Brca1 in development and tumorigenesis

在过去的一年中，我们生成并分析了一种携带突变的小鼠模型，该突变阻断了BRCA 1外显子10和11之间的切割。BRCA 1基因座中的选择性剪接产生多种蛋白产物，包括BRCA 1-Delta 11，其与BRCA 1全长同种型（BRCA 1-FL）相同，除了缺少外显子11。为了了解BRCA 1-Delta 11的生理功能，我们使用了一种敲入方法，阻断外显子10和12之间的选择性剪接，以防止这种形式的BRCA 1的形成。我们发现，纯合子突变小鼠（Brca 1（FL/FL））出生在孟德尔比率没有明显的发育缺陷。然而，大多数Brca 1（FL/FL）雌性小鼠在一岁后表现出乳腺异常和子宫增生，并自发形成肿瘤。培养的Brca 1（FL/FL）细胞表现出异常的中心体扩增和G（1）群体减少，并伴随着cyclin E和cyclin A的积累。在Brca 1（FL/FL）小鼠乳腺的扩张导管和过度增生小叶区域的上皮层中也发现了细胞周期蛋白E的积累。这些观察结果提供了证据表明，BRCA 1剪接变异体参与BRCA 1调节G（1）/S转换，中心体复制和抑制肿瘤形成的功能。因此，连同先前产生的突变小鼠，我们已经产生并报告了总共五种BRCA 1突变模型，包括两种无效突变、一种条件突变、两种亚型突变和一种点突变。我们利用这些模型的研究表明，BRCA 1在许多生物学过程中发挥着重要作用，包括转录调控，细胞周期进程，细胞凋亡，DNA损伤修复，中心体复制和动物衰老。

In the past year, we generated and analyzed a mouse model carrying a mutation that blocks the slicing between BRCA1 exons 10 and 11. Alternative splicing in the BRCA1 locus generates multiple protein products including BRCA1-Delta11, which is identical to the BRCA1 full-length isoform (BRCA1-FL) except for the absence of exon 11. To understand the physiologic functions of BRCA1-Delta11, we used a knock-in approach that blocks alternative splicing between exons 10 and 12 to prevent the formation of this form of BRCA1. We showed that homozygous mutant mice (Brca1(FL/FL)) were born at a Mendelian ratio without obvious developmental defects. However, the majority of Brca1(FL/FL) female mice showed mammary gland abnormalities and uterine hyperplasia after one year of age with spontaneous tumor formation. Cultured Brca1(FL/FL) cells exhibited abnormal centrosome amplification and reduction of G(1) population that was accompanied by accumulation of cyclin E and cyclin A. Accumulation of cyclin E was also found in epithelial layers of dilated ducts and hyperproliferative lobular regions in the mammary glands of Brca1(FL/FL) mice. These observations provide evidence that BRCA1 splicing variants are involved in BRCA1 functions in modulating G(1)/S transition, centrosome duplication, and repressing tumor formation. Thus, together with mutant mice generated earlier, we have generated and reported a total of five mutant models for BRCA1, including two null mutations, one conditional mutation, two isoform mutations and one point mutation. Our studies using these models demonstrate that BRCA1 plays essential functions in many biological processes, including transcription regulation, cell cycle progression, apoptosis, DNA damage repair, centrosome duplication and animal aging.