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Birds have developed a unique evolutionary solution to ensure the survival of males \u2013 a powerful microRNA. This tiny gene allows male embryos to survive despite a genetic imbalance between the sexes by balancing the activity of the sex chromosomes. An international research team led by biologists from Heidelberg University and the University of Edinburgh (Scotland) has discovered this previously unknown mechanism, which differs significantly from the system that mammals have developed in the course of evolution to address the same biological challenge.<\/p>\n
Sex chromosomes, which determine whether an individual is male or female, originated from an ordinary pair of chromosomes. In mammals, females carry two X chromosomes, while males have one X and one Y chromosome. In contrast, male birds have two Z chromosomes, and female birds have one Z and one W chromosome. Over time, the Y chromosome in mammals and the W in birds lost most of their genes due to their highly specialized sex-specific roles, meaning one sex retains two copies of most genes while the other has only one. Mammals compensate for this genetic imbalance by boosting the activity of the X chromosome in both sexes and \u201csilencing\u201d one of the two X chromosomes in females.<\/p>\n
Using chickens as an example, the international research team has now demonstrated how birds resolve this issue. The loss of genetic material on the female-specific W chromosome is offset by increased activity of key genes on the Z chromosome. While this is vital for the survival of female birds, it leads to genetic overactivity in males with two Z chromosomes, resulting in growth defects if left unbalanced. The researchers, led by Prof. Dr Henrik Kaessmann (Heidelberg University) and Dr Mike McGrew (University of Edinburgh), suspected that a previously discovered microRNA \u2013 a short regulatory ribonucleic acid \u2013 plays a crucial role in this process.<\/p>\n
\u201cThis microRNA is predominantly active in male birds, which led us to assume that it helps balance the activity of the Z chromosome,\u201d explains Prof. Kaessmann, who conducts research at the Center for Molecular Biology of Heidelberg University (ZMBH). To test their hypothesis, the researchers used gene editing to remove the microRNA and studied the effects during early chicken development. While male embryos could not survive without the microRNA, females developed normally. According to the researchers, the same tiny gene is found in all bird species examined thus far, but not in other animals. \u201cIt is the only known microRNA that is essential for the survival of one sex, but not the other,\u201d says Dr Amir Fallahshahroudi, former postdoc in Prof. Kaessmann\u2019s team at the ZMBH and current group leader at Uppsala University in Sweden.<\/p>\n
According to Dr McGrew, the mechanism of the male-specific microRNA works like a dimmer switch, dialing down the overactive genes on the two male Z chromosomes. \u201cOur findings show that birds have developed a distinct evolutionary solution to offset the genetic imbalance between sex chromosomes and ensure the survival of male animals,\u201d he emphasizes. They also highlight that evolution can arrive at different solutions for the same biological problem \u2013 and that tiny genes can have a dramatic impact on survival. \u201cWe now have to ask whether other animal species also use microRNAs to regulate their sex chromosomes, or whether they rely on different systems entirely,\u201d adds Prof. Kaessmann.<\/p>\n
Reference:\u00a0Fallahshahroudi A, Yousefi Taemeh S, Rodr\u00edguez-Montes L, et al. A male-essential miRNA is key for avian sex chromosome dosage compensation. Nature. 2025. doi:\u00a010.1038\/s41586-025-09256-9<\/a><\/p>\n This article has been republished from the following materials<\/a>. Note: material may have been edited for length and content. For further information, please contact the cited source. Our press release publishing policy can be accessed here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
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