Clemson scientist’s “News & Views” in Nature explores why humans don’t have tails

Nature's fascinating way of exhibiting patterns is partly what drew Clemson University Assistant Professor Miriam Konkel to the field of genetics.

When she was called upon by the science journal Nature to write a "News & Views" article, she had the opportunity to consider priorly unknown patterns underlying the absence of tails in humans.

In an article written by Konkel and Emily Casanova of Loyola University titled "A mobile DNA sequence could explain tail loss in humans and apes," the scientists discuss research led by Bo Xia, now a principal investigator at the Broad Institute of MIT and Harvard University, about why humans don't have tails. It's a seemingly simple question, but one that scientists have pondered for years.

Most animals with backbones have tails. But about 25 million years ago, the apes - humans' closest primate relatives - became tailless.

Jumping gene

So why don't humans have tails?

Scientists trying to figure out why we lost our tails were looking at certain genes that have been found in other species to be associated with tail loss. The goal was to find common ground across all tailless species. Nothing caught their eye until they spotted a "jumping gene" that is unique to apes.

A "jumping gene," more formally known as a transposable element, is a sequence of DNA that can transfer to a new area of the genome.

This transposable element was a short insertion - roughly 300 base pairs in length - into a gene known as TBXT. While it did not change the protein sequence, the insertion had an influence on gene splicing, particularly when it came to exon 6, a coding portion of the DNA. Gene splicing is where specific genes or gene sequences are inserted into the genome of a different organism.

Scientists then performed cell line analyses and used mouse models that mimicked the DNA architecture of the surrounding area of exon 6. Alternative splicing, resulting in fewer mRNA copies with exon 6 at a certain developmental time point, is likely a contributor to tail loss.

A new study suggests a genetic mutation is the reason that great apes, including humans, don't have tails.

By chance

"One hypothesis is that the losing our tail may have supported our upright walking style," explained Konkel, a faculty member in the Department of Genetics and Biochemistry and at the Center for Human Genetics. "However, I would say that we lost tails by chance."

As for the research, its applications could extend far beyond tails.

Scientists like Konkel have long studied "jumping genes," partly because they are sometimes the causes of disease. The new insertions discovered in the tail study can be a starting point for researchers' search for others.

"Understanding what's going on and seeing how things are happening and hopefully, at some point, understanding the mechanisms and timing how the mobilization of transposable elements happens excited me," said Konkel.

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