Physiology Commons^™

Dysregulation Of Daf-16/Foxo3a-Mediated Stress Responses Accelerates T Oxidative Dna Damage Induced Aging, Aditi U. Gurkar, Andria R. Robinson, Yuxiang Cui, Xuesen Li, Shailaja K. Allani, Amanda Webster, Mariya Muravia, Mohammad Fallahi, Herbert Weissbach, Paul D. Robbins, Yinsheng Wang, Eric E. Kelley, Claudette M. St. Croix, Laura J. Niedernhofer, Matthew S. Gill

Faculty & Staff Scholarship

DNA damage is presumed to be one type of stochastic macromolecular damage that contributes to aging, yet little is known about the precise mechanism by which DNA damage drives aging. Here, we attempt to address this gap in knowledge using DNA repair-deficient C. elegans and mice. ERCC1-XPF is a nuclear endonuclease required for genomic stability and loss of ERCC1 in humans and mice accelerates the incidence of age-related pathologies. Like mice, ercc-1 worms are UV sensitive, shorter lived, display premature functional decline and they accumulate spontaneous oxidative DNA lesions (cyclopurines) more rapidly than wild-type worms. We found that ercc-1 worms …

Sympatho-Excitatory Response To Pulmonary Chemosensitive Spinal Afferent Activation In Anesthetized, Vagotomized Rats, Julia A. Shanks, Zhiqiu Xia, Steven J. Lisco, George J. Rozanski, Harold D. Schultz, Irving H. Zucker, Han-Jun Wang

Journal Articles: Cellular & Integrative Physiology

The sensory innervation of the lung is well known to be innervated by nerve fibers of both vagal and sympathetic origin. Although the vagal afferent innervation of the lung has been well characterized, less is known about physiological effects mediated by spinal sympathetic afferent fibers. We hypothesized that activation of sympathetic spinal afferent nerve fibers of the lung would result in an excitatory pressor reflex, similar to that previously characterized in the heart. In this study, we evaluated changes in renal sympathetic nerve activity (RSNA) and hemodynamics in response to activation of TRPV1-sensitive pulmonary spinal sensory fibers by agonist application …

Effects Of A 60 Minute On Ice Game Simulation On The Balance Error Scoring System, Philip Cameron, Noelle C. Sotero, Justin Byers

Applied Health Sciences Student Works

Mild traumatic brain injuries (mTBIs) are common in contact sports. There is an association between mTBIs and altered motor function. BioSway technology measures individuals’ balance using the Balance Error Scoring System (BESS). Prior to incorporating BESS testing in concussion protocol, other variables that influence the BESS test require review. The objective of this study is to determine if game fatigue in hockey players also influences the BESS score. 23 male (21.08 ± 1.09) National Collegiate Athletic Association (NCAA) athletes were tested using the BioSway™ (Biodex, USA). The BESS test measures the Sway Index (SI) - a calculation of deviation from …

Spontaneous Dna Damage To The Nuclear Genome Promotes Senescence, T Redox Imbalance And Aging, Andria R. Robinson, Matthew J. Yousefzadeh, Tania A. Rozgaja, Jin Wang, Xuesen Li, Jeremy S. Tilstra, Chelsea H. Feldman, Siobhan Q. Gregg, Caroline H. Johnson, Erin M. Skoda, Marie-Celine Frantz, Harris Bell-Temin, Hannah Pope-Varsalona, Aditi U. Gurkar, Luigi A. Nasto, Rena A.S. Robinson, Heike Fuhrmann-Stroissnigg, Jolanta Czerwinska, Sara J. Mcgowan, Nadiezhda Cantu-Madellin, Jamie B. Harris, Salony Maniar, Mark A. Ross, Christy E. Trussoni, Nicholas F. Larusso, Eugenia Cifuentes-Pagano, Patrick J. Pagano, Barbara Tudek, Nam V. Vo, Lora H. Rigatti, Patricia L. Opresko, Donna B. Stolz, Simon C. Watkins, Christin E. Burd, Claudette M. St, Croix, Gary Siuzdak, Nathan A. Yates, Paul D. Robbins, Yinsheng Wang, Peter Wipf, Eric E. Kelley, Laura J. Neidernhofer

