We investigate whether dividend changes signal firms’ future profitability by considering firms’ earnings volatility and examining how earnings volatility affects dividend signaling. In general, we find a positive relation between dividend increases on firms’ future earnings. In other words, dividend increases tend to signal positive changes in future earnings. However, the effect largely depends on the firms’ earnings volatility such that higher earnings volatility tends to miti-gate the signaling effect of dividend increases on future earnings. Specifically, for firms that have high earnings volatility, dividend increases seem to signal a reduction in future earnings vol-atility rather than an increase in future earnings. On the other hand, we find no consistent results for dividend decreases. Our findings have three main implications: 1) The traditional dividend signaling theory is valid; 2) the effect of signaling depends on a firm’s earnings volatility; 3) for high-volatility firms, positive dividend changes signal earnings volatility reductions rather than earnings increases.

<p>Bioactive gibberellins (GAs) are phytohormones with various effects on plant development, from seed germination through fruit development. The signaling pathway of GA is centered on DELLA proteins (DELLAs), a group of growth repressors degraded upon perception of GA. Previous studies demonstrated that DELLAs administrate global regulation of gene expression. However, given that DELLAs do not contain any canonical DNA-binding domain and that DELLAs only have a moderate association to their target promoters, the nuclear-localized DELLAs are believed to interact with transcription factors for function. Indeed, quite a few transcription factors have been identified as DELLA interactors in the plant model Arabidopsis thaliana, some of which are well-known downstream transcription regulators involved in other signaling pathways. Nevertheless, the molecular mechanisms how DELLAs inhibit so many aspects of plant growth cannot be fully explained by the known DELLA interactors. </p><p>Recently, our lab discovered that INDETERMINATE DOMAIN 1 (IDD1), a C2H2 zinc-finger protein in Arabidopsis, and its closest homolog IDD2, have a strong physical interaction with DELLAs, revealing the potential involvement of these two IDD genes in GA signaling. Hence, the objectives of my doctoral research are (1) to evaluate the roles of IDD1 and IDD2 in GA-responsive phenotypes, (2) to investigate the genetic interaction between IDD1, IDD2 and DELLAs and (3) to identify the function of IDD1 and IDD2 and the significance of IDD-DELLA interaction in transcriptional regulation of IDD/DELLA targets. First, we found that both IDDs redundantly promote GA-induced hypocotyl elongation, and that they also play a positive role in stem elongation and floral initiation. Secondly, epistasis analyses exhibit that REPRESSOR OF ga1-3 (RGA) and GA INSENSITIVE (GAI), two DELLAs with a predominant role in vegetative growth, antagonize IDD1 and IDD2 in hypocotyl elongation, and that GAI also opposes IDD2 in stem elongation and floral initiation. These results entail an antagonistic relationship between IDDs and DELLAs via protein-protein interaction. We then showed that IDD1 and IDD2 repress the expression of canonical DELLA direct targets, including GA20ox2, GA3ox1, GID1b and SCL3. IDD1 also inhibits transcription of CAPRICE (CPC) and GLABRA2 (GL2), two crucial regulators of root epidermal cell patterning. Taking into account that IDD1 and RGA associate with the same region in CPC promoter, we conclude that CPC is a direct target of the IDD1/RGA complex. In addition, transient expression assays suggested that IDD1 and RGA counteract each other's effects on expression of GA20ox2, GID1b, SCL3, CPC and GL2, providing evidence that IDDs and DELLAs function antagonistically in transcriptional regulation of downstream genes in general. Although both IDDs bear a putative repression motif GLGLGL in their C termini, mutation of this motif did not affect the repressive activity of IDD1 in our transient expression system. On the other hand, fusion of the viral protein 16 (VP16) transcriptional activation domain to IDD1 seems to override the original repressive activity of IDD1. Together, these results uncover a new branch of GA signaling pathway through IDD1 and IDD2, shed light on the interplay of the two IDDs and DELLAs in GA feedback regulation and give insights into the molecular mechanism underlying IDD-mediated GA repression of root hair development.</p> / Dissertation

