Congress Abstracts - Society for Developmental Biology

conserved in amniotes other than chick? We are currently exploring axis formation in reptiles, focusing on chameleon (Squamata) and
turtles (Testudines).
Program/Abstract # 350
Building a Vertebrate Embryo Using a Combination of Morphogenetic Gradients
Xu, Peng-Fei; Ferri, Karine; Thisse, Christine; Thisse, Bernard (University of Virginia, USA)
We have previously shown that in zebrafish, the entire embryonic margin acts as a global and continuous organizer. The organizing
properties result from the combined activity of BMP and Nodal morphogenetic gradients and the gradual variation of their ratio of
activity observed from the ventral to the dorsal domains of the margin is the crucial parameter that controls the identity of the
embryonic structures formed. By recapitulating, within the field of uncommitted blastomeres of the animal pole, the continuous
variation of BMP/Nodal ratio of activities observed at the embryonic margin, we are able to induce the formation of a complete
secondary embryo that contains all tissues and organs of a wild-type embryo and that develops at the animal pole from animal pole
cells. Analysis of the respective contribution of the BMP and Nodal pathways to the formation of the secondary embryo reveals that
Nodal signalling results in the formation of a blastopore where an ectopic gastrulation occurs leading to the formation of radially
symmetrical structures of dorsal identity. Adding a BMP secreting centre adjacent to the domain stimulated by Nodal breaks the
symmetry of the blastopore lip, inducing ventral and lateral tissues to form and in addition that polarizes gastrula cell movements. Our
analysis reveals that the antero-posterior orientation of the ectopic embryonic axis depends only on the position of the BMP secreting
cells relative to the blastopore induced by Nodal and is completely independent of the primary embryo. Altogether, our study
establishes that, artificially imposing these morphogenetic gradients to receptive, yet uncommitted cells, is sufficient to turn on and
control the zygotic developmental pathways responsible for the formation of a whole embryo and supports that the main function of
the maternally provided spatial determinants is to induce and/or stabilize the morphogenetic gradients of BMP and Nodal.
Program/Abstract # 351
Role of FGF signaling in maintenance of cardiac chamber identity in zebrafish
Pradhan, Arjana; Zeng, Xin-Xin (Univ of California, San Diego, USA); Marques, Sara (Skirball Institute of Biomolecular Med, NYU
School of Med, USA); Chi, Neil; Yelon, Deborah (Univ of California, San Diego, USA)
The heart is composed of two types of cardiac chambers, atria and ventricles, each of which behaves as a distinct functional subunit
with unique morphological, electrophysiological, and contractile properties. Hence, the proper chamber-specific differentiation of
atrial and ventricular cardiomyocytes is crucial for the formation of a functional heart. Although there is some understanding of the
pathways important for initiating chamber-specific differentiation, little is known about the pathways required to maintain identities of
differentiated cardiomyocytes. In previous studies, we have demonstrated that fibroblast growth factor (FGF) signaling facilitates the
initial formation of ventricular cardiomyocytes. Here we show that FGF signaling is also required after the initial differentiation of
ventricular cells in order to preserve ventricular identity. We find that both pharmacological and genetic inhibition of FGF signaling
can generate ectopic atrial cardiomyocytes within the already differentiated ventricle. Analysis using chamber-specific reporter
transgenes suggests that these ectopic cells are produced through transdifferentiation of ventricular cardiomyocytes. In addition, we
find that administration of retinoic acid (RA) can disrupt ventricular chamber identity, suggesting the possibility of a genetic
interaction between the FGF and RA pathways. Together, our data suggest a model in which differentiated ventricular
cardiomyocytes retain some plasticity and require continuous FGF signaling to preserve their chamber-specific identity. Ongoing
work will identify the molecular pathway through which FGF signaling acts in this context.
Program/Abstract # 352
Modulation of fungiform papillae patterning by Fgf signaling
Prochazkova, Michaela (UCSF, USA), Häkkinen, Teemu (University of Helsinky, Finland); Prochazka, Jan; Jheon, Andrew (UCSF,
USA); Jervall, Jukka (University of Helsinky, Finland); Klein, Ophir (UCSF, USA)
Introduction: Fungiform papillae are epithelial structures that house taste buds on the anterior tongue. Many molecular pathways are
known to influence the patterning of the fungiform papillae. Canonical Wnt signaling was shown to initiate fungiform papillae
formation, whereas other pathways triggered by Shh, Egf or Bmp have inhibitory effects on papilla size and number. However,
mesenchyme-derived signaling factors have not yet been identified, hampering the development of a comprehensive model of papilla
patterning. Results: We have examined the role of Fgf10 in fungiform papilla development. Evaluation of Fgf10 and Spry2 knockout
phenotypes showed that Fgf10, which is expressed in the tongue mesenchyme underlying the papillary field, functions as a negative
regulator of fungiform papilla size. Using BATGAL mice, we demonstrated that this role is mediated by inhibition of canonical Wnt
signaling, which is the main activator of papilla development. A gene expression analysis using qRT-PCR revealed interactions
between Fgf10 and the Wnt and Shh pathways. We then represented these results mathematically using a reaction-diffusion model to
simulate activator-inhibitor dynamics in the system. Summary: Fgf10 functions as a negative regulator of fungiform papilla size
during embryonic development, suggesting a role in fine-tuning taste sensitivity. The proposed mechanism of Fgf10 action is via
inhibition of canonical Wnt activity. FGF10 is the first mesenchyme-derived factor to date involved in fungiform papillae patterning.
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