Recently, a team from the National Centre for Biological Sciences, Bengaluru, has developed a diagnostic system to detect the presence of Merkel cell polyomavirus in Merkel cell carcinoma tumours.


  • The researchers have developed a test using the CRISPR-CAS12 technology that can identify the virus in the tumour and give off fluorescence to indicate the presence of the virus.
  • It is an important development, both from the point of view of diagnostics and giving a prognosis for the condition.
  • Earlier studies showed that the Merkel cell carcinoma caused by the virus is less aggressive and progresses slower than that caused by excessive exposure to ultraviolet light.
  • Also shows that, in about 60-80% of Merkel cell carcinoma patients, the tumours were found to test positive for the virus.

Merkel cells 

  • They are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of vertebrates. 
  • They are abundant in highly sensitive skin like that of the fingertips in humans, and make synaptic contacts with somatosensory afferent nerve fibers.

Merkel cell carcinoma

  • A virus that is part of the normal skin flora – the Merkel cell polyomavirus – can get integrated in the human genome and undergo a mutation which causes it to promote cancer. 
  • Merkel cell carcinoma is a rare and aggressive type of skin cancer.It is associated with old age, excessive exposure to ultraviolet light and a weak immune system.

System to detect:

  • The Scientists adapted a system named DETECTR (DNA endonuclease-targeted CRISPR trans reporter) to help them in this endeavor.
  • The system consists of three components: identifier, switch and reporter.
    • The identifier is a “guide RNA” which can recognize and bind to a section of the Merkel cell polyomavirus.
    • The switch is a DNA-cutting enzyme known as Cas-12a which gets attached to the guide RNA after it finds its target DNA.
    • Further, the reporter consists of a single stranded DNA tagged with a fluorescent molecule.

Also, the strength of the glow depends on the number of activated Cas-12a molecules, which in turn depends on the number of virus DNA copies recognised in the tumour DNA. 

CRISPR- Cas System:

  • CRISPR(clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms (A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelles) such as bacteria and archaea. 
  • These sequences are derived from DNA fragments of bacteriophages that had previously infected the prokaryote.  A bacteriophage is a virus that infects and replicates within bacteria and archaea.  
  • Cas12 ("CRISPR-associated protein 12") is a compact and efficient enzyme that uses CRISPR sequences as a guide to recognize and cleave specific strands of DNA that are complementary to the CRISPR sequence. 
  • Cas12 enzymes together with CRISPR sequences form the basis of a technology known as CRISPR-Cas12 that can be used to edit genes within organisms
  • This editing process has a wide variety of applications including basic biological research, development of biotechnology products, and treatment of diseases.
  • The CRISPR-Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages that provides a form of acquired immunity. 
  • RNA harboring the spacer sequence helps Cas (CRISPR-associated proteins) recognize and cut foreign pathogenic DNA.



National Centre for Biological Sciences:

  • National Centre for Biological Sciences in Bangalore, Karnataka, is a research centre specialising in biological research. 
  • It is a part of the Tata Institute of Fundamental Research under the Department of Atomic Energy of the Government of India.