Telomere dysfunction cooperates with epigenetic alterations to impair murine embryonic stem cell fate commitment.

The precise relationship between epigenetic alterations and telomere dysfunction is still an extant question. Previously, we showed that eroded telomeres lead to differentiation instability in murine embryonic stem cells (mESCs) via DNA hypomethylation at pluripotency-factor promoters. Here, we uncovered that telomerase reverse transcriptase null (Tert-/-) mESCs exhibit genome-wide alterations in chromatin accessibility and gene expression during differentiation. These changes were accompanied by an increase of H3K27me3 globally, an altered chromatin landscape at the Pou5f1/Oct4 promoter, and a refractory response to differentiation cues. Inhibition of the Polycomb Repressive Complex 2 (PRC2), an H3K27 tri-methyltransferase, exacerbated the impairment in differentiation and pluripotency gene repression in Tert-/- mESCs but not wild-type mESCs, whereas inhibition of H3K27me3 demethylation led to a partial rescue of the Tert-/- phenotype. These data reveal a new interdependent relationship between H3K27me3 and telomere integrity in stem cell lineage commitment that may have implications in aging and cancer.

In vivo optical imaging of tumor and microvascular response to ionizing radiation.

Radiotherapy is a widely used cancer treatment. However, understanding how ionizing radiation affects tumor cells and their vasculature, particularly at cellular, subcellular, genetic, and protein levels, has been limited by an inability to visualize the response of these interdependent components within solid tumors over time and in vivo. Here we describe a new preclinical experimental platform combining intravital multimodal optical microscopy for cellular-level longitudinal imaging, a small animal x-ray microirradiator for reproducible spatially-localized millimeter-scale irradiations, and laser-capture microdissection of ex vivo tissues for transcriptomic profiling. Using this platform, we have developed new methods that exploit the power of optically-enabled microscopic imaging techniques to reveal the important role of the tumor microvasculature in radiation response of tumors. Furthermore, we demonstrate the potential of this preclinical platform to study quantitatively--with cellular and sub-cellular details--the spatio-temporal dynamics of the biological response of solid tumors to ionizing radiation in vivo.

Profiling microRNA expression with the Illumina BeadChip platform.

The complex mechanisms involved in the regulation of both gene and protein expressions are still being understood. When microarray technology was first introduced during the early to mid 1990s, they heralded a tremendous opportunity to study transcription on a global scale. Despite this promise, however, one thing that has become clear is that the expression of protein coding genes is not the only aspect of the transcriptome that researchers need pay attention to. Small noncoding RNAs, such as microRNAs, are now known to play a pivotal role in the control of both gene and protein expressions. Each microRNA may act upon a plurality of different targets, which makes the measurement of their expression levels a highly important part of understanding the entire cellular response. It has only been recently, however, that advancements and modifications to microarray technology have allowed us to study these important molecules in a high throughput and parallel manner.