Shi Y B, Hayes W P
Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Dev Biol. 1994 Jan;161(1):48-58. doi: 10.1006/dbio.1994.1006.
To investigate, at the molecular level, the remodeling of small intestine during amphibian metamorphosis, a subtractive hybridization approach was used to identify genes that are differentially regulated by thyroid hormone. A frog cDNA was isolated from Xenopus laevis and determined to be the gene encoding the intestinal fatty acid-binding protein (IFABP) based on its high sequence homology to the previously cloned mammalian IFABP gene. Northern blot analyses and in situ hybridization histochemistry also showed that, like the mammalian IFABP genes, frog IFABP gene expression is restricted to the intestinal epithelium. Xenopus embryos express detectable IFABP mRNA at stage 33/34, suggesting that intestinal epithelial cells differentiate well before feeding begins at stage 45. Moreover, during metamorphosis, levels of IFABP mRNA were gradually down-regulated over a period of about 20 days between stages 54 and 62, reaching a minimum at metamorphic climax, after which they were reelevated as the secondary epithelium forms. This reduction in IFABP gene expression could be reproduced in only 3 days by treating premetamorphic tadpoles with thyroid hormone. Our findings also show that this effect, while likely to be indirect, takes place before overt morphological changes are evident in primary epithelial cells. Thus, the down-regulation of IFABP mRNA is one of the early molecular events preceding epithelial cell death during intestinal remodeling.
为了在分子水平上研究两栖动物变态过程中小肠的重塑，采用消减杂交方法来鉴定受甲状腺激素差异调节的基因。从非洲爪蟾分离出一个青蛙cDNA，基于其与先前克隆的哺乳动物肠脂肪酸结合蛋白（IFABP）基因的高度序列同源性，确定其为编码IFABP的基因。Northern印迹分析和原位杂交组织化学也表明，与哺乳动物IFABP基因一样，青蛙IFABP基因表达局限于肠上皮。非洲爪蟾胚胎在第33/34阶段表达可检测到的IFABP mRNA，这表明肠上皮细胞在第45阶段开始进食之前就已经很好地分化了。此外，在变态过程中，IFABP mRNA水平在第54和62阶段之间的约20天内逐渐下调，在变态高潮时达到最低水平，之后随着次级上皮的形成又重新升高。通过用甲状腺激素处理变态前的蝌蚪，仅在3天内就能重现IFABP基因表达的这种降低。我们的研究结果还表明，这种作用虽然可能是间接的，但发生在初级上皮细胞明显的形态变化之前。因此，IFABP mRNA的下调是肠重塑过程中上皮细胞死亡之前的早期分子事件之一。
