1. Allorecognition within the Ascidian Botryllus schlosseri
Rebecca Williams and Marie Nydam, Biology Program, Centre College
Introduction
Methods
Results & Discussion
1 De Tomaso, A.W., Nyholm, S.V., Palmeri, K.J., Ishizuka,
W.B., Mitchel, L.K., and Weissman, I.L. 2005. Isolation and
characterization of a protochordate histocompatibility locus.
Nature 438: 454-459.
2 Nydam, M.L., Taylor, A.A., and De Tomaso, A.W. 2012.
Evidence for selection on a chordate histocompatibility
locus. Evolution: International Journal Of Organic Evolution
67: 487-500.
3
http://www.redorbit.com/education/reference_library/scienc
e_1/tunicates/1112518205/star-ascidian-botryllus-
schlosseri/
Several organisms practice
allorecognition, or the ability to
distinguish self from non-self1.
One such organism is the
ascidian Botryllus schlosseri2
(Figure 1). A single locus for B.
schlosseri called FuHC
(Fusion/Histocompatibility)
determines whether interacting
colonies will fuse or not, and this
locus exhibits high
polymorphism1. We are studying
which type of selection maintains
the polymorphism at FuHC.
RNA and cDNA were obtained from
whole B. schlosseri organisms
collected from the English Channel.
Two genes within the FuHC locus that
mediate allorecognition, FuHC Tm and
FuHC sec, were amplified and
prepared for ligation into a pGEM-T
Easy vector. The products were cloned
using Escherichia coli. Clones were
picked using blue/white selection, and
these were lysed to use as a template
for PCR of full length alleles to be
sequenced. The entire sequenced
gene will be edited and used for
population genetic testing to determine
the type of natural selection acting on
the genes.
Literature Cited
Figure 2: Fusion (top arrow) of B. schlosseri1
Figure 1: Individuals of B. schlosseri3
As of December of 2013, the
sequencing of FuHC Tm has been
completed. In the future, FuHC sec
will be sequenced and analysis will
begin on both FuHC Tm and FuHC
sec. Evidence for selection on
FuHC, rather than neutral evolution,
is expected to be seen from the
results of population genetic testing.
We expect this testing to reveal
which type of selection is acting
upon FuHC, and based on previous
research, we hypothesize this to be
balancing selection. In this type of
selection, no one allele is most fit
and polymorphism is maintained2.