Explained : How Epigenetics alters Inherited Genetics ? | UPSC

Explained : How Epigenetics alters Inherited Genetics ? | UPSC

      HEADLINES:

How epigenetics alters inherited genetics’ message

      WHY IN NEWS:

An exciting paper has appeared in Nature, authored by Lu et al titled “Reprogramming to recover youthful epigenetic information and restore vision”.

SYLLABUS COVERED: GS 3: Science : Biology : Cell Structure

      LEARNING: 

For PRELIMS it is important to understand the science behind ageing . Go through the concept of RCG’s . It is very important !

For MAINS describe the role of protein in cell structure . Let us dive in !

      ISSUE: 

Ageing leads to a progressive decline of cells in the retina. Epigenetics further modifies this

WHAT IS EPIGENETICS?

Epigenetics is the biochemical changes dictating expressivity of a gene in a cell.

  • Epigenetics is the study of heritable changes in gene expression (active versus inactive genes) that do not involve changes to the underlying DNA sequence.
  • It is a change in phenotype without a change in genotype — which in turn affects how cells read the genes.

Epigenetic change is a regular and natural occurrence but can also be influenced by several factors including age, the environment/lifestyle, and disease state.

  • Epigenetic modifications can manifest as commonly as the manner in which cells terminally differentiate to end up as skin cells, liver cells, brain cells, etc.
  • Or, epigenetic change can have more damaging effects that can result in diseases like cancer.

Explained : How Epigenetics alters Inherited Genetics ? | UPSC

Representation of the chromatin structure, including histones and DNA, which become available to epigenetic marks | Sources : epigenetic.com

RECENT FINDINGS

The cause of ageing is the accumulation of “epigenetic noise” that disrupts gene expression patterns lending to changes in inherent DNA function. 

  • If one can put them back by restoring them using specific genes (gene therapy) sight can be restored.

HUMAN EYE

  • The human (and mammalian) eye is a remarkable organ in the course of evolution which has allowed us to “see” the external world clearly and in colour.

The front part of the human eye (cornea, lens and the vitreous humour gel) is transparent, colourless and helps focus the incoming light into the retina, helping us see colour.

  • It is the retina that sends the message to the brain. Its main component, called the retinal ganglion cells (RGC).
  • RCG are the ones that help in this process of sending the message in the form of electrical signals, called neurons or nerve cells.
  • Thus, RGCs are the ones that convert optics into electronics.

CELLULAR REGULATORS

  • The functioning of cells and tissues in our body are controlled by thousands of proteins that regulate various cellular functions.

These proteins are in turn encoded by the respective genes which are a part of our genome or the cellular DNA.
 

  • Any minor or major changes to our inherited DNA (addition or mutation) can result in altered protein production.
  • This in turn leads to defective cellular functions. This forms the basis for many heritable genetic disorders affecting the mankind.
  • There are other biochemical changes too that influence and dictate if a gene should be active or inactive in a given cell type.

EXAMPLE
The gene that encodes for the insulin protein is present in exact form, in every cell of the body.

  • However, it is allowed to express only in the insulin secreting beta cells of the pancreas and is kept inactive in the rest of the cells of the body.
  • This phenomenon is tightly regulated by a combination of regulatory proteins that changes the expressivity of the gene.

HISTONE PROTEIN

  • The histone proteins that bind the DNA and help to compactly wrap it inside the chromosomes .
  • Histone proteins can undergo chemical modifications such as methylations and acetylations on different lysine amino acids within the protein.
  • These modifications both on the DNA and its associated proteins alter the chromosomal conformations and regulate gene expression.

These changes can either unwind the DNA and allow gene expression or can compact the DNA and render the genes in the region inactive or silent. 

  • Such biochemical changes that dictate the expressivity of a gene in a particular cell are collectively termed “epigenetics.”
  • Epigenetic changes are reversible and are mediated by regulatory proteins.

REGULATORY PROTEINS

  • DNA methyl transferases (DNMTs)
  • Istone acetyl transferases (HATs)
  • Histone deacetylases (HDACs) and so on.

These regulatory proteins can add or remove such modifications and can result in turning ON/OFF a specific gene in a tissue or organ specific manner.

  • This normal epigenetic control on our genes can get altered during normal ageing, stress and disease conditions.

TUMOUR SUPPRESSORS

  • In many cancers, there are a certain set of genes called tumour suppressors that regulate cell division.

These tumour suppressors get silenced either due to mutations or due to epigenetic alterations and result in uncontrolled proliferation of cells and tumour development.

  • Similarly many messages or youthful genes are also turned off by epigenetic changes during our normal ageing process.

      IASbhai WINDUP: 

  • RGCs help us the ability to see clearly and in colour.

Ageing leads to a slow and progressive decline in this ability of RGCs to maintain and regulate the stability and constancy to function properly. 

  • In addition, external factors such as family or hereditary history, diabetes (both type 1 and 2)play vital role in  inducing “epigenetic”.
  • New and ongoing research is continuously uncovering the role of epigenetics in a variety of human disorders and fatal diseases.
     SOURCES:  THE HINDU | Explained : How Epigenetics alters Inherited Genetics ? | UPSC

 

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