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See detailDer p 1 is the primary activator of Der p 3, Der p 6 and Der p 9 the proteolytic allergens produced by the house dust mite Dermatophagoides pteronyssinus
Herman, Julie ULg; Thelen, Nicolas ULg; Smargiasso, Nicolas ULg et al

in Biochimica et Biophysica Acta - General Subjects (2013), 1840

Background: The enzymatic activity of the four proteases found in the house dust mite Dermatophagoides pteronyssinus is involved in the pathogenesis of allergy. Our aim was to elucidate the activation ... [more ▼]

Background: The enzymatic activity of the four proteases found in the house dust mite Dermatophagoides pteronyssinus is involved in the pathogenesis of allergy. Our aim was to elucidate the activation cascade of their corresponding precursor forms and particularly to highlight the interconnection between proteases during this cascade. Methods: The cleavage of the four peptides corresponding to the mite zymogen activation sites was studied on the basis of the Förster Resonance Energy Transfermethod. The proDer p 6 zymogen was then produced in Pichia pastoris to elucidate its activation mechanismbymite proteases, especially Der p 1. The role of the propeptide in the inhibition of the enzymatic activity of Der p 6 was also examined. Finally, the Der p 1 and Der p 6 proteases were localised via immunolocalisation in D. pteronyssinus. Results: All peptides were specifically cleaved by Der p 1, such as proDer p 6. The propeptide of proDer p 6 inhibited the proteolytic activity of Der p 6, but once cleaved, it was degraded by the protease. The Der p 1 and Der p 6 proteases were both localised to the midgut of the mite. Conclusions: Der p 1 in either its recombinant formor in the natural context of house dustmite extracts specifically cleaves all zymogens, thus establishing its role as a major activator of both mite cysteine and serine proteases. General significance: This finding suggests that Der p 1 may be valuable target against mites. [less ▲]

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See detailClass V β Tubulin during the development of the organ of Corti in rat
Renauld, Justine ULg; Thelen, Nicolas ULg; Johnen, Nicolas ULg et al

Poster (2013, September 13)

In eutherian mammals, the organ responsible for the transduction of sound waves into nerve impulses is called the organ of Corti. This structure located within the cochlea, a portion of the inner ear, is ... [more ▼]

In eutherian mammals, the organ responsible for the transduction of sound waves into nerve impulses is called the organ of Corti. This structure located within the cochlea, a portion of the inner ear, is composed by two types of cells: sensory hair cells and non-sensory supporting cells. All these cells are distributed according to a specific arrangement along the whole length of the cochlea. A feature of the organ of Corti’s supporting cell is the presence of an abundant cytoskeleton. This one is mainly composed of microtubules, structures make up by tubulin heterodimers. The heterodimers consist of one molecule of α tubulin and one molecule of β tubulin. β tubulin isotypes are highly conserved in evolution and differ by only a few amino acid residues, implying that the isotypes may have functional significance. Organ of Corti’s supporting cells are constituted by class V β-tubulin, a minor mammalian tubulin (Bhattacharya et al., 2008). Moreover, their microtubules are formed by 15 protofilaments instead of the canonical 13, a unique fact among vertebrates (Banerjee et al., 2008). Such a configuration of protofilaments has been observed in C. elegans’ neurons which are responsible for the mechanosensory sense of touch (Bounoutas et al., 2009). It was also shown that these 15 protofilaments microtubules were essential to the proper functioning of these mechanosensory neurons (Bounoutas et al., 2009). Here we present the spatiotemporal localization of class V β-tubulin during the development of the organ of Corti in rats from embryonic day 18 (E18) until P25 (25th postnatal day). For this purpose, we have used immunolabelings on cryosections of whole cochlea. Our preliminary results demonstrate that class V β-tubulin has a unique distribution in the cochlea, being restricted to supporting cells, especially in pillar cells. [less ▲]

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See detailThe acetylation method
Thiry, Marc; Thelen, Nicolas ULg

in Exbrayat, Jean-Marie (Ed.) Histochemical and cytochemical methods of visualization (2013)

