Development of the post-natal growth plate requires intraflagellar transport proteins

Abstract

In the post-natal growth plate, chondrocytes are arranged in columns parallel to the long axis of the bone. Chondrocytes divide perpendicular to this axis and then move into position one on top of another in a process called "rotation" that maintains columnar organization. Primary cilia are non-motile microtubule base appendages extending from the surface of almost all vertebrate cells. Primary cilia were described on chondrocytes almost 40 years ago but the function of these structures in cartilage biology is not known. Intraflagellar transport (IFT) is the process by which primary cilia are generated and maintained. This study tested the hypothesis that IFT plays an important role in post-natal skeletal development. Kif3a, a subunit of the Kinesin II motor complex, that is required for intraflagellar transport and the formation of cilia, was deleted in mouse chondrocytes via Col2a-Cre-mediated recombination. Disruption of IFT resulted in subsequent depletion of cilia and post-natal dwarfism due to premature loss of the growth plate likely a result of reduced proliferation and accelerated hypertrophic differentiation of chondrocytes. Cell shape and columnar orientation in the growth plate were also disrupted suggesting a defect in the process of rotation. Alterations in chondrocyte rotation were accompanied by disruption of the actin cytoskeleton and alterations in the localization of activated FAK to focal adhesion-like structures on chondrocytes. This is the first report indicating a role for IFT and primary cilia in the development of the post-natal growth plate. The results suggest a model in which IFT/cilia act to maintain the columnar organization of the growth plate via the process of chondrocyte rotation.

Col2-Cre recombinase is co-expressed with endogenous type II collagen in embryonic renal epithelium and drives development of polycystic kidney disease following inactivation of ciliary genes

“…Col2-Cre;Kif3a conditional knockout mice described in this study displayed the skeletal defects described previously (Koyama et al, 2007;Song et al, 2007), such as dwarfism and early postnatal obliteration of cranial base synchondroses. Unexpectedly, the mutant mice also developed early postnatal polycystic kidney disease, similar to that seen in model with kidneyspecific inactivation of the Kif3a subunit of kinesin-2 (Lin et al, 2003).…”

“…In the process of studying the role of the ciliary proteins kinesin-2 and polycystin-1 during the endochondral bone growth we employed the Col2-Cre (Col2-Cre10) transgenic mouse strain, which was used in numerous previous studies for conditional gene inactivation in chondrocyte and osteoblast cell lineages (Long et al, 2001;Long et al, 2004;Razzaque et al, 2005). Consistent with the recently published studies (Koyama et al, 2007;Song et al, 2007), Col2-Cre; Kif3a knockout mice developed a severe form of dwarfism and displayed highly disorganized growth plates in the long bones and the cranial base synchondroses (Fig. 1A and data not shown).…”

Epiphyseal growth plate and secondary peripheral chondrosarcoma: the neighbours matter

“…Planar cell polarity pathway comprises molecules such as Wnt5A, the Rho family of GTPases and Gpi-anchored proteins. These molecules are shown to regulate orientated cell division and movements (intercalation) of chondrocytes ( Figure 1) [7][8][9].…”

“…In the mouse growth plate, Rho GTPase has been shown to control tissue polarity [9]. Moreover, conditional deletion of Kif3a in the growth plate chondrocytes results in the depletion of cilia and loss of columnar organization [8], suggesting the loss of tissue polarity. Kif3a, a subunit of the anterograde kinesin-II intraflagellar transport machinery, is required the formation of primary cilia [36].…”

“…Sox9 plays a key role in the differentiation of progenitor chondrocytes into chondrocytes by modulating the expression of cartilage-specific genes, such as type II and type XI collagen genes [3]. Down-regulation of N-CAM by the binding of syndecan to fibronectin and activation of the typical chondrocyte columns of the growth plate ( Figure 1) [7][8][9]. Once acquired, this columnar organization is maintained.…”