Abstracts - Society for Developmental Biology

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The through-gut, consisting of separate portals for ingestion and excretion, arose in organisms at the base of the bilaterian
tree and is a trait shared by the majority of protostomes and deuterostomes. Despite this shared origin, there are key
differences in gut lineage, cell types, and organization of the specialized cell types between protostomes and deuterostomes
– including the emergence of several unique gut organs within the vertebrate lineage (e.g. pancreas, gall bladder, and
liver). Because cell type specification and organization are controlled by earlier endodermal patterning events, comparing
these events between bilaterian lineages can clarify how differences and novelties in through-gut organization arose during
evolution. We are interested in the origin of those novel vertebrate gut organs, so we have chosen to investigate endoderm
patterning in the hemichordate Saccoglossus kowalevskii. Saccoglossus is a basal deuterostome with a relatively simple
tripartite gut and a body plan patterned along the anterior-posterior (A/P) axis similarly to chordates. Expression of the
patterning genes FoxA, GATA4/5/6s, Hox1, Pdx, and Cdx is highly conserved across bilaterians, suggesting an ancient
pattern for A/P gut regionalization. Expression of FoxA and Hox1 in the 1st gut partition of Saccoglossus is reminiscent of
FoxA/Hox1 expression in the vertebrate pharyngeal endoderm. Expression of GATA4/5/6 and Cdx in the 2nd and 3rd gut
partitions, respectively, is similar to GATA4/5/6s and Cdx expression in the posterior foregut and intestines, respectively.
We hypothesize that the 1st, 2nd, and 3rd gut partitions in Saccoglossus may be homologous, respectively, to the
vertebrate pharynx, posterior foregut, and intestines.
Program/Abstract # 228
Evolution of spinal cord expression and function of Lbx transcription factors.
Juarez-Morales, Jose-Luis, Syracuse University, Syracuse, United States; Weierud, Frida (Cambridge University, United
Kingdom); Lewis, Katharine (Syracuse University, Syracuse, United States)
The patterning and development of the spinal cord is very well conserved across vertebrates. For example, the expression
patterns of transcription factors in specific dorsal-ventral regions of the spinal cord are, in the main, highly conserved
across the vertebrate lineage. Lbx transcription factors are an exception to this rule as they are expressed differently in
zebrafish and mouse spinal cord. Zebrafish have three lbx genes, all of which have distinct spinal cord expression patterns.
In contrast, amniotes have two Lbx genes, but only Lbx1 is expressed in the spinal cord. This suggests that there may be
some evolutionary plasticity in the genomic networks that specify spinal interneurons in different vertebrates. To
understand how Lbx genes have evolved, we previously performed phylogenetic and synteny analyses of Lbx loci in bony
vertebrates 1. We demonstrated that teleosts have two lbx1 genes, as a result of the additional genome duplication in the
teleost lineage and one lbx2 gene. All other vertebrates studied had at most one Lbx1 and one Lbx2 gene1. To investigate
how lbx spinal cord expression patterns have evolved we have examined expression in the shark Scyliorhinus canicula
(dogfish) and frog Xenopus tropicalis. These results suggest that lbx1 spinal cord expression is highly conserved in
vertebrates. However, lbx2 is not expressed in the dogfish spinal cord suggesting that spinal cord expression of lbx2 may
have evolved in the ray-finned fish lineage. In mouse, Lbx1 is required to specify the inhibitory neurotransmitter
phenotypes of dI4 and dI6 spinal interneurons. We are using lbx mutants and morpholinos to determine if the additional
lbx spinal cord expression domains in zebrafish correlate with new spinal cord functions. 1 Wotton KR,Weierud
FK,Dietrich Sand Lewis KE.(2008). Comparative genomics of Lbx loci reveals conservation of identical Lbxohnologs in
bony vertebrates BMC Evol Biol. 8:171.
Program/Abstract # 229
Transcription factors with an ancient function in the specification of immunocytes
Solek, Cynthia M., University of Ottawa, Ottawa, Canada; Oliveri, Paola (University College London, London, United
Kingdom); Rast, Jonathan (Sunnybrook Research Institute, Toronto, Canada)
Vertebrate hematopoiesis is the focus of intense study, yet immunocyte development is well characterized in only a few
invertebrate groups. The sea urchin embryo provides a simple model for immune cell development in an organism that is
phylogenetically allied to vertebrates. Larval immunocytes, including pigment cells and subsets of the blastocoelar cells,
emerge from a small population of precursors specified at the blastula stage. A first step in immunocyte specification is the
division of this cell field into precursors with distinct blastocoelar and pigment cell gene regulatory programs. We
characterized the expression and function of key hematopoietic transcription regulators including SpGatac, an ortholog of
vertebrate Gata-1/2/3 and SpScl, an ortholog of Scl/Tal2/Lyl1. Both play critical roles in the specification of immunocytes.
Perturbation of SpGatac affects gastrulation, possibly through a secondary effect involving blastocoelar cell migration.
SpScl perturbation disrupts proper segregation of pigment and blastocoelar cell precursors by a non–cell-autonomous
mechanism. Orthologs of additional transcription regulators that interact with GATA and Scl factors invertebrate
hematopoiesis are also expressed in this system, including SpE2A, a homolog of vertebrate E2A/HEB/ITF2 and SpLmo2,
orthologous to a cofactor of the Scl-GATA transcription complex. Cis-regulatory analysis of SpGatac indicates that the
transcription factor SpGcm suppresses blastocoelar cell fate in pigment cell precursors by repressing SpGatac expression.