Histochemistry and cytochemistry are important fields for studying the inner workings of cells and tissues of the body. While visualization techniques have been in use for many years, new methods of ... [more ▼]

Histochemistry and cytochemistry are important fields for studying the inner workings of cells and tissues of the body. While visualization techniques have been in use for many years, new methods of detection developed recently help researchers and practitioners better understand cell activity. Histochemical and Cytochemical Methods of Visualization describes the essential techniques that can be used for histochemical investigations in both light and transmission electron microscopy. The book begins by discussing techniques in light microscopy. It reviews classical methods of visualization, histochemical and histoenzymatic methods, and methods used to visualize cell proliferation and apoptosis. Next, the book examines the cytochemical methods used in electron microscopy with traditional techniques, as well as more specialized methods. The final section provides an overview of image analysis and describes how image processing methods can be used to extract vital information. A 16-page insert supplies color illustrations to enhance the text. Techniques will continue to adapt to the latest technological innovations, allowing more and more precise quantification of images. These developments are essential to the biological as well as the medical sciences. This manual is a critical resource for novice and experienced researchers, technicians, and students who need to visualize what happens in the cell, the molecules expressed, the main enzymatic activities, and the repercussions of the molecular activities upon the structure of the cells in the body. [less ▲]

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See detailDifferentiation of Boettcher's Cells During Postnatal Development of Rat Cochlea
Cloes, Marie ULg; Renson, Thomas; Johnen, Nicolas ULg et al

Poster (2013, January 28)

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See detailWhole organ culture in rotating bioreactor: the rat embryonic inner ear
Renauld, Justine ULg; Johnen, Nicolas ULg; Hubert, Pascale ULg et al

Poster (2013, January 28)

In eutherian mammals, the organ responsible for the transduction of sound waves into nerve impulses is called the organ of Corti. This structure located within the cochlea, a portion of the inner ear, is ... [more ▼]

In eutherian mammals, the organ responsible for the transduction of sound waves into nerve impulses is called the organ of Corti. This structure located within the cochlea, a portion of the inner ear, is composed by two types of cells: sensory hair cells and non-sensory supporting cells. All these cells are distributed according to a specific arrangement along the whole length of the cochlea. So far, the mammalian inner ear is very sensitive to damage, with no hair cell replacement or cell proliferation occurring in the cochlea. That is why understanding the mechanisms that regulate the mammalian cochlear development is important for pursuing strategies to induce sensory hair cells regeneration. Here, we present a technique of whole embryonic inner ear culture in rotating bioreactors. Besides, we compare two different culture media, DMEM and Neurobasal-A. Rat inner ears are sampled at the 16th embryonic day (E16) and grown in rotating bioreactors during 48h or six days. After 48h, semithin sections realized in the growing cochlea show the development of the ventral epithelium and ultrathin sections confirm the differentiation of the sensory hair cells. Using immunochemistry techniques on our material after 48h or six days in vitro, we show that all the cells of the organ of Corti are differentiating, whichever the culture medium used. Our preliminary results demonstrate that organ culture of the embryonic inner ear in rotating bioreactor is possible. Such a method provides an in vitro model for the investigation of developmental, regulatory, and differentiation processes that could be helpful in the understanding of the mechanisms underlying the development of the mammalian cochlea. [less ▲]

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See detailDifferentiation of Boettcher's cells during postnatal development of rat cochlea
Cloes, Marie ULg; Renson, Thomas; Johnen, Nicolas ULg et al

Poster (2013)

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See detailEvidence for a partial epithelial-mesenchymal transition in rat auditory organ development
Johnen, Nicolas ULg; Francart, Marie-Emilie; Thelen, Nicolas ULg et al

Poster (2012, October 01)

An epithelial-mesenchymal transition is a biological process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype. During ... [more ▼]

