Molecular Genetics of the Inner Ear

Welcome to the Grillet Lab

RESEARCH

Genetics of Hearing and Vestibular Impairment


Hearing loss is a major health concern for our societies. In the United States of America, 17% of the adult population suffers from some degree of hearing loss. In addition, the elderly population frequently experiences debilitating hearing difficulties, and sometimes balancing issues.

 

Our goal is to identify the comprehensive list of genes required for hearing and head motion detection, and ultimately characterize the function of these genes at the molecular level.

 

This will improve our understanding of the inner ear physiology, but also will help the diagnosis of patients affected by hearing loss.

More about the Inner Ear

The inner ear contains the sensory cells that detect sound and head motion, the hair cells. In mammals, these cells are generated during the mid-gestation and will never be replaced during the entire life. The hair cells are in constant activity and their dysfunction is a major cause of deafness and peripheral vestibular disorders: they are both the core and the Achilles’ heel of the system.

More about the Genetics of Hearing loss

Hearing loss can result from exposure to excessive noise, chemicals and certain medications. However, susceptibility to deafness is generally dictated by genetic transmission. To this date, 136 human loci have been linked to hearing loss, but we know the corresponding affected genes for only 85 of them. These genes are very often required, directly or indirectly, for the proper hair cell function.

More about our Strategy

In order to identify these genes, we use mouse models either to precisely inactivate candidate genes (Reverse Genetics) or to generate randomly mutated animals and screen them for hearing or vestibular defects (Forward Genetics).

 

Using this later method, we identified the gene Loxhd1 as responsible for deafness in mice and humans (Grillet, AJHG, 2009), who are affected by a form of progressive hearing loss called DFNB77.

Function of Hair Cells and Other Inner Ear Cells

Differently from the sense of Vision, still little is known about Hearing and Balancing at their molecular level. This is due to the technical challenges associated with this organ: the paucity of the inner ear sensory cells, their inaccessibility and their fragility.

 

The inner ear is composed of two functional parts: the cochlea, which is the auditory organ, and the vestibule, organ responsible for head motion and balancing. In both parts, the sensory epithelia are composed of the sensory hair cells, called hair cells, always surrounded by supporting cells.

 

We want to characterize down to the molecular level the function of the cells that compose the inner ear, particularly the hair cells

More about Hair Cells

The hair cells have different functions:

1) to detect the mechanical stimuli induced by sound, and
2) to transmit this information to the central nervous system through their synapses.

More about Mechanotransduction

We are particularly interested in the organelle of mechanotransduction, the hair bundle. The hair bundle is located at the apical surface of the hair cells, consisting of a precise staircase arrangement of membrane protrusions filled with filamentous actin, bound to each other by extracellular linkages. Upon stimulation, force engages the bundle, and opening large conductance mechanically gated channels, generating the current that allows the sense of hearing and balancing. Cochlear hair bundles present different morphologies along the cochlea, differing from the elongated ones found in the vestibule.

 

We are interested in understanding the uniqueness of the hair bundles by identifying their key components and their functions.

More about our Strategy

In order to identify the key components of the stereocilia bundle we will be using different approaches such as mouse Genetics, Electronic Microscopy, Electrophysiology or Biophysics.

 

By using a mouse model, we have previously showed that the USH1C protein Harmonin is required for the proper sensitivity of the hair bundle to mechanical stimulation (Grillet et al., Neuron, 2009). More recently, we also have shown that the protein TMHS is associated with part of the mechanotransduction machinery and influences the mechano-channel properties (Xiong, Cell, 2012).

APPROACHES

molecular biology icon
Electrophysiology icon
Biochemistry icon
mouse genetics and mouse audiometry
Cellular biology icon
Bioinformatics icon
Histology icon

ABOUT THE TEAM

Principal Investigator

Nicolas Grillet

NICOLAS GRILLET, Ph.D.
Phone: 650.555.9393
ngrillet@stanford.edu

Stanford Profile

CV

Post-doctoral Fellow

ALIX TROUILLET, Ph.D.
Phone: 650.498-5229
alixt@stanford.edu

Stanford Profile

Life Science Research Professional 1

NAVID ZEBARJADI
Phone: 650.498.5229
navidz@stanford.edu

SELECTED PUBLICATIONS

Zhao B, Wu Z, Grillet N, Yan L, Xiong W, Harkins-Perry S, Müller U.

