Cell Biology Commons^™

Mitochondria Dynamics In Microglia During Health, Inflammation, And Aging, Alicia Nicole Pietramale

Dartmouth College Ph.D Dissertations

Microglia continually surveil the brain, allowing for rapid detection of tissue damage or infection. Microglial metabolism is linked to tissue homeostasis, yet how mitochondria are subcellularly partitioned in microglia and dynamically reorganize during surveillance, injury responses, and phagocytic engulfment in the intact brain has remained unclear. In this dissertation, I combine intravital imaging, ultrastructural analyses, and metabolic and cytoskeletal markers to investigate how mitochondrial organization relates to microglial function across health, inflammation, and aging.

I first show that microglial processes diverge in their mitochondrial content, with some containing multiple mitochondria while others are completely void. This heterogeneous partitioning is conserved …

Fluorescent Protein Imaging Approaches Uncover Dynamic Subcellular Distribution Of Core Clock Proteins In Neurospora Crassa, Ziyan Wang

Dartmouth College Ph.D Dissertations

Circadian clocks are endogenous self-sustained timekeeping systems that allow organisms to anticipate and adapt to daily environmental cycles. Found in diverse forms of life, these molecular clocks regulate the expression of ~ 40% of the genome in animals, fungi, and plants. In animals and fungi, circadian oscillators are built on transcription-translation feedback loops (TTFLs), in which positive regulators drive the expression of negative regulators which, once synthesized and imported into the nucleus, inhibit their own activators. This precisely regulated negative feedback incorporates multiple steps of delays that are essential for generating ~24-hour rhythms. Through these mechanisms, circadian clocks temporally coordinate …

Basal Autophagy Promotes Accurate Chromosome Segregation In Drosophila Oocytes And Declines During Oocyte Aging, Diana C. Hilpert

Dartmouth College Ph.D Dissertations

The frequency of trisomic pregnancies exponentially increases with advanced maternal age, a phenomenon known as the maternal age effect. The majority of these aneuploid pregnancies arise from meiotic segregation errors in the oocyte and premature loss of sister chromatid cohesion is a contributing factor. However, the mechanisms that lead to premature cohesion loss during oocyte aging are not fully understood.

Using Drosophila melanogaster as a model organism, work described in this dissertation demonstrates that basal levels of autophagy, a degradation process for damaged organelles and protein aggregates, are required during meiotic prophase for arm cohesion maintenance and accurate meiotic segregation …

Mitochondrial Network Expansion And Loss During Oligodendrocyte Life And Death, Xhoela Bame

Dartmouth College Ph.D Dissertations

Oligodendrocytes are the myelinating cells of the central nervous system, known for modulating signal transmission, refining neural circuits, and providing metabolic support to axons. Oligodendrocytes are generated throughout life from oligodendrocyte precursor cells (OPCs) and are damaged or lost in demyelinating and neurodegenerative diseases and age-related pathologies. Thus, understanding the cellular checkpoints that occur during the generation and degeneration of oligodendrocytes is crucial for maintaining their population in health and recovering it in disease and aging.

Using high-resolution optical imaging, I have discovered a dynamic redistribution and subcellular partitioning of mitochondria during oligodendrogenesis. Mitochondria transiently expanded towards the differentiating OPC …

Characterization Of The Erv41-Erv46 Complex As A Retrograde Receptor For Misfolded Secretory Proteins, John Andrew Fuesler

Dartmouth College Ph.D Dissertations

The Endoplasmic Reticulum (ER), the site of secretory protein biosynthesis

provides a favorable environment to promote polypeptide folding, protein

oligomerization and export. Although the ER contains many chaperones and other

factors that assist in protein folding, this process is error prone. Eukaryotes have

evolved protein quality control checkpoints to maintain homeostasis in the secretory

pathway, however these processes are imperfect and may result in proteotoxicity

when toxic levels or aggregates of proteins arise. Mutations in proteins involved in

trafficking in the early secretory pathway are closely associated with disease states.

