Rusty was a 26
year old llama. He lived across the parking lot from our lab in the
Stevenson Center. He was not really
ours at all. But we liked him and he seemed to like us. His hobbies
were grazing and expectoration. Unfortunately, Rusty went to live
with the great llama master in the sky in October 2016, but he will
forever live as the mascot for our lab.
So why the heck would a lab that studies sharks and frogs want a
llama as a mascot? Especially one with Rusty's manic temperament?
While his terrific posture and handsome eyes helped, the real
answer lies in his humoral immune system!
Antibodies are made by B cells and they are
comprised of heavy and light chains... usually! In a beautiful example
of homoplasy, both cartilaginous fish and camelids have evolved
antibodies that use pairs of heavy chains, but with no light
chains. These two very divergent groups of vertebrates both
convergently arrived at this antibody innovation in their
evolution. The stability and single-variable domain paratopes of
these antibodies are being exploited for diverse applications. The
sharks appear to go a step further and use a relative of the single
chain variable on some T cells, we call this
NARTCR. (No, even this wonderful molecule does not protect
sharks from cancer.) Incredibly, early mammalian lineages
(marsupials and monotremes) use a similar T cell
receptor usually with two variable domains as well, yet from a
different locus. More gorgeous convergent evolution demonstrating
the diverse paths that have arrived at similar contrivances in
lymphocyte receptor repertoires.
Next time you see a llama at the zoo or in the wild, bow down
and pay homage. They have a repertoire of antibody structures that
most of us bony Teleostomi can only dream of! Call out to them and
maybe they'll come running... but if their ears drop back you might
want to take cover.