Scientists have given a new meaning to the X chromosome factor that makes the female of the species more robust than their male counterparts.
The new study published in BioEssays, focuses on the role of MicroRNAs encoded on the X-chromosome. MicroRNA are tiny strains of ribonucleic acid which alongside DNA and proteins, make up the three major macromolecules essential for all known life forms.
Women with the double X-chromosome sequence as compared to the male XY sequencing have a built-in immune advantage. The new research attempts to provide possible evidence to why women tend to live longer than men or why females are likely to heal faster from cancer than men.
The research, led by Dr Claude Libert, from Ghent University in Belgium, and team proposed that genetic imprinting or biological mechanisms of the X-chromosome have a stronger impact on an individual's genes which also give females an immunological advantage as compared to males.
We believe this immunological advantage is due to the silencing of X-linked genes by these microRNAs, said Libert. Gene silencing and inactivation skewing are known mechanisms which affect X-linked genes and may influence X-linked microRNAs in the same way.
Statistics show that in humans, as with other mammals, females live longer than males and are more able to fight off shock episodes from sepsis, infection or trauma, said Libert.
We believe this is due to the X chromosome which in humans contains 10 percent of all microRNAs detected so far in the genome. The roles of many remain unknown, but several X chromosome-located strands of microRNA have important functions in immunity and cancer, Libert added.
That study also found that women had twice as many white blood cells as men in the lungs and stomach which act as the body's first line of defence against infection. Also, researchers noted that the white blood cells present in females are more responsive to bacteria and effective against other infectious invaders within biological parameters.
Most importantly, the defence mechanism did not release too many chemicals that stimulate the immune system response. The release of these toxins is what has a direct bearing on illness or a feeling of uneasiness in response to fighting off the infection.
To develop their hypothesis the team produced a detailed map of all described microRNAs that impact immune functions and cancer causing elements in both human and mouse X chromosomes.
Because males have only one X-chromosome, the genetic silencing leaves males at an immunological disadvantage. Also the Y-Chromosome in men contains fewer genes. In cases where these genes are involved in immunity and get silenced maternally, the male is left with no compensating genetic information.
How this unique form of genetic inheritance influences X-chromosone linked microRNAs will be a challenge for researchers for years to come, concluded Libert, not only from an evolutionary point of view, but also for scientists investigating the causes and cures of disease.