An approach for controlling the timing and order of engineered mutations in mice.

Significant advances in our understanding of normal development and disease have been facilitated by engineered mice in which genes can be altered in a spatially, temporally, or cell type restricted manner using site specific recombinase systems like Cre-loxP or Flp-frt. In many circumstances it is important to understand how interactions between multiple genes influence a given phenotype. Robust approaches for precisely controlling multiple genetic alterations independently are limited, however, thus the impact of mutation order and timing on phenotype is generally unknown. Here we describe and validate a novel Gt(ROSA)26Sor targeted transgene allowing precise control over the order and timing of multiple genetic mutations in the mouse. The transgene expresses an optimized, Flp-estrogen receptor fusion protein (Flpo-ERT2) under the control of a loxP-stop-loxP cassette. In this system, genes modified by loxP sites are altered first upon expression of Cre. Cre also eliminates the loxP-stop-loxP cassette, permitting widespread expression of Flpo-ERT2. Because of the estrogen receptor fusion, Flp activity remains inert until administration of tamoxifen, allowing genes modified by frt sites to be modified subsequently with controllable timing. This mouse transgene will be useful in a wide variety of applications where independent control of different mutations in the mouse is desirable.

Rb1 and Trp53 cooperate to suppress prostate cancer lineage plasticity, metastasis, and antiandrogen resistance.

Prostate cancer relapsing from antiandrogen therapies can exhibit variant histology with altered lineage marker expression, suggesting that lineage plasticity facilitates therapeutic resistance. The mechanisms underlying prostate cancer lineage plasticity are incompletely understood. Studying mouse models, we demonstrate that Rb1 loss facilitates lineage plasticity and metastasis of prostate adenocarcinoma initiated by Pten mutation. Additional loss of Trp53 causes resistance to antiandrogen therapy. Gene expression profiling indicates that mouse tumors resemble human prostate cancer neuroendocrine variants; both mouse and human tumors exhibit increased expression of epigenetic reprogramming factors such as Ezh2 and Sox2. Clinically relevant Ezh2 inhibitors restore androgen receptor expression and sensitivity to antiandrogen therapy. These findings uncover genetic mutations that enable prostate cancer progression; identify mouse models for studying prostate cancer lineage plasticity; and suggest an epigenetic approach for extending clinical responses to antiandrogen therapy.