Author: admin

Researchers at Columbia University have come closer to realising a longstanding goal of the scientific community by developing a new method of visualising small biomolecules inside living biological systems with minimum disturbance.

A general method has been developed to visualise a range of molecules such as small molecular drugs and nucleic acids, amino acids and lipids, determining where they are localised and how they function inside cells.

Fluorophores – molecules that glow when illuminated – have been used to label molecules of interest when studying their activity within cells. A fluorescence microscope is used to track and locate these molecules with high precision. This process became more common following the invention of green fluorescent protein in 1994.

Fluorophore tagging is not without its problems, however. Difficulties arise when tagging small biomolecules as the fluorophores are almost always larger or comparable in size to the small molecules of interest. As a result, they often disturb such molecules' functioning.

Assistant professor of Chemistry Wei Min's research team used an emerging laser-based technique called stimulated Raman scattering (SRS) microscopy. They combined this with a small but highly vibrant alkyne tag (C=C, carbon-carbon triple bond), a chemical bond that, when it stretches, produces a strong Raman scattering signal at a unique "frequency" (different from natural molecules inside cells). 

Using the tiny alkyne tag to label molecules avoids the problems associated with fluorophore tagging while obtaining high-detection specificity and sensitivity by SRS imaging.

The laser colours are tuned to the alkyne frequency and the focused laser beam quickly scanned across the sample, point-by-point, enabling SRS microscopy to pick up the unique stretching motion of the C=C bond carried by the small molecules. A three-dimensional map of the molecules inside living cells and animals is thus obtained.

Using this method, Min's team demonstrated tracking alkyne-bearing drugs in mouse tissues and visualising de novo synthesis of DNA, RNA, proteins, phospholipids and triglycerides through metabolic incorporation of alkyne-tagged small precursors in living cells.

The team intends to use this technique in further experiments; they are also creating other alkyne-labeled biologically active molecules for more versatile imaging applications.

Researchers have successfully created new nerve cells in the brains and spinal cords of living mammals without the need for stem cell transplants to replenish lost cells.

The new study, which was conducted at the University of Texas (UT) Southwestern Medical Center, offers hope to those suffering from traumatic brain injury or spinal cord damage and could be used to treat Alzheimer's disease.

However, the scientists involved have stressed that it is too soon to know whether the neurons created in these initial studies resulted in any functional improvements. 

Injuries to the spinal cord can lead to an irreversible loss of neurons. Along with scarring, they can ultimately lead to impaired motor and sensory functions. As adult spinal cords only have a limited ability to produce new neurons, biomedical scientists have sought to replace them using stem cells – but they have encountered difficulties with this approach.

Scientists in UT Southwestern's Department of Molecular Biology have successfully turned scar-forming astrocytes in the spinal cords of adult mice into neurons. Their findings are published in Nature Communications and follow previous findings published in Nature Cell Biology.

A transcription factor – a biological substance that regulates the expression of genes – was introduced into areas of the brain or spinal cord where that factor is not highly expressed in adult mice. A factor known as SOX2 switched fully differentiated, adult astrocytes to an earlier neuronal precursor, or neuroblast, stage of development.

The mice were then given a drug called valproic acid (VPA) that encouraged the survival of the neuroblasts and their maturation (differentiation) into neurons.

According to the study's senior author, Chun-Li Zhang, neurogenesis (neuron creation) occurred in the spinal cords of both adult and aged (over one-year old) mice of both sexes, although the response was much weaker in the aged mice.

SOX2-induced mature neurons created from reprogramming of astrocytes persisted for 210 days after the start of the experiment in the spinal cord study – the longest time the researchers examined.

A new technique has been developed to treat conditions such as Hepatitis B (HBV) without damaging cells infected by the virus.

Viruses such as HBV are able to survive by depositing their genes in their hosts' cell nuclei, where DNA is not normally degraded, which protects them from antiviral drugs. New research at the Helmholtz Zentrum, Munich and the Technische Universitat, Munich may pave the way to treating these viruses.

According to the World Health Organisation, more than 240 million people around the world are currently suffering from a chronic HBV infection, despite the availability of preventive vaccination. Sufferers of the disease are at risk of developing liver cirrhosis or even cancer as a result of the condition.

Antiviral medicines are available but they cannot completely eliminate the disease – as soon as treatment is discontinued, the virus is reactivated due to the presence of virus DNA (cccDNA: covalently closed circular DNA) "hidden" in the cell nucleus.

