Genetic Alterations During Multistep Carcinogenesis In M

BRCA1和BRCA2基因的遗传缺陷使女性极易患乳腺癌和卵巢癌。自从通过定位克隆鉴定了这些乳腺癌易感基因以来，我们利用基因打靶技术建立了BRCA2基因缺陷的实验小鼠模型。我们的研究主要集中在缺乏BRCA2蛋白(外显子27)的羧基末端结构域的小鼠身上，因为这部分基因产物被证明包含核定位信号，并且它直接与RAD51蛋白相互作用，RAD51蛋白被认为是在应对DNA损伤时维持基因组稳定性的关键。利用同源重组技术，我们产生了携带BRCA2外显子27的一个(半合子)或两个(纯合子)突变等位基因的小鼠。这些外显子27缺失的小鼠是可行的，尽管我们已经观察到BRCA2纯合子突变小鼠的预期数量存在微小但在统计学上显着的缺陷。对这些小鼠的初步研究表明，与杂合子和野生型小鼠相比，C57BL/6J背景下的纯合子突变BRCA2小鼠患自发性胃癌的几率较低。这些C57BL/6 BRCA2外显子27缺陷小鼠和BALB/c-P53缺陷小鼠之间的交叉杂交进行了高水平和低水平的伽马辐射研究(5&0.3Gy5周龄)，以观察乳腺和其他组织中肿瘤的发生。这项研究的初步结果表明，BRCA2基因缺失的小鼠的寿命缩短，癌症发病率和潜伏期增加。辐射进一步增加了杂合子小鼠的肿瘤发病率和降低了存活率。利用荧光微卫星标记辅助育种技术(SPEED COGENICS)将BRCA2外显子27突变转移到遗传背景(BALB/c和SWR)上，我们先前已经证明BALB/c和SWR更容易受到辐射诱发的乳腺癌的影响。目前正在对这些小鼠品系进行评估，以评估肿瘤的敏感性。

Inherited defects of the BRCA1 and BRCA2 genes confer a profound predisposition to breast and ovarian cancer in women. Since the identification of these breast cancer susceptibility genes by positional cloning, we have used gene targeting to develop experimental mouse models for defects in the Brca2 gene. Our studies have focused on mice lacking the carboxy terminal domain of the Brca2 protein (exon 27) because this portion of the gene product has been shown to contain nuclear localization signals and it interacts directly with the Rad51 protein which is thought to be critical for maintaining genomic stability in response to DNA damage. Using homologous recombination techniques, we generated mice that carry one (hemizygous ) or two (homozygous) mutant alleles of Brca2 exon 27. These exon 27 null mice are viable although we have observed a subtle but statistically significant deficiency in the expected number of homozygous Brca2 mutant mice. An initial study with these mice has shown that homozygous mutant Brca2 mice on a C57BL/6J background are predisposed to a low incidence of spontaneous gastric carcinoma compared to their heterozygous and wild type littermates. High- and low-level gamma radiation studies (5 & 0.3 Gy at 5 wks of age) with intercrosses between these C57BL/6 Brca2-exon 27 deficient mice and BALB/c-P53-deficient mice are being followed for neoplastic development in mammary gland and other tissues. Preliminary results from this study indicate that lifetime survival is reduced and carcinoma incidence and latency is increased in Brca2 null mice . Irradiation further increased tumor incidence and decreased survival in heterozygous mice. Fluorescent microsatellite marker-assisted breeding techniques (speed congenics) were used to transfer this Brca2 exon 27 mutation onto genetic backgrounds (BALB/c and SWR) that we have previously shown are more susceptible to radiation-induced mammary carcinogenesis. These mice strains are currently being evaluated to assess tumor susceptibility.