Forming and maintaining an intact epidermal permeability barrier (EPB) is necessary to mammalian health and dysregulation of this process can result in serious complications. Tight junctions (TJs) and their integral proteins the Claudins (Cldns) have both structural and signaling importance to the skin barrier and the latter is most likely mediated via Cldn tail interaction with cytoplasmic proteins. Given that the family member Cldn6 is known to be important to EPB function, we set out to determine the contribution of its cytoplasmic tail domain to TJ-mediated homoeostasis. Using transgenic mouse models, we overexpressed epidermal-targeted tail truncation mutants and assessed EPB formation and maintenance. We then used yeast 2-hybrid and quantitative proteomic approaches to identify proteins that interact with this tail region and to assess the downstream effects of overexpressing these proteins in human keratinocytes in culture. We demonstrate that a 10 amino acid region in the cytoplasmic tail is required for efficient epidermal maturation and injury repair and that our mouse models may be applicable to postnatal epidermal maturation and human skin aging studies. We show that in addition to the known interacting partner ZO1, the C-terminal tail of Cldn6 also binds FIZ1 (Flt3 interacting zinc finger protein-1), which we characterize for the first time as a mitogenic factor for keratinocytes. FIZ1 stimulates autocrine pathways involving secreted heparin-binding factors IGFBP3 and DKK1, sensitization to IGF signaling, MAP/ERK activation and increased G1 progression. Specific transcription factors, protein kinases and signaling scaffolds that we identified as novel FIZ1-binding partners likely mediate this signaling. Our studies on the Cldn6 cytoplasmic tail support the importance of this region for epidermal maturation and for maintenance of skin homeostasis throughout life. They also delineate the potential for tail interactors such as ZO1 and FIZ1 to act in concert with Cldns in TJ-based signaling networks to regulate the balance between proliferation and differentiation in keratinocytes. These findings provide new insight into the role of the Cldn6 cytoplasmic tail and will ultimately aid in the development of new diagnostic tools and therapeutic approaches for the treatment of skin conditions rooted in barrier defects.

Precise spatial and temporal control of cellular adhesion and signal transduction events are necessary for accurate animal development. Given the necessity for cell communication in carrying out processes like cell fate specification, growth, cell migration and differentiation, it is not surprising that signaling transduction pathways, such as EGFR, BMP, Notch, Wingless and Hippo, are intimately involved. All these pathways encompass a cascade of molecular events over which there is exquisite spatial and temporal control. A wide array of mechanisms, involving a diverse set of molecules, acts to provide this regulatory control. One such molecule implicated in the BMP signaling pathway in Drosophila development is Kek5, a Leucine rich repeat and Immunoglobulin domain (LIG) family member. Here I show that Kek5 modulates both BMP signaling and adherens junctions. For these functions, I further demonstrate that structural elements in both extracellular and intracellular region of Kek5 are critical, providing new insight into the LIG family and their roles in signaling pathways.

N-Acylphosphatidylethanolamines (NAPEs) are precursors of endogenous bioactive lipids, N-acylethanolamines (NAEs). NAPEs, which occur as a minor membrane lipid, are hydrolyzed in a single enzymatic step catalyzed by a type of phospholipase D (PLD) to generate fatty acid ethanolamides. Although, the occurrence of NAPE is widespread in the plant kingdom, the physiological roles remain under appreciated due to the lack of sensitive tools to quantify the pathway metabolites. In Kilaru et al. (2012, Planta, DOI 10.1007/s00425-012-1669-z), comprehensive mass spectrometry (MS)-based methods were developed to gain a clearer understanding of the complex network of metabolites that participate in NAE metabolic pathway. This targeted lipidomics approach allowed insights to be drawn into the implications of altered NAE levels on NAPE content and composition, and the overall regulation of PLD-mediated hydrolysis in Arabidopsis. Based on these results, we point out here the important need for the identification of the precise isoform(s) of PLD in plants that is (are) involved in the regulated hydrolysis of NAPE and formation of NAE lipid mediators in vivo.