Faculty & Staff Scholarship

Accumulation of senescent cells over time contributes to aging and age-related diseases. However, what drives senescence in vivo is not clear. Here we used a genetic approach to determine if spontaneous nuclear DNA damage is sufficient to initiate senescence in mammals. Ercc1-/Δ mice with reduced expression of ERCC1-XPF endonuclease have impaired capacity to repair the nuclear genome. Ercc1-/Δ mice accumulated spontaneous, oxidative DNA damage more rapidly than wild-type (WT) mice. As a consequence, senescent cells accumulated more rapidly in Ercc1-/Δ mice compared to repair-competent animals. However, the levels of DNA damage and senescent cells in Ercc1-/Δ mice never exceeded that …

Patient-Specific Quantification Of The Relationship Between The Left Atrium Pressure And The Ostial Diameter Of The Left Atrial Appendage, Sky Tianqi Gao

Electronic Theses and Dissertations

The left atrial appendage has been a historically understudied region of the heart until fairly recently with the new understanding of its role in the stroke pathway of patients with atrial fibrillation. The goal of this study is to take a look at the biomechanical behavior of the left atrium and left atrial appendage under normal physiological loading conditions using material properties taken from biaxial stretch tests. Several different options for material properties models were tested and biaxial stretch test data of cadaveric human tissue samples for the left atrium and appendage were fit to a Fung-type strain-energy function for …

Incidence Of Second Malignancy In Patients With Papillary Thyroid Cancer From Surveillance, Epidemiology, And End Results 13 Dataset, Mayumi Endo, Jessica Liu, Marcelle Dougan, Jennifer Lee

Faculty Publications

Increased risk of second primary malignancy (SPM) in papillary thyroid cancer (PTC) has been reported. Here, we present the most updated incidence rates of second primary malignancy from original diagnosis of PTC by using the data from the Surveillance, Epidemiology, and End Results. In this cohort, 3,200 patients developed SPM, a substantially higher number than in the reference population of 2,749 with observed to expected ratio (O/E) of 1.16 (95% CI; 1.12–1.21). Bone and joint cancer had the highest O/E ratio of 4.26 (95% confidence interval [CI] 2.33–7.15) followed by salivary gland (O/E 4.15; 95% CI 2.76–6.0) and acute lymphocytic …

Environmental Effects On Drosophila Brain Development And Learning, Xia Wang, Amei Amei, J. Steven De Belle, Stephen P. Roberts

Biological Sciences Faculty Research & Creative Works

Brain development and behavior are sensitive to a variety of environmental influences including social interactions and physicochemical stressors. Sensory input in situ is a mosaic of both enrichment and stress, yet little is known about how multiple environmental factors interact to affect brain anatomical structures, circuits and cognitive function. In this study, we addressed these issues by testing the individual and combined effects of sub-adult thermal stress, larval density and early-adult living spatial enrichment on brain anatomy and olfactory associative learning in adult Drosophila melanogaster. In response to heat stress, the mushroom bodies (MBs) were the most volumetrically impaired among …

Tissue Expression Patterns Identify Mouse Cilia Genes, Timothy S. Mcclintock

Physiology Research Data

A summary of 2,127 mouse genes linked to cilia by previous high-throughput approaches (reviewed in Inglis et al., 2006), published studies of individual gene products, or by McClintock et al. 2008. Each gene was viewed at Entrez Gene to verify and update the Gene ID and Gene Symbol. Each was also searched against PubMed (Gene Symbol AND (cili* OR flagel*)) for published evidence linking the mouse gene or putative orthologs to cilia or flagella. This searchable file lists identifying information about each gene, functional information about the encoded protein, the number of high-throughput studies linking the gene to cilia, and …

Early Contributions To Infants’ Mental Rotation Abilities, Mihaela Constantinescu, David S. Moore, Scott P. Johnson, Melissa Hines

Pitzer Faculty Publications and Research

Some cognitive abilities exhibit reliable gender differences, with females outperforming males in specific aspects of verbal ability, and males showing an advantage on certain spatial tasks. Among these cognitive gender differences, differences in mental rotation are the most robust, and appear to be present even in infants. A large body of animal research suggests that gonadal hormones, particularly testosterone, during early development could contribute to this gender difference in mental rotation. Also, substantial evidence supports an influence of socialization on mental rotation performance. The present study investigated the relationship of two types of factors, early postnatal testosterone exposure and parental …

Sex, Ethnicity, And Socioeconomic Status On Attitudes Toward Women As Managers And Perceived Career Impediment: A Study Of Young Adults In Malaysia, Li Teng Voon

