Abstracts - Society for Developmental Biology

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Program/Abstract # 13
Evolution and development in Lycophytes
Ambrose, Barbara A.; Smalls, Tynisha; Vasco, Alejandra, The New York Botanical Garden, New York, United States
Evolutionary developmental biology studies in lycophytes are integral to our understanding of land plant evolution and
development as the lycophytes occupy a key phylogenetic position within the land plants as sister to all other vascular
plants. In addition, lycophytes have interesting morphological structures, including microphylls, rhizophores and
heterospory, whose evolution and development has been debated for more than a century. Compared to the flowering
plants, lycophytes have not only simple sporophyte bodies but also simple genomes. Recent genome sequencing of the
lycophyte, Selaginella moellendorffii, shows that there is no whole genome duplication characterizing this species. We are
cloning and analyzing several key transcription factor families across the lycophytes as well as analyzing the expression of
known key regulators in leaf and reproductive organ development from angiosperms in S. moellendorffii. The Type II
MADS-box genes are well known for their role in flower development, and even though there are no orthologs ofthese
floral MADS-box genes in the S.moellendorffii genome, the Selaginella Type II MADS-box genes are expressed in
reproductive structures. Type I MADS box genes play a large role in gametophyte, embryo and seed development and our
analyses suggest that these may be important for sporangia development in S. moellendorffii. We have also analyzed the
leaf development network in S. moellendorffii and have found that a large number of the members of this network are
present in the S. moellendorffii genome and are expressed during microphyll development. Our analyses provide insights
into lycophyte evolution and development and highlight the need for a functional model system in the lycophytes.
Program/Abstract # 14
Development of a localized nervous system in a dipleurula-type larva.
Yankura, Kristen; Koechlein, Claire; Hughes, Stephanie; Hinman, Veronica Frances, Carnegie
Mellon University, Pittsburgh, United States
The development of centralized nervous systems in many species of arthropods and chordates is extremely well
characterized; however, very little is known about the formation of localized systems of neurons that are present in the vast
diversity of animals. We provide an explanation for the development of a localized system of neurons that is associated
with the ciliary bands of the dipleurula-type larvae of seastars. These larvae have two distinct ciliary bands, positioned
above and below the mouth, that extend posteriorly and anteriorly along the dorsal surface and loop back to the ventral
surface. Neurons associated with these bands are therefore located at multiple points along the anterior-posterior (AP) and
thedorsal-ventral (DV) axes of the larva, suggesting that they cannot be specified by a simple integration of the AP/DV
signaling system that is common to arthropods and chordates. Rather, we show that conserved Wnt, Nodal and BMP
signaling pathways establish a pro-ciliary band territory that is needed to establish a neurogenic potential “edge” along
which ciliary band associated neurons become specified. This constitutes a novel mechanism for neural specification in
animals. We discuss how this mechanism for neural patterning contributes to an understanding of the evolution of
centralized nervous systems in chordates.
Program/Abstract # 15
Evolution of development in the amniotes: New insights from genomic studies of somitogenesis in the lizard and
alligator
Eckalbar, Walter L., Arizona State University, Tempe, United States; Elsey, Ruth (Louisiana Dept of Wildlife and
Fisheries); Lasku, Eris (Arizona State U); Allen, April; Corneveaux, Jason (Translational Genomics Res Inst); DeNardo,
Dale; Wilson-Rawls, Jeanne (Arizona State U); Huentelman, Matthew (Translational Genomics Res Inst); Rawls, Alan;
Kusumi, Kenro (Arizona State U)
The segmented spine arises from the developmental process of somitogenesis, which is regulated through the cycling
mechanism termed the ‘segmentation clock’. Major regulatory changes in this developmental clock have been associated
with vertebrate evolution, but our ability to refine this analysis has been limited by major gaps, particular the lack of data
from reptiles. We have extended this comparative analysis to two key reptilian taxa: a squamate, the green anole Anolis
carolinensis, and an archosaurian reptile, the American alligator, Alligator mississippiensis. The newly sequenced
genomes as well as our own deep sequencing of embryonic transcriptomes has provided intriguing data for analysis in the
anole and alligator. Further, in situ hybridization was used to localize dynamic expression patterns. This analysis revealed
key changes in segmentation clock gene expression, reflecting convergence and divergence of regulatory mechanisms
within the amniotes. We found that cyclical genes in the clock were particularly divergent. This includes expression of
lunatic fringe, which has cyclical expression in mouse and chicken, but not in the lizard or alligator, as well as delta like 1,
which shares cyclical expression in the anole and mouse. Gradient and determination front components of the segmentation
clock were generally more conserved, with the exception of hes6, which is expressed in a posterio rgradient in anoles, like