The journey from embryonic stem cell to a fully developed liver, heart or muscle cell requires not only the right genes, but genes that are turned on and off at the right time — a job that is handled in part by DNA-packaging proteins known as histones. But it turns out that not all histones are created equally. New research from Rockefeller University shows that minute variations between histones play an important role in determining how and when genes are read. The findings, reported this week in the journal Cell, hint at an unimagined complexity of the genome and may open a new avenue of investigation regarding the mysterious causes of the human genetic disease known as ATR-X syndrome. “Our work shows that the regulation of histone variant localization —   Disappearing histone

They are considered to be the most important model organism for research into human biology: mice may look totally different, but they are in many ways similar to Homo sapiens on a fundamental level. For instance, an impressive 99 per cent of the mouse genes are matched by a corresponding sequence in the human genome. That is also why the law in this part of the world only permits scientists to conduct research on human embryo stem cells when they have “clarified in advance” their specific questions by using animal cells as far as possible. However, such tests are often pointless – and sometimes even misleading, as a recent study by scientists working with Hans Schöler at the Max Planck Institute for Molecular Biomedicine in Münster demonstrates. (Cell Stem Cell, March 5th, 2010) Fig.: Neural differentiation of mouse epiblast stem cells by inactivating the FGF signalling pathway.

By Kim McDonald David Traver (right) and Neil Chi used zebrafish, grown in tanks at UCSD, to track blood-forming stem cells. Biologists at UC San Diego have identified the specific region in vertebrates where adult blood stem cells arise during embryonic development. Their discovery, which appears in a paper in this week’s early online edition of the journal Nature, is a critical first step for the development of safer and more effective stem cell therapies for patients with leukemia, multiple myeloma, anemia and a host of other diseases of the blood or bone marrow.   The researchers say their time-lapse imaging of the process (seen here), by which primitive embryonic tissues first produce the parent stem cells that produce all adult blood cells over the life of an individual, should help guide future efforts to repair and replace this cell population for therapeutic purposes.  Current transplantation therapies rely on the infusion of donor stem cells into a patient’s bone marrow to generate new, healthy blood cells without disease.  But that procedure is often risky and can result in fatal complications, due in part to “graft-versus-host disease,” in which transplanted cells react against foreign tissues of the recipient.  One means of circumventing this immune rejection problem would be to generate hematopoietic stem cells, or HSCs, using the patient’s own precursor cells.  Such cells would be perfectly genetically matched, but in order to generate such cells, scientists must first understand the molecular processes that underlie specification of HSCs. “If we could generate healthy HSCs from patients and transplant them back into their own bone marrow, it would eliminate many complications,” said David Traver, an assistant professor of biology who headed the research team. Julien Bertrand (left) and Buyung Santoso observed and tracked individual stem cells in zebrafish embryos with a microscope. “Our findings are an important step toward this goal because they provide a better understanding of how HSCs, the cell type responsible for the clinical benefits of bone marrow transplants, are first specified during development,” he said.