An epithelial-mesenchymal transition is a biological process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype. During this process, epithelial cells loosen cell-cell adhesion, module their polarity and rearrange their cytoskeleton: intermediate filaments typically switch from cytokeratin to vimentin. They also enhance their motility capacity. The epithelial-mesenchymal transition plays key roles in the formation of the body plan and in the differentiation of multiple tissues and organs but it is also involved in tissue repair, tissue homeostasis, fibrosis, and carcinoma progression. Until now, epithelial-mesenchymal transition has been rarely mentioned in the inner ear organogenesis. In chick, epithelial-mesenchymal transition has been reported as a possible mechanism of semicircular canal morphogenesis. More recently, an in vitro study has also indicated that sensory epithelial cells from mouse utricle can undergo an epithelial-mesenchymal transition to become cells expressing features of prosensory cells. By contrast, epithelial-mesenchymal transition has never been observed during auditory organ morphogenesis. The auditory organ, the organ of Corti, is a highly specialized structure composed by specific cellular types. The sensory cells are characterized by stereocilia at their apex and are necessary for the sound perception. Theses cells are supported by supporting cells. Based on their morphology and physiology, at least four types of supporting cells can be identified in the organ of Corti: inner and outer pillar cells, phalangeal cell and Deiter’s cells. The inner pillar cells and outer pillar cells combine to form the tunnel of Corti, a fluid filled triangular space that separates the single row of inner hair cells from the first row of outer hair cells. The Nuel spaces are another interval in the organ of Corti that is situated between the outer pillar cells and the different rows of outer hair cells and Deiters cells. To determine whether an epithelial-mesenchymal transition may play a role in the morphogenesis of the auditory organ, we studied the spatial localization of several epithelial-mesenchymal transition markers, the cell-cell adhesion molecules and intermediate filament cytoskeletal proteins, in epithelium of the dorsal cochlea during development of the rat organ of Corti from 18th embryonic day until 25th postnatal day. We examined by confocal microscopy immunolabelings on cryosections of whole cochleae with antibodies anti-cytokeratins as well as with antibodies anti-vimentin, anti-E-cadherin and anti-beta-catenin.Our results showed a partial loss of E-cadherin and beta-catenin between supporting cells at P8 and P12, respectively, and a temporary appearance of vimentin in pillar cells and Deiters between P8 and P10. Our results show a local loss of adhesion between supporting cells of the OC from P8, an increase expression of cytokeratins in supporting cells around P10 and a temporary appearance of vimentin in supporting cells at P8-10. These observations suggest that a partial epithelial-mesenchymal transition might be involved in the remodeling of the Corti organ during the postnatal stages of development in rat. [less ▲]

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See detailStudy of the Boettcher cells along their development: Junctions and expression of the urea-transporter B (UT-B)
Cloes, Marie ULg; Renson, Thomas; Johnen, Nicolas ULg et al

Poster (2012, September 30)

The Boettcher cells (BC) lie on the sensory epithelium of the cochlea. Their function has never been clearly defined. However it has been suggested that they may influence the ionic composition of the ... [more ▼]

The Boettcher cells (BC) lie on the sensory epithelium of the cochlea. Their function has never been clearly defined. However it has been suggested that they may influence the ionic composition of the fluids of the inner ear, which play a central role in the conduction of the sensory information. In this context the compartimentating function of the BC around and after the onset of hearing may influence the subsequent refining of hearing. We collected ultrastructural and immunohistological data during the final maturation stage of the sensory epithelium. In particular the cell junctions were investigated to clarify the compartimentating function of the BC at early stages. As a potential actor in the ion flow in the sensory epithelium, the urea transporter-B (UT-B) was also immunolocalised during the development of the BC. At the mature stage (P25) the BC are linked to the adjacent cells by numerous adherens and non-adherens junctions. They rest on a basilar membrane to which they are attached by hemidesmosomes. They typically exhibit large basolateral interdigitations. We found that, at the 8th postnatal day, the BC are separated from the neighbouring cells by wide spaces entered by scarce cytoplasmic extensions. These spaces are interrupted by areas of close contact, where adherens and non-adherens junctions may be found. Thus, although there seems to be fewer interdigitations at P8, gap junctions probably still allow easy cell-to-cell exchanges. Moreover non-adherens junctions can systematically be identified apically. Although it was impossible to differenciate tight and gap junctions without specific labeling, we postulate that these non-adherens junctions correspond to tight junctions and seal the apex of the BC. This feature is necessary to enable the control of the ion concentrations surrounding the sensory epithelium. We also found that UT-B, known for water and urea transport in red blood cells, is present in the membranes of the BC from P12 (the earliest stage tested) to P25. Thus UT-B may play a role in the regulation of the ionic concentrations of the inner ear fluids. [less ▲]

