Abstracts - Society for Developmental Biology

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embryonic precursors to form an alternative cell type. For translational medicine it introduces a new possible source of
cardiomyocytes, derived from an adult tissue, which might be used for drug testing or for therapeutic transplantation.
Program/Abstract # 427
Specification of the ascidian larval PNS
Zeller, Robert W.; Chen, Jerry; Tang, Joyce ( San Diego State University, United States)
The ascidian larval peripheral nervous system (PNS) consists of a series of paired sensory neurons, called epidermal
sensory neurons (ESNs) that run along the midline of the larva. Other laboratories have shown that both BMP and FGF
signaling are required for the early specification of these cells and that the pattern of ESNs is further refined by Notch-
Delta signaling. Here we show that the entire larval epidermis is neurogenic and can be converted into ESNs by the
expression of the single ascidian Pou4 class transcription factor. In the context of a larger gene regulatory network (GRN)
for the larval PNS, we have identified at least four microRNAs and at least four transcription factors that operate
downstream of Notch-Delta signaling to pattern the larval ESNs. In Ciona intestinalis, the microRNA miR-124 is
expressed in both the PNS and central nervous systems. We computationally identified miR-124 targets and show that key
miR-124 targets include the Notch receptor, the three HES family genes that mediate Notch signaling and neutralized,
which regulates Delta levels. We show that miR-124 feeds back on Notch-Delta signaling and plays a role in ESN
specification. In addition to Pou4, we have identified at least three additional transcription factors that pattern the ESNs.
By analyzing a matrix of gene expression patterns in transgenic embryos ectopically expressing these transcription factors
we have established a temporal and spatial cascade of regulatory gene expression in the PNS. Interestingly, the
microRNAs and transcription factors we have identified play roles in the specification in the hair cells of the vertebrate
inner ear.
Program/Abstract # 428
Requirements for posterior growth in sequentially segmenting arthropods
Nagy, Lisa M.; Nakamoto, Ayaki; Ettling, Alexandria; Harrison, Christy (University of Arizona, Tucson, AZ, United
States); Kim, S.; Lazo del la Vega, Lorena; Tewksbury, Austin; Wambaa, Sam; Williams, Terri (University of Connecticut,
Hartford, United States)
A key feature of the arthropod body plan is the presence of segments along the body axis. Evolution of segments has
permitted broad diversification of arthropods. Most arthropods develop their segments in the same fashion: they add them
one by one from the posterior in a region commonly called the “growth zone”. Although this is the most common mode of
arthropod segmentation, the growth zone is mostly unstudied. We are studying the growth zone at the cellular level in two
groups within the Pancrustacea, crustaceans: the branchiopod Artemia and Thamnocephalus and an insect: the beetle,
Tribolium. Both exhibit features likely ancestral for their respective lineages: larval addition of segments in the
branchiopods and sequential addition of segments in the beetle embryo. Recently, a common set of genes - caudal, evenskipped
and Wnts – have been hypothesized to control the growth zone in diverse arthropods. We have characterized the
dimensions of the growth zone and analyzed the behavior of cells relative to the dynamic patterns of gene expression in the
posterior of the developing larvae and germ band. We are also completing a fate map of the blastoderm by tracing the fates
of small clusters of cells subsequent to activation of a photo activatable dye. Our results provide evidence for divergent
modes of sequential segmentation in branchiopods and beetles: in the branchiopod posterior growth contributes
continuously to the segmentation process, whereas posterior growth makes a discontinuous contribution to the
segmentation of the Tribolium germ band.
Program/Abstract # 429
A genetic circuit conferring robustness to dorsal patterning in Drosophila
Gavin-Smyth, Jackie; Ferguson, Chip, University of Chicago Ecology and Evolution, Chicago, United States
The robust and invariant development of the wild-type organism is widely thought to be adaptive and essential. Using
quantitative analyses of dorsal patterning in the Drosophila embryo we have assessed the robustness of this event and
determined the genetic mechanism required for invariance of wild type patterning. The DV axis of both arthropods and
vertebrates is patterned by the activity of Bone Morphogenetic Protein (BMP) signaling. In D. melanogaster the BMP
ligand Decapentaplegic (Dpp) is essential for the specification of dorsal fates in the pre-gastrular embryo. During
cellularization, Dpp signaling is initially localized in a low intensity, broad dorsal domain due to the activity of
extracellular ligand binding proteins. At the onset of gastrulation, the Dpp signaling domain is intensified and refined into
a sharp stripe on the dorsal midline. Previous work indicated that positive feedback was required for the formation of this
final signaling domain. Our current work characterizes and defines a component of the feedback circuit, and its interaction
with a BMP signaling antagonist. We find that the combined activity of positive and negative factors leads to the