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128 differentiated cell type, which may have broad implications in the treatment of disorders associated with cell invasive behavior. Program/Abstract # 385 Investigating the role of lin-42, the C. elegans period homolog, in developmental timing McCulloch, Katherine, University of Minnesota, MinneapolisUnited States; Wohlschlegel, James (Los Angeles, CA, United States); Rougvie, Ann (Minneapolis, United States) Precise temporal control is a critical component of developmental regulation. In humans, for example, puberty, the juvenile to adult transition, is regulated by a highly complex combination of genetic and environmental factors. Aberrant timing of puberty is predictive of serious health problems later in life, so understanding these processes is critical. Significant insights into developmental timing mechanisms have been achieved through studies in C. elegans, which uncovered several conserved temporal regulators termed heterochronic genes. These include lin-28, which has since been implicated in timing the onset of puberty in mice and humans. In addition, study of developmental timing revealed the first miRNAs identified: lin-4 and let-7. Let-7 miRNA is of particular interest. Its sequence is identical between C. elegans and humans, and in both systems, let-7 activity promotes differentiation. Another highly conserved heterochronic gene is lin-42, the C. elegans period homolog. period is a key component of the fly and vertebrate circadian clock, which synchronizes behavior and gene expression with the 24 hour cycle. In C. elegans, however, lin-42 acts largely as a developmental timer. In lin-42 mutant animals, the larval-to-adult transition occurs too early. Although lin-42 has long been known as a key component of the heterochronic pathway, the placement of lin-42 in the pathway and its molecular mechanism is unclear. We have found that one role of lin-42 is to act in parallel with lin-28 to regulate the accumulation of let-7 miRNA. Studies are ongoing to determine at what step in miRNA biogenesis lin-42 acts and how precocious expression of let-7 affects its targets in the pathway. In addition, we are using proteomic techniques to identify LIN-42 binding partners that will further elucidate its role in timing. Program/Abstract # 386 Plasticity of patterning information in the blastema during limb regeneration in Ambystoma mexicanum McCusker, Catherine D.; Gardiner, David, University of California at Irvine, United States The amphibian limb regenerate, called the limb blastema, has the fascinating capacity to replace exactly the missing limb structures regardless of its location along the proximal/distal limb axis. How is pattern established in the blastema? The popular hypothesis is that early blastema cells, which are dedifferentiated adult limb cells, retain information about their original position in the limb and independently establish the pattern of the regenerate. However, ourfindings using GFPlabeled blastema grafts suggest that the early blastema remains under the influence of the differentiated stump tissue for patterning information. To understand how changes in the blastema microenvironment correspond to the establishment of pattern we performed a detailed characterization of the organization of blastema cells, the surrounding extracellular matrix, and location of cell proliferation in the blastema as it develops. We found that the early blastema and the apical tip of the lateblastema share a similar microenvironment. By performing additional grafting experiments, we have found that patterning in the apical tip of the late blastema is plastic, while the basal regions closest to the stump are specified. Our hypothesis is that patterning information is gradually “hardwired” in the blastema starting with the blastema cells closest to the differentiated stump. Our current focus is on how the blastema microenvironment controls the level of pattern commitment in the blastema cells. Program/Abstract # 387 The role of Notch signaling in neurotransmitter phenotype specification and secondary neurogenesis in X. laevis McDonough, Molly; Tellis, Athena; Koshiya, Hitoshi; Saha, Margaret, College of William and Mary, Williamsburg, United States The acquisition of a neurotransmitter phenotype by individual neurons is crucial for the formation of a functioning nervous system. During primary neurogenesis, the Notch signaling pathway regulates neural differentiation via lateral inhibition. We hypothesized that Notch signaling may also regulate the specification of excitatory and inhibitory neurotransmitter phenotypes. We perturbed Notch signaling by injecting sense mRNA for different components of the pathway into Xenopus embryos at the two-cell stage. Embryos were then analyzed for gene expression using wholemount ISH. Results indicate that perturbing components of Notch signaling atearly stages of development does not affect specification of GABAergic or glutamatergic fates but does alter neural versus non-neural fate differentiation in early stages of neurogenesis. However, gene expression at later stages of development appears to compensate for these earlier effects. We utilized qPCR to determine the extent to which that compensation is occurring. Possible mechanisms of compensatory regulation were analyzed by performing ISH for neural progenitor markers and immunohistochemistry with PCNA to
129 determine cell cycle activity in response to Notch perturbations. Additionally, TUNEL assays were performed to examine altered rates of apoptosis in embryos in which Notch signaling was perturbed. These experiments elucidate the possible role of Notch signaling in secondary neurogenesis. We also injected embryos with mRNAs coding for hormone-inducible fusion proteins to activate Notch perturbations at later stages of development. We subsequently assayed these embryos using ISH to determine the potential role of Notch in GABAergic versus glutamatergic specification. Program/Abstract # 388 The Dkk1 receptor Kremen1 regulates progenitor cell identity during mechanosensory organ formation. McGraw, Hillary F.; Culbertson, Maya; Nechiporuk, Alexei, Oregon Heath & Sciences Univ, Portland, United States Canonical Wnt signaling regulates many cellular behaviors in development and disease. Here, we investigate how Wnt signaling is modulated in the context of the posterior lateral line primordium (pLLp) migration. The pLLp is a cohort of ~100 cells that collectively migrate along the trunk of the developing zebrafish embryo. ThepLLp is comprised of proliferating progenitor cells and differentiated cells that will form the mechanosensory organs of the pLL. Canonical Wnt signaling isactive in the leading progenitor zone of the pLLp and restricted from the differentiated trailing zone by activity of the secreted Wnt inhibitor Dkk1. Abrogation of Wnt signaling by ectopic expression of Dkk1 leads to decreased cellular proliferation and a concomitant increase in cell death in pLLp progenitors. We have identified a zebrafish strain that carries a mutation in kremen1 gene, a Dkk1 receptor. Previous studies showed that Kremen1 negatively regulated Wnt signaling. Surprisingly, we found that kremen1 mutants exhibited phenotypes associated with the loss rather then overactivation of Wnt signaling, including loss of proliferation in presumptive progenitor cells and an increase in cell death. Expression of Wnt target genes were progressively and prematurely downregulated in kremen1mutants. Mosaic analysis