published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / abstract / Clinical Oncology / Doctoral / Doctor of Philosophy

published_or_final_version / Molecular Biology / Master / Master of Philosophy

Neural crest cells (NCC) arise from the neural tube (NT) and migrate through given regions of embryos, where they generate most of the peripheral nervous system (PNS), facial skeleton and pigment cells. Defective NCC development gives rises to malformations in multiple NCC-derived structures, collectively known as neurocristopathies. NCC from the NT vagal and trunk levels express Hoxb5 plus a number of other Hox proteins. Hoxb5 is a member of Hox transcription factors family that binds to specific target nucleotide sequences in the genome via their DNA-binding domain, where they regulate gene expressions. Vagal NCC migrate to the intestine and generate the enteric nervous system (ENS). To test the Hoxb5 function in vagal NCC, we made use a transgenic mouse line (enb5) and showed that perturbation of Hoxb5 signaling in NCC resulted in down-regulation of Ret and defective ENS, indicating that normal Hoxb5 function was required for the development of vagal NCC. Current project aims to investigate the function of Hoxb5 in trunk NCC development. Transgenic mouse enb5 can be induced by Cre recombinase to express a hybrid protein namely engrailed-Hoxb5 (enb5), in which the transactivation domain of the mouse Hoxb5 is replaced with a repressor domain of the Drosophila engrailed (en) protein. With the intact DNA-binding domain, enb5 binds to target genes of Hoxb5, repressing the expression of target genes instead of induction. Therefore, enb5 produces a dominant negative effect on the developmental pathways that normally require Hoxb5. In this study, enb5 mice were crossed to Wnt1-Cre mice to express enb5 in NCC that arose from the entire length of NT. Wnt1-Cre/enb5 mutants displayed apoptosis of NCC, skin hypopigmentation and PNS defects (hypoplastic dorsal root ganglion and defective ENS). Expression of Sox9, Foxd3 and Ret was down-regulated in Wnt1-Cre/enb5 embryos. Conditional deletion of Sox9 and Foxd3 by Wnt1-Cre, or conventional deletion of Ret in mice produced NCC phenoptypes similar to those of Wnt1-Cre/enb5. Taken all these prompted me to further investigate if Hoxb5 functioned in the same pathway as Sox9 and Foxd3 for NCC development using multiple experimental approaches. In ovo electroporation of enb5 in chick embryos induced apoptosis of NT, and co-electroporation of Hoxb5, Ret, Sox9 or Foxd3 rescued enb5-induced cell death. By bioinformatics analysis, Hoxb5 binding sites were identified in SOX9 and FOXD3 promoter sequences. Binding of Hoxb5 protein onto these binding sites of SOX9 and FOXD3 promoters was revealed by electro-mobility shift assay and further confirmed by chromatin immuno-precipitation assay. In addition, enb5 was also shown to bind to the same regions of SOX9 and FOXD3 promoters as Hoxb5. Using dual luciferase reporter assay, Hoxb5 was shown to induce transcription from SOX9 and FOXD3 promoters, and enb5 blocked the induction. Taken all these indicate that (i) Hoxb5 binds and induces transcriptions from SOX9 and FOXD3 promoters, (ii) enb5 blocks the induction. In summary, Hoxb5 regulates NCC development by controlling the expression of Sox9, Foxd3 and Ret, and perturbation of Hoxb5 signaling results in NCC death and neurocristopathies. / published_or_final_version / Surgery / Doctoral / Doctor of Philosophy

published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / abstract / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Biochemistry / Master / Master of Philosophy

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