News release

From: Springer Nature

Insights into the genetic basis of tail loss during the evolution of humans and apes (hominoids) are reported in a Nature paper. The insertion of a hominoid-specific genetic element into a gene associated with tail development led to the production of a new isoform protein, which disrupts tail elongation when modelled in mouse embryonic development, suggesting that this element contributed to the shortening or loss of the tail in humans and apes. Additionally, the authors propose that tail-loss evolution may have led to an increased likelihood of neural tube defects in humans and apes.

Unlike other primate species, hominoids — including humans, chimpanzees, gorillas, orangutans and gibbons — do not have tails. This tail loss is among the most noticeable of bodily changes to have occurred along the evolutionary lineage that led to humans and other apes. However, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown.

Bo Xia, Jef Boeke, Itai Yanai and colleagues scanned 140 genes linked to vertebrate tail development for changes that might have driven tail loss in hominoids. They suggest that an individual insertion of an Alu element into the TBXT gene (associated with tail development in tailed animals) of the hominoid ancestor may have contributed to tail loss. To test this theory, they generated mouse models that expressed different forms of the Tbxt gene, both full-length and the new exon-skipped isoform (which in hominoids is induced by the Alu element insertion). The authors found that mice expressing both Tbxt forms did not have a tail or had a shortened tail, depending on the relative amount expressed at the embryonic tail bud. This provides evidence that the exon-skipped Tbxt isoform contributes to tail loss, the authors suggest. Additionally, they found that mice expressing the exon-skipped Tbxt isoform may develop neural tube defects, a condition that affects about 1 in every 1,000 newborn humans.

The authors suggest that tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects — such as spina bifida, when the spine does not develop properly in the womb — that continue to affect human health today.