Anatomy of the Cochlea and Vestibular System: Relating Ultrastructure to Function
John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed in Paediatrics, The Ear, Skull Base, 2018
The hair bundle is composed of rows of stereocilia that increase in height in one particular direction across the apical surface of the hair cell, and a single kinocilium located behind the row of longest stereocilia (Figures 47.5a and 47.6a), but which is absent from the hair bundles of mature hair cells in the cochlea (Figure 47.5b). Stereocilia are really giant microvilli, plasma membrane-bound projections from the apical surface of the hair cell that enclose a packed array of filaments of the cytoskeletal protein, actin2–4 (Figure 47.5d–f). The kinocilium is composed of microtubules similar in form to motile cilia but they are not motile.5 In cochlear hair cells, the kinocilium is present only during development, reducing down as the cochlea matures to remain only as the basal body in the apical cytoplasm at one side of the stereociliary bundle (Figure 47.5c).6 The position of the kinocilium (or the basal body) and the longest row of stereocilia define the polarity of the asymmetric hair bundle (Figures 47.3f, 47.4d,e and 47.5a,b). Deflection of the stereocilia towards the longest ones opens MET channels, K+ enters and the hair cell becomes depolarized. Deflection in the opposite direction closes the transducer channels and the hair cell becomes hyperpolarized. The transducer channels are located at the tips of the stereocilia of the shorter rows but not in the longest stereocilia.7
Structure and Function of Cartilage
Kyriacos A. Athanasiou, Eric M. Darling, Grayson D. DuRaine, Jerry C. Hu, A. Hari Reddi in Articular Cartilage, 2017
Recently, primary cilium has come into focus as a mechanosensor of fluid flow. The primary cilium is a small membrane protrusion containing microtubules present on almost all vertebrate cells that can act as an “extracellular antenna” for detection of the external environment (Marshall and Nonaka 2006; Singla and Reiter 2006) (Figure 1.12). It also acts as a signaling center for sonic hedgehog (Shh), patched (PTC), and other molecules that can regulate cell survival, growth and differentiation, and tissue homeostasis (Christensen et al. 2008; Veland et al. 2009). For instance, in bone the primary cilium has been demonstrated to deflect under flow and to be independent of Ca2+ flux and stretch-activated ion channels in fluid flow-induced PGE2 release (Malone et al. 2007). Interestingly, in the endothelium of the kidney (Yoder 2007) or vascular system, the primary cilium appears to transduce fluid flow through an increase in intracellular Ca2+ (Van der Heiden et al. 2006). In the kidney, this has been linked to interactions between the primary cilium and polycystins 1 and 2 to form a mechanosensitive ion channel (Forman et al. 2005) (Figure 1.13). In chondrocytes, the length of the primary cilium may be regulated by mechanical loading (McGlashan et al. 2010).
Bardet−Biedl Syndrome
Dongyou Liu in Handbook of Tumor Syndromes, 2020
Located on the surface of different types of cells, cilia are the tiny hair-like structures (either motile or immotile) that utilize an architectural element known as basal body to anchor to a cell. Possessing central microtubule pair necessary for ciliary mobility, motile cilia propel fluid (e.g., mucus) through the local environment and assist in cell motility. Immotile (primary) cilia have unique 9 + 0 structure with nine microtubule triplets arranged in a circle with an outer membrane, and participate in cell signaling, left-right asymmetry, tissue formation, and homeostasis. In the eyes, rod and cone photoreceptor cells of the retina are known to utilize their immotile cilia for light-perceiving function [5].
CT imaging features of paranasal sinuses in children with primary ciliary dyskinesia
Published in Acta Oto-Laryngologica, 2022
Huiying Lyu, Zhuoyao Guo, Chao Chen, Bo Duan, Zhengmin Xu, Wenxia Chen
Cilia are highly conserved organelles that can be divided into four types: 9 + 2 motile cilia, 9 + 0 motile cilia (nodal cilia), 9 + 2 non-motile cilia (primary cilia), and 9 + 0 non-motile cilia. The motile cilia are abundant in the respiratory tract, the Fallopian tubes, the deferent ducts, and the brain ependyma. Motile cilia are essential for mucociliary clearance and transport of fluid. The nodal cilia plays a vital role in establishing left–right body orientation during early embryonic development. Abnormalities in nodal cilia can lead to laterality defects that include situs inversus, heterotaxy, or dextrocardia that may be associated with congenital heart abnormalities. The underlying cause of PCD is mutations in genes encoding structural and/or functional proteins of the cilia. To date, over 50 PCD genes have been identified [13,14].
Hypoxic conditions promote a proliferative, poorly differentiated phenotype in COPD lung tissue progenitor cells in vitro
Published in Experimental Lung Research, 2023
Tina P. Dale, Michael D. Santer, Mohammed Haris, Wei Zuo, Nicholas R. Forsyth
Cells from both donors were differentiated at ALI with a commercial differentiation medium for 21 days in a 21% O2 environment. In well-differentiated cultures, motile cilia developed on the surface and were visible using light microscopy. Immunocytochemistry confirmed mucociliary differentiation with expression of βIV tubulin (cilia) apically, mucin5AC (Figure 5A) and mucin5B (Figure 5B) for donor 1 cells. Widespread staining was also present for the club cell marker CC10 (Figure 5C). Histological staining with AB-PAS confirmed extensive mucus production across the culture surface (Figure 5D). Donor 2 cells (Figure 5E) exhibited reduced differentiation capacity in both conditions; however, monolayers were less densely packed and ciliation was completely absent in cells expanded in 2% oxygen. In contrast, cilia were sparse but present in 21% expanded cultures. Mucin5AC staining was strongly positive in both culture conditions.
Renal ciliopathies: promising drug targets and prospects for clinical trials
Published in Expert Opinion on Therapeutic Targets, 2023
Laura Devlin, Praveen Dhondurao Sudhindar, John A. Sayer
There are also other specialized primary ciliary structures, including the connecting cilium within the photoreceptor cells of the retina and olfactory sensory neurons [32–34]. The other main subtype of cilia are motile cilia, which are found as groups of organelles on specialized cells such as the respiratory epithelium and reproductive tract [35]. Sperm flagella is also a specialized motile cilium. Additionally, nodal cilia found at the embryonic node have overlapping structures with both primary and motile cilia and are vital for left-right patterning during development [36]. However, the cilia type present on kidney epithelial cells are primary cilia, and therefore this will be focus of this renal ciliopathy review.