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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
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Home | Pregnancy Timeline | News Alerts |News Archive Oct 16, 2013

 

"Aerial" surface view of two neighbouring hair cells in the inner ear © IRCM.

On the surface of these developing mouse cells, large stereocilia can be noticed forming a V-shaped brush. The visualization technique used to capture this image is scanning electron microscopy, which allows us to see the morphology of the cell surface at high resolution.









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Identifying new proteins crucial for hearing

Montréal scientists identified a group of proteins crucial for shaping the cellular organ responsible for detecting sounds.

A team of researchers led by Dr. Michel Cayouette at the IRCM made an important discovery, published online yesterday by the scientific journal Developmental Cell, that could better explain some inherited forms of hearing loss in humans.


For a human to hear, sound-induced vibrations in the inner ear must first be transformed into electrical impulses before they can be relayed to the brain.

This transformation is performed by “hair cells” (or sensory cells) located in the inner ear.

On the surface of these cells, microscopic hair-like protrusions known as stereocilia act as specialized sensors to detect vibrations.


“During embryonic development, these stereocilia develop into a characteristic V-shaped brush. In addition, all cells orient their brush with the V pointing in the same direction. This polarized organization is critical for sensory function, but remains poorly understood," says Dr. Cayouette, Director of the Cellular Neurobiology research unit at the IRCM.

“We studied a group of proteins known to control cell division in the organism and discovered a new role they play in the auditory system. We showed that these proteins occupy a specific region at the cell surface to define the exact placement of stereocilia and enable the creation of the V-shaped brush,” added Dr. Basile Tarchini, postdoctoral fellow in Dr. Cayouette’s laboratory and first author of the study.


“Furthermore, we discovered that one of the proteins is also required for coordinating the orientation of the brushes among neighbouring cells, thereby ensuring that the V formed by each brush points in the same direction.

" Our results strongly suggest, for the first time, that this group of proteins could be the link between two important molecular mechanisms: the system responsible for the placement of stereocilia into a V-shaped brush at the cell surface, and the system that orients this V-shaped structure in the surrounding tissue.”


Dr. Basile Tarchini, postdoctoral fellow in Dr. Cayouette’s laboratory and first author of the study.


“Recent studies show that mutations in one of the proteins we studied are associated with inherited forms of hearing loss in humans,” concludes Dr. Cayouette. “By defining a function for this class of proteins in hair cells, our work helps explain the mechanisms that could cause these conditions.”

Abstract Highlights
mInsc/LGN/Gαi control the formation of a microvilli-free domain at hair cell apex
Extension of microvilli-free domain triggers inward relocalization of the kinocilium
mInsc/LGN/Gαi restrain aPKC medially, thereby defining the stereocilia bundle edge
Gαi signaling is also required for proper orientation of hair cells in the cochlea
Summary

Sound perception relies on the planar polarization of the mechanosensory hair cell apex, which develops a V-shaped stereocilia bundle pointing toward an eccentric kinocilium. It remains unknown how intrinsically asymmetric bundles arise and are concomitantly oriented in the tissue. We report here that mInsc, LGN, and Gαi proteins, which classically regulate mitotic spindle orientation, are polarized in a lateral microvilli-free region, or “bare zone,” at the apical hair cell surface. By creating and extending the bare zone, these proteins trigger a relocalization of the eccentric kinocilium midway toward the cell center. aPKC is restrained medially by mInsc/LGN/Gαi, resulting in compartmentalization of the apical surface that imparts the V-shaped distribution of stereocilia and brings the asymmetric bundle in register with the relocalized kinocilium. Gαi is additionally required for lateral orientation of cochlear hair cells, providing a possible mechanism to couple the emergence of asymmetric stereocilia bundles with planar cell polarity.

This research project was funded by the Canadian Institutes of Health Research (CIHR), as well as Dr. Tarchini’s postdoctoral award from the Human Frontier Science Program. For more information, please refer to the article summary published online by Developmental Cell: http://www.cell.com/developmental-cell/abstract/S1534-5807(13)00537-6.

About Michel Cayouette
Michel Cayouette obtained a PhD in neurobiology from Université Laval. He is Associate IRCM Research Professor and Director of the Cellular Neurobiology research unit. Dr. Cayouette is an associate research professor in the Department of Medicine (accreditation in molecular biology) at Université de Montréal. He is also Adjunct Professor in the Department of Medicine (Division of Experimental Medicine) and the Department of Anatomy and Cell Biology at McGill University. He is a member of the Vision Research Network (Fonds de recherche du Québec – Santé) and the Centre of Excellence in Neuroscience of Université de Montréal. Dr. Cayouette is a Research Scholar from the Fonds de recherche du Québec – Santé. For more information, visit www.ircm.qc.ca/cayouette.
About the IRCM

Founded in 1967, the Institut de recherches cliniques de Montréal (www.ircm.qc.ca) is currently comprised of 38 research units in various fields, namely immunity and viral infections, cardiovascular and metabolic diseases, cancer, neurobiology and development, systems biology and medicinal chemistry. It also houses four specialized research clinics, eight core facilities and three research platforms with state-of-the-art equipment. The IRCM employs 425 people and is an independent institution affiliated with the Université de Montréal. The IRCM Clinic is associated to the Centre hospitalier de l’Université de Montréal (CHUM). The IRCM also maintains a long-standing association with McGill University. The IRCM is funded by the Quebec ministry of Higher Education, Research, Science and Technology.

Original press releas:http://www.ircm.qc.ca/Medias/Communiques/Pages/detail.aspx?pID=85&PFLG=1033