06-P047 A role for fibroblast growth factor receptor - like 1 in Wolf–Hirschhorn syndrome

Abstract

Dynamic expressions of Homeobox (Hox) genes along the anterior-posterior axis of the neural tube (NT) are crucial in body patterning and neural crest (NC) development. At E12.5, Hoxb5 expression extends from the hindbrain throughout the entire NT with dorsally-restricted expression. By replacing the transactivation domain of Hoxb5 with a transcription repressor domain of the Drosophila engrailed (en) protein, we generate a chimeric protein enb5 that binds and represses the expression instead of inducing transcription of target genes. We have shown that Cre-mediated expression of enb5 in vagal NC caused defective NC migration and abnormal enteric nervous system (ENS) development.To further investigate the functions of Hoxb5 in nervous system development, we crossed enb5 mice to Wnt1-Cre mice.Wnt1-Cre/enb5 transgenic mice display hydrocephalus, abnormal skin pigmentation, and ENS defects.Hydrocephalus was firstly observed in P0 Wnt1-Cre/enb5 mice.In embryos, Hoxb5 was expressed by the brain structures responsible for the production and circulation of cerebrospinal fluid (CSF) namely the choroid plexus and the ependymal cell lining the brain ventricles. Therefore, hydrocephalus could be attributable to the defective flow and/or over-production of CSF in Wnt1-Cre/enb5 embryonic mice. Melanoblasts were found residing in the dermis and also penetrating into the epidermis in wildtype E12.5 embryos. In contrast, melanoblasts were undetectable and NC progenitors were drastically reduced in Wnt1-Cre/enb5 embryos, suggesting that NC induction and/or maintenance were defective in these embryos. We are investigating the molecular mechanisms by which perturbation of Hoxb5 signaling in the developing nervous system cause these anomalies in Wnt1-Cre/ enb5 mice.Hox genes encode a highly conserved family of transcription factors that play fundamental roles during embryonic development. In humans, mutations in HOXD13 cause the rare dominantly inherited limb synpolydactyly. Both polyalanine tract expansions and frameshift deletions in HOXD13 have been described to underlie this condition. We identified a new missense mutation substituting Alanine for Glycine at position 11 in the N-terminal part of HOXD13. We compared biochemical and biological properties of the HOXD13(G11A) mutant protein to wild-type HOXD13. We demonstrate, using invitro approaches, that the G11A mutation significantly impairs the stability of HOXD13. Furthermore, we observed a mild impairment of the DNA binding capacity of HOXD13(G11A) on TTAT, but not on TTAC target sequences. The subcellular localization of the protein is not affected by the mutation, suggesting distinct properties of the G11A mutant as compared to polyalanine tract expansions or the recently described HOXD13(G220V) mutant. To investigate biological activity of HOXD13(G11A), we are currently misexpressing it in the developing chick limb using RCAS system. Injection of RCAS expressing wild-type HOXD13 at stage HH10 of chick development induces a shortening of limb cartilages especially at the le...