ETD Archive

The current study aims at examining the effects of sex, race, and socioeconomic status on young Malaysians; attitudes toward women as managers and the perceived barriers to their own careers. This paper also examined a moderated mediation, with the moderator being the working status of an individual's mother and the mediator being gender role attitudes. A great wealth of research in this area has been conducted in the Western culture, but much less is known about Malaysia and its young adults. This study provides a historical and sociocultural overview of Malaysia, and how its unique sociopolitical and societal structure impacts …

Rumination In Borderline Personality Disorder: An Examination Of Interpersonal Contexts In Experimental And Daily Life Settings, Skye C. Napolitano

ETD Archive

This study examined whether Borderline Personality Disorder (BPD) features predict increased rumination in response to interpersonal contexts, leading to increased negative affect (NA) outcomes across self-report, experimental, and daily life settings. As BPD is characterized by sustained NA, emotion dysregulation, and pervasive difficulties in interpersonal relationships, interpersonal contexts may present a specific liability for individuals with BPD to ruminate, and subsequently, experience enduring NA. Undergraduate participants (N=119) completed measures of BPD features, dispositional rumination, emotion dysregulation, and both 1) a laboratory protocol that measured spontaneous rumination and affective reactivity to non-interpersonal (sad film clip) and interpersonal (Cyberball) stimuli and 2) …

The Effect Of Taboo Words And Reprimands In An Audio-Visual Modified Stroop Task, Rachel B. Fernandes

ETD Archive

Previous research has found that participants respond less efficiently to taboo words in a modified emotional Stroop task than to neutral words because of the emotional nature of taboo words. Additionally, there is some evidence that the extent to which these words impact performance depends on whether the words appear in a participant’s native language. More specifically, the taboo effect has been found to be more pronounced in a person’s native language. One purpose of the current study was to determine whether previous results in a taboo Stroop task would be replicated. Another purpose of this study was to determine …

Examining Effects Of Arousal And Valence Across The Adult Lifespan In An Emotional Stroop Task, Samantha E. Tuft

ETD Archive

As age increases, there is evidence that people tend to pay less attention to negative information, pay more attention to positive information, or both. There are many theoretical accounts that attempt to explain this positivity bias. In the current study, I examined positivity effects across the adult lifespan by evaluating competing predictions of two theories: Socioemotional Selectivity Theory, which is based in motivation, and Dynamic Integration Theory, which is based in capacity. Computer mouse tracking was used to examine effects across levels of Valence (negative, neutral, and positive) and Arousal (low, medium, and high) in an emotional Stroop task. Participants …

Rhythm: An Open Source Imaging Toolkit For Cardiac Panoramic Optical Mapping, Christopher Gloschat, Kedar Aras, Shubnam Gupta, N. Rokhana Faye, Hanyu Zhang, Matthew W. Kay, Igor R Efimov, +Several Additional Authors

Pharmacology and Physiology Faculty Publications

Fluorescence optical imaging techniques have revolutionized the field of cardiac electrophysiology and advanced our understanding of complex electrical activities such as arrhythmias. However, traditional monocular optical mapping systems, despite having high spatial resolution, are restricted to a two-dimensional (2D) field of view. Consequently, tracking complex three-dimensional (3D) electrical waves such as during ventricular fibrillation is challenging as the waves rapidly move in and out of the field of view. This problem has been solved by panoramic imaging which uses multiple cameras to measure the electrical activity from the entire epicardial surface. However, the diverse engineering skill set and substantial resource …

Can A Comprehensive Transition Plan To Barefoot Running Be The Solution To The Injury Epidemic In American Endurance Runners?, Michael A. Scarlett

CMC Senior Theses

Fossils belonging to the genus Homo, dating as far back as two million years ago, exhibit uniquely efficient features suggesting that early humans had evolved to become exceptional endurance runners. Although they did not have the cushion or stability-control features provided in our modern day running shoes, our early human ancestors experienced far less of the running-related injuries we experience today. The injury rate has been estimated as high as 90% annually for Americans training for a marathon and as high as 79% annually for all American endurance runners. There is an injury epidemic in conventionally shod populations that …

Direct Conversion Of Mouse Astrocytes Into Neural Progenitor Cells And Specific Lineages Of Neurons, Kangmu Ma, Xiaobei Deng, Xiaohuan Xia, Zhaohuan Fan, Xinrui Qi, Yongxiang Wang, Yuju Li, Yizhao Ma, Qiang Chen, Hui Peng, Jianqing Ding, Chunhong Li, Yunlong Huang, Changhai Tian, Jialin C. Zheng

Journal Articles: Cellular & Integrative Physiology

Background: Cell replacement therapy has been envisioned as a promising treatment for neurodegenerative diseases. Due to the ethical concerns of ESCs-derived neural progenitor cells (NPCs) and tumorigenic potential of iPSCs, reprogramming of somatic cells directly into multipotent NPCs has emerged as a preferred approach for cell transplantation.

