Analysis of mast cell-specific transcription by mutant mice

MITF是一种碱性-螺旋-环-螺旋亮氨酸拉链转录因子，对肥大细胞的发育起重要作用。编码MITF的mI基因座具有多种突变等位基因。这些都有助于在体内研究MITF的结构与功能的关系。MI/MI型肥大细胞表达正常数量的异常MITF(mi-MITF)，而TG/TG型肥大细胞不表达任何MITF。MI/MI小鼠的肥大细胞比TG/TG小鼠表现出更严重的异常，表明mi-MITF具有抑制作用。该突变等位基因(ce-MITF)编码的MITF缺乏Zip结构域。我们使用mI^&lt；ce&gt；/mi^&lt；ce&gt；小鼠研究了Zip结构域的重要性。肥大细胞中c-kit、颗粒酶B(GrB)和色氨酸羟化酶(TPH)mRNAs的含量降低，与TG/Tg小鼠相当，介于+/+和mi/mi小鼠之间。GR B介导肥大细胞的细胞毒活性，而TPH是合成5-羟色胺的限速酶。MI&lt；Ce&gt；/mI&lt；Ce&gt；肥大细胞的细胞毒活性和5-羟色胺含量与TG/Tg肥大细胞相当，显著高于mI/mI肥大细胞。肥大细胞的表型与TG/TG肥大细胞相似，而不是与MI/MI肥大细胞相似，提示Ce-MITF不具有功能。MITF的Zip结构域在肥大细胞的发育过程中起重要作用。我们还发现MITF在小鼠肥大细胞蛋白水解酶(MMCP)-6、-7、α-黑素细胞刺激素受体、N-脱乙酰酶-N-磺基转移酶2基因的转录中起重要作用。MITF通过与其他转录因子如PEBP2/CBF、c-jun和GABP的相互作用来调控它们的转录，MITF在肥大细胞特异性基因的转录调控中起着至关重要的作用。

MITF is a basic-helix-loop-helix leucine zipper (bHLH-Zip) transcription factor, which is important for the development of mast cells. The mi locus encoding MITF possesses various mutant alleles. These are useful for examining the structure-function relationship of MITF in vivo. Mast cells of mi/mi genotype express normal amount of abnormal MITF (mi-MITF), whereas mast cells of tg/tg genotype do not express any MITFs. Mast cells of mi/mi mice show more severe abnormalities than those of tg/tg mice, indicating that the mi-MITF possesses the inhibitory function. The MITF encoded by the mi^<ce> mutant allele (ce-MITF) lacks the Zip domain. We examined the importance of the Zip domain using mi^<ce>/mi^<ce> mice. The amounts of c-kit, granzyme B (Gr B), and tryptophan hydroxylase (TPH) mRNAs decreased in mast cells of mi^<ce>/mi^<ce> mice to levels comparable to those of tg/tg mice, and the amounts were intermediate between those of +/+ mice and those of mi/mi mice. Gr B mediates the cytotoxic activity of mast cells, and TPH is a rate-limiting enzyme for the synthesis of serotonin. The cytotoxic activity and serotonin content of mi^<ce>/mi^<ce> mast cells were comparable to those of tg/tg mast cells, and were significantly higher than those of mi/mi mast cells. The phenotype of mi^<ce>/mi^<ce> mast cells was similar to that of tg/tg mast cells rather than to that of mi/mi mast cells, suggesting that the ce-MITF had no functions. The Zip domain of MITF appeared to be important for the development of mast cells. We also revealed that MITF played an important role in the transcription of mouse mast cell protease (mMCP)-6, -7, alpha-melanocyte stimulating hormone receptor, N-deacetylase N-sulfotransferase 2 genes. MITF regulated their transcription through the interaction of other transcription factors, such as PEBP2/CBF, c-Jun and GABP.MITF appeared to play a crucial role in the transcriptional regulation of mast cell specific genes.