Program/Abstract #518 Withdrawn doi:10.1016/j.ydbio.2011.05.580 Program/Abstract #519 Endodermal patterning in the basal deuterostome, Saccoglossus kowalevskii Andrew L. Verardo a , Elena S. Casey b a Georgetown University Biology, Washington, DC, USA b Georgetown University, Washington, DC, USA The vertebrate gut develops from an undifferentiated tube of endodermal cells into discrete regions of specialized tissues and organs. Several patterning events during early endoderm formation, as well as cross-talk with overlying mesodermal tissue, progressively specify the gut into distinct regions along its A/P axis. These gut regions can be identified based on their expression of a unique constellation of transcription factors, and are roughly categorized into either fore-, mid-, or hindgut. The forkhead homeobox FoxA and members of the GATA transcription factor family have been shown to play a conserved role in the early patterning of vertebrate gut endoderm. The evolution of gut endodermal specification in deuterostomes, however, is still not well understood. To address this we are currently studying the expression of conserved endodermal gut gene markers in the hemichordate marine acorn worm, Saccoglossus kowalevskii. These basal deuterostomes show a remark- able similarity in early body plan A/P organization to vertebrates but lack a complex gut, making Saccoglossus an attractive model for studying the evolution of deuterostome endodermal patterning and development. Our results show that the Saccoglossus FoxA and GATA4 mark the developing endoderm: FoxA first marks presumptive endoderm during gastrulation, GATA4 marks endoderm within gastrulated embryos. FoxA later becomes a pan-endodermal marker while GATA4 is restricted to the midgut, expression patterns which are more reminiscent of vertebrate gut developmental expression than the uro- or cephalochordates. Taken together, we propose that Saccoglossus is an ideal organism for studying the evolution of deuterostome endodermal gut patterning. doi:10.1016/j.ydbio.2011.05.581 Program/Abstract #520 Did natural selection construct metazoan developmental sequences? Paul Nelson Biola University, Glenview, IL, USA The necessary and sufficient conditions of the process of natural selection (Endler, Natural Selection in the Wild, 1986) are (1) variation, (2) selection or fitness differences, and (3) inheritance. These conditions impose evidential demands on any investigator who wishes to employ natural selection in evolutionary (i.e., historical) explanation. Data from model systems (e.g., C. elegans, Drosophila, and Danio), as well as theoretical analyses, raise challenges for the use of natural selection as the causal process responsible for the origin of developmental sequences. In particular, the conditions of (2) selection differences and (3) inheritance have not been adequately described in current theories of the evolution of the Metazoa. doi:10.1016/j.ydbio.2011.05.582 Abstracts 256

Did natural selection construct metazoan developmental sequences?

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Page 1: Did natural selection construct metazoan developmental sequences?

Program/Abstract #518Withdrawn

doi:10.1016/j.ydbio.2011.05.580

Program/Abstract #519Endodermal patterning in the basal deuterostome,Saccoglossus kowalevskiiAndrew L. Verardoa, Elena S. CaseybaGeorgetown University Biology, Washington, DC, USAbGeorgetown University, Washington, DC, USA

The vertebrate gut develops from an undifferentiated tube ofendodermal cells into discrete regions of specialized tissues andorgans. Several patterning events during early endoderm formation,as well as cross-talk with overlying mesodermal tissue, progressivelyspecify the gut into distinct regions along its A/P axis. These gutregions can be identified based on their expression of a uniqueconstellation of transcription factors, and are roughly categorized intoeither fore-, mid-, or hindgut. The forkhead homeobox FoxA andmembers of the GATA transcription factor family have been shown toplay a conserved role in the early patterning of vertebrate gutendoderm. The evolution of gut endodermal specification indeuterostomes, however, is still not well understood. To address thiswe are currently studying the expression of conserved endodermalgut gene markers in the hemichordate marine acorn worm,Saccoglossus kowalevskii. These basal deuterostomes show a remark-able similarity in early body plan A/P organization to vertebrates butlack a complex gut, making Saccoglossus an attractive model forstudying the evolution of deuterostome endodermal patterning anddevelopment. Our results show that the Saccoglossus FoxA and GATA4mark the developing endoderm: FoxA first marks presumptive

endoderm during gastrulation, GATA4 marks endoderm withingastrulated embryos. FoxA later becomes a pan-endodermal markerwhile GATA4 is restricted to the midgut, expression patterns whichare more reminiscent of vertebrate gut developmental expressionthan the uro- or cephalochordates. Taken together, we propose thatSaccoglossus is an ideal organism for studying the evolution ofdeuterostome endodermal gut patterning.

doi:10.1016/j.ydbio.2011.05.581

Program/Abstract #520Did natural selection construct metazoandevelopmental sequences?Paul NelsonBiola University, Glenview, IL, USA

The necessary and sufficient conditions of the process ofnatural selection (Endler, Natural Selection in the Wild, 1986) are(1) variation, (2) selection or fitness differences, and (3) inheritance.These conditions impose evidential demands on any investigatorwho wishes to employ natural selection in evolutionary (i.e.,historical) explanation. Data from model systems (e.g., C. elegans,Drosophila, and Danio), as well as theoretical analyses, raisechallenges for the use of natural selection as the causal processresponsible for the origin of developmental sequences. In particular,the conditions of (2) selection differences and (3) inheritance havenot been adequately described in current theories of the evolutionof the Metazoa.

doi:10.1016/j.ydbio.2011.05.582

Abstracts256

http://dx.doi.org/10.1016/j.ydbio.2011.05.580

http://dx.doi.org/10.1016/j.ydbio.2011.05.581

http://dx.doi.org/10.1016/j.ydbio.2011.05.582