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See detailTrophic tracers reveal considerable diversity among diets of dominant amphipods from Posidonia oceanica seagrass meadows
Michel, Loïc ULg; Dauby, Patrick ULg; Gobert, Sylvie ULg et al

Poster (2012, August 20)

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning ... [more ▼]

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning of the ecosystem, notably in organic matter transfers from producers to higher level consumers. However, the situation in Posidonia oceanica meadows remains unclear, and little is known about the trophic ecology of amphipods, which are generally regarded as generalist herbivores/detritivores despite the lack of precise studies. Here, we combined gut content examination and trophic markers (fatty acids, stables isotopes of C and N) to delineate the diet of the dominant species of amphipods from Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that contribution of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. On the other hand, all dominant species heavily relied on macroalgal epiphytes, suggesting a certain extent of overlapping in the diets of the dominant species. Considerable interspecific differences nonetheless existed, notably concerning grazing preferences towards epiphytes from leaves or litter fragments vs. epiphytes from rhizomes. In addition, the use of the SIAR isotopic mixing model showed that most species had a mixed diet, and relied on several food items. None of the examined species seemed to graze on their seagrass host, but Gammarus aequicauda partly relied on seagrass leaf detritus. Overall, our findings demonstrate that amphipods have the potential to be key-items in trophic and functional interactions occurring among Mediterranean Posidonia oceanica meadows. [less ▲]

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See detailEvidence for a partial epithelial-mesenchymal transition in postnatal stages of rat auditory organ morphogenesis.
Johnen, Nicolas ULg; Francart, Marie-Emilie ULg; Thelen, Nicolas ULg et al

in Histochemistry & Cell Biology (2012)

The epithelial-mesenchymal transition (EMT) plays a crucial role in the differentiation of many tissues and organs. So far, an EMT was not detected in the development of the auditory organ. To determine ... [more ▼]

The epithelial-mesenchymal transition (EMT) plays a crucial role in the differentiation of many tissues and organs. So far, an EMT was not detected in the development of the auditory organ. To determine whether an EMT may play a role in the morphogenesis of the auditory organ, we studied the spatial localization of several EMT markers, the cell-cell adhesion molecules and intermediate filament cytoskeletal proteins, in epithelium of the dorsal cochlea during development of the rat Corti organ from E18 (18th embryonic day) until P25 (25th postnatal day). We examined by confocal microscopy immunolabelings on cryosections of whole cochleae with antibodies anti-cytokeratins as well as with antibodies anti-vimentin, anti-E-cadherin and anti-β-catenin. Our results showed a partial loss of E-cadherin and β-catenin and a temporary appearance of vimentin in pillar cells and Deiters between P8 and P10. These observations suggest that a partial EMT might be involved in the remodelling of the Corti organ during the postnatal stages of development in rat. [less ▲]

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See detailEvidence for a partial epithelial-mesenchymal transition in postnatal stages of rat auditory organ morphogenesis
Johnen, Nicolas ULg; Cloes, Marie ULg; Thelen, Nicolas ULg et al

Poster (2012, May 04)

An epithelial-mesenchymal transition is a biological process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype. During ... [more ▼]