Therefore, it is of great interest to further understand how …

Cell Competition Eliminates Aneuploid Human Pluripotent Stem Cells, Amanda I. Ya

Dartmouth College Ph.D Dissertations

Aberrant mitotic chromosome segregation results in the generation of cells with aneuploidy, an incorrect number of chromosomes. Aneuploidy can compromise the viability of the developing embryo and is the leading cause of pregnancy loss, failed embryo implantation, and congenital birth defects. Yet, widescale analysis of human embryos from in vitro fertilization (IVF) clinics suggests that aneuploidy is common, with upwards of 70% of preimplantation embryos being aneuploid.

Mitotic chromosome missegregation during post-zygotic development results in mosaic embryos made up of both diploid and aneuploid cells. Strikingly, upon transplant for pregnancy, mosaic embryos have been reported to result in healthy birth …

Characterization Of Stealth Liposome-Based Nanoparticles Encapsulating Acat1/Soat1 Inhibitor F26: Potential Therapeutics For Niemann-Pick Type C And Other Neurodegenerative Diseases., Junghoon Lee

Dartmouth College Ph.D Dissertations

Cholesterol dysregulation is implicated in neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and Niemann-Pick type C disease (NPCD). This study focused on evaluating the potent ACAT1 inhibitor, F26, as a therapeutic strategy for NPCD. F26 demonstrated superior ACAT1 inhibition and efficacy compared to the previously studied inhibitor, F12511, both in vitro and in vivo. Notably, F26 exhibited enhanced pharmacokinetic properties, including prolonged duration of action and better brain retention, making it a more promising candidate for treating neurodegenerative diseases.

F26 was encapsulated in a liposome-based nanoparticle system, DSPE-PEG2000 with phosphatidylcholine (PC), for enhancing its …

Wee1 And Cell Size Control In Fission Yeast By The Protein Kinase Cdr2, Rachel Berg-Murante

Dartmouth College Ph.D Dissertations

The mechanisms that govern cell size have long been topics of study in the field of cell biology. In eukaryotic cells this size control is tied to checkpoints, a set threshold of minimum necessary growth linked to cyclin dependent kinase activity regulation. In the fission yeast Schizosaccharomyces pombe, the Cdk1 regulatory network is conserved, and G2/M represents the major size checkpoint. Prior to mitosis, Cdk1 is inhibited by phosphorylation applied by Wee1 during G2 phase. Once S. pombe cells have satisfied the size checkpoint, Cdk1 is activated through dephosphorylation by Cdc25. Wee1 is a dose-dependent regulator of mitotic entry …

Causes And Consequences Of Mitotic Chromosome Missegregation In Human Pluripotent Stem Cells, Chenhui Deng

Dartmouth College Ph.D Dissertations

Mitosis is a fundamental process that ensures the equal distribution of replicated chromosomes, which carry an organism's genetic material, into two daughter cells. The fidelity of mitosis is paramount, as errors in chromosome segregation result in aberrant chromosome numbers, including gains or losses, a state termed aneuploidy. Aneuploidy impacts a broad range of human conditions, including being one of the major hurdles in early human development where it is the primary cause of miscarriages and birth defects. Strikingly, more than 70% of human preimplantation embryos are aneuploid with mitotic chromosome segregation errors being the most common source of aneuploidy. However, …

Quantitative Proteomic Strategies To Determine Substrate Specificities Of Phosphoprotein Phosphatases, Hieu Trung Nguyen

Dartmouth College Ph.D Dissertations

Reversible phosphorylation is a crucial regulatory mechanism of cellular signaling pathways. Being the most prevalent post-translational modification (PTM) in the cells, with over 75% of all proteins detected to be phosphorylated, phosphorylation regulates a significant number of important cellular processes that have implications in various diseases. Phosphorylation is carried out by protein kinases, which have been extensively studied. However, the opposite reaction, carried out by protein phosphatases, has lagged significantly, exposing a gap of knowledge that is required to be investigated to delineate the kinase-substrate-phosphatase relationship. Phosphoprotein phosphatase family (PPPs), containing seven members of phospho-Serine (pS) and phospho-Threonine (pT) phosphatases, …

Understanding The Non-Canonical Regulation Of Srebp In Aspergillus Fumigatus, Muhammad Abubakar Khan

Dartmouth College Ph.D Dissertations

Aspergillus fumigatus is an opportunistic fungal pathogen causing invasive pulmonary aspergillosis (IPA), with high mortality rates in immunocompromised individuals. Adaptation to the hypoxic microenvironment of IPA is crucial for fungal virulence. The transcription factor SrbA, a Sterol Regulatory Element-Binding Protein (SREBP) homolog, plays a key role in this hypoxic response and regulates genes involved in hypoxic growth, sterol biosynthesis, and azole resistance, making it an attractive therapeutic target.

