Brca1 in development and tumorigenesis

在过去的一年里，我们建立并分析了一个携带突变的小鼠模型，该突变阻止了BRCA1外显子10和11之间的切片。BRCA1基因座的选择性剪接产生了包括BRCA1-Delta11在内的多种蛋白质产物，除了缺少外显子11之外，它与BRCA1全长异构体(BRCA1-FL)相同。为了了解BRCA1-Delta11的生理功能，我们使用了一种敲入方法来阻止外显子10和12之间的选择性剪接，以防止这种形式的BRCA1的形成。我们发现纯合子突变小鼠(BRCA1(FL/FL))按孟德尔比例出生，没有明显的发育缺陷。然而，BRCA1(FL/FL)雌性小鼠在一岁后大多数表现为乳腺异常和子宫增生，并自发形成肿瘤。培养的BRCA1(FL/FL)细胞出现中心体异常扩增和G(1)群减少，并伴有细胞周期蛋白E和细胞周期蛋白A的积聚，BRCA1(FL/FL)小鼠乳腺导管上皮层和过度增殖的小叶区也有细胞周期蛋白E的积聚。这些观察结果表明，BRCA1剪接变异体参与了BRCA1调节G(1)/S转换、中心体复制和抑制肿瘤形成的功能。因此，连同之前建立的突变小鼠，我们总共建立并报告了BRCA1的5个突变模型，包括2个零突变、1个条件突变、2个异构体突变和1个点突变。我们利用这些模型进行的研究表明，BRCA1在许多生物学过程中发挥着重要的功能，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.