Xiong Kong M, Peterson Richard E, Heideman Warren
Departments of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin 53705, USA.
Mol Pharmacol. 2008 Dec;74(6):1544-53. doi: 10.1124/mol.108.050435. Epub 2008 Sep 10.
Exposure to environmental contaminants can disrupt normal development of the early vertebrate skeleton. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) impairs craniofacial skeletal development across many vertebrate species, and its effects are especially prominent in early life stages of fish. TCDD activates the aryl hydrocarbon receptor, a transcription factor that mediates most if not all TCDD responses. We investigated the transcriptional response in the developing zebrafish jaw after TCDD exposure using DNA microarrays. Zebrafish larvae were exposed to TCDD at 96 h after fertilization, and jaw cartilage tissue was harvested for microarray analysis at 1, 2, 4, and 12 h after exposure. Numerous chondrogenic transcripts were misregulated by TCDD in the jaw. Comparison of transcripts altered by TCDD in jaw with transcripts altered in embryonic heart showed that the transcriptional responses in the jaw and the heart were strikingly different. Sox9b, a critical chondrogenic transcription factor, was the most significantly reduced transcript in the jaw. We hypothesized that the TCDD reduction of sox9b expression plays an integral role in affecting the formation of the embryonic jaw. Morpholino knockdown of sox9b expression demonstrated that partial reduction of sox9b expression alone was sufficient to produce a TCDD-like jaw phenotype. Loss of a single copy of the sox9b gene in sox9b(+/-) heterozygotes increased sensitivity to jaw malformation by TCDD. Finally, embryos injected with sox9b mRNA and then exposed to TCDD blocked TCDD-induced jaw toxicity in approximately 14% of sox9b-injected embryos. These results suggest that reduced sox9b expression in TCDD-exposed zebrafish embryos contributes to jaw malformation.
接触环境污染物会扰乱早期脊椎动物骨骼的正常发育。2,3,7,8-四氯二苯并对二恶英（TCDD）会损害多种脊椎动物的颅面骨骼发育，其影响在鱼类的早期生命阶段尤为显著。TCDD激活芳烃受体，这是一种转录因子，介导了大部分（如果不是全部）TCDD反应。我们使用DNA微阵列研究了TCDD暴露后斑马鱼发育中的颌骨的转录反应。斑马鱼幼体在受精后96小时暴露于TCDD，暴露后1、2、4和12小时采集颌骨软骨组织进行微阵列分析。TCDD使颌骨中许多软骨形成转录本的表达失调。将TCDD在颌骨中改变的转录本与胚胎心脏中改变的转录本进行比较，发现颌骨和心脏中的转录反应明显不同。Sox9b是一种关键的软骨形成转录因子，是颌骨中表达降低最显著的转录本。我们推测TCDD降低sox9b表达在影响胚胎颌骨形成中起重要作用。通过吗啉代敲低sox9b表达表明，单独部分降低sox9b表达就足以产生类似TCDD的颌骨表型。sox9b(+/-)杂合子中sox9b基因单拷贝缺失增加了对TCDD诱导的颌骨畸形的敏感性。最后，注射sox9b mRNA然后暴露于TCDD的胚胎在约14%注射sox9b的胚胎中阻断了TCDD诱导的颌骨毒性。这些结果表明，TCDD暴露的斑马鱼胚胎中sox9b表达降低导致颌骨畸形。
