Significance of DNA base excision repair in the maintenance of mitochondrial function in Saccharomyces cerevisiae /

Mitochondria have an important role in cell metabolism, being the major site of ATP production via oxidative phosphorylation (OXPHOS). Accumulation of mtDNA mutations have been linked to the development of respiratory dysfunction, apoptosis, and aging. Base excision repair (BER) is the major and the only certain repair pathway existing in mitochondria that is in responsible for removing and repairing various base modifications as well as abasic sites (AP sites). In this research, Saccharomyces cerevisiae (S. cerevisiae) BER gene knockout strains, including 3 single DNA glycosylase gene knockout strains and Ap endonuclease (Apn 1 p) knockout strain were used to examine the importance of this DNA repair pathway to the maintenance of respiratory function. Here, I show that individual DNA glycosylases are nonessential in maintenance of normal function in yeast mitochondria, corroborating with previous research in mammalian experimental models. The yeast strain lacking Apn 1 p activity exhibits respiratory deficits, including inefficient and significantly low intracellular ATP level, which maybe due to partial uncoupling of OXPHOS. Growth of this yeast strain on respiratory medium is inhibited, but no evidence was found for increased ROS level in Apn 1 p mitochondria. This strain also shows an increased cell size, and this observation combined with an uncoupled OXPHOS may indicate a premature aging in the Apnlp knockout strain, but more evidence is needed to support this hypothesis. However, the BER is necessary for maintenance of mitochondrial function in respiring S.cerevisiae.

Effects of social context on endocrine function and Zif268 expression in response to an acute stressor in adolescent and adult rats

There is a paucity of studies comparing social buffering in adolescents and adults, despite their marked differences in social behaviour. I investigated whether greater effects of social buffering on plasma corticosterone concentrations and expression of Zif268 in neural regions after an acute stressor would be found in adolescent compared with adult rats. Samples were obtained before and after one hour of isolation stress and after either one or three hours of recovery back in the colony with either a familiar or unfamiliar cage partner. Adolescent and adult rats did not differ in plasma concentrations of corticosterone at any time point. Corticosterone concentrations were higher after one hour isolation than at baseline (p < 0.001), and rats with a familiar partner during the recovery phase had lower corticosterone concentrations than did rats with an unfamiliar partner (p = 0.02). Zif268 immunoreactive cell counts were higher in the arcuate nucleus in both age groups after isolation (p = 0.007) and higher in the paraventricular nucleus of adolescents compared with adults during the recovery phase irrespective of partner familiarity. There was a significant decrease in immunoreactive cell counts after one hour isolation compared to baseline in the basolateral amygdala, central nucleus of the amygdala, and in the pyramidal layer of the hippocampus (all p < 0.05). An effect of partner familiarity on Zif268 immunoreactive cell counts was found in the granule layer of the dentate gyrus irrespective of age (higher in those with a familiar partner, p = 0.03) and in the medial prefrontal cortex in adolescents (higher with an unfamiliar partner, p = 0.02). Overall, the acute stress and partner familiarity produced a similar pattern of results in adolescents and adults, with both age groups sensitive to the social context.

Cell-selective modulation of the neuromuscular system in Drosophila

The capacity for all living cells to sense and interact with their environment is a necessity for life. In highly evolved, eukaryotic species, like humans, signalling mechanisms are necessary to regulate the function and survival of all cells in the organism. Synchronizing systemic signalling systems at the cellular, organ and whole-organism level is a formidable task, and for most species requires a large number of signalling molecules and their receptors. One of the major types of signalling molecules used throughout the animal kingdom are modulatory substances (e.x. hormones and peptides). Modulators can act as chemical transmitters, facilitating communication at chemical synapses. There are hundreds of circulating modulators within the mammalian system, but the reason for so many remains a mystery. Recent work with the fruit fly, Drosophila melanogaster demonstrated the capacity for peptides to modulate synaptic transmission in a neuron-specific manner, suggesting that peptides are not simply redundant, but rather may have highly specific roles. Thus, the diversity of peptides may reflect cell-specific functions. The main objective of my doctoral thesis was to examine the extent to which neuromodulator substances and their receptors modulate synaptic transmission at a cell-specific level using D. melanogaster. Using three different modulatory substances, i) octopamine - a biogenic amine released from motor neuron terminals, ii) DPKQDFMRFa - a neuropeptide secreted into circulation, and iii) Proctolin - a pentapeptide released both from motor neuron terminals and into circulation, I was able to investigate not only the capacity of these various substances to work in a cell-selective manner, but also examine the different mechanisms of action and how modulatory substances work in concert to execute systemic functionality . The results support the idea that modulatory substances act in a circuit-selective manner in the central nervous system and in the periphery in order to coordinate and synchronize physiologically and behaviourally relevant outputs. The findings contribute as to why the nervous system encodes so many modulatory substances.