Heparan sulfate and the development of Exostoses

遗传性多发性外生骨疣综合征（HME）是一种以身材矮小和生长板外生骨疣（骨软骨瘤）为特征的显性遗传性人类疾病。在高达5%的患者中，这些分化为软骨肉瘤。HME由EXT 1或EXT 2突变引起，EXT 1或EXT 2编码合成硫酸乙酰肝素（HS）所必需的糖基转移酶。对低形态Ext 1（Ext 1gt/gt）小鼠的研究表明，HS水平降低导致Ihh信号传导范围增加，从而延迟软骨细胞的肥大分化。在这里，我们的目的是分析这些突变体的血管化和骨化过程，这两者也受到干扰。我们将进一步研究Ext 1gt/gt突变体骨骼中其他信号系统是否受到影响。同时，我们将研究嵌合小鼠，其中Ext 1突变细胞的克隆可以通过强力霉素依赖性外显子倒位诱导。初步结果表明，与Ext 1的杂合缺失相反，这些小鼠发展出中轴骨骼的外生骨疣。仔细的形态学分析将确定外生骨疣起源的组织。分子分析和复合突变体的产生应该揭示Ihh或其他骨发育调节因子的信号传导是否在突变克隆或其环境中受到干扰。通过单细胞PCR，我们将鉴定外生骨疣组织的等位基因状态，并揭示杂合性缺失是否是外生骨疣和/或软骨肉瘤发展所必需的。从长远来看，抑制所确定的信号通路应有助于开发可能的治疗策略。这些研究将有助于了解HME的分子起源。

Hereditary multiple exotoses syndrome (HME) is a dominant inherited human disorder characterized by short stature and exostoses (osteochondromas) of the growth plate. In up to 5% of patients these differentiate into chondrosarcomas. HME results from mutations in EXT1 or EXT2, which encode glycosyltransferases necessary for the synthesis of heparansulfate (HS). Investigation of hypomorphic Ext1 (Ext1gt/gt) mice demonstrated that reduced HS levels lead to an increased range of Ihh signaling and consequently to a delay in hypertrophic differentiation of chondrocytes. Here we aim to analyze the vascularization and ossification processes in these mutants, both of which are also disturbed. We will further investigate if other signaling systems are affected in Ext1gt/gt mutant bones. In parallel we will examine chimeric mice, in which clones of Ext1 mutant cells can be induced by Doxycyclinedependent exon inversions. Preliminary results indicate that, in contrast to heterozygous deletion of Ext1, these mice develop exostoses of the axial skeleton. Careful morphological analysis will identify the tissue in which the Exostoses originate. Molecular analysis and the generation of compound mutants should reveal if signaling of Ihh or other regulators of bone development are disturbed in the mutant clones or their environment. By single cell PCR we will identify the allelic status of the exostoses tissue and reveal if loss of heterozygosity is required for exostoses and or chondrosarcoma development. In the long run inhibition of the identified signaling pathway should help to develop possible treatment strategies. Together these studies will contribute to understand the molecular origin of HME.