Recently, Richt et al. of the National Animal Diseases Center of the US Department of Agriculture reported that they used genetic engineering techniques to cultivate for the first time a cow that is biologically unlikely to infect BSE. (Nat Biotechnol published online on December 31, 2006)
The pathogen of mad cow disease, known as the fleas, is caused by the misfolding of a normal protein prion protein in the brain, the immune system, and other tissues. The scorpion venom organism causes bovine spongiform encephalopathy (BSE), known as mad cow disease and human Creutzfeldt-Jakob disease (CJD). It can also cause scrapie in sheep and fatal wasting disease in deer and warts. The pathogenic fleas contain no genetic material and cannot reproduce themselves like bacteria and viruses. However, previous experiments have suggested that as long as there is a scorpion venom, the entire brain can be destroyed, because a misaligned scorpion venom in the brain can make normal prion protein nearby become abnormal. As long as normal prion protein is constantly being recruited by deafness, the disease can continue to spread.
In this experiment, scientists used genetic engineering techniques to knock down genes that control prion protein in cells, and used cloning techniques to breed 12 cows, each containing no prion protein. After more than 20 months, these cows were normal in clinical, physiological, histopathological, immune and reproduction. Further in vitro experiments showed that when the bovine brain tissue lacking prion protein was exposed to two different fleas, the fleas did not spread.
Researchers believe that these cattle may be resistant to fleas. However, these cattle are still very small, and lack of normal prion protein may cause problems when they grow up.
Scientists also mentioned that one experiment is in progress and the results will be more illustrative. Researchers directly injected prion venom into the brains of living animals that lack normal prion protein and observed whether those animals were infected.
The researchers emphasized that this kind of cattle is not cultivated for food, but for the further study of prion protein. In addition, such cattle can also provide bovine products without prion protein, which will be more safe for pharmaceuticals and the like.
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The fleas is a protein that does not contain nucleic acids. The American biologist SB Prusiner, the winner of the 1997 Nobel Prize in Medicine or Physiology, was honored for his outstanding contribution to the study of caries.
The replication of fleas does not use nucleic acid as a template, but instead uses a protein as a template. Like conventional viruses, it has specificity for filtration, infectivity, pathogenicity, and host range, but it does not exhibit immune effects, does not induce production of interferons, and is not interfered by interference. The fleas can cause human and livestock suffering from degenerative diseases of the central nervous system and eventually die. Therefore, the World Health Organization ranks Creutzfeldt-Jakob disease and AIDS at the turn of the century as a chronic disease that threatens human health.
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