and isthmus) are involved in partitioning the brain into functionaldomains. Homologous signaling centers have not been described inAmphioxus and ascidians leading to the prevailing view that localsignaling centers are a vertebrate regulatory innovation that facilitatedthe evolution of complex vertebrate neuroanatomy. We have begun tocharacterize similar ectodermal signaling centers in hemichordates,suggesting that these regulatory networks evolved much earlier indeuterostome history than previously recognized.

doi:10.1016/j.ydbio.2009.05.056

Program/Abstract # 46Small molecule-mediated “phenotypic engineering” reveals a rolefor retinoic acid in anuran gut evolutionStephanie Blooma, Carlos Infanteb, Anne Everlyb,James Hankenb, Nanette Nascone-YoderaaMolecular Biomedical Sciences, College of Veterinary Medicine,North Carolina State University, USAbMuseum of Comparative Zoology, Department of Organismicand Evolutionary Biology, Harvard University, USA

Changes in feeding strategy are often accompanied by noveldigestive organ morphology. Most anuran tadpoles, such as Xenopuslaevis, are omnivores with a rudimentary stomach, an acute gastro-duodenal (GD) loop, and long intestines. However, tadpoles of theSouth American frog Lepidobatrachus laevis are obligate carnivoreswith a large stomach, an exaggerated GD loop, and short intestines. Toinvestigate the developmental mechanisms that underlie digestiveevolution in these tadpoles, we employed a novel small molecule-mediated phenotypic engineering strategy, to identify compounds thattransform the foregut anatomy in each species to resemble the other.Treating Xenopus embryos with retinoic acid (RA) synthesis inhibitorsresults in the development of an elongated GD loop similar to thatfound in Lepidobatrachus tadpoles. Reciprocally, treating Lepidobatra-chus embryos with ectopic RA induces the development of arudimentary stomach and shortened GD loop resembling that foundin Xenopus tadpoles. The inhibition of RA posteriorized the expressionof a marker of GD looping morphogenesis, Pitx2, in Xenopus embryos,while ectopic application of RA shifted Pitx2 expression anteriorly inLepidobatrachus embryos. These results suggest that RA signaling and/or Pitx2 expression influences the anatomy of the anuran foregut, andthat alterations in these patterning events may have facilitated thetransition to larval carnivory in Lepidobatrachus.

doi:10.1016/j.ydbio.2009.05.057

Program/Abstract # 47Gene regulatory networks and the encoded logic of developmentEric DavidsonCaltech, CA, USA

Development of the body plan is controlled directly by networks ofregulatory gene interactions encoded in the genomic DNA. Theexperimentally determined gene regulatory network (GRN) for thesea urchin embryo endomesoderm, its input/output predictions nowextensively validated at the cis-regulatory level, provides proof ofprinciple that a GRN can explain causation of developmentalphenomena. Evolution of the body plan must thus be understood interms of changes in topology or architecture of developmental GRNs.These changes occur by alterations in the cis-regulatory apparatus ofregulatory genes, but because of the strongly hierarchical structure ofGRNs the consequences of such changes, great or small, depend onwhere in the GRN architecture they occur. A large scale GRN alteration

which occurred by “highjacking” awhole specification and differentia-tion subcircuit appears to account for the euechinoid embryonicskeletogenesis system, a morphological and developmental characterabsent in other echinoderm classes. We can now reconstruct how thismay have happened at the genomic regulatory level. Knowledge ofdevelopmental GRNs opens the way to synthetic experimentalevolution, in which a network feature producing a derived phenotypeis experimentally inserted into a related form displaying thepleisiomorphic character. We have had some preliminary success withthis approach using echinoderm species that do and do not normallyproduce a precociously invaginating skeletogenic cell lineage.

doi:10.1016/j.ydbio.2009.05.058

Program/Abstract # 48Decoding embryonic cis-regulatory modules at DrosophilaHox genesRobert A. Drewella, Margaret C. Hoa, Sara E. Goetza,Benjamin J. Schillera, Esther Baeb, John M. Allena, Welcome Benderc,William Fisherd, Susan E. Celnikerd, Robert A. DrewellaaBiology Department, Harvey Mudd College, Claremont, CA, USAbWestern University of Health Sciences. Pomona, CA, USAcHarvard Medical School Boston, MA, USAdLawrence Berkeley National Laboratory Berkeley, CA, USA

