Walpita Chaminda N, Crawford Alexander D, Janssens Els D R, Van der Geyten Serge, Darras Veerle M
Laboratory of Comparative Endocrinology, Division of Animal Physiology and Neurobiology, Katholieke Universiteit Leuven, Leuven, Belgium.
Endocrinology. 2009 Jan;150(1):530-9. doi: 10.1210/en.2008-0457. Epub 2008 Sep 18.
Despite the known importance of thyroid hormones (THs) in vertebrate growth and development, the role of tissue-specific TH activation in early embryogenesis remains unclear. We therefore examined the function of type 2 iodothyronine deiodinase (D2), one of the two tissue-specific enzymes catalyzing the conversion of T4 to T3, in developing zebrafish embryos (Danio rerio). Microinjection of early embryos with antisense oligonucleotides targeting either the D2 translation start site or the splice junction between the first exon and intron induced delays in development and pigmentation, as determined through the measurement of otic vesicle length, head-trunk angle, and pigmentation index at 31 h after fertilization. The antisense-induced delays in developmental progression and pigmentation were reversible through treatment with T3, suggesting that these phenotypic effects may be due to the depletion of intracellular T3 levels. Additional evidence for this hypothesis was provided by quantitative RT-PCR analysis of TH receptor-beta expression in D2 knockdown embryos, revealing a significant down-regulation of this T3-induced transcript that could be reversed by T3 treatment. Tyrosinase expression was also down-regulated in D2 knockdown embryos to a greater degree than could be predicted by the observed delay in developmental progression, suggesting that reduced D2 activity and resultant low intracellular T3 availability may directly influence pigmentation in zebrafish. These data indicate that TH activation by D2 is essential for embryonic development and pigmentation in zebrafish.
尽管甲状腺激素（THs）在脊椎动物生长和发育中的重要性已为人所知，但组织特异性TH激活在早期胚胎发生中的作用仍不清楚。因此，我们研究了2型碘甲状腺原氨酸脱碘酶（D2）的功能，D2是催化T4转化为T3的两种组织特异性酶之一，在斑马鱼胚胎（Danio rerio）发育过程中的作用。在受精后31小时，通过测量耳囊长度、头-躯干角度和色素沉着指数，发现向早期胚胎显微注射靶向D2翻译起始位点或第一外显子与内含子之间剪接位点的反义寡核苷酸会导致发育和色素沉着延迟。反义诱导的发育进程和色素沉着延迟可通过T3处理逆转，这表明这些表型效应可能是由于细胞内T3水平的耗尽所致。对D2敲低胚胎中TH受体β表达的定量RT-PCR分析为这一假设提供了额外证据，结果显示该T3诱导转录本显著下调，而T3处理可使其逆转。在D2敲低胚胎中，酪氨酸酶表达的下调程度也比根据观察到的发育进程延迟所预测的更大，这表明D2活性降低以及由此导致的细胞内T3可用性降低可能直接影响斑马鱼的色素沉着。这些数据表明，D2介导的TH激活对斑马鱼胚胎发育和色素沉着至关重要。
