Critical Time for Weed Removal in Corn (\u3ci\u3eZea mays\u3c/i\u3e L.) as Influenced by Pre Herbicides

A weed control program that utilizes PRE herbicides and ensures a timely post-emergence weed removal could protect growth and yield of corn. The use of pre-emergence (PRE) herbicides for weed control could reduce the need for multiple POST applications of glyphosate in glyphosate-tolerant (GT) corn and provide an additional mode of action for combating glyphosate-resistant weeds. Thus, field studies were conducted in 2017 and 2018 at Concord, NE with the following objectives develop weed management recommendations that considers soil applied herbicides and determine proper timing of glyphosate based on the crop growth stage. Therefore the material in this thesis is presented in three chapters: Chapter 1 outlines the integrated weed management, critical period of weed control, and pre-emergence (PRE) or post-emergence (POST) herbicide use in corn. Chapter 2 determines the critical time for weed removal in glyphosate-tolerant corn without pre-emergence (PRE) herbicide and atrazine or Verdict-Zidua applied pre-emergence (PRE). Chapter 3 determines how the timing of weed removal and PRE herbicides application could influence growth and yield of glyphosate-tolerant corn. Advisor: Stevan Z. Knezevi

Critical Time for Weed Removal in Corn (\u3ci\u3eZea mays\u3c/i\u3e L.) as Influenced by Pre Herbicides

A weed control program that utilizes PRE herbicides and ensures a timely post-emergence weed removal could protect growth and yield of corn. The use of pre-emergence (PRE) herbicides for weed control could reduce the need for multiple POST applications of glyphosate in glyphosate-tolerant (GT) corn and provide an additional mode of action for combating glyphosate-resistant weeds. Thus, field studies were conducted in 2017 and 2018 at Concord, NE with the following objectives develop weed management recommendations that considers soil applied herbicides and determine proper timing of glyphosate based on the crop growth stage. Therefore the material in this thesis is presented in three chapters: Chapter 1 outlines the integrated weed management, critical period of weed control, and pre-emergence (PRE) or post-emergence (POST) herbicide use in corn. Chapter 2 determines the critical time for weed removal in glyphosate-tolerant corn without pre-emergence (PRE) herbicide and atrazine or Verdict-Zidua applied pre-emergence (PRE). Chapter 3 determines how the timing of weed removal and PRE herbicides application could influence growth and yield of glyphosate-tolerant corn. Advisor: Stevan Z. Knezevi

alpha-Synuclein expression and Nrf2 deficiency cooperate to aggravate protein aggregation, neuronal death and inflammation in early-stage Parkinson's disease

Although -synuclein (-SYN) aggregation is a hallmark of sporadic and familial Parkinsons disease (PD), it is not known how it contributes to early events of PD pathogenesis such as oxidative and inflammatory stress. Here, we addressed this question in a new animal model based on stereotaxic delivery of an adeno-associated viral vector (rAAV) for expression of human -SYN in the ventral midbrain of mice lacking the transcription factor Nrf2 (Nrf2(/)). Two months after surgery, Nrf2(/) mice exhibited exacerbated degeneration of nigral dopaminergic neurons and increased dystrophic dendrites, reminiscent of Lewy neurites, which correlated with impaired proteasome gene expression and activity. Dopaminergic neuron loss was associated with an increase in neuroinflammation and gliosis that were intensified in Nrf2(/) mice. In response to exogenously added -SYN, Nrf2(/) microglia failed to activate the expression of two anti-inflammatory genes, heme oxygenase-1 (HO-1) and nicotinamide adenine dinucleotide phosphate quinone oxidorreductase-1 (NQO1). This impaired Nrf2 response correlated with a shift in the microglial activation profile, towards increased production of proinflammatory markers, IL-6, IL-1 and iNOS and reduced phagocytic capacity of fluorescent beads, and lower messenger RNA levels for TAM receptors Axl and Mer. Postmortem brain tissue samples from patients in early- to middle-stage progression of PD showed increased HO-1 expression in astrocytes and microglia, suggesting an attempt of the diseased brain to compensate these hallmarks of PD through activation of the Nrf2 pathway. This study demonstrates that -SYN and Nrf2 deficiency cooperate on protein aggregation, neuroinflammation and neuronal death and provides a bifactorial animal model to study early-stage PD

