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Lab Members

Principal Investigators

The Holt / Géléoc Lab operates with a non-conventional model.  We have one lab run by two principle investigators,

Jeffrey R. Holt and Gwenaelle, S.  Géléoc.  The arrangement works well as maintenance of a single lab helps to minimize expenses, while having two PIs facilitates scientific output.   Furthermore, while one PI is busy writing grants or manuscripts, the other can be in the lab doing experiments or working with lab members.  

Jeffrey R. Holt, Ph.D., Professor

I earned my doctorate from the Department of Physiology at the University of Rochester in 1995.  For my thesis work I studied inward rectifier potassium currents in saccular hair cells in Ruth Anne Eatock's lab.  I went on to a post-doctoral position in the Neurobiology Department at Harvard Medical School, where I characterized transduction and adaptation in vestibular hair cells and developed an adenoviral vector system to transfect cultured hair cells.  My first faculty position was at the University of Virginia.  In 2011 the lab moved to Boston Children’s Hospital / Harvard Medical School. I am currently a Professor in the Departments of Otolaryngology and Neurology in the F.M. Kirby Neurobiology Center where I am involved with graduate and medical student teaching; I am a member of the Harvard Medical School, Program in Neuroscience and the Program in Speech and Hearing Bioscience and Technology and the Biophysics Program.  As one of two principle investigators for the lab, I write grants and manuscripts for publication, supervise and mentor lab members and make time to work on my own research project.  I am currently working on several projects:  1) I am investigating the function of TMC genes in hair cells using viral vectors to deliver wild-type and mutant channel genes and 2) I am interested in identifying other genes and proteins required for hair cell mechanosensory transduction, and 3) I am working to develop inner ear gene therapy for patients with genetic hearing loss. 

Hobbies:  Working late, playing with my kids, sailing, kite surfing, red wine, soccer, astrophotography                                            Jeff's CV:


Gwenaelle S. Géléoc, Ph.D., Associate Professor

I am originally from France and moved to the United States in 1999.  My passion for inner ear research began as an undergraduate student at the University of Montpellier (France) when I first saw a sensory hair cell under the microscope. I have been fortunate to train with wonderful scientists including Corne Kros (Sussex University, UK), Guy Richardson (Sussex University, UK) and Jonathan Ashmore (UCL, UK). During my graduate work I developed a preparation which allowed me to record the first mechanotransduction currents from vestibular hair cells of the mammalian inner ear (Géléoc et al. 1996, 1997).  I realized that there was much to be learned by analyzing the pattern of functional developmental of inner ear hair cells. A prerequisite for understanding vestibular and auditory disorders is knowledge of how hair cells develop. Hair cells of the inner ear have the critical role of converting sound and head movement information into electrical signals which are transmitted to the brain.  Precisely how and when hair cells acquire mechanosensitivity is a major focus of my ongoing research. As an Associate Professor at Boston Children’s Hospital, I study molecules involved in the development and function of sensory hair cells and aim to develop new therapies for the treatment of deafness and balance, with a particular focus on Usher syndrome. My major contribution to the field of Usher syndrome research involved pioneering work demonstrating unprecedented recovery of auditory and balance function in an animal model of USH1C using gene replacement therapy with adeno-associated viral vectors (Pan et al. 2017). My team currently pursues research focused on USH1C, USH2A and USH3A.  My work is supported by the NIH, the Usher syndrome Society and others.                           

                                                                                                                                                Gwen's CV:

Hobbies: Doing artwork, running, cooking (and eating), sailing and hiking



Stephanie Mauriac, Ph.D., Post-Doctoral Fellow

I grew up in Bordeaux, France. In 2015, I received my undergraduate degree from the University of Bordeaux in cellular biology and physiopathology. My interest for the inner ear began when I join the lab of Dr. Mireille Montcouquiol and Dr. Nathalie Sans in Bordeaux as a PhD student.  During my PhD, I studied a very rare pathology, called the Chudley McCullough Syndrome, characterized by early onset sensorineural deafness and brain anomalies. During this project, I learned different technics including biochemistry, Immunocytochemistry, surgery and dissection that permit us to clarify the etiology and identify a new molecular basis of this pathology. During this exciting project, I realized how this work is essential to find a treatment for these patients in order to improve their lives. After receiving my PhD degree in June, 2019, I had the great opportunity to join the lab of Dr. Jeffrey Holt and Dr. Gwenaelle Geleoc in October 2019 to continue in hearing research. My goal is to discover and develop approaches to restore auditory function by gene therapy in models of human deafness.


