A New Era in Molecular Biology: CRISPR/Cas9 and Targeted Genome Editing
The development of efficient and reliable ways to make precise, targeted changes to the genome of living cells is a long-standing goal for biomedical researchers. Recently, a new tool based on a bacterial CRISPR-associated protein-9 nuclease (Cas9) from Streptococcus pyogenes has generated considerable excitement. This follows several attempts over the years to manipulate gene function, including homologous recombination and RNA interference (RNAi). RNAi became a laboratory staple enabling inexpensive and high-throughput interrogation of gene function but it is hampered by providing only temporary inhibition of gene function and unpredictable off-target effects. Other recent approaches to targeted genome modification – zinc-finger nucleases (ZFNs), and transcription-activator like effector nucleases (TALENs) enable researchers to generate permanent mutations by introducing doublestranded breaks to activate repair pathways. These approaches are costly and time-consuming to engineer, limiting their widespread use, particularly for large scale, high-throughput studies
The functions of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) and CRISPR-associated (Cas) genes are essential in adaptive immunity in select bacteria and archaea, enabling the organisms to respond to and eliminate invading genetic material. These repeats were initially discovered in the 1980s in E. coli, but their function wasn’t confirmed until 2007 by Barrangou and colleagues, who demonstrated that S. thermophilus can acquire resistance against a bacteriophage by integrating a genome fragment of an infectious virus into its CRISPR locus. Three types of CRISPR mechanisms have been identified, of which type II is the most studied. In this case, invading DNA from viruses or plasmids is cut into small fragments and incorporated into a CRISPR locus amidst a series of short repeats (around 20 bps). The loci are transcribed, and transcripts are then processed to generate small RNAs (crRNA – CRISPR RNA), which are used to guide effector endonucleases that target invading DNA based on sequence complementarity.
Drinking water may contribute significantly to oral intake in regions where there are high arsenic concentrations in well-water or river-water or mine drainage areas. The concentration in ground water depends on the arsenic content of the bed-rock. Arsenic contamination is spreading fast and entering the food chain through farm products in the region. As people take contaminated water along with contaminated food, the chances of damage become greater. The clinical picture of chronic poisoning with arsenic varies widely. It is usually dominated by changes in the skin and mucous membranes and by neurological, vascular and haematogical lesions. Arsenic and its inorganic compounds have been known to be neurotoxic. The skin is a common critical organ in people exposed to inorganic arsenical compounds. Eczematoid symptoms develop with varying degrees of severity. Hyperkerotosis, warts and melanosis of the skin are the most commonly observed lesions in chronic exposure. Arsenic contamination in water, vegetables, rice and other foods is spreading as reported in the Indian Parliament. An editorial report was published in the Hindustan Times dated 27th December, 2017.
Arsenic Speciation Analysis using High Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry
Speciation is the analytical activity of identifying and/or measuring in a sample the quantity of one or more individual chemical species. Arsenic has different toxicological properties dependent upon both its oxidation state for inorganic compounds as well as the different toxicity levels exhibited for organic arsenic compounds. HPLC is the technique of choice in modern speciation analyses due to their resolution and the ease with which they are coupled to ICP-MS, allowing for on-line separation and detection.