HSCI Science Update: March 2011

March 14, 2011

SCORE! – Genetics Scorecards Afford a New Generation of Stem Cell Screening Techniques

Embryonic stem (ES) and induced pluripotent stem (iPS) cells have the capacity to differentiate into any type of fetal or adult cell. They represent a powerful set of research tools with the potential to bring sweeping advances to the study of complex diseases, cell-based drug screenings, transplant medicine techniques, and other pressing medical applications. A better understanding of variation among these cells is necessary to fully harness their research potential, as is a manageable, systematic characterization method. Recent research from HSCI Principal Faculty member, Alexander Meissner, PhD, provides genetic and epigenetic maps of 32 pluripotent stem cell lines, demonstrating that iPS and ES cells are not as disparate as previously suspected. Using their extensive characterization data, Meissner’s team generated a set of “scorecards” against which new cell lines can be compared. The scorecards offer a streamlined approach for the selection of one cell line over another for a specific application. This research opens doors for more efficient and effective use of pluripotent stem cells, affording more power to already promising stem cell advances.

Bock, C., Kiskinis, E., Verstappen, G., Gu, H., Boultin, G., Smih, Z., Ziller, M., Croft, G., Amoroso, M., Oakley, D., Gnirke, A., Eggan, K., and Meissner, A. (2011) Reference Maps of Human ES and iPS cell Variation Enable High-Throughput Characterization of Pluripotent Cell Lines. Cell 144, 439-452.

A New TALE for Genetics Researchers

Many of the genetic engineering techniques in the researcher’s toolkit are time consuming, expensive, and often imprecise. HSCI Principal Faculty member, Paola Arlotta, PhD, has developed a new method that promises to overcome all three of these common shortfalls. Arlotta’s method uses a set of naturally occurring DNA targeting proteins called transcription activator-like effectors (TALEs), proteins secreted by the plant pathogen Xanthomonas sp. to activate gene expression in hosts. TALEs have a unique structure that is specifically associated with their individual DNA binding sites, making them a promising tool for biological system interrogation. But the very structure that makes TALEs interesting has presented a hurdle in customization. Arlotta’s team provides a new technique that not only overcomes this problem, but is also simple, scalable, and economical. The team went on to show that TALEs, while native to plant systems, can also work within mammalian cells and can be customized to target most DNA sequences of interest. While more work is necessary to tease out the nuances of TALE activity, Arlotta and her team have provided the research community with a new repertoire of programmable and precise genome engineering technologies.

Zhang, F., Cong, L., Lodato, S., Kosuri, S., Church, G., Arlotta, P. (2011) Efficient construction of sequence-specific TAL effectors for modulating mammalian transcription. Nature Biotechnology Epub 2011 January 19.

Understanding Tissue Regeneration in the Small Intestine

The small intestine lining is among the most highly regenerative mammalian tissues, renewing itself every 2-3 days to protect against environmental pathogens. In the case of a normal mouse, that amounts to two hundred million cells each day. Multipotent intestinal stem cells are well-established as the source of this continual renewal process. Recently, researchers identified two intestinal stem cell lineages (Lgr5+ and Ascl2+) in the mouse with uncharacteristically high cycling rates.  More recently, HSCI Principal Faculty member, David Breault, MD, PhD, identified another cell line (mTERT) that seems to work in conjunction with Lrg5+ and is, in contrast, slow cycling. While the highly proliferative Lrg5+ cells may play a role in tissue homeostasis, mTERT cells are resistant to injury and contribute to the regenerative response following injury. They are also able to give rise to their fast-cycling counterparts. The discovery of this cell line expands our understanding of the small intestine epithelium and may translate into improved care for intestinal disease and cancer patients.

Montgomery, R., Carlone, D., Richmond, C., Farilla, L., Kranendonk, M., Henderson, D., Baffour-Awuah, N., Ambruzs, D., Fogli, L., Algra, S., Breault, D. (2011) Mouse telomerase reverse transcriptase (mTert) expression marks slowly cycling intestinal stem cells. Proceedings of the National Academy of Sciences 108, 179-184.

The Humble Zebrafish Affords New Hope for Kidney Disease Patients

Unlike many vertebrates, mammals have lost the ability to regenerate the kidney’s basic functional unit, the nephron. Nephrons make up the vast network of renal filtering equipment responsible for keeping the blood clean and healthy. Damaged nephrons can be repaired, but destroyed nephrons are lost forever from adult mammals. Destroyed nephrons are the cause of several renal diseases and, for many patients, nephron regeneration could mean the difference between life and death. In recently published work, HSCI Principal Faculty member Alan Davidson, PhD, and colleagues look to the zebrafish, which are capable of nephron regeneration, for insights into nephron physiology. The team found that, notably, individual nephrons do not come from individual progenitor cells. Rather, two different cell types coalesce to form nephrogenic aggregates, a process reminiscent of embryonic mammalian nephron generation. The next step in this research is to search for similar nephrogenic aggregates in the adult mammalian kidney that may be blocked or dormant. Such a discovery could open the door for manipulative therapies to treat renal disease patients.

Diep, C., Ma, D., Deo, R., Holm, T., Naylor, R., Arora, N., Wingert, R., Bollig, F., Djordjevic, G., Lichman, B., Zhu, H., Ikenaga, T., Ono, F., Englert, C., Cowan, C., Hukriede, N., Handin, R., Davidson, A. (2011) Identification of adult nephron progenitors capable of kidney regeneration in zebrafish. Nature 470, 95-100.