Abstracts - Society for Developmental Biology

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approach. A similar strategy was used to identify miRNAs enriched or excluded from the neural crest, as these small
regulatory RNAs are understudied in the context of this network. We report that many miRNAs enriched in pre-migratory
populations of zebrafish neural crest (14 hpf) have also been categorized as inhibitors of metastasis found in invasive
cancers. We use the zebrafish model to probe the expression and function of identified novel NC-GRN components.
Program/Abstract # 266
Hearing regeneration: zebrafish as a model for a large-scale mutation screening
Pei, Wuhong; Varshney, Gaurav; Huang, Sunny; Liang, jin; Gildea, Derek; Wolfsberg, Tyra; Burgess, Shawn, NHGRI,
NIH, Bethesda, United States
Hearing loss, primarily caused by a loss of sensory hair cells in the inner ear, affects an estimated one-third of the US
population between the ages of 65 and 75 and close to one-half of those older than 75. There is also an increasing trend of
young people experiencing hearing loss, due to excessive noise exposure, usually listening to music too loudly. In humans
and other mammals, hearing loss is an irreversible process, since the hair cells do not regenerate, the lost hair cells are not
replaced. Zebrafish is a good model for studying hearing regeneration, because of the conservation in gene function, the
similarity in inner ear structure, and mostly importantly, the ability to regenerate its inner ear hair cells. In our study, we
performed a gene expression profiling analysis on adult zebrafish recovering from a noise-induced inner ear hair cell loss,
and identified approximately 2000 genes involved in the hair cell regeneration process. We created a zebrafish mutation
library by retroviral insertions in the zebrafish genome and established large-scale genotyping methods to genotype
mutants using real-time PCR or high-resolution melting analysis. Mutation screening and phenotype examination are
ongoing to assess the contribution of each from thetranscriptional profiling to both hearing development and hair cell
regeneration. Functional studies, pathway analysis and environmental perturbations will be carried out to illustrate the
gene-gene and gene-environment interaction networks underlying inner ear hair cell regeneration in zebrafish, with an
ultimate goal to shed a light on the prevention and treatment of hearing loss in humans.
Program/Abstract # 267
Extracellular regulation of FGF signaling in the early Xenopus embryo
Acosta, Helena; Iliev, Dobromir; Min Grahn, Tan Hooi; Pera, Edgar M., Lund University, Lund, Sweden
Fibroblast growth factors play an important role in development and homeostasis, and their activity needs to be precisely
regulated to ensure proper signaling. We previously presented the secreted serine protease xHtrA1 as positive regulator of
FGF signaling in the extracellular space (Hou et al., (2007) Developmental Cell 13:226-41). xHtrA1 through cleaving
proteoglycans release cell-surface bound FGF ligands and stimulate long-range FGF signaling during establishment of the
embryonic body plan. It is obvious that, if not tightly controlled, the activity of xHtrA1 would lead to an unlimited
amplification and propagation of FGF signals. We have isolated a full-length cDNA clone encoding a secreted serine
protease inhibitor (xSPI) that may act as a negative regulator of xHtrA1/FGF signals.xSPI shows distinct expression in the
early embryo and promotes anterior development in mRNA-injected Xenopus embryos. xSPImRNA induced enlargement
of head structures, suppression of mesoderm and reduction of neuronal differentiation. These effects are reminiscent of
those caused by knockdown of xHtrA1 or inhibition of FGF signaling. In contrast, down regulation of xSPI by antisense
morpholino oligonucleotides caused microcephaly, a phenotype that is also induced by misexpression of xHtrA1 or
components of the FGF-MAPK pathway. Moreover, xSPI immunoprecipitates with xHtrA1, suppresses xHtrA1-induced
FGF signaling, and prevents xHtrA1 from degrading Syndecan-4 in mRNA-injected embryos. Together, the data suggest
that xSPI via suppression of xHtrA1 proteolytic activity and stabilization of cell surface proteoglycans may add another
layer to the extracellular regulation of FGF signals.
Program/Abstract # 269
The relationship between centrosomal PKA and Hedgehog signaling
Agbu, Stephanie; Bazzi, Hisham; Anderson, Kathryn, Sloan-Kettering Institute, New York, NY, United States
The Sonic Hedgehog (Shh) pathway is essential for embryonic development as well as tissue homeostasis in the adult
organism. Loss or gain of Shh function can result in developmental abnormalities and cancers such as holoprosencephaly
and basal cell carcinoma, respectively. In vertebrates, Shh signaling requires the primary cilium, a microtubule-based
structure present on almost all cells in the body. Protein Kinase A (PKA) is a cAMP-dependent protein kinase that serves
as a negative regulator of Shh signaling, and loss of PKA function results in full activation of the pathway. Studies have
shown that PKA localizes to the centrosome, which serves as the basal body of the primary cilium in interphase cells.
Biochemical experiments suggest that this association between PKA and the centrosome is mediated through interactions
with the pericentriolar proteins pericentrin and AKAP9. PKA is localized to the basal body of the primary cilium in the
presence and absence of Shh ligand, but it is unclear if centrosomal localization of PKA is required for its regulatory role