Y chromosomes not junk after all !

They have vital regulatory functions, reveals a study led by CCMB scientist

Hyderabad: The junk DNA in Y chromosome, which many researchers believed did not have any functions, is not a junk anymore!

The Y chromosome has male-determining genes in humans and other mammals. Apart from that, the chromosome was considered as functionally inert because it contains DNA repeat sequences with no genes to code proteins, which earned it many names like junk DNA, Gene Deserts and even Gene-poor chromosome.

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However, recent studies by a team of geneticists led by senior molecular biologist from city-based Centre for Cellular and Molecular Biology (CCMB), Prof Rachel Jesudasan, on Y chromosomes in mouse, have indicated otherwise.

The study, published recently in noted journal BMC Biology, said that there was striking novel regulatory functions of Y chromosome DNA and they have given rise to a class of small RNAs called piRNAs and this is the first report of piRNAs from Y chromosomes, CCMB in a statement said.

“Our earlier studies on human Y chromosome had shown sex and species-specific repeats on the Y chromosome regulate a reproductively important protein-coding RNA transcribed from chromosome number 1. Along with this study, these are the first reports of interaction between the Y chromosome and other chromosomes. Thus, consolidating the two studies, we see a more pervasive regulation of genes associated with reproduction by Y chromosome,” says Prof Jesudasan.

The Y chromosome is a male determining chromosome and it is smaller in comparison to the X, its partner. The Y chromosome was not known to have any function except sex determination. The DNA sequences on Y chromosomes are by and large present in multiple copies (repeats) and were earlier thought to function just as packing material for the few protein coding genes on Y chromosome. Given no obvious function, most part of DNA of Y chromosome was considered junk, CCMB said.

Dr Rachel, who is also advisor (research) at Department of Genetics, Osmania University, said, “As species evolve, these repeats also co-evolve and gradually are no longer able to regulate reproduction of the species. Thus, it appears that these repeats are at the fulcrum of species identity and evolution,” she added.

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