Leaven in a molecular era.

[The Leaven – exploring the relationship between science and religion (cont)]

Not only does yeast now serve as one of the most important organisms throughout domestic history, in recent years it has also substantially contributed to biological research. The numerous molecular techniques that have evolved in yeast have allowed it to make an important contribution to a number of areas in science. Through studying various types of yeast and other microbes, scientists now know a great deal about the molecular processes involved in cell division, rapid evolution and disease.

Fortunately, individuals with skin diseases are no longer thought of as unclean and are normally treated within the community. Scientists have greater understanding of disease management and although quarantine and hygiene are still practiced they are now carried out in order to reduce disease transmission. In the majority of cases, people are not ostracised when they are infected by disease, although fears and anxieties can still be generated through sensational media coverage. Nevertheless, even in this molecular age, some transmissible diseases are still associated with sins of the flesh and can lead to social ostracisation.

Yeast colonies in an array. Each spot contains thousands of yeast cells. The plate shows synthetic lethal interactions when the interaction of 2 or more genes cause cell death (shown by colonies with reduced/no growth colonies). Image uploaded by Masur

There are still many diseases that generate fear because they are untreatable. Some of these have evolved through human activities, such as Bovine spongiform encepthalopathy (BSE) which gives rise to a human form of spongiform encepthalopathy called variant Creutzfeldt-Jakob Disease (CJD). The causative agent of BSE is a defective version of a protein called prion that is similar to one found in the brains of sheep with Scrapies. The prion protein is transmitted horizontically and causes disease through disrupting the normal function of the native protein. Studying the molecular mechanisms by which proteins change conformation to become prions in yeast has led to a greater understanding in the pathology of this disease. Many other human diseases, especially cancers, can be researched by studying molecular processes first in yeast.

Cancers arise when cells begin to divide abnormally due to mutations in DNA. Cancer research investigates the mechanisms that encourage these mutations to arise. The mechanism of cell division is often studied in fission yeast, Schizosaccharomyces pombe. Unlike Saccharomyces cerevisiae, which divides by budding, S. pombe divides symmetrically in a similar way to human cells. Fission yeast originates from Africa were it is found growing on banana skins and is used to ferment beer. Through research in this area scientists have reached many milestones in the mechanisms that have caused various cancers leading to greatly improved clinical treatments. Work yeast genetics has greatly contributed to our understanding of cell cycle research and has led to the award of a Nobel prize in 2001 to three scientists who led pioneering work in this area: Paul Nurse, for his work in S. pombe and human model systems; Leland Hartwell, for his work in S. cerevisiae; and Tim Hunt who used sea urchins as a model system. Researchers later found similar cell division genes in human genomes.

Scanning electron micrographs of Fission yeast (Schizosaccharomyces pombe). Image by David O Morgan.

In addition to investigating diseases, yeast is also used as a model system to research ageing. Saccharomyces cells can divide by budding a number of times but the new bud is always physiologically younger than the mother cell. Each cell produces about thirty buds depending on the environmental conditions and other factors. About thirty genes in yeast have already been found to be involved in ageing. The main factors seem to be related to metabolic capacity, resistance to stress, gene dysregulation and genetic stability. Encountering certain environments that would overload any of these factors would also affect longevity. For instance, excessive oxidative damage or radioactivity would lead to a high level of mutations that will reduce the number of times that a cell can bud. Excessive oxidation is associated with the consumption of calories; so caloric restriction should result in increased longevity. This has been demonstrated in yeast, limiting the amount of nutrients and carbohydrates available in growth medium leads to a longer generation time and life span.


…could religious practices have prevented vCJD?

[The Leaven –  exploring the relationship between science and religion (cont)]

Scientific investigation usually comes under scrutiny when  unexpected biological catastrophes occur. It is pressured into finding solutions even if the initial catastrophe is not entirely science related. A good example of this would be  Bovine spongiform encephalopathy (BSE), a mysterious neurological disease, with visibly distressing symptoms, that infected British dairy cattle in the 1980s. The way it affected entire herds led the  media to speculate that it was some kind of horizontally transmitted contagion.

The public demanded answers to several questions. What was causing the epidemic, could it be transmitted to humans and was there a cure? Pressure was on scientific investigation to provide answers.

Fortunately, disease diagnosis was fairly rapid as a significant amount of work on Transmissible Spongiform Encephalopathies (TSEs) already existed. This was as a consequence of the Nobel awarded research of Stanley Prusiner, who in 1972 began investigating a human form of TSE, Creutzfeldt-Jakob Disease (CJD). Following a decade of research on human forms of the disease, Prusiner discovered that the causative agent for CJD was a single protein, which he named a prion, an acronym derived from ‘proteinaceous infectious particle’.  Further research found that it could be transmitted though contact with spinal nerve tissue or blood-related products and that there was no known cure.

Prion protein structure in an amphibian, mammalian and avian species.

There was some evidence that TSEs could be associated with the consumption of diseased tissues but none that showed that the Bovine variant of this disease (affecting members of the Bovidae family including sheep and cattle) could cross the species barrier to humans. Inevitably, this query was gruesomely answered when a variant of the disease, vCJD,  emerged in humans.

The media was quick to criticise how the Government, and their appointed scientists, had conducted risk reporting and disease control measures. The mishandling of the  crisis provoked controversies because it was influenced by a number of conflicting interests. The agricultural community and commercial retailers were suffering financially. While, health officials and consumers were concerned about public safety. The Government had to find a mutual accord that would satisfy all parties. This conflict of interests led to anxieties that attracted media attention and fuelled public debate. Spurred on by public criticism and armed with available scientific knowledge, the Government and agricultural community eventually managed to control the BSE epidemic.

Total fatalities: Sporadic CJD= 883, vCJD= 158
Data from The Lancet (1996) and CJD surveillance unit in Edinburgh (1990- December 2006)

The number of people physically affected were fewer then anticipated but those few victims suffered the most appalling neurological degeneration. Coverage of this by the media greatly impacted social concern. The overall loss of economy to the British beef industry was extreme, with many export restrictions remaining in place twenty years after the initial outbreak.

If science-related knowledge had not been able to contain an epidemic of vCJD  could alternative solutions have been found within religion?

Despite the lack of scientific knowledge in the Bible, following rules and regulations stated in the Old Testament, it would have been possible to contain some infectious diseases and zoonoses. The Hebrews were only permitted to eat certain animals, such as those that had cloven hooves, stomaches divided into two parts and that chewed the cud. Animals that did not fulfil this description, such as pigs, camels and hares, were not  eaten. Additionally, animals that were permitted to be eaten but had died of natural causes were not to be touched or eaten. In the book of Leviticus there are strict regulations in dealing with diseased animals [Lev. 11.39-40]:

If one of the animals that you use as food dies, then anyone who touches the carcase will be unclean until evening. And if anyone eats the dead meat he must wash his clothes, but he will still be unclean until evening; anyone who carries the carcase must wash his clothes, but he will still be unclean until evening.

Those individuals that had come in contact with dead animals were isolated to ensure that infections did not spread through the community. This provides an unexpected example of how, by following practices stated in the Old Testament, disease transmission could possibly be prevented thereby protecting the welfare of the community.