Methods: Mouse astrocytes were reprogrammed into NPCs by the overexpression of transcription factors (TFs) Foxg1, Sox2, and Brn2. The generation of subtypes of neurons was directed by the force expression of cell-type specific TFs Lhx8 or Foxa2/Lmx1a.

Results: Astrocyte-derived induced NPCs (AiNPCs) share high similarities, including the expression of NPC-specific genes, DNA methylation …

Novel Antioxidant Properties Of Doxycycline, Dahn L. Clemens, Michael J. Duryee, Cleofes Sarmiento, Andrew Chiou, Jacob D. Mcgowan, Carlos D. Hunter, Sarah L. Schlichte, Jun Tian, Lynell W. Klassen, James R. O'Dell, Geoffrey M. Thiele, Ted R. Mikuls, Matthew C. Zimmerman, Daniel R. Anderson

Journal Articles: Cellular & Integrative Physiology

Doxycycline (DOX), a derivative of tetracycline, is a broad-spectrum antibiotic that exhibits a number of therapeutic activities in addition to its antibacterial properties. For example, DOX has been used in the management of a number of diseases characterized by chronic inflammation. One potential mechanism by which DOX inhibits the progression of these diseases is by reducing oxidative stress, thereby inhibiting subsequent lipid peroxidation and inflammatory responses. Herein, we tested the hypothesis that DOX directly scavenges reactive oxygen species (ROS) and inhibits the formation of redox-mediated malondialdehyde-acetaldehyde (MAA) protein adducts. Using a cell-free system, we demonstrated that DOX scavenged reactive oxygen …

Asymmetric Patterns Of Small Molecule Transport After Nanosecond And Microsecond Electropermeabilization, Esin B. Sözer, C. Florencia Pocetti, P. Thomas Vernier

Bioelectrics Publications

Imaging of fluorescent small molecule transport into electropermeabilized cells reveals polarized patterns of entry, which must reflect in some way the mechanisms of the migration of these molecules across the compromised membrane barrier. In some reports, transport occurs primarily across the areas of the membrane nearest the positive electrode (anode), but in others cathode-facing entry dominates. Here we compare YO-PRO-1, propidium, and calcein uptake into U-937 cells after nanosecond (6 ns) and microsecond (220 µs) electric pulse exposures. Each of the three dyes exhibits a different pattern. Calcein shows no preference for anode- or cathode-facing entry that is detectable with …

Space Operations In The Suborbital Space Flight Simulator And Mission Control Center: Lessons Learned With Xcor Lynx, Pedro Llanos, Christopher Nguyen, David Williams, Kim O. Chambers, Erik Seedhouse, Robert Davidson

Journal of Aviation/Aerospace Education & Research

This study was conducted to better understand the performance of the XCOR Lynx vehicle. Because the Lynx development was halted, the best knowledge of vehicle dynamics can only be found through simulator flights. X-Plane 10 was chosen for its robust applications and accurate portrayal of dynamics on a vehicle in flight. The Suborbital Space Flight Simulator (SSFS) and Mission Control Center (MCC) were brought to the Applied Aviation Sciences department in fall 2015 at Embry-Riddle Aeronautical University, Daytona Beach campus. This academic and research tool is a department asset capable of providing multiple fields of data about suborbital simulated flights. …

Bilateral Deficit: A Comparison Between Upper-Body And Lower-Body Maximal Strength, James Lee Ramsey

Master's Theses and Doctoral Dissertations

Purpose: The study’s primary purpose was to determine if maximal unilateral strength is greater than maximal bilateral strength for the leg press and vertical dumbbell press exercises. The secondary purpose was to determine if blood glucose levels differ between the unilateral and bilateral conditions for the leg press exercise. Methods: Thirty college-aged volunteers reported on two separate occasions, 72 hours apart, for maximal strength testing. Blood glucose was obtained before and after strength testing for the leg press exercise. A paired samples t-test was conducted to determine significance (p < .05). Results: Participants were significantly stronger for the bilateral leg press; however, no significant differences were observed for the vertical dumbbell press exercise. No significant differences were observed in plasma blood glucose for the leg press exercise. Conclusion: Participants did not display a bilateral lateral deficit, which may have been a result of their resistance training prior to the study.

