When treated with 17β-estradiol, female ACI rats (Rattus norvegicus) rapidly develop mammary cancers that share multiple phenotypes with luminal breast cancers. Seven distinct quantitative trait loci that harbor genetic determinants of susceptibility to 17β-estradiol−induced mammary cancer have been mapped in reciprocal intercrosses between susceptible ACI rats and resistant Brown Norway (BN) rats. A panel of unique congenic rat strains has now been generated and characterized to confirm the existence of these quantitative trait loci, designated Emca3 through Emca9, and to quantify their individual effects on susceptibility to 17β-estradiol−induced mammary cancer. Each congenic strain carries BN alleles spanning an individual Emca locus, introgressed onto the ACI genetic background. Data presented herein indicate that BN alleles at Emca3, Emca4, Emca5, Emca6, and Emca9 reduce susceptibility to 17β-estradiol−induced mammary cancer, whereas BN alleles at Emca7 increase susceptibility, thereby confirming the previous interval mapping data. All of these Emca loci are orthologous to regions of the human genome that have been demonstrated in genome-wide association studies to harbor genetic variants that influence breast cancer risk. Moreover, four of the Emca loci are orthologous to loci in humans that have been associated with mammographic breast density, a biomarker of breast cancer risk. This study further establishes the relevance of the ACI and derived congenic rat models of 17β-estradiol−induced mammary cancer for defining the genetic bases of breast cancer susceptibility and elucidating the mechanisms through which 17β-estradiol contributes to breast cancer development.

Estrogens control many aspects of pituitary gland biology, including regulation of lactotroph homeostasis and synthesis and secretion of prolactin. In rat models, these actions are strain specific and heritable, and multiple quantitative trait loci (QTL) have been mapped that impact the responsiveness of the lactotroph to estrogens. One such QTL, Ept7, was mapped to RNO7 in female progeny generated in an intercross between BN rats, in which the lactotroph population is insensitive to estrogens, and ACI rats, which develop lactotroph hyperplasia/adenoma and associated hyperprolactinemia in response to estrogen treatment. The primary objective of this study was to confirm the existence of Ept7 and to quantify the impact of this QTL on responsiveness of the pituitary gland of female and male rats to 17β-estradiol (E2) and diethylstilbestrol (DES), respectively. Secondary objectives were to determine if Ept7 influences the responsiveness of the male reproductive tract to DES and to identify other discernible phenotypes influenced by Ept7. To achieve these objectives, a congenic rat strain that harbors BN alleles across the Ept7 interval on the genetic background of the ACI strain was generated and characterized to define the effect of administered estrogens on the anterior pituitary gland and male reproductive tissues. Data presented herein indicate Ept7 exerts a marked effect on development of lactotroph hyperplasia in response to estrogen treatment, but does not affect atrophy of the male reproductive tissues in response to hormone treatment. Ept7 was also observed to exert gender specific effects on body weight in young adult rats.

The ACI rat model of 17β-estradiol (E2)-induced mammary cancer is highly relevant for use in establishing the endocrine, genetic and environmental bases of breast cancer etiology and identifying novel agents and strategies for preventing breast cancer. E2 treatment rapidly induces mammary cancer in female ACI rats and simultaneously induces pituitary lactotroph hyperplasia and adenoma. The pituitary tumors can result in undesired morbidity which compromises long term studies focused on mammary cancer etiology and prevention. We have defined the genetic bases of susceptibility to E2-induced mammary cancers and pituitary tumors and have utilized the knowledge gained in these studies to develop a novel inbred rat strain, designated ACWi, that retains the high degree of susceptibility to E2-induced mammary cancer exhibited by ACI rats but lacks the treatment related morbidity associated with pituitary lactotroph hyperplasia/adenoma. When treated with E2, female ACWi rats developed palpable mammary cancer at a median latency of 116 days, an incidence of 100% by 161 days and exhibited an average of 15.6 mammary tumors per rat following 196 days of treatment. These parameters did not differ from that observed for contemporaneously treated ACI rats. None of the E2 treated ACWi rats were euthanized prior to the intended experimental end point due to any treatment related morbidity other than mammary cancer burden, whereas 20% of contemporaneously treated ACI rats exhibited treatment related morbidity that necessitated premature euthanasia. The ACWi rat strain is well suited for use by those in the research community focusing on breast cancer etiology and prevention.

In forensic casework, compromised samples often possess limited or degraded nuclear DNA, rendering mitochondrial DNA a more feasible option for forensic DNA analyses. The emergence of massively parallel sequencing (MPS) has enabled the recovery of extensive sequence information from very low quantities of DNA. We have developed a multiplex PCR method that amplifies the complete mitochondrial genome in a range of forensically relevant samples including single cells, cremated remains, bone, maggot and hairs isolated from dust bunnies. Following library preparation, MPS yields complete or nearly complete mitochondrial genome coverage for all samples. To confirm concordance between sample types and between sequencing platforms, we compared sequencing results from hair and buccal swabs from two references. Low initial DNA input into the multiplex PCR allows for conservation of precious DNA while MPS maximizes recovery of genetic information.