Hobbies : traveling, cooking, sewing, reading, music, movies


Wang Zheng, Ph.D., Post-Doctoral Fellow

I was born and grew up in the central part of China and graduated from Beijing Institute of Technology (BIT) with a B.A. in Biotechnology in 2008. Then I went to Wuhan University for a master’s degree in Microbiology, during which I developed a strong interest in ion channel proteins. In 2011, I moved to Canada and joined Dr. Xing-Zhen Chen's lab at University of Alberta to study gating mechanisms of polycystin ion channels, which were mutated in human autosomal dominant polycystic kidney disease. After receiving my PhD degree in 2017, I continued to pursue my interests in ion channels by joining Slav Bagriantsev's lab at Yale University where I studied inactivation mechanisms of mechanosensitive Piezo ion channels and how their inactivation processes are regulated by temperature. My research interests then drove me to join the Holt/Geleoc group in 2019 to explore mechano-electrical transduction (MET) apparatus in the inner ear. My goal is to figure out how the MET channels convert mechanical force into electrical signals, which would establish a foundation to develop therapeutic treatment for hearing loss.


Hobby: Skiing, fishing, hiking, traveling, music, reading

Evan Ratzan, Post-Doctoral Fellow

I grew up in the Rocky Mountains of Colorado but headed east to Amherst, MA where I obtained my Bachelor's degree in Cognitive Neuroscience from Hampshire College in 2009. My passion for neuroscience propelled me through a dual-degree program at the University of Utah where I received a Master's in Clinical Investigations and Ph.D. in Neuroscience. I worked in the lab of Dr. Michael R. Deans examining mechanisms of cell polarity acquisition in the developing vestibular system. This work lead to the interesting discovery that Fgf8 expression is a specific and perhaps the earliest marker of Type-I vestibular hair cell identity thus far identified. My graduate work also identified important factors downstream from Emx2  which contribute to regional specification within the developing vestibular maculae. My graduate experience included a variety of molecular biology techniques including RNAseq, FISH, mouse genetics, immunohistochemistry, and more which I was excited to apply to scientific questions with a clinically relevant focus. I was fortunate to join the Holt/Géléoc lab where I focus on molecular mechanisms of vestibular and auditory pathophysiology.


Hobbies: Rock and ice climbing, snowboarding, music, drawing, painting, and reading


Thibault Peineau, Post-Doctoral Fellow

I was born and raised in Tours, a charming city of the Loire Valley in France. In 2016, I graduated with a biology degree from Rennes. Then I went to Bordeaux for a Neuroscience Master’s degree. I had the opportunity to do my internship in the lab of Dr Didier DULON where I discovered the world of the Hearing research. During this internship I learned ABR (Auditory Brainstem Responses) and Patch Clamp techniques.  I was so passionate about this internship that I followed with a PhD. During my PhD, among others things, I used my training to characterize the molecular and physiological changes of ribbon synapses in inner hair cells during aging (Peineau et al. 2021). Working on old mice (1 year-old) contributed to improve my skills including the patch clamp technique. Moreover, I learned a lot of different techniques such as Intracochlear Injection, Live Calcium Imaging, Immunochemistry, Recording of Mechanotransduction.  In September 2022, I had the opportunity to join the Holt/Géléoc Lab to continue working in hearing research and learning the secrets of the cochlea.  My goal is to characterize the electrophysiological changes in deaf mice.  


Hobbies: Cooking, movies, gym, soccer, formula1 and learning new things.

Chloe Petit, Post-Doctoral Fellow

I was born and raised in France. During high school, one of my friends was hearing impaired and I became very interested in hearing problems. I graduated as a hearing aid fitter in 2017. Then, I wanted to specialize in cochlear implants so I got a master’s degree from the University of Montpellier (France) in sensory and motor neuro-prosthetics where my interest in hair cell physiology and inner ear mechanisms grew. I did my PhD at the Institute for Neurosciences in Montpellier, under the supervision of Regis Nouvian. During my PhD, I worked on two projects, in the first one I studied the phenotype of a VGLUT3 mutant mouse, mimicking the auditory deafness DFNA25. In the second one, I studied the role of the ferritin light-chain, known to store iron in the cytoplasm of the cochlea. During these projects, I learned different techniques and performed electrophysiological recordings (Auditory Brainstem Responses, Distortion Product Otoacoustic Emissions, Patch-clamp) and morphological examinations (confocal microscopy, super resolution microscopy, scanning and transmission electron microscopies). In January 2023, I joined the Holt/Geleoc lab to study the role of mechanotransduction system in sound coding.