S-Nitrosation Of Protein Phosphatase 1 Mediates Alcohol-Induced Ciliary Dysfunction, Michael E. Price, Adam J. Case, Jacqueline A. Pavlik, Jane M. Devasure, Todd A. Wyatt, Matthew C. Zimmerman, Joseph H. Sisson

Journal Articles: Cellular & Integrative Physiology

Alcohol use disorder (AUD) is a strong risk factor for development and mortality of pneumonia. Mucociliary clearance, a key innate defense against pneumonia, is perturbed by alcohol use. Specifically, ciliated airway cells lose the ability to increase ciliary beat frequency (CBF) to β-agonist stimulation after prolonged alcohol exposure. We previously found that alcohol activates protein phosphatase 1 (PP1) through a redox mechanism to cause ciliary dysfunction. Therefore, we hypothesized that PP1 activity is enhanced by alcohol exposure through an S-nitrosothiol-dependent mechanism resulting in desensitization of CBF stimulation. Bronchoalveolar S-nitrosothiol (SNO) content and tracheal PP1 activity was increased in wild-type (WT) …

Environmental And Physiological Regulation Of Yellow Stingray Color Change, Theresa Rose Gunn

College of Graduate Studies: Theses & Dissertations

Many reef fishes exhibit dynamic coloration and body patterns that can change under nervous or hormonal control. Several species of benthic sharks and rays likely alter melanin in the skin to provide background matching for camouflage. The yellow stingray (Urobatis jamaicensis) is a benthically-oriented elasmobranch with elaborate spot patterns that provide effective camouflage within its habitats. This patterning, when coupled with the ability to alter melanin in response to background color, could increase background matching effectiveness in these species. The yellow stingray has been anecdotally noted to lighten or darken skin color.However, it is unclear whether this type …

Interleukin-6 And Exercise; Early Evidence Of A Novel Myokine, Brendan Hogg Mr.

Graduate Student Theses, Dissertations, & Professional Papers

Interleukin-6 (IL-6) was first identified as a pleiotropic cytokine, with a host of body-wide functions. Cytokine functions are characterized by chronically elevated levels within various inflammatory states. In this regard, IL-6 is largely associated with the acute phase response to many stimuli and performs specific actions when produced from certain cell types. Accrued evidence indicates IL-6 release from skeletal muscle often includes myokine functions. Novel myokine functions are adaptive in nature, and as compared to inflammatory/cytokine roles, exhibit a transient time course. Following exercise plasma IL-6 peaks and returns to resting levels within 1-2 hours. In contrast, IL-6 is observed …

The Effect Of Stride Frequencies On Running Performance At The Velocity Of Vo2max, Boram Lim

Cal Poly Humboldt theses and projects

Running economy(RE) is considered to be a critical factor to improve running performance. Stride frequency(SF) is an important variable for determining RE. The importance of SF has gained more attention in recent years, especially for recreational runners. However, no previous research has investigated the interaction between running performance and SF at the velocity of VO₂max. PURPOSE: To investigate the effect of five different SF variations on running performance until volitional fatigue at the velocity of VO₂max. METHODS: Fourteen male recreational runners (Age = 25.8 ± 4.96 years, Height = 171 ± 6.2cm, Body Mass = 71.9 …

Regulation Of Hcn Channel Function By Direct Camp Binding And Singlet Oxygen, Vinaykumar Idikuda

Theses and Dissertations

Hyperpolarization-activated, cyclic-nucleotide gated ion channels (HCN channels) are activated by membrane hyperpolarization and modulated by cyclic nucleotides. HCN channels are important to maintain the resting membrane potential and input resistance in neurons and have important physiological functions in the brain and heart. Four mammalian HCN isoforms, HCN1-4, and the isoform cloned from sea urchin, spHCN, have been extensively studied. Among these, only spHCN channel shows a voltage dependent inactivation. Previous studies have shown that the ligand binding in mHCN2 channel is activity dependent: cAMP binding increases along with channel opening or channels in the open state have higher binding affinity …