An epithelial-mesenchymal transition is a biological process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype. During this process, epithelial cells loosen cell-cell adhesion, module their polarity and rearrange their cytoskeleton: intermediate filaments typically switch from cytokeratin to vimentin. They also enhance their motility capacity. The epithelial-mesenchymal transition plays key roles in the formation of the body plan and in the differentiation of multiple tissues and organs but it is also involved in tissue repair, tissue homeostasis, fibrosis, and carcinoma progression. Until now, epithelial-mesenchymal transition has been rarely mentioned in the inner ear organogenesis. In chick, epithelial-mesenchymal transition has been reported as a possible mechanism of semicircular canal morphogenesis. More recently, an in vitro study has also indicated that sensory epithelial cells from mouse utricle can undergo an epithelial-mesenchymal transition to become cells expressing features of prosensory cells. By contrast, epithelial-mesenchymal transition has never been observed during auditory organ morphogenesis. The auditory organ, the organ of Corti, is a highly specialized structure composed by specific cellular types. The sensory cells are characterized by stereocilia at their apex and are necessary for the sound perception. Theses cells are supported by supporting cells. Based on their morphology and physiology, at least four types of supporting cells can be identified in the organ of Corti: inner and outer pillar cells, phalangeal cell and Deiter’s cells. The inner pillar cells and outer pillar cells combine to form the tunnel of Corti, a fluid filled triangular space that separates the single row of inner hair cells from the first row of outer hair cells. The Nuel spaces are another interval in the organ of Corti that is situated between the outer pillar cells and the different rows of outer hair cells and Deiters cells. To determine whether an epithelial-mesenchymal transition may play a role in the morphogenesis of the auditory organ, we studied the spatial localization of several epithelial-mesenchymal transition markers, the cell-cell adhesion molecules and intermediate filament cytoskeletal proteins, in epithelium of the dorsal cochlea during development of the rat organ of Corti from 18th embryonic day until 25th postnatal day. We examined by confocal microscopy immunolabelings on cryosections of whole cochleae with antibodies anti-cytokeratins as well as with antibodies anti-vimentin, anti-E-cadherin and anti-beta-catenin.Our results showed a partial loss of E-cadherin and beta-catenin between supporting cells at P8 and P12, respectively, and a temporary appearance of vimentin in pillar cells and Deiters between P8 and P10. Our results show a local loss of adhesion between supporting cells of the OC from P8, an increase expression of cytokeratins in supporting cells around P10 and a temporary appearance of vimentin in supporting cells at P8-10. These observations suggest that a partial epithelial-mesenchymal transition might be involved in the remodeling of the Corti organ during the postnatal stages of development in rat. [less ▲]

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See detailSpatio-temporal localization of the cytoskeleton during auditory organ development in mammalia
Johnen, Nicolas ULg; Thelen, Nicolas ULg; Cloes, Marie ULg et al

Poster (2011, March 31)

The auditory organ, the organ of Corti (OC), is a highly specialized structure composed by specific cellular types. The sensory cells (HC) are characterized by stereocilia at their apex and are necessary ... [more ▼]

The auditory organ, the organ of Corti (OC), is a highly specialized structure composed by specific cellular types. The sensory cells (HC) are characterized by stereocilia at their apex and are necessary for the sound perception. Theses cells are supported by supporting cells. Based on their morphology and physiology, at least four types of supporting cells (SC) can be identified in the OC: inner and outer pillar cells (PC), phalangeal cell and Deiter’s cells. Sensory and supporting cells possess characteristic cytoskeleton proteins in direct relation with their morphological features and their development. Indeed, this organ had morphological changes such as the setting up of the sensory epithelium after the birth or the openings of the Corti’s tunnel at P8 and of the Nuel’s spaces at P10. In the present study, by using confocal microscopy, we investigated the spatio-temporal localization of the three cellular cytoskeletal filaments : microtubules (β-1, 2, 3, 4-tubulin), microfilaments (cytoplasmic β- and γ-actin) and intermediate filaments (CK4, 5, 7, 8, CKpan and vimentin) during the development of the OC in rat from the embryonic day 18 (E18) to the post-natal day 25 (P25). The immunolabellings indicated clearly that β-1, 2, 3-tubulins were only present the SC and nervous fibers during development whereas β-4-tubulin was found firstly in the HC and then in the SC. The two actin-isotypes were detected in the HC apex but were also seen in the PC from P8 to P25 for β-actin isoform and in the basal membrane from E18 to P8 for the γ-actin isoform. All intermediate filament proteins were only found in the SC, especially between P8 and P12. Our results show that the localization of the cytoskeleton proteins during the auditory organ development depends on the cellular type and the developmental stage. A profound modification of cytoskeleton occurs between P8 and P12. [less ▲]