Tais Castagnola, Post-Doctoral Fellow

I was born in Bahia Blanca, a small town in Argentina. For as long as I can remember I was always eager to understand how even the simplest things work. Driven by that curiosity I decided to study Biology at the University of Buenos Aires. While still an undergrad, I had my first approach to what being in a lab and doing research meant. During that time I started investigating the efferent system of Zebrafish neuromasts. Once I graduated from college, I decided to keep investigating the auditory efferent system, in particular, GABA's role during development. By performing electro-physiological recordings of inner hair cells along with optogenetic stimulation, we were able to demonstrate that GABA and ACh are co-released from Medial Olivocochlear Neurons. After getting my PhD degree, I had the honor of joining Holt/Geleoc lab as a postdoctoral fellow, where I hope to contribute to our understanding of hair cell mecanotransduction, and ultimately, help develop gene therapy methods to restore auditory function.


Hobbies: cooking, dancing, sailing, diving, traveling.

Matthew Mun, SHBT Graduate Student

I was born and raised in Dallas-Fort Worth, Texas and went to school at the University of Texas at Austin, where I studied chemistry, biochemistry, and linguistics. Having an interest in both language and molecular biology, I joined two labs: the Stuttering and Linguistic Processing Lab under Dr. Zoi Gkalitsiou where I studied the interactions between age, multilingualism, and manifestations of stuttering, as well as the lab of Dr. Richard Aldrich, where I studied the coupled calcium/voltage gating mechanism of BK channels and the functional domains of other ion channels. Wishing to combine my interests in speech-hearing and molecular biology, I joined the Harvard Speech and Hearing Bioscience and Technology program as a PhD student, where I have since joined the lab of Drs. Jeffrey Holt and Gwenaelle Geleoc at Boston Children’s Hospital/Harvard Medical School. While here, I plan to characterize molecular components important for sensory transduction and auditory function in the inner ear, as well as potential new therapeutics for the treatment of hearing loss.


Hobbies: Biking, music, drawing, learning (about) languages, playing saxophone 


Will Davis, Lab Manager

I was born in Louisiana and grew up in Ohio. I graduated with a BS in biology from Kent State University, then with a MSc in clinical embryology from the University of Oxford. I worked as a research assistant for several years at Case Western Reserve University in Cleveland, where I studied the development of the stria vascularis of the inner ear with Dr. Martin Basch. I then joined Boston Children’s Hospital as a lab manager. In my spare time I enjoy cycling, visiting the library, and pickling.


Hobbies: cycling, visiting the library, pickling


Cristobal Von Muhlenbrock, Research Assistant

I was born and raised in a small town called Iquique in the north of Chile. At 15, I had the incredible opportunity to participate in a six-month exchange program that took me to Massachusetts. It was a life-changing experience. At 17, I managed to return into the United States to pursue my dream of delving deeper into the world of science by completing a BS in Biochemistry and Molecular Biology at the University of Massachusetts, Amherst with the ultimate goal of attending Med School in the future. My interest in the Holt/Géléoc Lab's ongoing research was sparked by a personal connection. One of my family members was born with a genetic disorder that caused hearing loss.  Witnessing how profoundly it affected their life motivated me to understand the intricate mechanisms of the auditory system. The complexities of auditory transduction intrigued me, from the different structures, proteins, and processes involved in converting sound waves into electrical signals that reach the brain. I believe that gaining in-depth knowledge in this field can lead to potential treatments that can greatly improve the lives of individuals suffering from hearing impairments.

Hobbies: Kiteboarding, Calisthenics, Weightlifting, Snowboarding, Surfing, Music

Sydney O'Malley, Research Assistant

I was born and raised in Freehold, New Jersey, though I eventually traveled up north to receive my college education at the University of Massachusetts, Amherst. Within this charming and scenic town in Western Massachusetts, I pursued my passion for studying science, specifically biology. Woven into my affinity for science is also a dream – attending medical school and becoming a physician, hopefully in the realm of orthopedics and sports medicine. During my undergraduate experience I developed a connection to conducting research, as I had the opportunity to work alongside great minds, as well as formulate my own research inquiry/project relating to neurobiology. While immersing myself in an undergraduate research journey, I made the realization that I wanted to take some time to continue doing research before going to medical school. The Holt-Geleoc lab caught my eye for numerous reasons when looking for positions after college. The close-knit dynamic of this lab, in addition to the profound and important work that is completed regarding Usher Syndrome and other forms of inherited hearing loss drew me towards joining this team. While here, I hope to put my best efforts towards developing novel gene therapies that have clinical relevance.


Hobbies: Singing, running, skiing, cooking, and traveling

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For a list of previous lab members please visit:  

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