Cilia of adult canine articular chondrocytes

doi:10.1016/S0022-5320(78)90036-9

Journal of Ultrastructure Research

Volume 64, Issue 3, September 1978, Pages 270-281

https://doi.org/10.1016/S0022-5320(78)90036-9 Get rights and content

The incidence and morphology of canine chondrocytic cilia were studied using serial sections and transmission electron microscopy. Of the 111 chondrocytes available for study, 104 cells had one cilium. In each of the other seven cells, although no cilium was observed, one of the centrioles appeared to contact the plasma membrane. The structure of a chondrocytic basal body included rootlets, a striated basal foot, nine alar sheets, and A-C and A-A linkers. The outside diameter, inside diameter, and triplet angle gradually decreased from base to apex. The basic axonemal structure consisted of nine peripheral doublets. Arms, radial spokes, and central microtubules typical of motile cilia appeared to be absent. Toward the base of the ciliary shaft certain doublets bent toward the center of the shaft and terminated. The remaining peripheral doublets also terminated one doublet at a time along the length of the shaft. Three potential functions of chondrocytic cilia are discussed.

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Primary cilia in the Syrian hamster biliary tract: Bile flow antennae and outlooks about signaling on the hepato-biliary-pancreatic stem cells
2020, Translational Research in Anatomy
Citation Excerpt :
If motility is the primary function for a cilium, the primary cilia are immotile and are only involved in sensory function(s), as shown long ago by the photoreceptors of the retinal epithelium [57,79,80]. A plethora of reviews about the primary cilia that have appeared in several biomedical journals [e.g. 29–48,59,60,71–81,84–88,90,93,97–107] are certainly informative about the diverse tissue's occurrence, but some of those, published with a few weeks apart, often make information redundant and have not brought new morphological information. In fact, there are reviews that make the topic hard to be understood by the unprepared readers because did not distinguish between the typical, motile ‘cilium’ and ‘flagellum’ from ‘primary cilium’ or even classified them as one ‘immotile cilium’ even if this cilium has never been motile… because it does not have central microtubules as reviewed in Ref. [57] and recently brilliantly shown in 3-D views [59].
Microscopic anatomy investigations about the liver and biliary tract of the Syrian hamster, in reference with human structure, functions and defects in biliary tract and other organs.
Electron microscopy technique and literature review.
The author reports the finding of primary cilia in the biliary outflow channels. By places, the widest ducts also show blunted, or even enclosed, primary cilia, either as remnants or growing primary cilia.
The report should trigger further translational interest in human hepatology because, as seen in rodents, these sensing cell appendages, transducing antennae of biliary flow and quality, could feed back to be part of regulation of the hepatic tract motility and the secretory liver. There, adjacent oval or intermediate cells could be, through some intercellular transduction mechanism(s), influenced to differentiate into either cholangiocytes or hepatocytes.
IFT88 influences chondrocyte actin organization and biomechanics
2016, Osteoarthritis and Cartilage
Primary cilia are microtubule based organelles which control a variety of signalling pathways important in cartilage development, health and disease. This study examines the role of the intraflagellar transport (IFT) protein, IFT88, in regulating fundamental actin organisation and mechanics in articular chondrocytes.
The study used an established chondrocyte cell line with and without hypomorphic mutation of IFT88 (IFT88^orpk). Confocal microscopy was used to quantify F-actin and myosin IIB organisation. Viscoelastic cell and actin cortex mechanics were determined using micropipette aspiration with actin dynamics visualised in live cells transfected with LifeACT-GFP.
