This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: A colony of the hydrozoan Hydractinia symbiolongicarpus comprises genetically identical yet
morphologically distinct and functionally specialized polyp types. The main labor divisions are between feeding,
reproduction and defense. In H. symbiolongicarpus, the feeding polyp (called a gastrozooid) has elongated tentacles
and a mouth, which are absent in the reproductive polyp (gonozooid) and defensive polyp (dactylozooid). Instead,
the dactylozooid has an extended body column with an abundance of stinging cells (nematocysts) and the
gonozooid bears gonophores on its body column. Morphological differences between polyp types can be
attributed to simple changes in their axial patterning during development, and it has long been hypothesized that
these specialized polyps arose through evolutionary alterations in oral-aboral patterning of the ancestral gastrozooid.
Results: An assembly of 66,508 transcripts (>200 bp) were generated using short-read Illumina RNA-Seq libraries
constructed from feeding, reproductive, and defensive polyps of H. symbiolongicarpus. Using several different
annotation methods, approximately 54% of the transcripts were annotated. Differential expression analyses were
conducted between these three polyp types to isolate genes that may be involved in functional, histological, and
pattering differences between polyp types. Nearly 7 K transcripts were differentially expressed in a polyp-specific
manner, including members of the homeodomain, myosin, toxin and BMP gene families. We report the spatial
expression of a subset of these polyp-specific transcripts to validate our differential expression analyses.
Conclusions: While potentially originating through simple changes in patterning, polymorphic polyps in Hydractinia
are the result of differentially expressed functional, structural, and patterning genes.
The differentially expressed genes identified in our study provide a starting point for future investigations of the
developmental patterning and functional differences that are displayed in the different polyp types that confer a
division of labor within a colony of H. symbiolongicarpus.
Sanders, S.M., Shcheglovitova, M., and Cartwright, P. (2014) Differential gene expression between functionally specialized polyps of the colonial hydrozoan Hydractinia symbiolongicarpus (Phylum Cnidaria). BMC Genomics, 15:406, 1471-2164. http://dx.doi.org/10.1186/1471-2164-15-406
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