revealed that the effects of loss of Kremen1 arenon-cell autonomous. Based on our results, we propose that Kremen1 is required to sequester Dkk1 in the trailing zone of the pLLp and loss of Kremen1 leads toan ectopic expansion of Dkk1, down regulating Wnt signaling in the leading progenitor cells. Understanding the precise regulation of Wnt signaling during development may shed light on how the pathway is misregulated in disease. Program/Abstract # 389 Re-examination of the primordial germ cells of the mouse: a general stem cell pool for building the posterior region? Mikedis, Maria; Downs, Karen, University of Wisconsin-Madison Cell and Regenerative Biology, Madison, United States Over the past several years, results from our laboratory have revealed that the posterior region of the mouse conceptus is more architecturally complex than was previously known. In particular, we have reported the existence of a putative stem cell reservoir, called the Allantoic Core Domain (ACD), within the mouse allantois, or precursor umbilical cord. The ACD is required, at a minimum, for allantoic elongation to the chorion to create the chorio-allantoic placenta. The presence of the ACD in the posterior region spatiotemporally coincides with the presence of STELLA-positive putative primordial germ cells (PGCs), which also localize to the proximal region of the allantois. It is thought that these STELLA-positive cells translocate to the hindgut endoderm and, from there, migrate to and colonize the gonads. However, contrary to previous reports, we have discovered that STELLA is not confined to the putative PGC lineage. Rather, it is found in multiple cell types within the posterior conceptus, including the amnion, allantois, hindgut, and tailbud. Fate mapping the posterior region, including the STELLA-positive ACD and adjacent embryonic component of the primitive streak, has revealed that STELLA-positive cells within both regions contribute to the allantois, hindgut, and tailbud, and raise the question of whether the cells traditionally regarded as PGCs in mouse maybe part of a generalized stem cell population required to build the posterior end of the fetus. Future work will examine PGC formation and development in mutants for Brachyury (T), which is required for the formation of the ACD. Program/Abstract # 391 The characterization of GABAA α and GABAB receptor subunits and the role of calcium activity in the developing nervous system of Xenopus Rabe, Brian A.; Kaeser, Gwendolyn; Saha, Margaraet, The College of William and Mary, Williamsburg, United States The predominating inhibitory neurotransmitter in the adult nervous system, gamma-aminobutyric acid (GABA), acts primarily in an excitatory manner during early neural development, causing the depolarization of cell membranes. During development, GABA has been implicated as a factor involved in multiple processes including cell migration, proliferation, synapse formation, and neurotransmitter phenotype specification. It has been hypothesized that GABA signaling affects these processes by altering calcium activity in developing neural cells. We predicted that GABA receptor subunits are expressed in embryos at the neurula stages of development which serves as a critical period for neurotransmitter specification. Using in situ hybridization and semi quantitative real time RT-PCR to show spatiotemporal expression of
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1 Program/Abstract # 1 Role of the
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3 Program/Abstract # 7 Forward gene
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5 Program/Abstract # 13 Evolution a
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7 Program/Abstract # 19 Lethal gian
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9 Program/Abstract # 26 On the comb
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11 Program/Abstract # 32 Imaging in
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13 and electron microscopy studies
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15 paracellular space, and interact
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17 the proximal to distal axis of t
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19 Dominguez-Castellano, Maria; Gar
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21 We are interested in the role of
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23 more likely than students who di
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25 was a significant loss of cells
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27 Fgfr3 expression in the limb cho
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29 division, but rapidly loses its
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31 and migration (ADAM13). They act
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33 Program/Abstract # 101 The influ
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35 Program/Abstract # 107 Shroom3-d
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37 Program/Abstract # 113 Requireme
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39 (Queens College, Flushing, Unite
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41 these data imply that Dynamin is
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43 Congenital renal malformations a
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45 Elevated nuclear translocation o
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47 progenitor cells that cover the
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49 abnormally dilated capillaries i
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51 malformations in murine limb bud
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53 Yuqing (Mouse Imaging Centre, To
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55 in the villi at E14. At E11, the
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57 Program/Abstract # 173 The role
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59 Boldt, Clayton, UT Southwestern,
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61 examine stem cell-based CNS rege
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63 Incubation of regenerating cells
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65 learn which dynamic behaviors oc
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67 cell proliferation and for norma
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69 Program/Abstract # 209 Drosophil
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71 cranial neural crest cells, as t
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73 experimental analysis. The jerbo
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75 The through-gut, consisting of s
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Page 81 and 82: 81 Lee, Hu-Hui, National Chiayi ers
Page 83 and 84: 83 understood. Here, we have establ
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Page 91 and 92: 91 Program/Abstract # 278 Heterogen
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Page 99 and 100: 99 Program/Abstract # 301 Dual role
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Page 119 and 120: 119 Program/Abstract # 359 The meth
Page 121 and 122: 121 Misregulation of molecular path
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Page 151 and 152: 151 Program/Abstract # 456 Thoracic
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Abstracts - Society for Developmental Biology

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