# Your search: "author:"Alexander, S""

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## Scholarly Works (32 results)

Despite recent progress in genetic manipulations of mosquitoes, there is a much needed improvement and development of specific research tools to further facilitate research of these disease vectors. The focus of this dissertation is to extend and refine upon the Gal4/UAS system for the yellow fever mosquito, Aedes aegypti. The first part of the dissertation focuses on the development the blood-meal-activated, gut-specific Gal4/UAS system by utilizing a 1.1-kb, 5' upstream region of the carboxypeptidase A (CP) gene to genetically engineer the CP-Gal4 driver mosquito line. The generated driver successfully drive the expression of the effect gene followed a similar pattern as endogenous CP gene. Using the CP-Gal4/UAS-EGFP mosquitoes, we demonstrated that the CP gene is regulated by insulin and amino acids. In the second part of the dissertation, the gut-specificCP-Gal4/UAS and the fat-body specific Vg-Gal4/UAS systems were utilized in a combination with microRNA decoy to investigate the function of the, aae-miR-275 (miR-275). This approach allowed demonstrating a gut-specific function of miR-275.Specific miR-275 silencing in the midgut resulted in dramatic defects in blood digestion and egg development in female mosquitoes. The predicted miR-275 target gene- sarco/endoplasmic reticulum Ca2+-ATPase (SERCA)-was confirmed to directly bind miR-275 by means of luciferase assay. RNA interference silencing of SERCA or application of SERCA-specific inhibitor Thapsigargin (TG) resulted in an apparent lack of blood digestion, inhibition of egg development, as well as diminished egg number in comparison to controls. Application of the miR-275 mimic in the CP-Gal4/UAS-miR275decoy mosquitoes restored SERCA transcript level and rescued the phenotype. In the last part of this thesis, I described two additional midgut-specific Gal4 driver lines that are currently under development. Together, my work provide considerable advance in developing the binary Gal4/UAS system for research of essential gene and microRNA functions in the mosquito Ae. aegypti.

Given a field *F* of arbitrary characteristic and an algebraic torus *T/F* we calculate degree 2 and 3 cohomological invariants of *T* with values in *Q/Z(1)* and *Q_p/Z_p(2)* respectively, the latter for *p* not equal to 2, *char(F) and generalize the former to other algebraic groups. Moreover, we obtain descriptions of the corresponding unramified cohomology groups, and in particular of H^{3}_{nr}(F(T), μ_{n}^{\otimes 2}) for n prime to 2 and char(F). In the process, we construct a useful short exact sequence for cohomological invariants and make connections with recent results on Chow groups of codimension 2.*

**Part 1:** Consider a continuous action of a countable group *G* on a Polish space *X*. A countable Borel partition *P* of *X* is called a *generator* if the σ-algebra generated by the set of the *G*-translates of P is the Borel σ-algebra of *X*. It was asked by Benjamin Weiss in ’87 whether the nonexistence of an invariant probability measure implies the existence of a finite generator. The main result of this part is obtaining a positive answer to this question in case *X* is σ-compact (in particular, when *X* is locally compact). We also show that finite generators always exist modulo a meager set, answering positively a question raised by Alexander Kechris in the mid-’90s.

**Part 2:** We investigate pairs of countable Borel equivalence relations (*E*, *F*), where *E* is a finite index subequivalence relation of *F*. Our main focus is the well-known problem of whether the treeability of *E* implies that of *F*: we provide various reformulations of it and reduce it to one natural universal example. In the measure-theoretic context, assuming that *F* is ergodic, we characterize the case when *E* is normal. Finally, in the ergodic case, we characterize the equivalence relations that arise from almost free actions of virtually free groups.

**Part 3:** We consider natural complexity measures for recursive programs from given primitives and derive inequalities between them, answering a question asked by Yiannis Moschovakis.