However, SrbA activation in A. fumigatus lacks critical components of the canonical SREBP pathway, such as SCAP, Site-1 protease (S1P), and Site-2 protease (S2P). Instead, the rhomboid protease RbdB, signal peptide peptidase …

Microglial Dynamics And Mechanisms Underlying The Phagocytosis Of Dying Oligodendrocytes, Genaro E. Olveda

Dartmouth College Ph.D Dissertations

Myelin is a complex multilamellar structure, generated by oligodendrocytes, that ensheaths axons and is a vital component for neural processing. Degeneration of both oligodendrocytes and their myelin sheaths is a common pathological feature associated with aging and neurodegenerative diseases. Efficient removal of the cellular and myelin debris is crucial for remyelination and prevention of further degeneration. Microglia, the primary phagocytes of the CNS, are thought to play a key role in this process. To investigate the cellular dynamics underlying microglia-mediated clearance of degenerating oligodendrocytes and myelin sheaths, at the single cell level, we developed a novel model for inducible cortical …

Formation Of New Cohesive Linkages And Regulation Of Cohesion Rejuvenation During Meiotic Prophase In Drosophila Oocytes, Muhammad Abdul Haseeb

Dartmouth College Ph.D Dissertations

During meiosis, faithful segregation of chromosomes requires maintenance of sister chromatid cohesion from premeiotic S phase until its stepwise dissolution at anaphase I and anaphase II. Research in humans and model organisms indicates that premature loss of meiotic cohesion is a major determinant of age-induced aneuploidy in human oocytes, a phenomenon known as the maternal age effect. Because cohesin turnover after S phase has not been detected in mice oocytes, the prevailing model for mammalian oocytes is that cohesion cannot be replenished after its initial establishment in S phase. However, previous research from the Bickel lab suggested that a cohesion …

Mitochondrial Quality Control By Tail-Anchored Proteins, Jose M. Delgado

Dartmouth College Ph.D Dissertations

Autophagy is a lysosome-mediated pathway responsible for the degradation of unwanted cytosolic content. During autophagy, cytoplasmic components are enveloped by a newly generated vesicle (the autophagosome), trafficked to the lysosome, and degraded. The power of autophagy lies in its ability to selectively target specific substrates for degradation—a phenomenon known as selective autophagy.

Specialized proteins known as selective autophagy receptors play a crucial role in identifying and targeting autophagy cargo. Although historically overlooked as potential regulators, our understanding of autophagy receptors is evolving beyond the assumption that receptors merely bridge targets to pre-formed autophagosomal membranes. Previous insights were often based on …

Chromatin Regulation By Swi/Snf Remodelers In Somatic Stem Cell Maintenance And Transformation, Luke Thomas Deary

Dartmouth College Ph.D Dissertations

Cell identity is defined by the epigenome, whereby chromatin regulators work in concert to promote gene expression programs that serve a cell’s specialized purpose. Mutations in chromatin regulators are amongst the most frequent drivers of human disease, underscoring the importance of understanding their activities in maintaining cell identity and tissue function. In particular, mutations in subunits of the evolutionarily conserved SWI/SNF chromatin remodeling complexes drive diseases across human tissues in both development and adult tissue maintenance5. Three major SWI/SNF complexes exist: BAF, PBAF, and GBAF, which differ in their composition and genomic targeting but share an ATP-dependent catalytic activity to …

Oligodendrocyte 2phatal Reveals Dynamics Of Myelin Degeneration And Repair, Timothy W. Chapman

