Genetic Alterations During Multistep Carcinogenesis In M

BRCA 1和BRCA 2基因的遗传缺陷赋予女性患乳腺癌和卵巢癌的深刻易感性。由于这些乳腺癌易感基因的位置克隆的识别，我们已经使用基因靶向开发实验小鼠模型中的Brca 2基因的缺陷。我们的研究主要集中在缺乏Brca 2蛋白（外显子27）的羧基末端结构域的小鼠，因为这部分基因产物已被证明含有核定位信号，它直接与Rad 51蛋白相互作用，这被认为是维持基因组稳定性响应DNA损伤的关键。使用同源重组技术，我们产生的小鼠携带一个（半合子）或两个（纯合子）突变体等位基因的Brca 2外显子27。这些外显子27缺失小鼠是可行的，虽然我们已经观察到一个微妙的，但在预期数量的纯合子Brca 2突变小鼠的统计学显着不足。对这些小鼠的初步研究表明，与其杂合和野生型同窝小鼠相比，C57 BL/6 J背景的纯合突变型Brca 2小鼠易患自发性胃癌的发病率较低。对这些C57 BL/6 Brca 2-外显子27缺陷小鼠和BALB/c-P53缺陷小鼠之间的杂交进行了高和低水平γ辐射研究（5周龄时5和0.3戈伊），以观察乳腺和其他组织中的肿瘤发展。这项研究的初步结果表明，在Brca 2基因敲除小鼠中，终生存活率降低，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，降低了存活率。荧光微卫星标记辅助育种技术（速度同源）被用来转移到遗传背景（BALB/c和SWR），我们以前已经证明是更容易受到辐射诱导的乳腺癌的Brca 2外显子27突变。目前正在评估这些小鼠品系以评估肿瘤易感性。

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.