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Comparative
developmental biology of marine annelids
In general, I am interested in the origins of body plan novelty
during evolution, and my lab has a developmental perspective, utilizing
a number of cellular and molecular approaches. My lab focuses on
polychaete annelids, and other vermiform lophotrochozoans such as
sipunculids, myzostomids and echiurans. We study multiple species
with distinct life history characteristics and body plan morphologies
to utilize the strengths of a comparative approach.
One of the
main research interests of the lab is the study of the evolution
of a segmented body plan. The evolution of segmentation in the Metazoa
has been the subject of a long-staining controversy. Segmented animals
are found within 3 major clades: the chordates, arthropods and annelids.
The annelids are the least understood at the molecular level of
how they generate segments during development, and we are trying
to understand the cellular and molecular basis by which segments
are generated in polychaetes during larval development, adult growth
and regeneration. One approach we have taken is to determine whether
genes involved in the segmentation process of arthropods influence
segment formation in polychaetes. We are also analyzing components
of the vertebrate somitogenesis pathway to determine whether annelids
and vertebrates utilize a common segmentation pathway.
The cellular origins of the segmented tissues in polychaetes are
poorly understood. Utilizing both time lapse video microscopy and
intracellular marking techniques, we are establishing fate maps
of the cleavage stage blastomeres, and in particular determining
which cells give rise to segmental tissues. Using markers of cell
division, we have also characterized the nature of the growth zone,
the generative zone of the segmental tissues, in Hydroides and Capitella
and how it changes between pre- and post- metamorphic stages.
Another area of
interest includes the specification of differences along the anterior-posterior
body axis. The large variation in body plan and tagmatization across
polychaetes makes them an ideal group of animals to study this issue,
and we are currently characterizing expression patterns of genes
involved in anterior-posterior patterning including members of the
Hox gene complex and closely related paraHox cluster in Capitella
and Hydroides. Other projects include the evolution of the nervous
system in annelids, and cell fate specification during early development.
Publications:
Seaver, E. C., Thamm, K. and Hill, S. (2005). Growth patterns during
segment formation in the annelids H. elegans and Capitella sp. I:
comparison of distinct life history stages in polychaetes. Evolution
and Development 7(4): 312-326.
Seaver, E. C. (2003)
Segmentation: mono or polyphyletic? Int. J. Dev Biol, 47: 583-596.
Seaver, E. C.,
Paulson, D., Irvine, S. Q. and Martindale, M. Q. 2001. The spatial
and temporal expression the Ch-en, the engrailed gene in the polychaete
Chaetopterus does not support a role in body axis segmentation.
Developmental Biology 236: 195-209.
Seaver, E. C.,
and Shankland, M. 2000. Extablishment of segment polarity in the
ectoderm of the leech Helobdella. Development 128: 1629-1641.
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