Dartmouth College Ph.D Dissertations

Oligodendrocytes are responsible for producing myelin in the central nervous system. This lipid-rich coating along axons helps to increase action potential velocity, provide metabolic support to axons, and facilitate fine-tuning of neuronal circuitry. Demyelination and/or myelin dysfunction is widespread in neurodegenerative diseases and aging. Despite this, we know very little about how individual oligodendrocytes, or the myelin sheaths they produce, degenerate. Myelin repair, carried out by resident oligodendrocyte precursor cells (OPCs), is known to occur following myelin damage in certain contexts. We sought to investigate the cellular dynamics of oligodendrocyte degeneration and repair by developing a non-inflammatory demyelination model, combining …

Molecular Mechanisms Regulating Prometaphase And Metaphase States For Faithful Chromosome Segregation, Sarah Yvette Valles

Dartmouth College Ph.D Dissertations

Cells progress through different stages of the cell cycle as they ultimately prepare to divide during mitosis. Mitosis relies on many interconnected networks to carry out the coordinated events required for faithful chromosome segregation. When a cell enters mitosis, chromosomes are highly condensed and sister chromatids are held together by cohesion. Kinetochores assemble at the constricted regions on each chromosome. The kinetochore is a large macromolecular structure composed of many proteins that form the binding site for microtubules of the mitotic spindle to attach. These kinetochore-microtubule (k-MT) attachments serve to align chromosomes at the center of the cell and are …

Proteomic Approaches To Identify Unique And Shared Substrates Among Kinase Family Members, Charles Lincoln Howarth

Dartmouth College Ph.D Dissertations

Protein phosphorylation is a reversible post-translational modification that is a critical component of almost all signaling pathways. Kinases regulate substrate proteins through phosphorylation, and nearly all proteins are phosphorylated to some extent. Crucially, breakdown in phosphorylation signaling is an underlying factor in many diseases, including cancer. Understanding how phosphorylation signaling mediates cellular pathways is crucial for understanding cell biology and human disease.

Targeted protein degradation (TPD) is a strategy to rapidly deplete a protein of interest (POI) and is applicable to any gene that is amenable to CRISPR-Cas9 editing. One TPD approach is the auxin-inducible degron (AID) system, which relies …

Regulation Of The Wnt/Wingless Receptor Lrp6/Arrow By The Deubiquitylating Complex Usp46, Zachary T. Spencer

Dartmouth College Ph.D Dissertations

The evolutionarily conserved Wnt/Wingless signal transduction pathway is critical for the proper development of all animals and implicated in numerous diseases in adulthood. Upon binding of the Wnt/Wingless ligand, a cascade of events culminates in inactivation of the destruction complex, a negative regulator of the pathway, and the subsequent formation of singalosomes which mediate pathway activation. A critical component of signalosome formation is the Wnt/Wingless receptor LRP6/Arrow. Upon canonical pathway activation, LRP6/Arrow undergoes activation via phosphorylation by several kinases and complexes with another Wnt/Wingless receptor Frizzled, along with several cytoplasmic components. While many studies have investigated the regulatory mechanisms of …

Anillin And Dunk: The Conserved And Non-Conserved Players Regulating Myosin Dynamics In Drosophila Cleavage, Jiayang Chen

Dartmouth College Ph.D Dissertations

Cleavage is a common process during early embryogenesis. Similar to conventional cytokinesis, Drosophila cellularization, a unique form of cleavage, requires precise regulation of non-muscle myosin II ("myosin") at cleavage furrows, where myosin forms an interconnected basal array before reorganizing into individual cytokinetic rings. However, how myosin is regulated through both conserved and cellularization-specific mechanisms during this special form of cytokinesis remains unclear.

In my first project, I investigated the molecular mechanisms by which the cellularization-specific zygotic gene dunk regulates myosin at the basal array. I identified anillin (Scraps in Drosophila), a conserved scaffolding protein in cytokinesis, as the primary …

The Molecular And Cellular Response To Acat1/Soat1 Inhibition, Taylor C. Harned

Dartmouth College Ph.D Dissertations

Cholesterol is an important component of all mammalian cell membranes. It governs the membrane’s physical properties and creates the membrane order and heterogeneity required for complex membrane-related processes. Tight regulation of cholesterol levels and distribution are necessary for maintaining proper cell health. Likewise, disruptions in cholesterol homeostasis have been implicated in a variety of diseases, including Alzheimer’s disease (AD). Our lab, and others, have demonstrated the benefits of blocking acyl-CoA:cholesterol acyltransferase1/sterol O:acyltransferase 1 (ACAT1/SOAT1) in AD models by genetic ablation or pharmacological inhibition. We understand that blocking ACAT1/SOAT1 activity reduces amyloid and tau pathology, and that this is, at least …

