How scientists ‘dramatically’ shortened the legs of this spider-like species

As the name would suggest, arachnids ‘daddy long legs’ derive their name from the unusually long limbs that give them their spider-like look. But now, using the
gene-altering mechanism of  RNA
interference (RNAi), scientists in the United States were able to “dramatically”
shorten the leg segments. The successful experiment was carried out on the house-dwelling
Phalangium opilio species of daddy long legs. The daddy long legs are considered
to be closely related to scorpions despite their striking resemblance to spiders.

A team of scientists led by Dr Guilherme Gainett from the
University of Wisconsin-Madison sequenced the daddy long legs’ genome by isolating
key genes and blocking their activation in embryos.  

The team assessed the function of the Hox genes Deformed
(Dfd) and Sex combs reduced (Scr), and a homologue of Epidermal growth factor
receptor (Egfr) to investigate the developmental genetic basis for the  elongate legs.

“Knockdown of Dfd incurred homeotic transformation of two
pairs of legs into pedipalps, with dramatic shortening of leg segments in the
longest leg pair, whereas homeosis in L3 is only achieved upon double Dfd + Scr
knockdown. Knockdown of Egfr incurred shortened appendages and the loss of
tarsomeres,” they said in a paper published in The Royal Society journal.

The scientists hope that the genome of opilio will “facilitate the development of more sophisticated tools for functional genetics,
toward refining the understanding of how daddy long-legs make their long legs.”

“The genome of the daddy long legs holds great
potential to clarify the complex history of arachnid genome evolution and body
plan, as well as to reveal how daddy long legs make their unique long legs,”
Dr Gainett said.

“Looking forward, we are interested in understanding
how genes give rise to novel features of arachnids, such as spider fangs and
scorpion pinchers, and also leveraging the genome to develop the first
transgenic harvestmen (daddy long legs).”