Activation of the DNA damage response in vivo in synucleinopathy models of Parkinson\xe2\x80\x99s disease

The involvement of DNA damage and repair in aging processes is well established. Aging is an unequivocal risk factor for chronic neurodegenerative diseases, underscoring the relevance of investigations into the role that DNA alterations may have in the pathogenesis of these diseases. Consistently, even moderate impairment of DNA repair systems facilitates the onset of pathological features typical of PD that include derangement of the dopaminergic system, mitochondrial dysfunction, and alpha-synuclein stress. The latter establishes a connection between reduced DNA repair capacity and a cardinal feature of PD, alpha-synuclein pathology. It remains to be determined, however, whether alpha-synuclein stress activates in vivo the canonical signaling cascade associated with DNA damage, which is centered on the kinase ATM and substrates such as \xce\xb3H2Ax and 53BP1. Addressing these issues would shed light on age-related mechanisms impinging upon PD pathogenesis and neurodegeneration in particular. We analyzed two different synucleinopathy PD mouse models based either on intranigral delivery of AAV-expressing human alpha-synuclein, or intrastriatal injection of human alpha-synuclein pre-formed fibrils. In both cases, we detected a significant increase in \xce\xb3H2AX and 53BP1 foci, and in phospho-ATM immunoreactivity in dopaminergic neurons, which collectively indicate DNA damage and activation of the DNA damage response. Mechanistic experiments in cell cultures indicate that activation of the DNA damage response is caused, at least in part, by pro-oxidant species because it is prevented by exogenous or endogenous antioxidants, which also rescue mitochondrial anomalies caused by proteotoxic alpha-synuclein. These in vivo and in vitro findings reveal that the cellular stress mediated by alpha-synuclein\xe2\x80\x94a pathological hallmark in PD\xe2\x80\x94elicits DNA damage and activates the DNA damage response. The toxic cascade leading to DNA damage involves oxidant stress and mitochondrial dysfunction The data underscore the importance of DNA quality control for preservation of neuronal integrity and protection against neurodegenerative processes

The transcription factor BCL11A defines distinct subsets of midbrain dopaminergic neurons.

Midbrain dopaminergic (mDA) neurons are diverse in their projection targets, effect on behavior, and susceptibility to neurodegeneration. Little is known about the molecular mechanisms establishing this diversity during development. We show that the transcription factor BCL11A is expressed in a subset of mDA neurons in the developing and adult murine brain and in a subpopulation of pluripotent-stem-cell-derived human mDA neurons. By combining intersectional labeling and viral-mediated tracing, we demonstrate that Bcl11a-expressing mDA neurons form a highly specific subcircuit within the murine dopaminergic system. In the substantia nigra, the Bcl11a-expressing mDA subset is particularly vulnerable to neurodegeneration upon α-synuclein overexpression or oxidative stress. Inactivation of Bcl11a in murine mDA neurons increases this susceptibility further, alters the distribution of mDA neurons, and results in deficits in skilled motor behavior. In summary, BCL11A defines mDA subpopulations with highly distinctive characteristics and is required for establishing and maintaining their normal physiology

Gender biased neuroprotective effect of Transferrin Receptor 2 deletion in multiple models of Parkinson’s disease