The Impact Of Insulin Dysregulation On Protein Metabolism In Horses, Caroline Margot Marcelle Loos

Theses and Dissertations--Animal and Food Sciences

Insulin plays a vital role in whole-body metabolism and provides a major anabolic stimulus for cellular signaling pathways, including those involved in the metabolism of glucose and protein. Consequently, insulin dysregulation (ID) is known to alter molecular signal transduction in insulin-sensitive tissues such as skeletal muscle, thereby disrupting glucose metabolism and compromising protein synthetic capacity. Our first objective was to induce ID in healthy horses by administering dexamethasone (DEX), a potent glucocorticoid, for 21 days. We evaluated the effects on insulin-stimulated muscle protein signaling components involved in the mammalian target of rapamycin (mTOR) pathway. DEX-induced ID reduced insulin-stimulated activation of …

Does A Family History Of Type 2 Diabetes Affect Exercise Induced Improvements In Insulin Sensitivity, Metabolic Flexibility, And Myokine Expression In Mexican-American Males?, Manuel Amador

Open Access Theses & Dissertations

A family history of diabetes (FH+) is considered a risk factor for the development of insulin resistance and type 2 diabetes. However, it is not known whether exercise induced improvement in insulin sensitivity (IS) and metabolic flexibility (MF) are impacted by a FH+. Purpose: To determine if a FH+ limits exercise induced improvements in Insulin sensitivity, MF, body composition, and strength following an 8-week combined aerobic and resistance training intervention compared to those without a family history of diabetes (FH-). Methods: 19 (FH- n=9, age 21.89 ± 0.60 years, BMI 27.51 ± 1.68 kg/m2; FH+ n=10, age 23.41 ± 0.86 …

Mechanical And Physical Characteristics Of Knee Flexors And Extensors Following Different Warm Up Protocols In Collegiate Male Soccer Athletes, Michael Redd

Electronic Theses and Dissertations

PURPOSE: To compare potential differences in mechanical and physical characteristics of knee flexors and extensors in collegiate male soccer players following different warm up protocols. METHODS: Sixteen collegiate male soccer players (20.33 ± 1.33 years, 176.97 ± 6.72 cm, and 78.43 ± 7.42 kg) participated in this study. A small sided games warm up (SSG), a dynamic warm up (DYN), and a plyometric warm up (PLY) were completed using a randomized crossover design. Tensiomyography (TMG) was used to assess contraction time (Tc), delay time (Td) and maximal displacement (Dm) of the rectus femoris (RF) and biceps femoris (BF) of both …

Lrrk2 Deficiency Impairs Trans-Golgi To Lysosome Trafficking And Endocytic Cargo Degradation In Human Renal Proximal Tubule Epithelial Cells, Nathan J. Lanning, Calvin Vanopstall, Megan L. Goodall, Jeffrey P. Mackeigan

University Faculty Publications and Creative Works

Defects in vesicular trafficking underlie a wide variety of human diseases. Genetic disruption of leucine-rich repeat kinase 2 (LRRK2) in rodents results in epithelial vesicular trafficking errors that can also be induced by treatment of animals with LRRK2 kinase inhibitors. Here we demonstrate that defects in human renal cells lacking LRRK2 phenocopy those seen in the kidneys of Lrrk2 knockout mice, characterized by accumulation of intracellular waste vesicles and fragmentation of the Golgi apparatus. This phenotype can be recapitulated by knockdown of N-ethylmaleimide-sensitive factor, which physically associates with LRRK2 in renal cells. Deficiency in either protein leads to a defect …

Myosin-Xva Is Key Molecule In Establishing The Architecture Of Mechanosensory Stereocilia Bundles Of The Inner Ear Hair Cells, Shadan Hadi

Theses and Dissertations--Medical Sciences

Development of hair cell stereocilia bundles involves three stages: elongation, thickening, and supernumerary stereocilia retraction. Although Myo-XVa is known to be essential for stereocilia elongation, its role in retraction/thickening remains unknown. We quantified stereocilia numbers/diameters in shaker-2 mice (Myo15^sh2) that have deficiencies in “long” and “short” isoforms of myosin-XVa, and in mice lacking only the “long” myosin-XVa isoform (Myo15^ΔN). Our data showed that myosin-XVa is largely not involved in the developmental retraction of supernumerary stereocilia. In normal development, the diameters of the first (tallest)/second row stereocilia within a bundle are equal and grow simultaneously. …