Abstracts - Society for Developmental Biology

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overexpression is proposed to result in the engulfment and internalization of the lumenal matrix along with the apical
membrane domain, resulting in a profound loss of cell polarity.
Program/Abstract # 104
The role of tbc-1 in Drosophila salivary gland development
Johnson, Dorothy M.; Andrew, Deborah Johns Hopkins School of Medicine, Baltimore, United States
Rabs are small GTPases involved in vesicle targeting, tethering, and fusion. Rabs’ GTPase activity is accelerated by Rab-
GAPs (GTPase activating proteins). Recently, a highly conserved Drosophila Rab-GAP, known as tbc-1,was discovered to
be expressed in the embryonic salivary gland under control of the FoxA transcription factor Fork head (Fkh). An analysis
of deficiencies and RNAi of tbc-1 revealed irregular apical membranes in embryos in which tbc-1 was knocked down in
the salivary gland, suggesting that tbc-1has a role in salivary gland development. Based on these preliminary findings, tbc-
1 knockout lines were generated by homologous recombination and verified by PCR analysis. Future plans include a full
characterization of the null salivary gland phenotypes as well as studies to learn which Rab and which membrane fusion
events are normally modulated by this GTPase.
Program/Abstract # 105
Wnt/ß-catenin has progressive, spatially-restricted roles in taste epithelium development.
Barlow, Linda; Thirumangalathu, Shoba, University of Colorado AMC, Aurora, United States
Taste buds, located in epithelial-mesenchymal papillae on the tongue, are neuroepithelial cells associated with epithelial
appendages early in development. Postnatally, taste bud cells acquire neuronal properties, while papillae maintain a nontaste
epithelium. In mice, Wnt governs specification and differentiation of buds and papillae, but its precise role in taste vs
non-taste development have not been defined. Because taste precursors express Shh early on and can be distinguished from
cells destined to form papillae, we can now test the cell type-specific function(s) of Wnt at precise stages of development.
In this study, to distinguish taste precursor from papilla specific functions of Wnt, we activated ß-catenin exclusively
within Shh expressing taste precursors during (E12.5) or after (E15.5) their specification. We demonstrate that β-catenin
function within Shh expressing taste domains is stage specific with early activation resulting in expanded taste precursors
with precocious differentiation of Type I taste cells, and these enlarged buds are situated in enlarged papillae. Importantly,
Wnt activity is only reported within taste precursors, indicating that the effect of ß-catenin on papillae is indirect. Late ß-
catenin activation causes accelerated differentiation of Type I cells, without taste bud or papilla expansion. Thus, Wnt
functions autonomously within taste precursors to define the size of this population early, and regulates differentiation of
Type I taste cells later. The impact of ß-catenin on papillae is indirect, but likewise temporally specific. In sum, our data
support a model where Wnt/ß-catenin has progressive, spatially-restricted roles in taste epithelium development. Supported
by DC008373 to LB
Program/Abstract # 106
Shh is required for development of the circumvallate taste papilla complex
Thirumangalathu, Shoba, Univ of Colorado Health Sci Ctr, United States; Barlow, Linda (UC Denver Anschutz Medical
Campus, Aurora, United States)
The tongue is composed of anterior taste field housing rows of fungiform taste papillae each with a single taste bud, and
posteriorly with bilateral foliate and a single midline circumvallate papilla (CVP). The CVP has deep epithelial trenches
embedded with taste buds in association with lingual salivary glands named Von-Ebner glands (VEG). Sonic hedgehog
(Shh) is a key regulator of anterior taste buds, where it represses taste specification, however, its role in the development of
CVP/VEG complex has not been explored. Here we tested the temporal and spatial requirement of Shh in CVP/VEG
complex development by genetic fate mapping and loss of function analyses. Shh is expressed in the early CV placode at
E12.5, well before the VEG primordia have emerged. At birth, Shh-descendent placode cells identified by genetic fate
tracking populate the apical epithelium of the circumvallate papilla, as well as the trenches, as immature taste cells. In
adults, by contrast, Shh-descendent cells are lost from the trenches, and instead persist only as a scanty population in the
apical epithelium. Conditional deletion of Shh in Shh-expressing cells commencing at the CVP placode stage (E12.5)
results in impaired trench formation and to a complete absence of VEG at birth. These findings indicate, in contrast to its
repressive function in anterior taste precursor specification, that Shh is required for CVP development. Thus, our data
support the growing consensus that molecular regulation of the anterior and posterior taste fields differ significantly.
Moreover, our findings indicate that Shh expressed by developing taste epithelium is a key regulator of salivary gland
morphogenesis.