Alterations in the metabolism of iron and its accumulation in the substantia nigra pars compacta accompany the pathogenesis of Parkinson’s disease (PD). Changes in iron homeostasis also occur during aging, which constitutes a PD major risk factor. As such, mitigation of iron overload via chelation strategies has been considered a plausible disease modifying approach. Iron chelation, however, is imperfect because of general undesired side effects and lack of specificity; more effective approaches would rely on targeting distinctive pathways responsible for iron overload in brain regions relevant to PD and, in particular, the substantia nigra. We have previously demonstrated that the Transferrin/Transferrin Receptor 2 (TfR2) iron import mechanism functions in nigral dopaminergic neurons, is perturbed in PD models and patients, and therefore constitutes a potential therapeutic target to halt iron accumulation. To validate this hypothesis, we generated mice with targeted deletion of TfR2 in dopaminergic neurons. In these animals, we modeled PD with multiple approaches, based either on neurotoxin exposure or alpha-synuclein proteotoxic mechanisms. We found that TfR2 deletion can provide neuroprotection against dopaminergic degeneration, and against PD- and aging-related iron overload. The effects, however, were significantly more pronounced in females rather than in males. Our data indicate that the TfR2 iron import pathway represents an amenable strategy to hamper PD progression. Data also suggest, however, that therapeutic strategies targeting TfR2 should consider a potential sexual dimorphism in neuroprotective response

Modeling pathophysiological aspects of Parkinson’s disease: Manipulating DA handling and alpha-synuclein expression in the nigrostriatal pathway using viral vectors

The pathological hallmark of Parkinson’s disease is dopaminergic neurodegeneration in the substantia nigra pars compacta neurons and accumulation of α-synuclein containing aggregates in the surviving neurons. The cause of cell death in Parkinson’s disease and the involvement of α-synuclein in the pathophysiology of the disease are unknown. Although other neuronal cell types exhibit α-synuclein positive aggregates, substantia nigra dopamine neurons display a selective vulnerability to α-synuclein mediated neurodegeneration. In this thesis work I have focused on the possible mechanisms underlying the vulnerability of dopamine producing neurons against α-synuclein induced neurotoxicity. To study the molecular interactions playing role in α-synuclein mediated dopaminergic neurodegeneration, we investigated putative mechanisms that has been implicated in α-synuclein toxicity. Interaction of the α-synuclein protein with other molecules has been suggested to enhance the aggregation. We studied the interaction between the full-length α-synculein protein and truncated α-synuclein in the rat substantia nigra. When the two forms are co-expressed the truncated form promotes full-length α-syn aggregation and enhance the pathology caused by the full-length protein. We next investigated the specific role of dopamine handling machinery in Parkinson’s disease pathophysiology and treatment related motor complications. To study the involvement of cytosolic DA and age related increase in the reactive DA species on α-syn toxicity, we utilized a transgenic mouse model carrying a hypomorphic VMAT2 mutation. The elevated cytosolic dopamine in these mice led to an increased vulnerability to α-synuclein overexpression. To show that this vulnerability was indeed dopamine dependent, we generated recombinant adeno-associated viral vectors to transfer short hairpin RNA sequences targeting the rate-limiting enzyme, tyrosine hydroxylase. Reducing dopamine production using the shRNA approach in these mice rescued the vulnerability against α-synuclein in the nigral dopamine neurons. Our results implicate the critical role of dopamine handling in Parkinson’s disease pathophysiology, thus suggest that regulating the specific pathways through which DA mediates its toxic effects can prevent the potential neurodegeneration

Can overexpression of parkin provide a novel strategy for neuroprotection in Parkinson's disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder caused by selective degeneration of the dopamine producing neurons in the substantia nigra. There is currently no clinically applicable therapy for treating or preventing Parkinsonian neurodegeneration. Great effort is put behind the development of novel therapeutic approaches that aim to alter the natural progression of the disease. For example, a disease-modifying strategy based on the use of glial cell line-derived neurotrophic factor family of ligands have yielded successful results in animal models and later in initial clinical trials. More recently, identification of the gene mutations underlying the familial forms of the disease opened new frontiers in tackling the underlying neuropathological changes seen in PD brains. Overexpression of parkin, in particular, emerged as a powerful approach with complementary effects to those described with use of neurotrophic factors. In light of the fact that the mechanism of disease in the affected patient population might be significantly variable, the ability to intervene the disease process at multiple levels should be seen as a key point in devising effective treatments