Effect of Manipulation of Notch Signaling Pathway on Neural Stem Cell Proliferation in the Hippocampus Following Traumatic Brain Injury By Seung L. Kim A thesis statement submitted for degree requirement in Mater of Science Virginia Commonwealth University, 2019 Advisor: Dong Sun, MD. PhD. Department of Anatomy & Neurobiology The Notch signaling pathway is known as a core signaling system in maintaining neural stem cells (NSCs) in embryonic development and adulthood including cell proliferation, maturation, and cell fate decision. Proliferation of NSCs persists throughout lifespan in neurogenic niches and is often upregulated following neurological insults including traumatic brain injury (TBI). Therefore, NSCs are viewed as the brain’s endogenous source for repair and regeneration. We speculate Notch signaling pathway is also involved in injury-induced cell proliferation in the neurogenic niche following TBI. TBI, which is a leading cause of death and disability, has been a huge burden to our society. Many efforts have been made in attempt to treat and manage TBI. In this study, we examined the involvement of Notch signaling pathway in injury induced NSC proliferation in the neurogenic niche, by administering exogenous Notch ligands including, Notch agonist or antagonist. Adult rats were intraventricularly infused with Notch1 receptor agonists (anti-Notch1 antibody at the dose of 0.5, 2 or 4μg/ml), Notch1 receptor antagonist (recombinant Jagged1 fusion protein at the dose of 25, 50 or 100μg/ml) or vehicle for 7 days following TBI. 5-bromo-2-deoxyuridine (BrdU) was administered single daily via intraperitoneal injection to label proliferating cells for 7 days post injury. The animals were sacrificed on the 7th day at 2 hours after the last BrdU injection. Sequential vibratome sliced coronal brain sections were processed for proliferation marker BrdU, Ki67 or immature neuronal marker DCX staining. BrdU, Ki67 or DCX-labeled cells in the dentate gyrus of the hippocampus were quantified using unbiased stereological method. We found TBI in the form of moderate lateral fluid percussion injury (LFPI) induced cell proliferation was further augmented by 7-day infusion of Notch agonist (Notch1-2μg/ml) as shown by BrdU and Ki67 labeling. Further, 7-day infusion of Notch antagonist (Jagged1-50μg/ml) post-injury greatly reduced the number of BrdU+ cells. However, ambiguous dose related responses were also observed where 7-day infusion of higher dose of Notch agonist (Notch1-4μg/ml) resulted in reduced cell proliferation. No major changes in the numbers of newly generated neurons were observed across the animals, except a slight reduction in Notch agonist (Notch1-2μg/ml) and Notch antagonist (Jagged1-50μg/ml) infused animals as shown by DCX labeling. Infusion of Notch agonist or antagonist affects NSC proliferation following TBI suggesting the involvement of Notch signaling pathway in regulating post-TBI NSC proliferation in the neurogenic niche. For the unexpected opposite results of higher dosing of Notch 1 agonist, the presence of other Notch receptors regulating NSC in the neurogenic niche should be considered. Future studies involving selective manipulation of these Notch receptors and their downstream effectors would clear some results.

The SH2D5 signaling molecule is a previously uncharacterized adaptor-like protein, containing an N-terminal phosphotyrosine binding (PTB) domain and a noncanonical Src Homology-2 (SH2) domain. With an antibody that I developed, I have shown that SH2D5 is highly enriched throughout adult brain regions. Furthermore, SH2D5 is localized to purkinjie cells in the cerebellum, the cornu ammonis (CA) of the hippocampus and pyramidal cells in the cortex. Despite harbouring two potential phosphotyrosine (pTyr) recognition domains, SH2D5 binds minimally to pTyr ligands. To discover the interaction partners of SH2D5 I conducted an immunoprecipitation/ mass spectrometry (IP/MS) screen from cultured Human Embryonic Kidney (HEK) 293T and Neuro2A cells along with murine brain lysates. These experiments revealed novel binding partners to SH2D5 including a prominent association with the RacGAP protein, Breakpoint Cluster Region protein (BCR), which is also highly expressed in brain. I have defined the interaction between SH2D5 and BCR and show that the PTB domain of SH2D5 engages an NxxF motif located within the N-terminal region of BCR. To address the biological significance of SH2D5, I utilized an siRNA approach to deplete the neuroblastoma cell-line, B35, of iii SH2D5. In these assays, B35 cells display a cell rounding phenotype and grow in a lattice formation. Furthermore, upon SH2D5 depletion these cells display low levels of activated Rac, associated with cell rounding. Taken together, these data reveal the first characterization of the SH2D5 signaling protein, its novel interaction with BCR and phenotype in neuronal-like cells. These data signify a biological function for SH2D5 in neurobiologic signaling perhaps applicable to learning and memory.

