PDF(Pubmed)
Abstract：
Syndactyly type V (SDTY5) is an autosomal dominant extremity malformation characterized by fusion of the fourth and fifth metacarpals. In the previous publication, we first identified a heterozygous missense mutation Q50R in homeobox domain (HD) of HOXD13 in a large Chinese family with SDTY5. In order to substantiate the pathogenicity of the variant and elucidate the underlying pathogenic mechanism causing limb malformation, transcription-activator-like effector nucleases (TALEN) was employed to generate a Hoxd13Q50R mutant mouse. The mutant mice exhibited obvious limb malformations including slight brachydactyly and partial syndactyly between digits 2-4 in the heterozygotes, and severe syndactyly, brachydactyly and polydactyly in homozygotes. Focusing on BMP2 and SHH/GREM1/AER-FGF epithelial mesenchymal (e-m) feedback, a crucial signal pathway for limb development, we found the ectopically expressed Shh, Grem1 and Fgf8 and down-regulated Bmp2 in the embryonic limb bud at E10.5 to E12.5. A transcriptome sequencing analysis was conducted on limb buds (LBs) at E11.5, revealing 31 genes that exhibited notable disparities in mRNA level between the Hoxd13Q50R homozygotes and the wild-type. These genes are known to be involved in various processes such as limb development, cell proliferation, migration, and apoptosis. Our findings indicate that the ectopic expression of Shh and Fgf8, in conjunction with the down-regulation of Bmp2, results in a failure of patterning along both the anterior-posterior and proximal-distal axes, as well as a decrease in interdigital programmed cell death (PCD). This cascade ultimately leads to the development of syndactyly and brachydactyly in heterozygous mice, and severe limb malformations in homozygous mice. These findings suggest that abnormal expression of SHH, FGF8, and BMP2 induced by HOXD13Q50R may be responsible for the manifestation of human SDTY5.
摘要：
SyndactylyV型（SDTY5）是一种常染色体显性四肢畸形，其特征是第四和第五掌骨融合。在以前的出版物中，我们首先在一个具有SDTY5的大型中国家庭中，在HOXD13的同源异型盒结构域（HD）中发现了杂合错义突变Q50R。为了证实该变异体的致病性并阐明导致肢体畸形的潜在致病机制，转录激活因子样效应核酸酶(TALEN)用于产生Hoxd13Q50R突变小鼠.突变小鼠表现出明显的肢体畸形，包括杂合子中2-4指之间的轻微短指和部分连指，严重的并肢，纯合子短指和多指。关注BMP2和SHH/GREM1/AER-FGF上皮间充质（e-m）反馈，肢体发育的关键信号通路，我们发现了异位表达的Shh，Grem1和Fgf8以及在E10.5至E12.5的胚胎肢芽中下调Bmp2。在E11.5对肢芽（LB）进行转录组测序分析，揭示了31个基因在Hoxd13Q50R纯合子和野生型之间的mRNA水平显着差异。已知这些基因参与各种过程，如肢体发育，细胞增殖，迁移,和凋亡。我们的发现表明，Shh和Fgf8的异位表达与Bmp2的下调一起导致沿前-后轴和近端-远端轴的图案化失败。以及减少叉指程序性细胞死亡（PCD）。这种级联最终导致杂合小鼠中的并肢和短肢的发展，纯合小鼠的严重肢体畸形。这些发现提示SHH的异常表达,由HOXD13Q50R诱导的FGF8和BMP2可能负责人SDTY5的表现。
