CARD-CARD interaction and downstream signalling. The results show that the interaction is critically dependent on three acidic residues on NOD1 CARD and three basic residues on RICK CARD and thus is likely to have a strong electrostatic component, similar to other characterised CARD-CARD interactions.     

Pitavastatin prevents NMDA-induced retinal ganglion cell death by suppressing leukocyte recruitment

Excitotoxicity is a major cause of retinal ganglion cell (RGC) death during ischemic diseases such as vessel occlusion and diabetic retinopathy. However, the underlying mechanisms are not well understood. Statins, inhibitors of the HMG-CoA reductase, have neuroprotective effects in addition to their original role in lowering cholesterol. We hypothesize that pitavastatin, a recently introduced potent statin, is protective against N-methyl-d-aspartic acid (NMDA)-induced RGC death. Pitavastatin, administered by gavage, abolished NMDA-induced loss of RGCs. To elucidate the mechanisms underlying the neuroprotective effect of pitavastatin, we investigated its impact on inflammation. NMDA increased the expression of interleukin-1beta and TNF-alpha, and endothelial adhesion molecules, including ICAM-1, and induced leukocyte accumulation in the retinal vessels. Pitavastatin significantly reduced NMDA-induced leukocyte accumulation and up-regulation of endothelial adhesion molecules, whereas cytokine expression was unaffected. Systemic blockade of ICAM-1 in wild-type mice or absence of CD18 in gene-deficient (CD18(-/-)) mice significantly suppressed NMDA-induced leukocyte accumulation and RGC death. These findings suggest a novel and causative role for inflammatory leukocyte recruitment in NMDA-induced excitotoxicity. Furthermore, we show the novel neuroprotective effect of statins against excitotoxicity-induced RGC death. Statins or other anti-inflammatory agents may thus have therapeutic benefits in excitotoxicity-associated neuronal diseases through blockade of leukocyte recruitment.     

Climate and demography of the planktivorous Cassin's auklet Ptychoramphus aleuticus off northern California: implications for population change

1. We performed demographic analyses on Cassin's auklet Ptychoramphus aleuticus, a zooplanktivorous seabird inhabiting the variable California Current System, to understand how temporal environmental variability influences population dynamics. 2. We used capture-recapture data from 1986 to 2002 to rank models of interannual variation in survival, breeding propensity, breeding success, and recruitment. 3. All demographic parameters exhibited temporal variability. Interannual variation in survival was best modelled as a nonlinear function of the winter Southern Oscillation Index (SOI). Breeding propensity was best modelled as a threshold function of local sea surface temperature. Breeding success and recruitment were best modelled with year-dependent annual variation. 4. Changes in the SOI force El Ni?o/La Ni?a events, which in turn alter prey availability to seabirds in this system. Demographic responses varied during El Ni?os/La Ni?as. Survival diminished substantially during the 1997-98 El Ni?o event, while breeding propensity was affected during both the 1992 and 1998 El Ni?os. Breeding success was reduced during the 1992, 1993, and 1998 El Ni?os, but was unusually high in 2002. Recruitment was higher at the beginning and end of this time-series. 5. While demographic responses varied interannually, parameter values covaried in a positive fashion, a situation conducive to rapid population change. During the 11 years study period, the Farallon auklet breeding population declined at 6.05 +/- 0.80% (SE) per year, a cumulative decline of 49.7%. This study demonstrates how climate variability has influenced key demographic processes for this diminished marine bird population.     

Climate and body size influence nest survival in a fish with parental care

1. The current study examined the effect of broad-scale climate and individual-specific covariates on nest survival in smallmouth bass over a 20-year period. 2. Large-scale climate indices [winter North Atlantic Oscillation (NAO) and winter El Ni?o/Southern Oscillation (ENSO)] and body size of parental males were important covariates in nest survival along with nest age and a quadratic trend in survival. 3. We did not find an effect due to a habitat covariate (total effective fetch) or a phenology covariate (degree-days at start of nesting) on nest survival. 4. Male size in the second half of the nesting season was a more influential covariate on nest success than male size in the first half or throughout the nesting period. 5. We present evidence showing that winter NAO/ENSO indices establish limnological conditions the following spring that influence thermal stability of the lake during the nesting period. 6. The combined climate and body size covariates point to nest survival as a function of lagged climate-scale influences on limnology and the individual-scale influence of bioenergetics on the duration of parental care and nest success.     

Eel community structure,fluvial recruitment of <Emphasis Type="Italic">Anguilla marmorata</Emphasis> and indication for a weak local production of spawners from rivers of Réunion and Mauritius islands

Anguillid eels were sampled from permanent rivers in the Réunion and Mauritius islands, western Indian Ocean, with a standardized electrofishing method. A. marmorata was very dominant, corresponding to 91.7 and 90.7% of all the eels collected in Réunion and Mauritius, respectively. Three other species (A. mossambica, A. bicolor bicolor and A. nebulosa labiata) were also present in both islands. A. marmorata showed a strong altitudinal gradient of densities from the lower to upper zones, especially in the younger stages (TL <250 mm), while A. mossambica was only found in the upper zones and A. bicolor bicolor occurred only in the lower zones (A. nebulosa labiata was rare). The eel species composition in freshwaters of both islands is very similar because these two adjoining islands are located in the same trail of drifting marine larvae. Mean estimated eel biomasses were noticeably low (11.1 and 22.2 kg ha⁻¹ in Réunion and Mauritius islands, respectively), especially when compared to those of other tropical insular systems without any eel fishery (Comoros or Polynesia, more than 100 kg ha⁻¹). Nevertheless, the fluvial recruitment of A. marmorata seemed to be regular during the surveyed period, staggering from October to April. The obvious lack of large eels in Mauritius but more significantly in Réunion suggests a high pressure from traditional fishery, and the local reproductive turnover is uncertain. Because sexual maturation seems to occur at a large body size for A. marmorata, as for temperate species, the Réunion and Mauritius rivers may only have a weak contribution to the regional production of spawners. However, the giant mottled eel population in the western Indian Ocean is believed to be panmictic at the regional scale, and may not rely exclusively on these islands’ contribution. A comparison is made with those of freshwater systems in other tropical islands.