Guzzo Rosa M, Andreeva Viktoria, Spicer Douglas B, Drissi M Hicham
Department of Orthopaedic Surgery, University of Connecticut Health Center, Farmington, CT 06030, USA.
Int J Dev Biol. 2011;55(6):641-7. doi: 10.1387/ijdb.103274rg.
Evidence from various in vitro gain and loss of function studies indicate that the bHLH transcription factor Twist1 negatively regulates chondrocyte differentiation; however limited information regarding Twist1 function in postnatal cartilage development and maintenance is available. Twist1 expression within the postnatal growth plate is restricted to immature, proliferating chondrocytes, and is significantly decreased or absent in hypertrophic chondrocytes. In order to examine the effect of maintaining the expression of Twist1 at later stages of chondocyte differentiation, we used type II collagen Cre (Col2-Cre) mice to activate a Cre-inducible Twist1 transgene specifically in chondrocytes (Col2-Twist1). At two weeks, postnatal growth was inhibited in Col2-Twist1 mice, as evidenced by limb shortening. Histological examination revealed abnormal growth plate structure, characterized by poor columnar organization of proliferating cartilaginous cells, decreased cellularity, and expansion of the hypertrophic zone. Moreover, structural defects within the growth plates of Col2-Twist1 transgenic mice included abnormal vascular invasion and focal regions of bony formation. Quantitative analysis of endochondral bone formation via micro-computed topography revealed impaired trabecular bone formation in the hindlimbs of Col2-Twist1 transgenic mice at various timepoints of postnatal development. Taken together, these findings indicate that regulated Twist1 expression contributes to growth plate organization and endochondral ossification to modulate postnatal longitudinal bone growth.
来自各种体外功能获得和丧失研究的证据表明，bHLH转录因子Twist1对软骨细胞分化起负调控作用；然而，关于Twist1在出生后软骨发育和维持中的功能的信息有限。出生后生长板内的Twist1表达仅限于未成熟的增殖软骨细胞，在肥大软骨细胞中显著降低或缺失。为了研究在软骨细胞分化后期维持Twist1表达的影响我们使用II型胶原Cre（Col2-Cre）小鼠在软骨细胞中特异性激活Cre诱导的Twist1转基因（Col2-Twist1）。出生两周时，Col2-Twist1小鼠的出生后生长受到抑制，肢体缩短证明了这一点。组织学检查显示生长板结构异常，其特征是增殖软骨细胞的柱状排列不佳、细胞数量减少和肥大区扩大。此外，Col2-Twist1转基因小鼠生长板内的结构缺陷包括异常的血管侵入和骨形成的局灶区域。通过微计算机断层扫描对软骨内骨形成进行定量分析，发现在出生后发育的各个时间点，Col2-Twist1转基因小鼠后肢的小梁骨形成受损。综上所述，这些发现表明，受调控的Twist1表达有助于生长板组织和软骨内骨化，从而调节出生后纵向骨生长。