TMIE Is an Essential Component of the Mechanotransduction Machinery of Cochlear Hair Cells.

Neuron. 2014 Dec 3;84(5):954-67. PubMed PDF

Xiong W, Wagner TF, Linxuan Y, Grillet N, Müller U.

Using injectoporation to deliver genes to mechanosensory hair cells.

Nat Protoc. 2014 Oct;9(10):2438-49. PubMed  PDF

Xiong W, Grillet N, Elledge HM, Wagner TF, Zhao B, Johnson KR, Kazmierczak P, Müller U.

TMHS is an integral component of the mechanotransduction machinery of cochlearhair cells.

Cell. 2012 Dec 7;151(6):1283-95. PubMed PDF

Webb SW, Grillet N, Andrade LR, Xiong W, Swarthout L, Della Santina CC, KacharB, Müller U.

Regulation of PCDH15 function in mechanosensory hair cells by alternative splicing of the cytoplasmic domain.

Development. 2011 Apr;138(8):1607-17. PubMed PDF

Grillet N, Schwander M, Hildebrand MS, Sczaniecka A, Kolatkar A, Velasco J, Webster JA, Kahrizi K, Najmabadi H, Kimberling WJ, Stephan D, Bahlo M, Wiltshire T, Tarantino LM, Kuhn P, Smith RJ, Müller U.

Mutations in LOXHD1, an evolutionarily conserved stereociliary protein, disrupt hair cell function in mice and cause progressive hearing loss in humans.

Am J Hum Genet. 2009 Sep;85(3):328-37. PubMed PDF

Grillet N, Xiong W, Reynolds A, Kazmierczak P, Sato T, Lillo C, Dumont RA, Hintermann E, Sczaniecka A, Schwander M, Williams D, Kachar B, Gillespie PG, Müller U.

Harmonin mutations cause mechanotransduction defects in cochlear hair cells.

Neuron. 2009 May 14;62(3):375-87. PubMed PDF

JOIN US

We are currently open to STUDENT ROTATION

and we also are offering a
POSTDOCTORAL
POSITION in
BIOINFORMATICS & GENOMICS
at the Stanford University
School of Medicine


THANK YOU FOR YOUR SUPPORT

We want to warmly thank the donors of the Stanford Initiative to Cure Hearing Loss for their support!!! Your participation makes a real difference for our endeavor.

 

If you want to foster our research, you too can become a contributor to the Grillet lab. Simply click the “Contribute” button below. In “Special Instructions/Other Designation” specify “Grillet lab”.

CONTACT INFORMATION

Location &

Mailing Address:

Otolaryngology Department
Stanford School of Medicine
Stanford University
300 Pasteur Drive
Edwards Building
Lab: Room R213
Office: Room R113B
Stanford, CA 94305

Office: (650) 497-9393
Lab: (650) 498-5229
Fax: (650) 721-2163

Shipping Address:

Otolaryngology Department
Stanford School of Medicine
Stanford University
1291 Welch Road
(Edwards Building)
GRILLET LAB
Lab: Room R213
Stanford, CA  94305

Email: ngrillet@stanford.edu
Phone: (650) 497-9393
Fax: (650) 721-2163

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SCIENTIFIC PICTURES GALLERY

Sometimes pictures are more telling than words to describe scientific experiments.

We present here some images from our research on the inner ear.

These pictures are copyright protected; please contact the lab to obtain permission for use.

HISTOLOGY

  • Section through the cochlea
  • photograph of section trough a sensory epithelium of the vestibule sensitive to angular acceleration
  • Organ of Corti of a deaf animal, hair cells are absent
  • Organ of Corti of a normal animal, hair cells are present
  • Low density of cochlear neurons in a deaf animal
  • High density of cochlear neurons in a normal animal

MOLECULAR
BIOLOGY

  • In situ hybridization on embryonic inner ear sections. The left one is using a supporting cells-specific probe, and the right one a hair cell-specific probe.
  • In situ hybridization on postnatal inner ear section using a hair cell-specific probe.