IFT88^orpk cells exhibited a significant increase in acto-myosin stress fibre organisation relative to wild-type (WT) cells in monolayer and an altered response to cytochalasin D. Rounded IFT88^orpk cells cultured in suspension exhibited reduced cortical actin expression with reduced cellular equilibrium modulus. Micropipette aspiration resulted in reduced membrane bleb formation in IFT88^orpk cells. Following membrane blebbing, IFT88^orpk cells exhibited slower reformation of the actin cortex. IFT88^orpk cells showed increased actin deformability and reduced cortical tension confirming that IFT regulates actin cortex mechanics. The reduced cortical tension is also consistent with the reduced bleb formation.
This study demonstrates for the first time that the ciliary protein IFT88 regulates fundamental actin organisation and the stiffness of the actin cortex leading to alterations in cell deformation, mechanical properties and blebbing in an IFT88 chondrocyte cell line. This adds to the growing understanding of the role of primary cilia and IFT in regulating cartilage biology.
Depletion of chondrocyte primary cilia reduces the compressive modulus of articular cartilage
2014, Journal of Biomechanics
Citation Excerpt :
The primary cilium functions as a signaling hub for an expanding range of pathways including hedgehog signaling, wnt signaling and mechanotransduction (for review see Berbari et al., 2009; Satir et al., 2010). Articular chondrocytes express primary cilia, which are typically 1–2 µm in length in situ, but longer in isolated cells in 2D culture (Wilsman, 1978; Poole et al., 1997; Jensen et al., 2004; McGlashan et al., 2008; Farnum and Wilsman, 2011). Recent studies have shown that chondrocyte primary cilia are required for mechanotransduction and associated up-regulation of extracellular matrix synthesis (Wann et al., 2012).
Primary cilia are slender, microtubule based structures found in the majority of cell types with one cilium per cell. In articular cartilage, primary cilia are required for chondrocyte mechanotransduction and the development of healthy tissue. Loss of primary cilia in Col2aCre;ift88^fl/fl transgenic mice results in up-regulation of osteoarthritic (OA) markers and development of OA like cartilage with greater thickness and reduced mechanical stiffness. However no previous studies have examined whether loss of primary cilia influences the intrinsic mechanical properties of articular cartilage matrix in the form of the modulus or just the structural properties of the tissue. The present study describes a modified analytical model to derive the viscoelastic moduli based on previous experimental indentation data. Results show that the increased thickness of the articular cartilage in the Col2aCre;ift88^fl/fl transgenic mice is associated with a reduction in both the instantaneous and equilibrium moduli at indentation strains of greater than 20%. This reveals that the loss of primary cilia causes a significant reduction in the mechanical properties of cartilage particularly in the deeper zones and possibly the underlying bone. This is consistent with histological analysis and confirms the importance of primary cilia in the development of a mechanically functional articular cartilage.
IFT80 is essential for chondrocyte differentiation by regulating Hedgehog and Wnt signaling pathways
2013, Experimental Cell Research
Citation Excerpt :
So far, it remains largely unknown how IFT proteins contribute to chondrocyte differentiation and function during bone development and remodeling. Primary cilia are present on almost every vertebrate cell, and their existence on chondrocytes was first reported about 40 years ago [14,15]. Later Poole and Jensen groups further analyzed the ultrastructure and function of primary cilia in chondrocytes [16,17].
Partial mutation of intraflagellar transport 80 (IFT80) in humans causes Jeune asphyxiating thoracic dystrophy (JATD) and short-rib polydactyly (SRP) syndrome type III. These diseases are autosomal recessive chondrodysplasias that share clinical similarities, including shortened long bones and constricted thoracic cage. However, the role and mechanism of IFT80 in the regulation of chondrocyte differentiation and function remain largely unknown. We hypothesize that IFT80 is required for the formation and function of cilia and plays a critical role in chondrogenic differentiation by regulating Hedgehog (Hh) and Wingless (Wnt) signaling pathways. To test this hypothesis, we first analyzed the IFT80 expression pattern and found that IFT80 was predominantly expressed in growth plate chondrocytes and during chondrogenic differentiation. Silencing IFT80 impaired cilia formation and chondrogenic differentiation in mouse bone marrow derived stromal cells (BMSCs), and decreased the expression of chondrocyte marker genes—collagen II and aggrecan. Additionally, silencing IFT80 down-regulated Hh signaling activity whereas up-regulated Wnt signaling activity. The overexpression of Gli2 in IFT80-silenced cells promoted chondrogenesis and recovered the chondrogenic deficiency from IFT80 silencing. Overall, our results demonstrate that IFT80 is essential for chondrocyte differentiation by regulating the Hh and Wnt signaling pathways.
