Welcome to the wonderfully strange world of piRNAs (Domingues, 2018)

What are piRNAs, and what about RNA(s) in general?

• To understand what piRNAs are and what their function is, we should first understand how a single cell, the fundamental unit of life, works.
  For that reason I suggest you to read this post first.
  

Have you read it? No? It’s ok I’ll just remind you that:

Life has only one purpose, preserve life; therefore by design, DNA is the molecule that has enough information to “create” life.

The genetic information in DNA has to be “compiled” from a sequence of nucleotides to a molecule that will perform a particular set of tasks to preserve the integrity of the cell. The flow of information from DNA to protein is performed in two steps: transcription and translation. Through transcription, RNA is synthesized from DNA, and through translation proteins (poly-peptides) are made from RNA (mRNA).

 What is the RNA?

• The ribonucleic acid is the molecule that gets the job* done (combined or not with proteins). 

*A lot of different jobs actually and probably in the past had played as well the role of DNA (RNA world hypothesis).

RNA

RNAs have various functions, and that is why scientists have separated them into different categories (list with several types of RNAs).  Cellular RNAs derive from DNA templates through transcription and then follow different kinds of maturation processes with regard to their type. Messenger RNA (mRNA) is the type of RNA that is translated into protein, also known as coding RNA. Every other type of RNA that is not translated into protein is considered as a non-coding RNA.

If we follow the different functions of RNA then we can group them in coding and non-coding RNAs. With coding RNA we refer to mRNA.
mRNA  acts as template in order to be translated by the protein-synthesizing machinery of cell to protein.

rRNA is the main component of the protein-synthesizing machinery, called ribosome, which is constituted from two subunits, one large and one small in which various lengths of rRNA cofunctions with proteins.

tRNA (transferRNA) is the non-coding RNA which carries amino-acids to the protein-synthesizing machinery. It can pair with the mRNA sequence while it is translated, and add an amino acid to the polypeptide chain.

Except of these categories of RNA a lot more exist with various functions, such as gene regulation, epigenetic regulation, splicing, RNA maturation etc.
To name just a few of these categories :
miRNA, snRNA, snoRNA and lncRNA.

The sub-group of non-coding RNAs  that I’m interested in my project is the Piwi-interacting RNAs (piRNAs)
and you would ask:

~ Hey, wait! What does the Piwi abbreviation means?

• It stands for P-element Induced Wimpy testis.

~ Strange name for a subgroup of RNA?

Well, the name was given to the gene that had been discovered in the study of Lin et. al¹, regarding a regulatory protein that was named PIWI with primary function germ and stem cell differentiation in Drosophila and other organisms. piRNAs were discovered later^2–4 and were named after the protein(s) that interact with them to form a complex of RNA-protein (known as ribonucleoprotein).

Have a wonderful week!
Konstantinos

References

Domingues, A. M. d. J., 2018. Biostars. [Online]
Available at: https://www.biostars.org/p/347827/#348543

1. Lin, H. & Spradling, A. A novel group of pumilio mutations affects the asymmetric division of germline stem cells in the Drosophila ovary. Development (1997).
2. Grivna, S. T., Beyret, E., Wang, Z. & Lin, H. A novel class of small RNAs in mouse spermatogenic cells. Genes Dev. 20, 1709–14 (2006).
3. Aravin, A. et al. A novel class of small RNAs bind to MILI protein in mouse testes. Nature (2006). doi:10.1038/nature04916
4. Girard, A., Sachidanandam, R., Hannon, G. J. & Carmell, M. A. A germline-specific class of small RNAs binds mammalian Piwi proteins. Nature (2006). doi:10.1038/nature04917