Abstracts - Association for Chemoreception Sciences

postnatal. Thus, a very early period of dietary sodium restriction
leads to a late-onset expansion of terminal fields in the rat
NST. To begin identifying the cellular/molecular mechanisms
responsible for this brainstem plasticity, we explored the terminal
field organization in adult mice that either received a sodiumreplete
diet throughout development (controls) or mice fed the
sodium-deficient diet from E3-E12. Moreover, we counted the
number of ganglion cells, representing the three nerves, recorded
whole-nerve neurophysiological taste responses from the CT and
IX, and conducted 48hr. 2-bottle preference tests to concentration
series of NaCl, sucrose, quinine, and citric acid. Terminal field
volumes for each nerve were significantly greater (2X – 4X)
in early sodium-restricted mice, and the overlapping zone that
received all three nerves was over 15X greater in restricted mice.
The differences in terminal fields were accompanied by increased
preferences to NaCl and decreased aversions to citric acid, no
differences in CT and IX whole-nerve taste responses, and no
differences in number of GSP, CT, and IX ganglion cells. We
conclude that the early dietary manipulation had a profound
effect on early NST development and that the terminal field
alterations impacted taste-related behaviors. Acknowledgements:
R01 DC00407
#P225 POSTER SESSION V:
HUMAN TASTE PSYCHOPHYSICS;
OLFACTION RECEPTORS; TASTE DEVELOPMENT
Renewal Kinetics of Taste Bud Cells in Adult Mice
Linda A. Barlow 1,2 , Brendan W. Ross 1,2 , Lauren A. Gross 1,2
1
Dept of Cell & Developmental Biology, University of Colorado School
of Medicine Aurora, CO, USA, 2 Rocky Mountain Taste & Smell Center,
University of Colorado School of Medicine Aurora, CO, USA
Taste bud cells are continuously renewed from a population
of progenitor cells, which express cytokeratin (K)5. These
progenitors reside outside taste buds and give rise to daughter
cells, which exit the cell cycle, enter buds and differentiate into
one of 3 taste cell types (I, II, III). Differentiated taste cells live,
on average, for 10 days, although variance around this mean is
large, suggesting different cell types have different longevities
(Beidler & Smallman ‘65 J Cell Biol 27:263). To explore the idea
of cell type-specific lifespans, we employed inducible genetic
birthdating, comprising a K5rtTA driver and a tetracyclineinducible
reporter allele, which encodes a nucleosomal protein,
Histone2B fused with GFP (tetO-H2BGFP, Tumbar et al.,
2004 Science 303:359). When K5rtTA;tetO-H2BGFP mice eat
doxycycline (dox) chow, K5+ cells produce H2BGFP, which is
incorporated into nucleosomes during S phase. Once mice are
taken off dox, H2BGFP is no longer transcribed, and the cohort
of GFP labeled cells comprises the “pulse”. Here, bigenic mice
were fed dox chow for 12 hours, and tongues harvested between
3 and 28 days. In the posterior circumvallate papilla, an average
of 2 cells/ bud was GFP+ after a 3 day chase. This increased to 4
GFP+ cells/bud by 14 days, and persisted through 21 days postdox.
At 28 days, however, only 2 cells/bud were GFP+. At 14
days, 2 GFP+ cells/bud were PLCß2+ type II cells, whereas on
average, less than 1 GFP+ cell/ bud were Snap25+ type III cells.
The number of type II cells/bud began to decline at 21 days,
while type III cells/bud were fewer by 28 days. We are currently
determining if type II cell lifespan is less than that of type III
cells, and/or if type III cells are generated less frequently from
later divisions of GFP+ K5+ progenitors. Acknowledgements:
R01 DC012383 to LAB P30 DC004657 to D. Restrepo
#P226 POSTER SESSION V:
HUMAN TASTE PSYCHOPHYSICS;
OLFACTION RECEPTORS; TASTE DEVELOPMENT
Bitter taste similarities among heterozygous MZ twins
compared with homozygous MZ twins.
Suzie Alarcon 1 , Ashley Sharples 1 , Paul A. S. Breslin 1,2
1
Rutgers, The State University of New Jersey New Brunswick, NJ,
USA, 2 Monell Chemical Senses Center Philadelphia, PA, USA
Heterozygous alleles of select genes are known to be expressed
differentially in different individuals. And for some genes,
expression in heterozygous monozygotic (MZ) twins is
under strong genetic control (twins resemble each other in
allele expression, but differ from twin pair to twin pair).
The mechanism of action of differential allelic expression is
unclear. In order to investigate the potential genetic influence
of differential expression of taste genes, we examined the bitter
taste phenotypic response of MZ (identical) twin pairs to the
bitter tastant 6n -propyl-2-thiouracil (PROP). Volunteers at the
Twinsburg Twins Days Festival in Cleveland OH tasted PROP
and recorded their perceived bitterness intensity on a generalized
labeled magnitude scale (LMS). DNA samples were collected by
cheek swab from each subject and were genotyped at TAS2R38
amino acid codon positions 49, 262, and 296. MZ twins
were grouped by their TAS2R38 diplotype. We compared the
similarity of Twin A vs Twin B for heterozygous MZ twins to the
similarity of Twin A vs Twin B for homozygous MZ twins. The
heterozygous MZ group displayed greater perceptual variation
between twins than the homozygous MZ group, despite the fact
that the homozygous group was comprised of both AVI/AVI
and PAV/PAV homozygous subgroups. Thus, to the degree that
phenotype reflects expression, it appears that allelic expression
of bitter taste receptors is under significant non-genetic control
within heterozygous MZ twins. Acknowledgements: Funded in
part by NIH DC 02995 to PASB.
POSTER PRESENTATIONS
Abstracts are printed as submitted by the author(s).
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