While sex chromosomes have been playing vital roles in determining one's sex and distinguishing the sex differences across females and males, they also appear to have vital functions that go beyond these purposes.
Role of Chromosomes in Gene Regulation
A new study entitled "The human Y and inactive X chromosomes similarly modulate autosomal gene expression" uncovers the shared role of sex chromosomes as gene regulators that are influential. The study reveals that genes that are expressed from both the X and Y chromosomes affect cells all over the body, not just the reproductive system's cells. It does so by dialing up or down the gene expression of thousands of genes that can be found in different chromosomes.
On top of this, the researchers also discovered that the gene pair ZFX and ZFY that accounts for roughly half of the regulatory behavior has essentially the same regulatory effects with one another. With this, it is suggested that both inherited the function as influential gene regulators from a common ancestor and have maintained it independently, even when their own chromosomes diverged. This is due to how the regulatory role is crucial for the development and growth of humans.
The genes that ZFY and ZFX regulate play a role in different kinds of biological processes. This reveals that sex chromosomes widely contribute to functions that go beyond sex-related characteristics.
To measure how the X and Y chromosomes impacted global gene expression, the researchers graphed how the expression of the genes altered in the cells depending on the present number of X or Y chromosomes. They made use of tissue samples from individuals with a natural number variation in chromosomes. More specifically, this involved individuals born with one to four X chromosomes or zero to four Y chromosomes.
Adrianna San Roman, a postdoc at the lab of biology professor David Page, explains that they were able to mathematically model how the quantity of chromosomes affects gene expressions in a manner that has never been previously done. With this approach, they were able to learn more about the great impact both the X and Y genes have on the genome.
As part of the project, the researchers examined two different cell types, namely, skin-cell derived fibroblasts and lymphoblastoid cells. They then measured the changes in gene expressions with added X or Y chromosomes.
The researchers discovered that thousands of genes had different levels of expression as a response to changes in the count of X or Y chromosomes. The effects were observed to linearly scale, which means that each added chromosome altered gene expression by the same definitive amount. The exact affected genes and the extent of the effects varied across cell types, which suggests that each body cell type may uniquely respond to gene regulation by both chromosomes.
Several things about male and female cells remain unexplained. The gene regulators on the chromosomes that could be altering expression across the body appear to be candidates that could affect such differences. The researchers specifically narrowed down to the ZFX and ZFY gene pair being responsible for roughly half of the chromosome's effect on gene expression, with the pair exhibiting functional equivalence, though ZFX may have a modestly stronger impact compared to ZFY at times.
However, the authors also suspect that certain X and Y genes must be altering gene expression in various ways or to different extents.
ALSO READ: What Chromosomes Do Male Have? Y Chromosome Gender Explained
Mysterious Sex Differences
The work of the researchers has led them to think that current knowledge regarding chromosomes is quite imprecise. Though chromosomes are defined as either X or Why, each human has an "active X" chromosome that is universally present and does not affect sex.
What is different across both males and females are the active X pairs. Males usually have a Y chromosome, while females have an inactive X chromosome. Among individuals with atypical sex chromosome compositions, every added X chromosome will be inactive.
In the study, the researchers were looking into the impact of adding more inactive X chromosomes.
The researchers found that the inactive X as well as the Y are, more precisely, the sex chromosomes that were found to affect gene expression. David Page, who is a biology professor from the Massachusetts Institute of Technology as well as a Howard Hughes Medical Investigator, explains that as more is uncovered about chromosomes and the gene pair, it may completely alter what is known about human X and Y chromosome genetics.
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