Question

1. Describe the somatic nuclear transfer experiment by Gurdon and its result. What did the result imply?
2. The fungus Amanita phalloidesis highly toxic. Describe the molecular basis of its toxicity.
3. Describe the mechanism that is thought to couple the transcription to promoter clearance. How does this mechanism explain abortive initiation?

Answer 1

The first interspecies somatic cell nuclear transfer (iSCNT) experiments were carried out between Rana species in the 1950s. These early studies concluded that egg cytosol cannot maintain replication of foreign nuclei, and that changes induced in nuclei are heritable through mitosis, and species-specific. In 1973, Dr Tong Dizhou reported the first successful iSCNT in fish, creating the first interspecies clone between Asian and European carp. In mammals, more than 50 iSCNT studies have reported using a wide array of oocyte/somatic cell combinations between animals. The most successful experiments (measured as blastocyst development) in iSCNT used donor cells and recipients from closely related species. The main motivation of iSCNT, from the applied aspect of this scientific pursuit, is proposed to be its use as a potential alternative to preserve endangered species and to revive extinct species, as well as to generate embryonic stem cells that are compatible with the donor. At the basic level, iSCNT would allow us to study divergence during evolution. This chapter will focus on the potential utility of this technique for human medicine, its applications in animal reproduction, and the utility of this model for providing new knowledge in areas such as epigenetics, imprinting regulation, and nucleus–cytoplasm interactions.

Mushroom poisoning may be a comparatively rare reason behind acute liver failure (ALF). The present paper analyzes the pathologic process, clinical options, prognostic indicators, and therapeutic ways of ALF secondary to consumption of destroying angel, that represents the foremost common and deadly cause of mushroom poisoning. Liver damage from Amanita phalloides is related to the amanitins, powerful toxins that inhibit RNA polymerase II resulting in a deficient protein synthesis and cell necrosis. After an asymptomatic lag phase, the clinical picture is characterized by gastrointestinal symptoms, followed by the liver and kidney involvement. Amatoxin poisoning could progress into ALF and eventually death if liver transplantation isn't performed. The death rate once destroying angel poisoning ranges from ten to twenty. The management of amatoxin poisoning consists of preliminary medical aid, supportive measures, detoxification therapies, and orthotopic liver transplantation. The clinical effectiveness of any modality of treatment is troublesome to demonstrate since irregular, controlled clinical trials have not been reported. The use of extracorporeal liver assist devices still as auxiliary liver transplantation could represent further therapeutic choices.

The toxicity of agaric is said to 2 distinct teams of toxins: phallotoxins and amatoxins.
The phallotoxins encompass a minimum of seven compounds, all of that have seven similar amide rings. Their toxicity reside in the thiamide bond of the sulphur atom located on the indole ring. These toxins cause injury of the cellular membrane of the enterocytes and square measure so accountable of the initial gi symptoms of nausea, vomiting, and diarrhea exhibited by almost all the patients. Even if phallotoxins are highly toxic to liver cells, they add little to the Amanita phalloides toxicity as they are not adsorbed from the intestine and do not reach the liver [4].
The amatoxins are bycyclic octapeptides, formed by at least nine different compounds [5]. Of the amatoxins, α-amanitin is the main component and along with β-amanitin is likely responsible for the toxic effect [6, 7]. They are not destroyed by cooking and can be still present in the mushroom after long periods of cold storage [8]. The dose is extremely low: as very little as zero.1 mg/kg body weight may be lethal in adults and this amount can be adsorbed even by ingesting a single mushroom.
Amanitins are adsorbed through the intestinal epithelium and bind weakly to serum proteins. The liver is the principal organ affected, as it is the first organ encountered after absorption in the gastrointestinal tract [9]. Once within the liver, amanitins are transported by a nonspecific transport system into hepatocytes, producing an extensive centrolobular necrosis [4, 10]. About hour of absorbed α-amanitin is excreted into the digestive juice and is came back to the liver via the enterohepatic circulation [4, 11–15]. However, other organs, especially the kidney, are susceptible to their toxicity. Amatoxins are not significantly protein bound and are cleared from plasma within 48 h of ingestion [16, 17]. They are filtered by the glomerulus and reabsorbed by the renal tubules, resulting in acute tubular necrosis [18]. Finally, in animal and human post-mortem studies, cellular injury conjointly has been found within the exocrine gland, adrenal glands, and testes [19, 20].
Amanitins directly interact with the enzyme RNA polymerase II in eucaryotic cells and inhibit the transcription, causing a progressive decrease in mRNA, deficient protein synthesis, and cell death. For this reason, metabolically active tissues dependent on high rates of protein synthesis, such as the cells of the gastrointestinal tract, hepatocytes, and the proximal convoluted tubules of kidney, are disproportionately affected.
Among other potential toxic mechanisms, it has been proposed that alpha-amanitin acts in synergy with endogenous cytokines (e.g., tumor necrosis factor) and that this might cause cell damage through the induction of apoptosis