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See detailNucleolar structure across evolution : the transition between bi- and tricompartmentalized nucleoli lies within the class Reptilia
Franck, Claire; Lamaye, Françoise; Thelen, Nicolas ULg et al

Poster (2011, January 31)

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See detailSpatio-temporal localization of the glial fibrillary acidic protein (GFAP) in the spiral ganglion from the 16th embryonic day until the 25th postnatal day in rats
Cloes, Marie ULg; Thelen, Nicolas ULg; Johnen, Nicolas ULg et al

Poster (2011, January 31)

The spiral ganglion (SG) is responsible for the conduction of the information between the sensory epithelium of the auditory organ (the organ of Corti) and the central nervous system. The origin and ... [more ▼]

The spiral ganglion (SG) is responsible for the conduction of the information between the sensory epithelium of the auditory organ (the organ of Corti) and the central nervous system. The origin and nature of the SG glial cells in mammals are barely known, although glial cells are essential to the development and the working of the nervous system. Using confocal microscopy, we studied the spatio-temporal distribution of the GFAP in the rat SG from the 16th embryonic day (E16) until the 25th postnatal day (P25). We performed a double-labelling experiment targeting GFAP- and betaIIItubulin-positive cells. BetaIII-tubulin is used for the labelling of (pro)neural cells, according to a previous preliminary study from our team. Our first results show clearly that the GFAP is expressed in the SG from P0 until P25. A homogenous labelling is found in the cytoplasm of a few dispersed unidentified cells among the (pro)neurons, whereas a granular labelling appears among a group of cells neighbouring the bundle of fibers innervating the organ of Corti. The identity of the GFAP-positive cells will be further investigated by electron microscopy. The reason why the labelling of the GFAP adopts those two different aspects is still unknown. Moreover, it seems that, surprisingly, some cells of the ganglion are not labelled by either marker. The possibility that such cells correspond to fibroblasts will be tested thanks to the labelling of vimentin. [less ▲]

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See detailDistribution of glycogen during the development of the organ of Corti
Thelen, Nicolas ULg; Cloes, Marie ULg; Johnen, Nicolas ULg et al

Poster (2011, January 31)

Although the structure of the auditory organ in mature mammals, the organ of Corti, is clearly established, its development is far from being elucidated. Using cytochemical methods at the light and ... [more ▼]

Although the structure of the auditory organ in mature mammals, the organ of Corti, is clearly established, its development is far from being elucidated. Using cytochemical methods at the light and electron microscope levels, we examined the spatiotemporal distribution of polysaccharides during the development of the organ of Corti in rats from embryonic day 16 (E16) to postnatal day 15 (P15). At E16, small polysaccharide inclusions were detected in the cytoplasm of the future inner pillar cells by electron microscope only. These inclusions became obvious at the light microscope level at E17. At E19, the polysaccharide deposits were important within the inner pillar cells and they arose in the Hensen cells cytoplasm. Polysaccharide accumulations also appeared in the outer pillar cells and the Deiters cells from P3-P4. As the organ of Corti developed, the amount of polysaccharide inclusions within the inner and outer pillar cells decreased. At P15, large amount of polysaccharide deposits were visible in the Deiters cells whereas they had almost disappeared from the inner and outer pillar cells. Finally, we showed that the polysaccharide deposits present in the developing organ of Corti are PAS-positive and can be digested with a salivary amylase, suggesting that they are essentially constituted of glycogen. [less ▲]

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See detailSpatio-temporal localisation of β-actin and γ-actin isoforms during the development of the organ of Corti in rat from the embryonic day 18 (E18) to the post-natal day 25 (P25).
Johnen, Nicolas ULg; Thelen, Nicolas ULg; Cloes, Marie ULg et al

Poster (2011, January 31)

The auditory organ, the organ of Corti (OC), is a highly specialized structure composed by specific cellular types. The sensory cells (HC) are characterized by stereocilia at their apex and are necessary ... [more ▼]