The cccDNA stored in the nuclei of infected liver cells (hepatocytes) serves as a template for the virus's own proteins and new viral genomes. The international team of scientists headed by Prof Ulrike Protzer and Prof Mathias Heikenwalder has found a way to selectively attack and eliminate the viral DNA without damaging the host liver cells in the process. 

"The degradation of viral DNA in the cell nucleus that we describe represents an important mechanism in the defence against the virus," Protzer reports. "Moreover, for the first time, the results offer the possibility to develop a treatment that can heal hepatitis B."

According to the scientists, in addition to interferons (the immune system's defence agents), activation of the lymphotoxin-beta receptor in the host cell promotes certain proteins and supports their function so that they chemically modulate and degrade viral cccDNA.

As a result of this process, the virus is prevented from reactivating and the disease cannot break out again following the cessation of treatment. The proteins do not affect the genetic information of the host cells and the team believe their research could lead to new treatments becoming available.

Regenerative medicine offers hope to sufferers of chronic conditions such as heart failure. Previous attempts to transform skin cells into heart muscle have only been partially successful, however, as the transformation is often incomplete.

Scientists at the Gladstone Institutes in California have come up with a new method of reprogramming skin cells in a way which renders them almost indistinguishable from heart muscle cells. Their findings are based on animal models and are described in the latest issue of Cell Reports. 

While heart disease remains the world's biggest killer, the chances of surviving a heart attack have been greatly improved due to recent medical advances. However, many people are now living with heart failure – a condition in which the heart does not beat at full capacity due to damage sustained during a cardiac arrest.

Previous research into regenerating heart muscle has required the insertion of several genetic factors to spur the reprogramming process. However, scientists have recognised problems with scaling this gene-based method into successful therapies.

Gladstone senior investigator Sheng Ding and colleagues used skin cells extracted from adult mice to screen for chemical compounds, known as 'small molecules', that could replace the genetic factors.

The team tested various combinations of small molecules before settling on a four-molecule 'cocktail' called SPCF that could aid the transformation of skin cells into heart cells. Although the resulting cells exhibited some behaviour characteristic of heart muscle cells, the transformation was incomplete.

An additional factor, Oct4, was therefore added to the cocktail, enabling the team to generate a completely reprogrammed, beating heart cell.

"Once we added Oct4 to the mix, we observed clusters of contracting cells after a period of just 20 days," explained Dr Ding. "Remarkably, additional analysis revealed that these cells showed the same patterns of gene activation and electric signaling patterns normally seen in the ventricles of the heart."

The researchers believe this may be a more desirable reprogramming method and are confident it represents progress towards their goal of an developing an entirely pharmaceutical-based method to regrow heart muscle.

New research conducted at the Warwick Medical School has solved an enduring mystery of biology by uncovering the key role of a protein in shutting down endocytosis during mitosis.

Their study outlines the role of actin, a protein, in shutting down clathrin-dependent endocytosis during mitosis.

Endocytosis is the process by which cells absorb molecules that are too large to pass through the plasma membrane, such as proteins. Normally, this takes place via clathrin-dependent endocytosis.

During this process, clathrin forms a pit on the inner surface of the membrane which allows the cell to engulf and bring in a small volume of fluid from outside the cell.

The question of how clathrin-dependent endocytosis shuts down during mitosis was first posed by American cell biologist Don Fawcett in 1965. He became aware of the phenomenon but scientists have hitherto been unable to find out the reason behind it.

Two competing theories emerged as possible explanations. One suggested the tension of the plasma membrane is too high for endocytosis to occur; the other that mitotic phosphorylation – the addition of a phosphate group to the cell proteins – switches off the proteins.

Recently, it was found that endocytosis can still occur in non-dividing cells with high membrane tensions because actin can be recruited to help clathrin overcome the high tension in the membrane.

The Warwick team found membrane tension in dividing cells is much higher than in non-dividing cells, raising the question of why actin does not help in this case. They found that actin is used to form a stiff cortex in cells during mitosis and thus cannot be used to facilitate endocytosis.

Endocytosis was re-started in mitotic cells when the researchers tricked them into making actin available during mitosis. According to the team, mitotic phosphorylation does not inhibit the process and their paper argues against the alternative theory.

Team leader Dr Steve Royle commented: "The implications for human health are truly fascinating; by knowing the role played by actin we can look to use it to restart endocytosis during cell division. That could mean that we're able to make dividing cells receptive to pharmaceuticals or other medical treatments in a way that we haven't before."