https://phys.org/news/2024-02-gene-code-human-ancestors-lost.html
A genetic change in our ancient ancestors may
partly explain why humans don't have tails
like monkeys, finds a new study led by
researchers at NYU Grossman School of Medicine.
Published online February 28 as the cover story
of the journal Nature, the work compared the
DNA of tail-less apes and humans to that of
tailed monkeys, and found an insertion of DNA
shared by apes and humans, but missing in
monkeys.
When the research team engineered a series of
mice to examine whether the insertion, in a gene
called TBXT, affected their tails, they found a
variety of tail effects, including some mice
born without tails.
...
Remarkably, say the study authors, the new study
found that the differences in tails came not from
TBXT mutations, but instead from the insertion of
a DNA snippet called AluY into the gene's
regulatory code in the ancestors of apes and
humans.
...
https://www.nature.com/articles/s41586-024-07095-8
On the genetic basis of tail-loss evolution in
humans and apes
Abstract
The loss of the tail is among the most notable
anatomical changes to have occurred along the
evolutionary lineage leading to humans and to
the ‘anthropomorphous apes', with a proposed
role in contributing to human bipedalism. Yet,
the genetic mechanism that facilitated tail-loss
evolution in hominoids remains unknown. Here we
present evidence that an individual insertion
of an Alu element in the genome of the hominoid
ancestor may have contributed to tail-loss
evolution. We demonstrate that this Alu
element—inserted into an intron of the TBXT
gene—pairs with a neighbouring ancestral Alu
element encoded in the reverse genomic
orientation and leads to a hominoid-specific
alternative splicing event. To study the
effect of this splicing event, we generated
multiple mouse models that express both
full-length and exon-skipped isoforms of
Tbxt, mimicking the expression pattern of its
hominoid orthologue TBXT. Mice expressing both
Tbxt isoforms exhibit a complete absence of
the tail or a shortened tail depending on the
relative abundance of Tbxt isoforms expressed
at the embryonic tail bud. These results support
the notion that the exon-skipped transcript is
sufficient to induce a tail-loss phenotype.
Moreover, mice expressing the exon-skipped Tbxt
isoform develop neural tube defects, a condition
that affects approximately 1 in 1,000 neonates
in humans10. Thus, tail-loss evolution may have
been associated with an adaptive cost of the
potential for neural tube defects, which
continue to affect human health today.
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