NEW YORK: Human tail loss may trace partly to a DNA insertion that altered the TBXT gene in the common ancestor of humans and apes about 25 million years ago, researchers found.
The peer-reviewed study, led by Bo Xia and published in Nature on February 28, 2024, compared genetic differences between tailless hominoids and tailed primates.
Researchers identified an ape-specific AluY element inserted inside an intron of TBXT, a gene involved in embryonic tail development.
The inserted AluY sequence interacts with a neighbouring Alu element in the opposite orientation. That interaction changes RNA processing and produces a TBXT form in which exon 6 is skipped during alternative splicing.
Researchers then engineered mouse models to reproduce the altered TBXT expression pattern. Depending on the relative amount of the altered and full-length forms, mice developed shortened tails or no tails.
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Some mice expressing the exon-skipped form also developed neural tube defects. The authors said this raises the possibility that the evolutionary change carried a biological cost.
But the experiments do not establish that the same mutation directly causes such defects in humans. The study does not prove that one mutation alone eliminated ancestral tails.
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Nature noted that other genetic changes may also have contributed, while the idea that tail loss aided later upright locomotion remains an evolutionary hypothesis rather than a demonstrated consequence.
