p53 null fluorescent yellow direct repeat (FYDR) mice have normal levels of homologous recombination.

The tumor suppressor p53 is a transcription factor whose function is critical for maintaining genomic stability in mammalian cells. In response to DNA damage, p53 initiates a signaling cascade that results in cell cycle arrest, DNA repair or, if the damage is severe, programmed cell death. In addition, p53 interacts with repair proteins involved in homologous recombination.

Tissue-specific differences in the accumulation of sequence rearrangements with age.

Mitotic homologous recombination (HR) is a critical pathway for the accurate repair of DNA double strand breaks (DSBs) and broken replication forks. While generally error-free, HR can occur between misaligned sequences, resulting in deleterious sequence rearrangements that can contribute to cancer and aging. To learn more about the extent to which HR occurs in different tissues during the aging process, we used Fluorescent Yellow Direct Repeat (FYDR) mice in which an HR event in a transgene yields a fluorescent phenotype.

Three-dimensional tissue cytometer based on high-speed multiphoton microscopy.

Image cytometry technology has been extended to 3D based on high-speed multiphoton microscopy. This technique allows in situ study of tissue specimens preserving important cell-cell and cell-extracellular matrix interactions. The imaging system was based on high-speed multiphoton microscopy (HSMPM) for 3D deep tissue imaging with minimal photodamage.

Applications of fluorescence for detecting rare sequence rearrangements in vivo.

Homologous recombination (HR) is an important pathway for the accurate repair of potentially cytotoxic or mutagenic double strand breaks (DSBs), as well as double strand ends that arise due to replication fork breakdown. Thus, measuring HR events can provide information on conditions that induce DSB formation and replicative stress. To study HR events in vivo, we previously developed Fluorescent Yellow Direct Repeat (FYDR) mice in which a recombination event at an integrated transgene yields a fluorescent signal.

Age-dependent accumulation of recombinant cells in the mouse pancreas revealed by in situ fluorescence imaging.

Mitotic homologous recombination (HR) is critical for the repair of double-strand breaks, and conditions that stimulate HR are associated with an increased risk of deleterious sequence rearrangements that can promote cancer. Because of the difficulty of assessing HR in mammals, little is known about HR activity in mammalian tissues or about the effects of cancer risk factors on HR in vivo. To study HR in vivo, we have used fluorescent yellow direct repeat mice, in which an HR event at a transgene yields a fluorescent phenotype.

A single acute exposure to a chemotherapeutic agent induces hyper-recombination in distantly descendant cells and in their neighbors.

Homologous recombination can induce tumorigenic sequence rearrangements. Here, we show that persistent hyper-recombination can be induced following exposure to a bifunctional alkylating agent, mitomycin C (MMC), and that the progeny of exposed cells induce a hyper-recombination phenotype in unexposed neighboring cells. Residual damage cannot be the cause of delayed recombination events, since recombination is observed after drug and template damage are diluted over a million-fold.

In vivo recombination after chronic damage exposure falls to below spontaneous levels in "recombomice".

All forms of cancer are initiated by heritable changes in gene expression. Although point mutations have been studied extensively, much less is known about homologous recombination events, despite its role in causing sequence rearrangements that contribute to tumorigenesis. Although transgenic mice that permit detection of point mutations have provided a fundamental tool for studying point mutations in vivo, until recently, transgenic mice designed specifically to detect homologous recombination events in somatic tissues in vivo did not exist.

"Recombomice": the past, present, and future of recombination-detection in mice.

Homology directed repair (HDR) provides an efficient strategy for repairing and tolerating many types of DNA lesions, such as strand breaks, base damage, and crosslinks. Recombinational repair and lesion avoidance pathways that involve homology searching are integral to normal DNA replication. Indeed, it is estimated that at least ten HDR events take place each time a mammalian cell divides.

Spontaneous mitotic homologous recombination at an enhanced yellow fluorescent protein (EYFP) cDNA direct repeat in transgenic mice.

A transgenic mouse has been created that provides a powerful tool for revealing genetic and environmental factors that modulate mitotic homologous recombination. The fluorescent yellow direct-repeat (FYDR) mice described here carry two different copies of expression cassettes for truncated coding sequences of the enhanced yellow fluorescent protein (EYFP), arranged in tandem. Homologous recombination between these repeated elements can restore full-length EYFP coding sequence to yield a fluorescent phenotype, and the resulting fluorescent recombinant cells are rapidly quantifiable by flow cytometry.