The prefrontal cortex is believed to play a major role in depression and suicidal behavior through regulation of cognition, memory, recognition of emotion, and anxiety-like states, with numerous post-mortem studies documenting a prefrontal serotonergic dysregulation considered to be characteristic of depressive psychopathology. This study was carried out to detect changes in gene expression associated with both suicide and major depression using oligonucleotide microarrays (Affymetrix HG-U133 chip set) summarizing expression patterns in primarily ventral regions of the prefrontal cortex (BA44, 45, 46 and 47). A total of 37 male subjects were included in this study, of which 24 were suicides (depressed suicides = 16, nondepressed suicides = 8) and 13 were matched controls. All subjects were clinically characterized by means of psychological autopsies using structured interviews. Unique patterns of differential expression were validated in each of the cortical regions evaluated, with group-specific changes highlighting the involvement of several key neurobiological pathways that have been implicated in both suicide and depression. An overrepresentation of factors involved in cell cycle control and cell division (BA44), transcription (BA44 and 47) and myelination (BA46) was seen in gene ontology analysis of differentially expressed genes, which also highlights changes in the expression of genes involved in ATP biosynthesis and utilization across all areas. Gene misexpression in BA46 was most pronounced between the two suicide groups, with many significant genes involved in GABAergic neurotransmission. The pronounced misexpression of genes central to GABAergic signaling and astrocyte/ oligodendrocyte function provides further support for a central glial pathology in depression and suicidal behavior.

These data suggest a role for SSAT, the rate-limiting enzyme in the catabolism of polyamines, in suicide and depression and a role for the SSAT342 locus in the regulation of SSAT gene expression.

The limbic system has consistently been associated with the control of emotions and with mood disorders. The goal of this study was to identify new molecular targets associated with suicide and with major depression using oligonucleotide microarrays in the limbic system (amygdala, hippocampus, anterior cingulate gryus (BA24) and posterior cingulate gyrus (BA29)). A total of 39 subjects were included in this study. They were all male subjects and comprised 26 suicides (depressed suicides = 18, non depressed suicides = 8) and 13 matched controls. Brain gene expression analysis was carried out on human brain samples using the Affymetrix HG U133 chip set. Differential expression in each of the limbic regions showed group-specific patterns of expression, supporting particular neurobiological mechanisms implicated in suicide and depression. Confirmation of genes selected based on their significance and the interest of their function with reverse transcriptase-polymerase chain reaction showed consistently correlated signals with the results obtained in the microarray analysis. Gene ontology analysis with differentially expressed genes revealed an overrepresentation of transcription and metabolism-related genes in the hippocampus and amygdala, whereas differentially expressed genes in BA24 and BA29 were more generally related to RNA-binding, regulation of enzymatic activity and protein metabolism. Limbic expression patterns were most extensively altered in the hippocampus, where processes related to major depression were associated with altered expression of factors involved with transcription and cellular metabolism. Additionally, our results confirm previous evidence pointing to global alteration of gabaergic neurotransmission in suicide and major depression, offering new avenues in the study and possibly treatment of such complex disorders. Overall, these data suggest that specific patterns of expression in the limbic system contribute to the etiology of depression and suicidal behaviors and highlight the role of the hippocampus in major depression.

An association between low levels of serum cholesterol and violent or suicidal behaviour has frequently been reported, but it remains unclear how cholesterol in the peripheral system might be related to the brain functions involved in mediating suicidal behaviour. To our knowledge, there have been no previous studies aimed at answering the important question of whether there are differences in cholesterol within the brains of suicide completers. In the present study, cholesterol content was measured in cortical and subcortical tissue of brains from 41 male suicide completers and 21 male controls that died of sudden causes with no direct influence on brain tissue. No significant differences in cholesterol content were found between suicides and controls in the frontal cortex, amygdala or hippocampus. However, when the suicide completers were stratified into violent (n=31) or non-violent (n=10) groups based on the method of death, violent suicides were found to have lower grey-matter cholesterol content overall compared to non-violent suicides [F(1,111)=4.75, p=0.03], specifically in the frontal cortex (t=-4.16, d.f.=37, p<0.0005). Further exploration of the frontal cortex revealed that violent suicides had lower cholesterol content compared to non-violent suicides in the orbitofrontal cortex (t=-2.01, d.f.=36, p=0.05) and the ventral prefrontal cortex (t=-2.49, d.f.=37, p=0.02). This study represents the first direct examination of cholesterol content in brain tissue from suicide completers, and the present findings provide added support for the relationship between low cholesterol and violent or suicidal behaviour.

