MOLECULAR ANALYSIS OF REVERSE MUTATIONS FROM NONAGOUTI (A) TO BLACK-AND-TAN (A(T)) AND WHITE-BELLIED AGOUTI (A(W)) REVEALS ALTERNATIVE FORMS OF AGOUTI TRANSCRIPTS
MOLECULAR ANALYSIS OF REVERSE MUTATIONS FROM NONAGOUTI (A) TO BLACK-AND-TAN (A(T)) AND WHITE-BELLIED AGOUTI (A(W)) REVEALS ALTERNATIVE FORMS OF AGOUTI TRANSCRIPTS
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DOI：
10.1101/gad.8.4.481
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发表时间：
1994-02-15
影响因子：
10.5
通讯作者：
WOYCHIK, RP
中科院分区：
文献类型：
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作者：
BULTMAN, SJ;KLEBIG, ML;WOYCHIK, RP
刺鼠基因调节小鼠毛囊中黑素细胞产生真黑素（黑色或棕色）和褐黑素（黄色）色素颗粒的差异。原始的非刺豚鼠 (a) 等位基因主要赋予黑色的毛色，已被证明会以异常高的频率恢复为另外两个更占优势的刺豚鼠等位基因：黑棕褐色 (a(t)) 和白腹刺豚鼠 (A(W))。 a(t) 和 A(W) 等位基因赋予动物背侧和腹侧表面色素分布不均匀的表型；在这两种情况下，由于褐黑色素产生的增加，动物的腹侧表面明显比背侧表面浅。为了了解 a 向 a(t) 或 A(W) 异常高的逆转率，并破译与这三个刺豚鼠等位基因相关的不同色素沉着模式相关的分子事件，我们在分子水平上表征了 a、a(t) 和 A(W)。在这里，我们报道了 11、6 和 0.6 kb 的插入分别出现在 a、a(t) 和 A(W) 的agouti 基因第一个内含子中的完全相同的位置。 a 插入由 5.5 kb VL30 元件组成，该元件内部并入了 5.5 kb 的附加序列；该内部序列的两侧是 526 bp 的同向重复序列。 a(t) 等位基因仅包含 VL30 元件和单个内部 526 bp 重复序列。 A(W) 等位基因只有一个单独的 VL30 LTR。基于a(t)和A(W)插入结构的比较，我们提出通过同源重组切除插入序列来发生反向突变，利用526-bp同向重复序列生成a(t)或VL30 LTR生成A(W)。此外，对这三个等位基因的分析使我们能够识别出刺豚鼠基因的其他外显子，这些外显子产生了刺豚鼠 mRNA 的替代加工农场。我们证明，a、a(t) 和 A(w) 中的不同插入通过选择性地灭活不同形式的刺豚鼠转录本的表达而导致色素沉着差异。
The agouti gene regulates the differential production of eumelanin (black or brown) and phaeomelanin (yellow) pigment granules by melanocytes in the hair follicles of mice. The original nonagouti (a) allele, which confers a predominantly black coat color, has been shown to revert to two other more dominant agouti alleles, black-and-tan (a(t)) and white-bellied agouti (A(W)), with an exceptionally high frequency. The a(t) and A(W) alleles confer phenotypes in which the pigmentation is not uniformly distributed over the dorsal and ventral surfaces of the animal; in both cases the ventral surface of the animal is markedly lighter than the dorsal surface due to an increase in phaeomelanin production. To understand the unusually high reversion rate of a to a(t) or A(W), and to decipher the molecular events associated with the different pigmentation patterns associated with these three agouti alleles, we have characterized a, a(t) and A(W) at the molecular level. Here, we report that insertions of 11, 6, and 0.6 kb are present at precisely the same position in the first intron of the agouti gene in a, a(t), and A(W), respectively. The a insertion consists of a 5.5-kb VL30 element that has incorporated 5.5 kb of additional sequence internally; this internal sequence is flanked by 526 bp direct repeats. The a(t) allele contains only the VL30 element and a single, internal 526-bp repeat. The A(W) allele has only a solo VL30 LTR. Based on the comparison of the structure of the a(t) and A(W) insertions, we propose that reverse mutations occur by excision of inserted sequences in a through homologous recombination, utilizing either the 526-bp direct repeats to generate a(t) or the VL30 LTRs to generate A(W). Moreover, the analysis of these three alleles has allowed us to identify additional exons of the agouti gene that give rise to alternatively processed farms of agouti mRNA. We demonstrate that the distinct insertions in a, a(t) and A(w) cause pigmentation differences by selectively inactivating the expression of different forms of agouti transcripts.