Engineered protein systems have been created to impart new functions, or “re-program” mammalian cells for applications including cancer and HIV/AIDS therapies. The successful development of mammalian cells for re-programming will depend on having well-defined, modular systems. Migration is a particularly important cell function that will determine the efficiency and efficacy of many re-programming applications in vivo, and Rho proteins are responsible for regulation of cell migration natively. While there have been several reports of photo-activated Rho proteins, no strategy has been developed such that Rho proteins and cell migration can be controlled by a variety of extracellular stimuli that may be compatible with signaling in large organisms. Here, several methods are described for engineering Ca2+-sensitive Rho proteins so that the large, natural toolbox of Ca2+-mobilizing proteins can use the Ca2+ intermediate to activate Rho proteins in response to a variety of exogenous stimuli, including chemicals, growth factors, and light. First, an unreported calmodulin binding site was identified in RhoA. This knowledge was used to create a tandem fusion of RhoA and calmodulin that mediated Ca2+-sensitive bleb retraction in response to a variety of Ca2+-elevating chemicals. Ca2+-mobilizing modules including channelrhodopsin-2 and nicotinic acetylcholine receptor α4 were used for light- and acetylcholine-dependent bleb retraction. Second, a more robust morphology switch was created by embedding a calmodulin binding site into RhoA to enable Ca2+-responsive bleb formation. A wider range of Ca2+-mobilizing modules were also used here including LOVS1K/Orai1 and vascular endothelial growth factor 2. Combining Ca2+-mobilizing and Ca2+-responsive modules increased amoeboid-like cell migration in wound closure and transwell assays. Finally, the embedded peptide design was applied to Rac1 and Cdc42 to enable control of new morphologies and migration modes. The modular Ca2+ control over Rho proteins developed here is an important contribution to cell re-programming because it shows that control over cell migration can be rewired in a way that is flexible and tunable.

The SH2D5 signaling molecule is a previously uncharacterized adaptor-like protein, containing an N-terminal phosphotyrosine binding (PTB) domain and a noncanonical Src Homology-2 (SH2) domain. With an antibody that I developed, I have shown that SH2D5 is highly enriched throughout adult brain regions. Furthermore, SH2D5 is localized to purkinjie cells in the cerebellum, the cornu ammonis (CA) of the hippocampus and pyramidal cells in the cortex. Despite harbouring two potential phosphotyrosine (pTyr) recognition domains, SH2D5 binds minimally to pTyr ligands. To discover the interaction partners of SH2D5 I conducted an immunoprecipitation/ mass spectrometry (IP/MS) screen from cultured Human Embryonic Kidney (HEK) 293T and Neuro2A cells along with murine brain lysates. These experiments revealed novel binding partners to SH2D5 including a prominent association with the RacGAP protein, Breakpoint Cluster Region protein (BCR), which is also highly expressed in brain. I have defined the interaction between SH2D5 and BCR and show that the PTB domain of SH2D5 engages an NxxF motif located within the N-terminal region of BCR. To address the biological significance of SH2D5, I utilized an siRNA approach to deplete the neuroblastoma cell-line, B35, of iii SH2D5. In these assays, B35 cells display a cell rounding phenotype and grow in a lattice formation. Furthermore, upon SH2D5 depletion these cells display low levels of activated Rac, associated with cell rounding. Taken together, these data reveal the first characterization of the SH2D5 signaling protein, its novel interaction with BCR and phenotype in neuronal-like cells. These data signify a biological function for SH2D5 in neurobiologic signaling perhaps applicable to learning and memory.

Firms form marketing and technology alliances to access other firms’ resources, and these alliances act as signals to investors. Investors use these signals to adjust expectations about new venture performance prospects, but our understanding of investor responses is incomplete because limited research examines them as a function of factors other than the alliance announcements. To better understand alliances as signals, we must incorporate factors influencing the resources alliances make available. Thus, my research question is as follows: To what extent do partner firm, focal firm, and alliance characteristics provide signals to investors about the resources alliances make accessible? My theory integrates signaling theory and resource-based theory on strategic alliances, and an event study is used to analyze investor responses to alliances formed by high technology new ventures recently having undergone initial public offerings. The findings provide evidence both in support and in contradiction to signaling theory and resource-based theory on strategic alliances. For example, signaling theory logic suggests both that the visibility and prestige of large partners and that the uncertainty associated with small and young firms enhance the strength of signals associated with alliance announcements. In this study, there is no support for the former hypotheses and limited support for the latter. Moreover, although both perspectives suggest that the new venture’s alliance experience increases investor responses, such effects were not found. There was some evidence to support the signaling theory argument that signal consistency strengthens responses. Specifically, investors respond favorably to marketing alliances when the new ventures’ alliance partners have strong commercial resources (many new products per year). There is also evidence that investors respond to the possibility of resource complementarity, contingent on which firm has the resources that complement the alliance. For instance, investors value marketing alliances when new ventures have strong R&D resources. In technology alliances, investors may respond more favorably when new ventures have strong commercial resources (high advertising intensity), but may respond negatively when partners have such resources. In sum, this study provides some support for signaling theory and resource-based theory on strategic alliances, but also provides null results that are inconsistent with either.