The homeotic (Hox) genes regulate segment identity duringdevelopment of the embryo in all metazoans and are important in theevolution of animal morphology. The bithorax complex (BX-C) inDrosophila provides a striking example of the exquisite regulationrequired to direct gene expression in the developing embryo. The BX-C is over 300 kb in size, but contains only three Hox genes. Thespecific patterns of expression of the Hox genes during earlyembryonic development are controlled by an interacting network ofcis-regulatory modules (CRMs), including enhancers. We have beeninvestigating the functional evolution of the early embryonic CRMs inthe BX-C. The publication of the genomic sequences of a number ofdifferent Drosophila species has allowed us to examine the underlyingevolutionary conservation of the CRMs. We applied bioinformaticapproaches to perform cross-species analysis of the CRMs. The CRMsdemonstrate a distinct lack of underlying evolutionary conservation,suggesting that they are evolving rapidly. In our most recent studieswe have tested the functional activity of the enhancer CRMs fromdifferent species in transgenic assays. In addition, we have initiated amolecular dissection of these CRMs in order to determine whichsequences are necessary for the functional activity of the enhancer.This research was supported by grants awarded to RAD — NIHHD54977 and NSF IOS-0845103.

doi:10.1016/j.ydbio.2009.05.059

Program/Abstract # 49Choanoflagellate colonies and the origin of animal developmentNicole KingDepartment of Molecular and Cell Biology, University of California,Berkeley, USA

The evolution of animals from their single celled ancestorsrepresents one of the major transitions in life's history. While theenvironmental context of animal origins has beenwell studied, little isknown about the roles of genome evolution and interspeciesinteractions in the transition to multicellularity. Choanoflagellates, agroup of colony forming and unicellular eukaryotes, represent theclosest living relatives of animals and provide insights into animal

Abstracts / Developmental Biology 331 (2009) 399–401400

origins and ancestral features of animal biology. The genome of thechoanoflagellate Monosiga brevicollis reveals that cell–cell signalingand adhesion genes (including receptor tyrosine kinases and cadher-ins) evolved in the pre-metazoan era, predating the origin of multi-cellularity. Choanoflagellates use tyrosine kinase signaling to interpretnutrient availability in their extracellular environment, highlighting apotentially ancient linkage between cell signaling genes and environ-mental sensing. In addition, choanoflagellates contain an abundance ofcadherins, two of which localize to the choanoflagellate feeding collar,where evidence is building that they participate in bacterial preyrecognition or capture. Finally, we find that the induction of colonydevelopment in the choanoflagellate Proterospongia sp. requires achemical signal from the bacterial prey speciesAlgoriphagus. This inter-kingdom signaling interaction is specific and experimentally tractable,promising to provide mechanistic insights into the regulation ofeukaryotic morphogenesis by bacteria.

doi:10.1016/j.ydbio.2009.05.060

Program/Abstract # 50Evidence for multiple signaling events during the early cleavagesof the mollusc IlyanassaLisa M. Nagya, Maey Gharbiaha, Ayaki Nakamotoa, Jessie WandeltbaMolecular and Cellular Biology, University of Arizona, Tucson, AZ, USAbSchool of Biological Sciences, University of Texas, Austin, TX, USA

Metazoan embryos use multiple and diverse signaling pathwaysto establish positional information during the earliest cleavagecycles. Despite widespread evidence for early signaling in manymodel systems, few signaling events have been identified, ormolecularly characterized, in the early Ilyanassa embryo. In Ilyanassa,the inheritance of the polar lobe enables the D quadrant to functionas the signaling center that organizes the dorsal–ventral embryonicaxis. We have found evidence for a signal from the micromeres to theD quadrant macromere that is required to establish the D quadrantmacromere as the organizing center of the embryo. In addition, wereport that early Notch signaling is required to appropriatelyestablish embryonic pattern. Treatment with DAPT, which inhibitssignaling through the Notch pathway, results in larvae with severedefects in internal organs and defects in shell, foot and velum. DAPTtreated larvae activate MAPK in the 3D organizer and micromeresappropriately. Thus, Notch does not appear to be required toestablish the 3D signaling center. DAPT treated larvae resemblelarvae that result from the early ablation of the mesendodermalprecursor, 4d, with the exception that cell fates that develop as directlineage descendants of 4d are present. This result suggests that 4dsignals to other micromeres via Notch signaling. We use this data,and existing evidence from the classic literature, to build a model fora sequence of signaling events that regulate early embryonicdevelopment in Ilyanassa.

doi:10.1016/j.ydbio.2009.05.061

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