碩士 / 中山醫學大學 / 生物醫學科學學系碩士班 / 95 / Homeobox genes are transcription factors that play important roles in the regulation of embryonic development. Iroquois homeobox-like 1 (Irxl1) is a new member of the TALE superfamily of homeobox genes that is most-closely related to the Iroquois class. Recent studies in mice showed that Irxl1 mRNA was highly expressed in craniofacial mesenchyme, somites, limb buds, kidneys and testis cords; however, its function has not been well characterized. To investigate the role of Irxl1 during embryonic development, we choose zebrafish as a vertebrate model. The zebrafish Irxl1 gene was identified by a BLAST search of the NCBI database with homology to the mouse ortholog. Using RT-PCR and rapid amplification of cDNA ends (RACE), full-length cDNA of two splicing variants were cloned. Sequence analysis showed that zebrafish Irxl1 gene was located on chromosome 12 and contained 7 exons with homeodomain exhibiting 100 % sequence identity to human and mouse orthologs. During embryonic development, the transcription of Irxl1 was detected from 18 hours postfertilization (hpf) to 5 days postfertilization (dpf). Both isoforms were broadly expressed in adult fish tissues, including brain, eyes, muscle, ovary, testis and gills. Whole-mount in situ hybridization analysis of zebrafish embryos at various developmental stages revealed that Irxl1 was expressed mainly in the first two pharyngeal arches. Knocking down of Irxl1 by antisense morpholino oligonucleotides resulted in several morphological defects in zebrafish embryos. The gross phenotype included small head, inflated ventricle of hindbrain, curved body axes, shrinkage of yolk stalk and string-like heart. Most deformed larvae only survive for 5 to 7 days. In these affected embryos, differentiation and regional specification of the nervous system were normal as judged by the expression of several tissue-specific genes, but morphogenesis was defective. The most prominent defect were observed in the mesoderm and cartilage in pharyngeal arches. Inhibition of Irxl1 translation resulted in reduction of the numbers of pharyngeal muscles and cranial neural crest cells. Moreover, alcian blue staining revealed severe cartilage defects in the arches at 5 dpf. This phenotype is reminiscent of a mouse Twirler (Tw) mutation, to which the Irxl1 gene is linked. These observations suggest that the Irxl1 protein may regulate factors that are involved in brain and arch morphogenesis in zebrafish.
| Identifer | oai:union.ndltd.org:TW/095CSMU5114012 |
| Date | January 2007 |
| Creators | Hsiao-Yun, 鄭曉芸 |
| Contributors | 潘惠錦 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 85 |
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