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- Parent Category: Biology
- Category: Cell & Molecular
by Monya Baker
The protein Runx1 matters in most progenitors, but just for a while
A single haematopoietic stem cell can re-form an animal's entire blood system, but how these cells form in the embryo is a much-studied mystery. Now researchers at the University of Pennsylvania in Philadelphia piece together when and where an important gene in this process functions.
Haematopoietic stem (HS) cells are found at several sites in the early mouse conceptus (that is, the foetus and its extra-embryonic tissues). The transcription factor Runx1 is expressed at each of them. Runx1 is known to be necessary for HS cells to form in the vascular areas — the early aorta, yolk sac, placenta, umbilical vessels and vitelline arteries of the early digestive tract — but it's less clear which cells produce HSCs. Do blood cells come from the endothelial lining of blood vessels or from other progenitors?
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- Parent Category: Biology
- Category: Anatomy & Physiology
by Monya Baker
Transient expression of a single gene has lasting effects on others
Despite the bad publicity provided by One Flew Over the Cuckoo's Nest, electroconvulsive treatments can be effective for treating depression, and the procedure is known to cause adult mice to grow new neurons in their hippocampus. Now, researchers led by Hongjun Song at Johns Hopkins Medical School have found a mechanism through which this happens. A stimulus, in this case electrical activity, temporarily activates a gene whose protein product modifies DNA in such a way to affect the long-term expression of other genes.
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- Parent Category: Biology
- Category: Cell & Molecular
by Monya Baker
Wnt signalling stimulates the beginnings of gastrulation
Left to their own devices, cultured pluripotent stem cells clump together. A hotchpotch of differentiated cells forms within these so-called 'embryoid bodies', and in fact, the formation of embryoid bodies is a preliminary assay of good quality in embryonic stem (ES) cells and induced pluripotent stem (iPS) cells. Researchers led by Roel Nusse at Stanford School of Medicine in California have now observed something surprising in these much studied structures: they spontaneously begin a process called gastrulation, the cell movements that occur in mammalian embryos after implantation and which result in the formation of the three germ layers of the animal body.
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- Parent Category: Biology
- Category: Cell & Molecular
by Monya Baker
A new screening technique identifies molecules that control the cell cycle
Short stretches of RNA molecules known as microRNAs (miRNAs) coordinate gene expression. Although their importance as gene regulators is now accepted, it can be hard to figure out the functions of particular miRNAs. An individual miRNA molecule can interact with multiple gene transcripts, and multiple miRNAs often serve similar functions and so mask each others' effects.
Using a new screening technique, Robert Blelloch and colleagues at the University of California, San Francisco, have identified a collection of miRNAs that allow embryonic stem (ES) cells to divide rapidly1. The team had previously engineered a line of mouse ES cells that cannot process miRNA because they lack a crucial gene called Dgcr8. Unlike normal ES cells, these knockout ES cells do not proliferate rapidly. By introducing commercially available miRNA mimics, however, the researchers were able to get the cells to start dividing more quickly. After screening nearly 300 mouse miRNAs, the researchers found 14 that greatly improved proliferation of the Dgcr8-knockout ES cells but had no effect on wild-type ES cells. The researchers then concentrated their analysis on five of the miRNAs that are also highly expressed in human ES cells.
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- Parent Category: Biology
- Category: Anatomy & Physiology
by Sarah Webb
CDK5 plays a critical role in integrating new neurons into the adult brain
Stem cells in the hippocampus continue to produce new neurons throughout our lives. But the birth of these neurons is not enough: they have to both reach their appropriate location and integrate into the neural circuitry.
A team led by Fred Gage at the Salk Institute in La Jolla, California, has demonstrated that cells with low levels of cyclin-dependent kinase 5 (CDK5) don't home in on the appropriate location within the hippocampus. However, the loss of the homing signal doesn't keep the cells from integrating into the neural tissue around them, the researchers report in PLoS Biology. "A single gene seems to control orientation," Gage says. "We've separated the appropriate dendritic organization from the ability to make connections."
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- Parent Category: Biology
- Category: Cell & Molecular
by Alicia Chung1
VEGF prompts cells to get out and help
Part of the body's inherent healing response is to mobilize progenitor cells from the bone marrow to the site of injury. Rather than trying to collect and purify sufficient numbers of progenitor cells from bone marrow and blood donors, many clinicians hope to find better ways to summon the right types of cells from their natural reservoir in the bone marrow. In a recent study published in Cell Stem Cell, Sara Rankin and colleagues at Imperial College London demonstrate how naturally occurring growth factors can call different types of progenitor cells into duty1.
Read more: How different progenitor cells are called from the bone marrow