Deuterium is the naturally occurring, heavier stable isotope of hydrogen, which comprises a known proportion of the hydrogen in seawater. As evaporated water travels inland, heavier molecules containing deuterium are rained out preferentially. The deuterium/hydrogen ratio (δ2H) in precipitation is controlled by climatic and geographic factors such as temperature, elevation, and latitude. Terrestrial plants use rainwater as their primary source of hydrogen, so this climatic and topographic marker is recorded in their compounds, which allows for their use in the sedimentary record as paleoclimate proxies. In this study I examine δ2H in n-alkanes, the hydrocarbon chains that make up leaf waxes, extracted from plants, leaf litter (duff), and soils across Washington state. Due to rainout effects influenced by the Cascade Mountains’ rain shadow, δ2H is expected to show a trend of depletion across the state. Samples were collected from sites along an east-west transect across the Cascades. I have processed these samples for isotope analysis and am now conducting literature review to compare our results with a global dataset. Preliminary results show the expected depletion of deuterium across the transect and correlation with rainwater δ2H, modeled using the Online Isotopes in Precipitation Calculator (OIPC). My goal is to assess the local trend of δ2H depletion across this gradient through comparison with existing literature, and to examine the poorly-studied pathway of isotopic signature from plant tissue into soils. I am to provide new insight into the pattern of isotopic signals preserved from live plants into soils and sedimentary rocks, and to further explore and refine the use of hydrogen isotopes in sedimentary n-alkanes as paleoclimate indicators. This research is part of a larger study on the persistence of the isotopic signal of the Cascade Mountains’ rain shadow into the rock record to potentially constrain the timing of their uplift. 

Alzheimer's disease (AD) is the most common form of dementia. Improper cleavage of amyloid precursor protein by a complex containing presenilin 1 or presenilin 2 (PSEN2) can result in pathological amyloid beta plaques. Recent work from the Valdmanis group found novel PSEN2 RNA isoform variants in AD. Specifically, we identified two PSEN2 3'UTR isoforms - a short (507bp) and a long (3976bp) 3'UTR. The 3'UTR harbors essential regulatory elements such as microRNA binding sites and Alu elements that control transcript maturation, stability, and abundance. Here, we sought to elucidate the functional significance of the PSEN2 3'UTR isoforms. To accomplish this, we completed small RNA sequencing to identify microRNA levels in human AD and control frontal cortex brains and used TargetScan7 to map these reads to the PSEN2 3'UTR isoforms. Our analysis identified 53 miRNAs with significant differential regulation in AD frontal cortex bulk homogenate and 76 miRNAs in purified synaptosomes. One miRNA, miR-34c, was significantly downregulated in both fractions. We identified five different miRNAs with significant regulation changes in AD, including miR-326, miR-346, miR-548p, miR-890, and miR-217. Of note, the long PSEN2 3'UTR had nine miRNA binding sites and two Alu elements, while the short PSEN2 3'UTR only contained one miRNA binding site. We next tested PSEN2 3'UTR isoform localization in human AD and control frontal cortex brain tissue using BaseScope in-situ hybridization. We found a marked decrease in PSEN2 expression in AD samples. To develop in vitro PSEN2 3'UTR isoform models, we designed constructs containing the PSEN2 3'UTR isoforms to overexpress in either HMC3 human microglial or SH-SY5Y human neuroblastoma cell lines. In vitro validation results indicated increased long PSEN2 3'UTR isoform abundance to the short isoform. Determining the functional relevance of the short and long 3'UTR of the PSEN2 transcript will further our understanding of AD pathology.