Female mosquitoes require a blood meal for reproduction, providing the underlying mechanism for the spread of many devastating parasitic and viral vector-borne diseases in humans. A deeper understanding of the molecular mechanisms linked to mosquito blood meal processes, reproductive events and anti-pathogen immunity is of particular importance for devising innovative vector control strategies. Acquisition of blood initiates a cascade of events – including dynamic changes in microRNA (miRNAs) expression – in various tissues in the female mosquito. miRNAs are a class of endogenous regulatory RNA molecules 21-24 nucleotides in length that modulate gene expression at the post-transcriptional level via base pairing to target sites within messenger RNAs (mRNA). Reports have indicated that miRNAs are differentially expressed in various tissues of the female mosquito upon the uptake of a blood meal. miRNAs have been shown to play important roles in regulation gene expression throughout the adult mosquitoes life cycle – including the regulation of adult development, blood digestion and mosquito-pathogen interaction. Furthermore, several lineage-specific miRNAs have been identified in mosquitoes and may underlie mosquito-specific events, including blood meal-initiated events. This thesis describes the fat body specific function of the conserved miRNA, miR-8, in the female mosquito post-blood meal and its involvement in regulating essential reproductive events through targeting the Wingless signaling pathway. Additionally, this thesis details the function of two lineage-specific miRNAs, miR-1174 and miR-1890, and their involvement in regulating digestive processes in the female mosquito midgut. Together, these studies have established a fundamental role for both conserved and lineage-specific miRNAs in the adult female mosquito.

This dissertation is concerned with calculating the group of degree three cohomological

invariants of a reductive group over a ﬁeld of arbitrary characteristic. We prove a formula

for the group of degree three cohomological invariants of a split reductive group G with coeﬃcients in Q/Z(2) over a ﬁeld F of arbitrary characteristic. As an application, we then use this to deﬁne the group of reductive invariants of split semisimple groups, and compute

these groups in all (almost) simple cases. We additionally prove the existence of a discrete

relative motivic complex for any reductive group, which could be used to compute the degree

two and three invariants of arbitrary reductive groups.

Kisspeptin, encoded by the Kiss1 gene, is required for reproductive function. There are several distinct Kiss1 populations in the brain, and how these kisspeptin neurons are regulated is still not fully understood. The two largest hypothalamic Kiss1 populations reside in the ARC and AVPV and respond to sex steroids in opposing manners, one being negatively regulated and the other being positively regulated, respectively. As a result, in research experiments it has been technically difficult to visualize Kiss1 expression of both populations in the same animal. Here, we sought to establish a dose of estradiol (E2) for which both ARC and AVPV kisspeptin populations can be visualized with in situ hybridization. Using this E2 treatment in conjunction with the inducible diphtheria toxin receptor mouse line, we next aimed to exploit the different developmental ontogenies of the Kiss1 populations to selectively remove only the ARC Kiss1 neurons, which have been implicated in the maintenance of the reproductive axis. We discovered that administration of diphtheria toxin (DT) during early juvenile stage to transgenic mice with selective sensitivity to DT led to specific ablation of ARC Kiss1 neurons. Finally, to address lesser understood Kiss1 populations outside the hypothalamus, we used two transgenic mouse models lacking either ERα or ERβ and found that E2 positively regulates Kiss1 cells in the lateral septum (LS) via ERα. Understanding the role of the ARC and LS Kiss1 neurons may lead to a better understanding of how the reproductive axis is regulated and provide potential therapeutics for reproductive disorders.

No need for Master's Thesis

This dissertation is concerned with calculating the group of unramified Brauer invariants of a finite group over a field of arbitrary characteristic. We present a formula for the group of degree-two cohomological invariants of a finite group G with coefficients in Q/Z(1) over a field F of arbitrary characteristic. We then specialize this formula to the case of decomposable invariants and compute the unramified decomposable cohomological invariants with coefficients in Q/Z(1) for various finite groups G. When the order of G is prime to the characteristic of F, we obtain a formula for the degree-two unramified normalized decomposable invariants of finite abelian G and certain nonabelian groups G. We additionally compute the degree-two unramified normalized decomposable invariants with coefficients in Q/Z(1) in the case that G is cyclic of order p over a field of characteristic p.