Measuring How Kinetochore-Microtubule Detachment Contributes To Chromosome Movement And The Correction Of Attachment Errors, Melissa K. Parks

Dartmouth College Ph.D Dissertations

The goal of mitosis is to achieve faithful chromosome segregation; ensuring that the daughter cells inherit equal numbers of chromosomes. This is vital to cell health and viability and if mis-regulated can result in birth defects and disease such as cancer. There are many intricately regulated processes that occur throughout mitosis to achieve proper chromosome segregation, and one such example is the dynamic attachments formed between cytoskeletal structures, known as microtubules, and chromosomes, the carriers of genetic material. These attachments occur at structures called kinetochores, and the microtubules attached here are referred to as kinetochore-microtubules (k-MTs). These k-MTs are inherently …

Regulation Of Tissue Mechanics And Adherens Junctions By Small Gtpase Rhoa During Drosophila Embryogenesis, Hanqing Guo

Dartmouth College Ph.D Dissertations

Actomyosin contractility plays an important role at both the cell and tissue level during developments. In this study, we developed an optogenetic tool that can acutely inhibit actomyosin contractility by targeting its main activator Rho1. This optogenetic tool can achieve myosin inhibition within one minute and thus enable further dissection of actomyosin function in development. In my first two projects, I used Drosophila mesoderm invagination (also known as ventral furrow formation) as a model to study epithelial folding, a fundamental mechanism for constructing complex 3D tissues. Apical constriction mediated by actomyosin contractility is a common mechanism for epithelial folding. However, …

Mechanisms And Roles Of Dynamic Actin Assembly Around Dysfunctional Mitochondria, Tak Shun Fung

Dartmouth College Ph.D Dissertations

Possessing the ability to efficiently generate ATP required to sustain cellular functions, mitochondria are often considered the ‘powerhouses of the cell’. However, our understanding of mitochondria in cell biology was further expanded when we recognized that communication between this unique organelle and the rest of the cell regulates cellular bioenergetics, metabolism and signaling processes such as mitophagy and apoptosis. Here, I investigate signaling between mitochondria and the actin cytoskeleton, and how this signaling regulates mitochondrial dynamics and cellular function. Specifically, I find that, upon mitochondrial dysfunction, actin polymerizes rapidly around the dysfunctional organelle, which we term ‘acute damage-induced actin’ (ADA). …

Novel Functions For Arp2/3 Complex-Mediated Actin Networks Discovered In Chlamydomonas Reinhardtii, Brae M. Bigge

Dartmouth College Ph.D Dissertations

Chlamydomonas reinhardtii, a unicellular member of the Chlorophyta or Green Algae phylum, has been used for decades as a model for ciliary studies. Using this tool, previous work from our lab found a role for actin in ciliary assembly and maintenance. However, while the microtubule-based, membrane-ensheathed cilia of Chlamydomonas are highly conserved in relation to mammalian cells, the actin cytoskeleton is not as simple. Chlamydomonas contains two actin genes: IDA5, a conventional actin, and NAP1, a divergent actin. Here, we find that despite the divergence of NAP1, it is still able to interact with the actin nucleator, the Arp2/3 complex. …

Deciphering Phosphoprotein Phosphatase Signaling Networks Using Proteomics Approaches, Brooke Brauer

Dartmouth College Ph.D Dissertations

Protein phosphorylation is a highly regulated mechanism of cell signaling control and its deregulation is implicated in disease. The kinases that catalyze the addition of phosphate groups onto their substrate proteins have been well studied, their signaling pathways mapped, and their effects on cell and organismal health observed. Knowledge of the phosphatases that reverse the reaction only recently began to come into focus. Phosphoprotein phosphatases (PPPs), long thought to be housekeeping enzymes, are now known to be exquisitely specific towards their substrates, but the exact nature of phosphatase regulation—both upstream and downstream of the phosphatase—is unclear.

PPPs recognize substrates through …