Altered stress reactivity is considered to be a risk factor for both major depressive disorder and suicidal behavior. The authors have sought to expand their previous findings implicating altered expression of spermidine/spermine N(1)-acetyltransferase 1 (SAT1), the rate-limiting enzyme involved in catabolism of the polyamines spermidine and spermine in the polyamine stress response (PSR), across multiple brain regions between control individuals and depressed individuals who have died by suicide. Microarray expression of probesets annotated to SAT1 were examined across 17 brain regions in 13 controls and 26 individuals who have died by suicide (16 with a diagnosis of major depression and 10 without), all of French-Canadian origin. Profiling conducted on the Affymetrix U133A/B chipset was further examined on a second chipset (U133 Plus 2.0) using RT-PCR, and analyzed in a second, independent sample. A reduction in SAT1 expression identified through multiple probesets was observed across 12 cortical regions in depressed individuals who have died by suicide compared with controls. Of these, five cortical regions showed statistically significant reductions which were supported by RT-PCR and analysis on the additional chipset. SAT1 cortical expression levels were also found to be significantly lower in an independent sample of German subjects with major depression who died by suicide in comparison with controls. These findings suggest that downregulation of SAT1 expression may play a role in depression and suicidality, possibly by impeding the normal PSR program or through compensation for the increased polyamine metabolism accompanying the psychological distress associated with depressive disorders.

No abstract

Natural leaf senescence has a negative influence on yield. Postharvest induced senescence contributes to the losses of quality in flowers, foliage, and vegetables. Strategies designed to control the senescence process in crop plants could therefore have great applied significance. Senescence is regulated by differential gene expression yet, functional characterization of the genes specifically induced and study of their expression control, is still in its infancy. Study of senescence-specific genes is required to allow identification of regulatory elements participating in senescence-induced expression and thus provide insights into the genetic regulation of senescence. A main feature of senescence is the hydrolysis of macromolecules by hydrolases of various types such as RNases and proteases. This study was aimed a analysis of senescence-inducible RNases in tomato with the following objectives: Isolation of senescence-inducible RNase cDNA clones; Expression analyses of RNase genes during senescence; Identification of sequences required for senescence-induced gene expression; Functional analyses of senescence-inducible RNases. We narrowed our aims somewhat to focus on the first three objectives because the budget we were awarded was reduced from that requested. We have expanded our research for identification senescence-related RNase/nuclease activities as we thought it will direct us to new RNase/nuclease genes. We have also carried out research in Arabidopsis and parsley, which enabled us to draw mire general conclusions. We completed the first and second objectives and have made considerable progress on the remaining two. We have defined growth conditions suitable for this research and defined the physiological and biochemical parameters characteristic to the advance of leaf senescence. In tomato and arabidopsis we have focused on natural leaf senescence. Parsley was used mainly for study of postharvest senescence in detached leaves. We have identified a 41-kD a tomato nuclease, LeNUCI, specifically induced during senescence which can degrade both RNA and DNA. This activity could be induced by ethylene in young leaves and was subjected to detailed analysis, which enabled its classification as Nuclease I enzyme. LeNUCI may be involved in nucleic acid metabolism during tomato leaf senescence. In parsley senescing leaves we identified 2 main senescence-related nuclease activities of 41 and 39-kDa. These activities were induced in both naturally or artificially senescing leaves, could degrade both DNA and RNA and were very similar in their characteristics to the LeNUCI. Two senescence-induced RNase cDNAs were cloned from tomato. One RNase cDNA was identical to the tomato LX RNase while the second corresponded to the LE RNase. Both were demonstrated before to be induced following phosphate starvation of tomato cell culture but nothing was known about their expression or function in plants. LX gene expression was much more senescence specific and ethylene could activate it in detached young leaves. LE gene expression, which could be transiently induced by wounding, appeared to be activated by abscisic acid. We suggest that the LX RNase has a role in RNA catabolism in the final stage of senescence, and LE may be a defense-related protein. Transgenic plants were generated for altering LX gene expression. No major visible alterations in the phenotype were observed so far. Detailed analysis of senescence in these plants is performed currently. The LX promoter was cloned and its analysis is performed currently for identification of senescence-specific regulatory elements. In Arabidopsis we have identified and characterized a senescence-associated nuclease 1 gene, BFN1, which is highly expressed during leaf and stem senescence. BFN1, is the first example of a senescence- associated gene encoding a nuclease I enzyme as well as the first nuclease I cloned and characterized from Arabidopsis. Our progress should provide excellent tools for the continued analysis of regulation and function of senescence-inducible ribonucleases and nucleases in plants. The cloned genes can be used in reverse genetic approaches, already initiated, which can yield a more direct evidence for the function of these enzymes. Another contribution of this research will be in respect to the molecular mechanism, which controls senescence. We had already initiated in this project and will continue to identify and characterize regulatory elements involved in senescence-specific expression of the genes isolated in this work.