Research & Innovation 2015-16 - Page 121

Bats are the only mammals capable of powered flight –
an ability that evolved about 50 million years ago. The
structure of the bat wing, as noted by Charles Darwin
in 1859 in On the Origin of Species, is widely used
among biologists as an example of both evolutionary
novelty (the appearance of a new trait) and vertebrate
homology (shared ancestry between two seemingly
different structures) – in this case, the wing of the bat
and the forelimb of other mammals.
Mining the origin of flight in mammals
The path of bat evolution is unclear, says Professor
Nicola Illing, co-senior investigator based in the
Department of Molecular and Cell Biology: “The
fossil record does not show the transition from treeclimbing mammals with short, free digits to ones that
have elongated fingers supporting a wing. We have
had the privilege of being able to use the tools of
modern genetics to decipher how genes are turned
on and off during bat embryonic development, to
transform a mammalian forelimb into a wing.
“While some attempts have been made to identify
the molecular events that led to the evolution of the
bat wing, these have primarily been done on a ‘gene
by gene’ basis,” said co-senior investigator Nadav
Ahituv, a UCSF professor of bioengineering and
therapeutic sciences and faculty member of the
UCSF Institute for Human Genetics. 
“This work lays out a genome-wide blueprint
for the causes that led to the development of
the bat wing, a key evolutionary innovation that
contributed to bats becoming the second most
diverse order of mammals.”
Over 7 000 genes identified
The researchers identified over 7 000 genes that are
expressed differently in forelimbs compared to hind
limbs, at three key stages of bat-wing development.
They found that many signalling pathways are
activated differentially as well, including pathways
important in limb formation, digit growth, long-bone
development and cell death.
It took bats millions of years to evolve wings.
This research shows that they did this through
thousands of genetic alterations, involving both
genes used by all animals during limb development,
and genes whose usage in limb development may
be unique to bats.
“This gives us our first detailed picture of the
genomics behind bat-wing development,” said
Ahituv. “Importantly, this work identified not just
which genes are expressed at what stage of growth,
but the genetic switches in the genome that are
responsible for turning those genes on and off.”
“It is gratifying seeing this work come to fruition after
a decade of research,” says Illing.
Ahituv agrees: “This work will increase our
understanding of how alterations in limb
development could lead to limb malformations
in humans. Potentially, it could eventually help
contribute to the development of tools and
techniques to prevent such malformations.” 
Read more about this research in The Washington Post,
or access the original research papers in the Nature
Genetics and PLoS Genetics journals.
Shortened version of UCT/UCSF media release.
Images supplied by Nicola Illing (UCT)
and Nadav Ahituv (UCSF)​.
Life below water and life on land 116

Read more Nature GeneticsNature GeneticsPLoS GeneticsUCT/UCSF media release

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