Scientists have made a groundbreaking discovery regarding the genetic link to tail loss in humans and apes. The research, led by geneticist Bo Xia and his colleagues, sheds light on the shared genetic change that may have contributed to the loss of tails in humans and other apes around 25 million years ago. The study involved the use of gene-edited mice to demonstrate the effects of the genetic alterations.
Xia’s interest in the subject was sparked by his own personal experience with a tailbone injury during his PhD at New York University. This led him to investigate a gene called TBXT, known for its role in tail development. The team discovered that humans and other apes carry a DNA insertion in TBXT that is not present in primates with tails, such as monkeys.
In a preprint published on bioRxiv, Xia and his colleagues showed that the ape insertion can result in a shortened form of the protein encoded by TBXT. They hypothesized that this shortening occurs during the splicing of gene transcripts. To test their hypothesis, they created gene-edited mice with one clipped copy of the mouse version of TBXT. These mice exhibited various tail defects, including shortened or missing tails, kinked tails, and extra-long tails.
The initial preprint received significant media attention, but it lacked the main experiment demonstrating that the ape genetic insertion could cause tail loss in mice. However, these experiments were conducted during the submission process to Nature, and the researchers found that the genetic insertion did not lead to high levels of the shortened protein in mice. As a result, these mice had normal tails.
Nevertheless, the researchers continued their investigations and engineered mice with a different insertion in the mouse version of TBXT. This insertion caused the gene to be mis-spliced in the same way as it is in humans, resulting in mice born with short or entirely missing tails. These additional experiments added rigor to the study and reinforced the conclusion that the genetic change contributes to tail loss.
The study also analyzed 140 genes involved in tail development and identified thousands of genetic changes unique to apes that may have played a role in tail loss. However, it is important to note that tail loss is not exclusive to apes, as other primates such as mandrills, macaques, and lorises also lack tails. This suggests that the trait evolved independently multiple times.
The implications of tail loss in apes are still a subject of debate. Some researchers believe that tail loss may have contributed to apes’ ability to walk upright and spend less time in trees. However, fossil evidence suggests that early apes moved on all fours like tree-dwelling monkeys, and bipedality evolved millions of years later.
Overall, this groundbreaking research provides valuable insights into the genetic mechanisms underlying tail loss in humans and apes. It highlights the complexity of the trait and opens up avenues for further exploration into the evolutionary history of tail loss. The study’s rigorous approach and additional experiments have strengthened its findings, making it a significant contribution to the field of genetics and evolutionary biology.