The auditory organ, the organ of Corti (OC), is a highly specialized structure composed by specific cellular types. The sensory cells (HC) are characterized by stereocilia at their apex and are necessary for the sound perception. Theses cells are supported by supporting cells. Based on their morphology and physiology, at least four types of supporting cells can be identified in the OC: inner and outer pillar cells (PC), phalangeal cell and Deiter’s cells. Sensory and supporting cells have cytoskeletons containing β-actin and γ-actin isoforms. In the adult mammalian cochlea, amounts of γ-actin increase and β-actin decrease in the order: outer pillar cells, inner pillar cells, Deiters’ cells and hair cells. In sensory cells, γ-actin appears to be the most prominent component with an apparent γ-actin/β-actin ratio of approximately 2:1 (Hofer et al., 1997). β-actin is present in the cuticular plate but is more concentrated in the stereocilia, especially at the base where the stereocilia insert into the cuticular plate. The amount of γ-actin differs less between these structures, the stereocilia and cuticular plate, although its expression is apparently higher towards the tip of stereocilia and it is the predominant isoform of the hair cell's lateral wall (Furness et al., 2005). The differential subcellular localization of two actin isoforms suggests they may play different functions in auditory organ. In the brain, β-actin is restricted to dynamic structures whereas γ-actin is more ubiquitously distributed and occurs in relatively quiescent regions (Micheva et al., 1998). In the present study, by using confocal microscopy, we investigated the spatio-temporal localisation of β-actin and γ-actin isoforms during the development of the OC in rat from the embryonic day 18 (E18) to the post-natal day 25 (P25). Our results indicated that the labelling for both actin isoforms changed during the OC development. Between E18 and P25, we observed a labelling for β-actin in the apical region of the HC. Between P8 and P25, the feet of PC are also β-actin-positive. Unlike β-actin, between E18 and P10, γ-actin is detected in the basal region of supporting cells. Between P12 and P25, the labelling for γ-actin is preferentially localized in the apical surface of the HC. Our results revealed that during development β-actin isoform preceded γ-actin isoform in the apical region of HC. They also suggest that γ-actin isoform might be involved in attachment of supporting cells with their basal membrane and that β-actin isoform might play a role in PC reorganization during the formation of Corti tunnel. [less ▲]

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See detailSPATIO-TEMPORAL LOCALIZATION OF BETA TUBULIN III IN THE ORGAN OF CORTI AND IN THE SPIRAL GANGLIA BETWEEN THE EMBRYONIC DAY (E18) AND THE POST-NATAL DAY (P25) IN RAT.
Johnen, Nicolas ULg; Thelen, Nicolas ULg; Cloes, Marie ULg et al

Poster (2010, October 22)

The mammalian auditory organ, the organ of Corti (OC), is composed of mechanosensory hair cells and nonsensory supporting cell types. Based on their morphology and physiology, at least two types of ... [more ▼]

The mammalian auditory organ, the organ of Corti (OC), is composed of mechanosensory hair cells and nonsensory supporting cell types. Based on their morphology and physiology, at least two types of sensory cells can be identified in the OC: inner and outer hair cells. The structure of this organ is well reported in adult but its development is still little-known. By using confocal microscopy, we studied the spatial-temporal distribution of beta tubulin III during the differentiation of the OC in rat from the embryonic day 18 (E18) to the postnatal day (P25). The beta tubulin III is typical for neural cells in the OC. We observed that beta III tubulin is present in the extensions innerving the row of inner hair cells at E18. At E19, the extensions innerving the inner hair cells and the two first rows of outer hair cells were immunolabelled. From E21 to P25, all of hair cells were connected to the spiral ganglion. In the latter, the intensity of immunolabelling decreased between E18 to P25 and the labelling only concerned some cells. These results reveal that beta III tubulin appears before birth in the nervous extensions connecting the sensory cells of the OC according to a modiolar-to-striolar gradient. In the spiral ganglia, the labelling progressively decreases during its development. [less ▲]

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