Chondrocyte primary cilia shorten in response to osmotic challenge and are sites for endocytosis
2012, Osteoarthritis and Cartilage
Citation Excerpt :
Because our methods were consistent across specimens and experimental manipulations however, we believe that differences in primary cilia length are the result of actual biological variation. The percentage of live cells with primary cilia reported in this study (87%) compares well with the early in situ work of Wilsman et al.6,18,32 but is larger than that reported in cultured cells in agarose14,20 (Table I). This discrepancy is perhaps due to chondrocytes moving out of the G0 and G1 phases of the cell cycle during isolation and culture28,29.
The purpose of this study was to examine the influence of cartilage site and osmolarity on primary cilia incidence, length and orientation in live chondrocytes in undisturbed cartilage. Additionally, we imaged endocytotic markers to test our hypothesis that the ciliary pocket is a site for endocytosis.
We measured primary cilia incidence, length and orientation in the coronal plane using ex vivo live cell confocal imaging of intact murine femoral chondrocytes. Measurements were taken from five regions of the medial and lateral condyles of the left and right femur and also after one minute of osmotic challenge. Transmission electron microscopy and immunocytochemistry were used to characterize the orientation and position of chondrocyte primary cilia in the saggital plane and to determine the colocalization of clathrin coated vesicles, endosomal and lysosomal proteins and CD44 with the ciliary pocket.
Chondrocyte primary cilia length decreased significantly after a one minute hypo- or hyper-osmotic challenge and varied between condyles and across the surface of each condyle. The majority of the length of the chondrocyte primary cilia was positioned within a membranous invagination rather than projecting out from the cell membrane and clathrin coated vesicles, endosomal proteins and CD44 colocalised with the ciliary pocket.
We demonstrate that live ex vivo chondrocyte primary cilia are capable of shortening within minutes in response to osmotic challenge and provide subcellular and cellular evidence that chondrocyte primary cilia are deeply invaginated in a ciliary pocket which contains sites for endocytosis.
The solitary (primary) cilium-A mechanosensory toggle switch in bone and cartilage cells
2008, Cellular Signalling
Osteocytes and articular chondrocytes sense and respond to the strains imposed on bones and joints by various activities such as breathing and walking. This mechanoresponsiveness is needed to maintain bone and cartilage microstructure and strength. In bone the large number of osteocytes form a vast osteointernet in which the gap junctionally interconnected members are lodged in an extensive lacunocanalicular network. The much smaller number of articular chondrocytes are not interconnected in a chondrointernet. Instead, they are separately lodged in capsules called chondrons. While there are many possible strain-sensing devices, it now appears that the non-motile solitary (primary) cilia protruding like aerials from osteocytes (as well as osteoblasts) and chondrocytes are switches that when toggled by cyclical pulses of lacunocanalicular fluid or cartilage compression send signals such as Ca²⁺ surges into the cell to trigger a cascade of events that include appropriate gene activations to maintain and strengthen bone and cartilage. Moreover, the chondrocyte cilium with its Ihh(Indian hedgehog)-activated Smo receptor is a key player along with PTHrP in endochondral bone formation.

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Cilia of adult canine articular chondrocytes

Arch. Oral Biol.

J. Ultrastruct. Res.

J. Cell Biol.

Science

Cell Tissue Res.

Connect. Tissue Res.

J. Anat.

Nature (London)

J. Anat.

Calcif. Tissue Res.

J. Cell Biol.

J. Cell Sci.

J. Cell Biol.

J. Anat.

Anat. Rec.

Amer. J. Vet. Res.

Cornell Vet.

Bull. Rheum. Dis.

J. Reprod. Fert.