MOUSE GENETICS

  • Visualization of the sensory cells of the inner ear detecting angular acceleration. We are able to detect head movement because of the ability of the vestibular part of the inner ear to detect such changes. Here we visualize the anatomy of this nervous system at the level of a semi-circular canal. The sensory cells, called hair cells, are positioned at the base of a dome. They will be stimulated upon specific angular acceleration giving us the sense of spatial positioning. Here a mouse ampulla was stained for actin (green) and the hair cells were genetically stained with TdTomato (red). This picture was finalist in the 2012 GE Healthcare Life Sciences Cell imaging competition.
  • Visualization of the sensory cells of the inner ear detecting sound The cochlear part of the inner ear able us to detect sound. The sensory cells, called hair cells, are able to detect specific sound frequencies and generate an electric signal that will be sent to the brain. Hair cells are aligned along the cochlea according to their frequency sensitivity. The hair cells of the cochlea are therefore decomposing the complex sounds into individual signals, playing the inverted function of a musical instrument. Here the hair cells of a mouse cochlea were genetically stained for TdTomato (red). This picture was finalist in the 2012 GE Healthcare Life Sciences Cell imaging competition.

FLUORESCENCE MICROSCOPY

  • Mechanosensitive hair bundles of Vestibular Hair Cells
  • Mechanosensitive hair bundles of Cochlear Hair Cells

SCANNING EM

  • Unmatured cochlear hair cell bundle and its linkage
  • Vestibular hair cells bundles
  • Cochlear hair cell bundle
  • Vestibular hair cells bundles
  • Array of tip-links from cochlear hair cells
  • Early stage of the cochlear hair cell bundle formation

TRANSMISSION
E M

  • Synaptic contacts between a hair cell (bottom) and its connected neuron (top). Note the synaptic vesicles arranged along the electron-dense ribbons just in front of the synaptic cleft.
  • Immuno-gold labeling on a cochlear hair cell sagittal section (Grillet, 2009, Neuron).

BIOINFORMATICS

  • With the Bioinformatics we can model mutations leading to deafness in humans and assess the consequences on the protein structure. Here is a domain mutated in the Loxhd1 gene in the mouse model Samba (Grillet, AJHG, 2009).
  • With the Bioinformatics we can model mutations leading to deafness in humans and assess the consequences on the protein structure. Here is a domain mutated in the Loxhd1 gene in the mouse model Samba (Grillet, AJHG, 2009).

COVERS

  • As in the strings of a guitar, tension must be adjusted in the mechanotransduction machinery of cochlear hair cells, which is essential for our ability to perceive sound. Tension in guitar strings is adjusted at the headstock in the upper part of the instrument. In hair cells, helical tip-link filaments, which gate mechanotransduction channels, terminate at their upper end in electron-dense structures. In the current issue (May 14, 2009), Grillet et al. (pp. 375–387) show that the PDZ-domain protein harmonin localizes to this structure and establishes tension in the hair cell's mechanotransduction machinery. Mutations in the gene for harmonin are linked to inherited forms of deafness, suggesting that defects in mechanotransduction are the underlying cause for some forms of the human disease. (Cover graphic design: johnforceps.com).
  • Mechanosensory hair cells of the cochlea play an essential role in converting mechanical vibrations into electrical signals that are subsequently transferred to afferent neurons. On pages 220–229 (April 2012, V35 issue 4), Piotr Kazmierczak and Ulrich Müller review recent studies that have provided insight into the molecular building-blocks of the mechanotransduction machinery. The cover design is a graphical representation of sound waves entering the cochlear of the inner ear. Image credit: Nicolas Grillet.

GRILLET LAB
Stanford University
300 Pasteur Drive
Edwards Building
Stanford, CA  94305

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LINKS
Stanford Initiative to Cure Hearing Loss
Stanford OHNS
Stanford Medicine
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