Abstracts - Association for Chemoreception Sciences

#P136 POSTER SESSION III: OLFACTORY
PERCEPTION, HUMAN PSYCHOPHYSICS &
ANIMAL BEHAVIOR; PERIPHERAL TASTE
DEVELOPMENT & SIGNALING
Wnt/b-catenin Signaling within Taste Bud Progenitor Cells
Impacts Both Taste bud and Taste Papilla Development
Shoba Thirumangalathu, Linda A. Barlow
Dept of Cell and Developmental Biology, UC Denver Anschutz
Medical Campus and Rocky Mountain Taste and Smell Center
Aurora, CO, USA
Taste receptor cells on the tongue are localized within epithelialmesenchymal
specializations called papillae. Their development
initiates with formation of epithelial placodes that invaginate to
form papillae. In mice, taste receptor cells differentiate within
papillae around birth. Recently we have shown that Shh
expressing cells of taste placodes are exclusively taste bud
progenitors, which do not contribute to the surrounding papillae
(Thirumangalathu et al., 2009). We have also demonstrated that
increased Wnt/b-catenin signaling broadly yet exclusively in
lingual epithelium induces de novo additional taste progenitors
and papillae from what would otherwise be non-gustatory
epithelium (Liu, Thirumangalathu et al., 2007); however, these
findings do not distinguish between a role for Wnt in progenitor
versus papillary development. Here, we test if increased Wnt/
b-catenin within Shh-expressing taste bud progenitors impacts
taste bud development directly, and if taste papillae are also
affected, presumably indirectly by signals downstream of Wnt.
Forced activation of b-catenin within Shh expressing placodes as
these structures first form results in enlarged taste organs due to
increases in both taste progenitor and papillary epithelial cells;
papillary mesenchyme appears unaffected in the mutants. Mitotic
activity within these developing taste organs is also increased in
mutant tongues, and may account for the increase in progenitor
pool and/or papillary size; we are currently testing both
hypotheses. As Wnt/b-catenin signaling is active within the taste
epithelium throughout embryonic development, we are
continuing to use conditional molecular genetic approaches to
temporally and spatially dissect the function(s) of this pathway
in taste patterning, morphogenesis, and differentiation.
Acknowledgements: Supported by DC008373 to LAB
#P137 POSTER SESSION III: OLFACTORY
PERCEPTION, HUMAN PSYCHOPHYSICS &
ANIMAL BEHAVIOR; PERIPHERAL TASTE
DEVELOPMENT & SIGNALING
Adult Mice with Genetic Deletion of SHH in Tongue
Epithelium Have Fungiform Taste Buds and Papillae with
Aberrant Morphology
Elizabeth A. Harvey, Linda A. Barlow
Department of Cell and Developmental Biology and Rocky
Mountain Taste and Smell Center, University of Colorado
Anschutz Medical Campus Aurora, CO, USA
Sonic hedgehog (SHH) is a secreted factor, which regulates
embryonic taste development in rodents (Hall et al., 2003;
Mistretta et al., 2003). SHH is also expressed in a subset of
intragemmal basal cells in adult mice (Miura et al., 2001), but its
function in mature taste buds has not been assessed. Here we used
2 strains of genetically engineered mice to specifically knock out
SHH in basal keratinocytes of the lingual epithelium. These cells
have been shown to give rise to differentiated taste bud cells and
taste papilla epithelial cells in adult mice (Okubo et al., 2009).
Using taste cell type specific immunomarkers, we have found that
fungiform taste buds are distorted in postnatal mice assessed at 3
weeks of age. Overall, the shape of mutant taste buds is narrower
and more elongate than that of control littermates; gustducin-ir
type II cells are also deranged in the mutants. The morphology of
fungiform papillae is frequently distorted, and in many cases is
distinctly filiform, despite the presence of differentiated taste buds
within them. Importantly, these aberrant taste buds and papillae
are innervated, in that antisera against PGP9.5 and neurofilaments
reveal extensive neurites within mutant papillae and taste buds.
Expression of Sox2, a transcription factor associated with stem
cell function and expressed in and around adult taste buds (Suzuki
2008) is also disturbed in mutants compared with control
littermates. Our data suggest that SHH may function to maintain
adult taste buds via its classic role as a mitogen. Thus, we are
currently testing the hypothesis that SHH positively regulates
taste cell renewal from adjacent Sox2-expressing taste progenitors.
Acknowledgements: Funded by DC003947 and DC008373 to
LAB
#P138 POSTER SESSION III: OLFACTORY
PERCEPTION, HUMAN PSYCHOPHYSICS &
ANIMAL BEHAVIOR; PERIPHERAL TASTE
DEVELOPMENT & SIGNALING
Gli Transcriptional Activity in Hedgehog Signaling Regulates
Tongue Epithelial Integrity and Postnatal Papilla and Taste
Bud Support
Hong-Xiang Liu 1 , Marina Grachtchouk 2 , Andrzej A. Dlugosz 2,3 ,
Charlotte M. Mistretta 1
1
Department of Biologic and Materials Sciences, School of
Dentistry Ann Arbor, MI, USA, 2 Department of Dermatology,
Medical School Ann Arbor, MI, USA, 3 Department of Cell and
Developmental Biology, Medical School Ann Arbor, MI, USA
Sonic hedgehog (Shh) is a principal molecule regulating taste
papilla development and differentiation. Gli2 is a transcriptional
activator of Hedgehog signaling and in postnatal rodent tongue
Gli2 is expressed throughout basal cells of the lingual epithelium,
whereas Shh is produced within taste bud cells. To test whether
Gli2 might participate in postnatal maintenance of tongue
epithelium and fungiform papillae and taste buds, we used
transgenic mice with conditional activation of Gli2 under control
of keratin promoters active in basal cells of skin and tongue
epithelium. In tongues from 7 to 12 week mice with doxycyclineregulated
Gli2 activation during a period of several days, the
lingual epithelium was profoundly altered. Filiform papillae had
blunted tips, lacking the typical sharp, keratin spines of postnatal
tongue. Whereas fungiform papillae in control mouse tongue
typically have one taste bud per papilla, in epithelium from Gli2
activated tongues, large numbers of papillae were misshapen and
had no taste bud. Gli2 also is important in early development of
lingual epithelium. In late embryonic mice with reduced Gli2
function, achieved by keratin promoter driven expression of a
dominant-negative form of Gli2, the tongue epithelium was thin
and undifferentiated, with no filiform or fungiform papillae.
Our results strongly suggest that Gli transcriptional activity is an
important regulator of tongue epithelial integrity. Uncontrolled
Hedgehog signaling by Gli2 activation disturbs support and
maintenance of postnatal tongue epithelium and fungiform
papillae and taste buds. Acknowledgements: Supported by
NIH NIDCD Grant DC000456 (CMM) and NIAMS AR045973
(AAD).
P O S T E R S
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