Kato Kenji, Bhattaram Pallavi, Penzo-Méndez Alfredo, Gadi Abhilash, Lefebvre Véronique
Department of Cellular & Molecular Medicine, Orthopaedic and Rheumatologic Research Center, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA.
J Bone Miner Res. 2015 Sep;30(9):1560-71. doi: 10.1002/jbmr.2504. Epub 2015 May 21.
Growth plates are specialized cartilage structures that ensure the elongation of most skeletal primordia during vertebrate development. They are made by chondrocytes that proliferate in longitudinal columns and then progress in a staggered manner towards prehypertrophic, hypertrophic and terminal maturation. Complex molecular networks control the formation and activity of growth plates, but remain incompletely understood. We investigated here the importance of the SoxC genes, which encode the SOX4, SOX11 and SOX12 transcription factors, in growth plates. We show that the three genes are expressed robustly in perichondrocytes and weakly in growth plate chondrocytes. SoxC(Prx1Cre) mice, which deleted SoxC genes in limb bud skeletogenic mesenchyme, were born with tiny appendicular cartilage primordia because of failure to form growth plates. In contrast, SoxC(Col2Cre) and SoxC(ATC) mice, which deleted SoxC genes primarily in chondrocytes, were born with mild dwarfism and fair growth plates. Chondrocytes in the latter mutants matured normally, but formed irregular columns, proliferated slowly and died ectopically. Asymmetric distribution of VANGL2 was defective in both SoxC(Prx1Cre) and SoxC(ATC) chondrocytes, indicating impairment of planar cell polarity, a noncanonical WNT signaling pathway that controls growth plate chondrocyte alignment, proliferation and survival. Accordingly, SoxC genes were necessary in perichondrocytes for expression of Wnt5a, which encodes a noncanonical WNT ligand required for growth plate formation, and in chondrocytes and perichondrocytes for expression of Fzd3 and Csnk1e, which encode a WNT receptor and casein kinase-1 subunit mediating planar cell polarity, respectively. Reflecting the differential strengths of the SOXC protein transactivation domains, SOX11 was more powerful than SOX4, and SOX12 interfered with the activity of SOX4 and SOX11. Altogether, these findings provide novel insights into the molecular regulation of skeletal growth by proposing that SOXC proteins act cell- and non-cell-autonomously in perichondrocytes and chondrocytes to establish noncanonical WNT signaling crosstalk essential for growth plate induction and control.
生长板是特殊的软骨结构，在脊椎动物发育过程中确保大多数骨骼原基的伸长。它们由在纵向柱中增殖的软骨细胞形成，然后以交错的方式向肥大前期、肥大期和终末成熟期发展。复杂的分子网络控制着生长板的形成和活动，但仍未完全被理解。我们在此研究了编码SOX4、SOX11和SOX12转录因子的SoxC基因在生长板中的重要性。我们发现这三个基因在软骨膜细胞中强烈表达，而在生长板软骨细胞中表达较弱。在肢芽骨骼发生间充质中缺失SoxC基因的SoxC(Prx1Cre)小鼠，由于未能形成生长板，出生时附肢软骨原基很小。相比之下，主要在软骨细胞中缺失SoxC基因的SoxC(Col2Cre)和SoxC(ATC)小鼠出生时患有轻度侏儒症，生长板发育尚可。后一种突变体中的软骨细胞正常成熟，但形成不规则的柱，增殖缓慢并异位死亡。VANGL2的不对称分布在SoxC(Prx1Cre)和SoxC(ATC)软骨细胞中均有缺陷，表明平面细胞极性受损，平面细胞极性是一种非经典WNT信号通路，控制生长板软骨细胞的排列、增殖和存活。因此，SoxC基因在软骨膜细胞中对于Wnt5a的表达是必需的，Wnt5a编码生长板形成所需的一种非经典WNT配体，而在软骨细胞和软骨膜细胞中对于Fzd3和Csnk1e的表达是必需的，Fzd3和Csnk1e分别编码介导平面细胞极性的一种WNT受体和酪蛋白激酶-1亚基。反映SOXC蛋白反式激活结构域的不同强度，SOX11比SOX4更强大，并且SOX12干扰SOX4和SOX11的活性。总之，这些发现通过提出SOXC蛋白在软骨膜细胞和软骨细胞中以细胞自主和非细胞自主的方式发挥作用，以建立对生长板诱导和控制至关重要的非经典WNT信号串扰，为骨骼生长的分子调控提供了新的见解。
