Abstracts - Association for Chemoreception Sciences

fide adult stem cell marker. Because canonical Wnt signaling
is activated at sites of mature taste buds, we asked if Lgr5
expression identifies analogous stem/progenitor cells in the
taste system. Knock-in mice with the Lgr5-EGFP-ires-CreERT2
transgene replacing one Lgr5 allele were bred to the tamoxifen
(TM)-inducible mTmG reporter strain. The progeny express
soluble GFP (sGFP) under endogenous Lgr5 regulation and,
following TM treatment, membrane-bound tdTomato (mT)
is replaced by GFP (mG). sGFP is present in all papillae of
7 day-old non-induced mice, but by 12 weeks of age is seen
only in circumvallate (CV) and foliate papillae. Expression in
the CV is highest where salivary ducts intersect papilla walls,
decreases dorsally in the papilla, and is absent from taste buds.
In salivary ducts, sGFP is limited to the outer layer of the bilayered
epithelium. One day after a single TM injection, induced
mG marks small round cells at the papilla base and, rarely, in
the lateral wall of the CV papilla. By 2-3 days post-injection,
labeled cells lie both within taste buds and in the surrounding
stratified epithelium. Although mG-positive cell numbers decline
by 7 days, induced labeling is still apparent in taste buds after
2 months. Importantly, we found no evidence for TM-induced
labeling of cells outside of taste papilla boundaries. These
data indicate that Lgr5 expression marks long-term taste cell
progenitors, that Lgr5 may be a regulator of taste epithelium
homeostasis, and that a duct-basal trench-papilla axis of
epithelial renewal may exist. Acknowledgements: Supported by
NSF REU #1062645
#P220 POSTER SESSION V:
HUMAN TASTE PSYCHOPHYSICS;
OLFACTION RECEPTORS; TASTE DEVELOPMENT
Temporal and spatial differences in BDNF and NT4 expression
determine their unique roles in gustatory development
Tao Huang 1 , Robin Krimm 1
1
University of Louisville/Department of Anatomical Sciences and
Neurobiology Louisville, KY, USA, 2 University of Louisville/
Department of Anatomical Sciences and Neurobiology Louisville,
KY, USA
A limited number of growth factors are capable of regulating
numerous developmental processes, but how they accomplish
this is unclear. In the gustatory system, brain-derived
neurotrophic factor (BDNF) and neurotrophin-4 (NT4) have
different developmental roles but exert their effects through
the same receptors (TrkB and p75). Using genome wide
expression analysis, we determined that BDNF and NT4
regulate the expression of different sets of genes downstream
of receptor signaling in gustatory ganglion. These differences
in gene expression likely determine their different roles during
development. BDNF and NT4 could function differently
because of temporal or spatial differences of expression or the
activation of different signaling pathways. Using mice in which
the coding region for BDNF is replaced with NT4 (Bdnf Nt4/
Nt4
), we show that NT4 can mediate most of the unique roles
of BDNF. Specifically, caspase-3-mediated cell death, which
is increased in Bdnf -/- mice (p