The tail loss in human evolution is considered one of the most remarkable anatomical changes in the evolution process. Tail loss has led to people becoming bipedal and the formation of anthropomorph monkeys, but the genetic mechanism that initiated tail loss evolution is not completely known. Xia and his colleagues revealed that the Alu (Arthrobacter luteus) element found in the genome of hominoids may have contributed to tail loss evolution.
More than 60% of the human genome, including 1 million Alu elements, contains approximately 1.8 million short copies of nuclear elements. Detailed investigation of such elemental structures enables the identification of mechanisms that affect human development and diseases. Xia and his colleagues showed that in hominoids the AluY element inserted into TBXT (T-box transcription factor T) intron, was paired with a neighboring ancestral Alu element encoded in the reverse genomic orientation, leading to an alternative splicing event specific to hominoids. To investigate the effects of alternative splicing events, they created mouse models containing both full-length and exon-skipping isoforms of the TBXT intron and mimicking the working principle of hominid orthologs TBXT introns.
In the obtained models, mice that express two TBXT isoforms containing the Alu element, produced the same exon skipping splice isoform as the human TBXT gene structure. Thus, by creating TBXT isoforms that produce a completely absent tail or a shortened tail phenotype, they provided evidence that exon-skipping transcription promotes the tail loss phenotype; furthermore, findings have shown that a non-Alu repeat sequence in introns surrounding an exon can also lead to exon skipping. Therefore, even if the insertion of Alu element greatly affected the tail loss in hominoids, it should not be forgotten that different genetic changes may also happen. Additionally, Xia and his colleagues, found similarities between mice that produce exon-skipping TBXT isoform and the formation of neural tube defects in humans and stated that tail evolution may be linked to neural tube defects.
As a result, Xia and his colleagues have revealed the potential effect of the Alu element in the mechanisms underlying the tail loss of our hominoid ancestors. It is anticipated that future studies will yield more findings about the evolutionary mechanisms of tail loss and how it affects human health.
Translator: Doğa Topçu
Editor: Elif Duymaz
Reference: Xia, B., Zhang, W., Zhao, G. et al. On the genetic basis of tail-loss evolution in humans and apes. Nature 626, 1042-1048 (2024). https://doi.org/10.1038/s41586-024-07095-8
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