The nature of the scrapie agent

Transgenic mice expressing bovine PrP with a four extra repeat octapeptide insert mutation show a spontaneous, non-transmissible, neurodegenerative disease and an expedited course of BSE infection

Transgenic (Tg) mice carrying four extra octapeptide repeats (OR) in the bovine PrP gene (10OR instead of 6) have been generated. In these mice, neuropathological changes were observed depending upon the level of transgene expression. These changes primarily involved a slowly advancing neurological disorder, characterized clinically by ataxia, and neuropathologically, by vacuolization in different brain areas, gliosis, and loss of cerebellar granule cells. Accumulation of insoluble bovine 10OR-PrP (bo10OR-PrP) was observed depending on the level of expression but no infectivity was found associated with this insoluble form. We also compared the behavior of bo6OR-PrP and bo10OR-PrP Tg mouse lines in response to BSE infection. BSE-inoculated bo10ORTg mice showed an altered course of BSE infection, reflected by reduced incubation times when compared to bo6ORTg mice expressing similar levels of the wild type 6OR-PrP. In BSE-inoculated mice, it was possible to detect PrP(res) in 100% of the animals. While insoluble bo10OR-PrP from non-inoculated bo10ORTg mice was non-infectious, brain homogenates from BSE-inoculated bo10ORTg mice were highly infectious in all the Tg mouse lines tested. This Tg mouse model constitutes a new way of understanding the pathobiology of bovine transmissible spongiform encephalopathy. Its potential applications include the assessment of new therapies against prion diseases.

Different behavior toward bovine spongiform encephalopathy infection of bovine prion protein transgenic mice with one extra repeat octapeptide insert mutation

In humans, insert mutations within the repetitive octapeptide region of the prion protein gene (Prnp) are often associated with familial spongiform encephalopathies. In this study, transgenic mice expressing bovine PrP (boTg mice) bearing an additional octapeptide insertion to the wild type (seven octapeptide repeats instead of six) showed an altered course of bovine spongiform encephalopathy (BSE) infection, reflected as reduced incubation times when compared with boTg mice expressing similar levels of the wild-type six-octapeptide protein. In both boTg mouse lines (bo6ORTg and bo7ORTg), incubation times were affected drastically depending on transgene expression levels and the inoculum used. In accordance with the lack of an interspecies barrier to BSE infection, we detected the typical signs of CNS spongiform degeneration by histopathological analysis and the presence of the bovine prion PrP(res) by Western blot or immunohistochemical analyses. When 7OR-PrP(res) was propagated in bo7ORTg mice, a similar earlier onset of clinical signs was observed compared with bo6ORTg mice. Proteins PrP(C) and PrP(res) containing seven octapeptides (7OR-PrP(C) and 7OR-PrP(res)) showed similar protease sensitivity and insolubility in nondenaturing detergents to homologous 6OR-PrP(C) and 6OR-PrP(res). In addition, bo7ORTg mice showed a higher sensitivity than bo6ORTg mice for detecting prion infection in specimens previously diagnosed as negative by conventional biochemical techniques. In the absence of clinical signs of disease, 7OR-PrP(res) could be detected as early as 120 d after inoculation by immunohistochemical and Western blot analyses. These findings may help us improve the current mouse bioassays and understand the role of the octapeptide repeat region in susceptibility to disease.

Does the infective agent of scrapie replicate without nucleic acid? An assessment

The dogma of a unique status for the scrapie agent falling outside the virological spectrum is critically examined in the light of the circumstances which gave rise to it, and it is concluded that such an extreme view cannot be justified. The dogma arose in the first place by a combination of inadequate methodology and the lack of comparable data from other systems. It has been sustained partly by the same factors, and partly by a general failure to understand the impact on all relevant investigations of the exceptionally tenacious binding of infective agent to host-cell (membrane) components. This has not only greatly distorted the experimental findings, but as a consequence has resulted in extensive data misinterpretation. It is concluded that there is no hard evidence for the absence of a nucleic acid core in the scrapie agent so long as it is accepted that this is very small--i.e., of the order of 30 KDa (kilodaltons)--and is embedded within a cell membrane component matrix which protects it by forming a sequestered microenvironment: further that this is by far the simplest hypothesis.

Bovine spongiform encephalopathy--a new disease transmissable to humans?

Current concerns about the cattle disease bovine spongiform encephalopathy do not appear to take cognisance of the parallel with scrapie, the similar/identical disease of sheep/goats. This has existed for 200 years, and clearly involved a longstanding consumption of meat/offal from affected animals, but apparently without consequential human disease. A summary is given of the characteristics of the human and animal spongiform encephalopathy diseases and their causative agents. The conclusion of the official Southwood Report that the bovine disease is caused by the inclusion of sheep scrapie material in cattle fodder is critically discussed: an alternative mechanism is proposed for its emergence.

Self-organisation and living systems: Is DNA an 'artificial intelligence'?

There seems little doubt that the maintenance and development of living systems is crucially dependent on an internal organisation of monumental complexity--particularly in higher living species. It is suggested that current thinking--particularly relating to the role of DNA in the total process cannot explain the underlying mechanisms and that a radical rethinking will be necessary. To this end it is proposed that DNA has a unique molecular electronic structure enabling it to operate as a computer analogue system for the highly efficient storage of information and as a type of artificial intelligence through which the information is translated and implemented to organise and control all aspects of the construction and activity of living systems.

The chick embryo fibroblast cytosolic DNA complex--a possible cell-cell messenger

1. The uptake of [3H]thymidine and [3H]uridine labelled DNA-RNA cytosol complex has been studied in chick embryo fibroblast cells. 2. The complex appears to be cleaved into DNA and RNA containing fragments in the recipient cell nucleus: both then enter the cell cytosol fraction, but the RNA fragment in particular is rapidly degraded. 3. Although [3H]thymidine labelled material present in the nucleus co-extracts with bulk nuclear DNA, caesium gradienting shows little or no evidence that integration of host and imported DNA has occurred. 4. It is suggested that the cytosolic/extruded DNA complex may be a "messenger" DNA, capable of the transfer of regulatory information between cells on a transient basis.

The triplet code: is it enough?

It is suggested that the triplet code dogma that the role of DNA as an information carrier can only be defined in terms of a code for amino acids embodied in the sequence of nucleotides, is inadequate to encompass the totality of information/instruction/organisation necessary for the maintenance of living systems. It is proposed that, as a minimum, a second independent but complementary mechanism is necessary involving direct DNA--DNA intercommunication. Further, that this mechanism may operate on the basis of a chemically switched microprocessor network system with individual DNA sequences able to act as individual microprocessors.