Transcriptome analysis in Hydractinia echinata reveals species-specific and phylum-wide gene loss
Doonan, Liam B.
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The advances and subsequent widespread use of next-generation sequencing, in particular transcriptomics, has allowed biologists to approach questions and study many more powerful and previously underappreciated model animals in much greater detail. One such creature is the cnidarian Hydractinia echinata, which is often used in stem cell, developmental and regenerative studies. Recent advances in transgenics and the near completion of a sequenced genome has propelled Hydractinia to the forefront of cnidarian biology. Here a new and up-to-date reference transcriptome for H. echinata is presented. Quality metrics and annotation results are comparable to other cnidarians and demonstrates a high level of completeness. It also reveals a well conserved genetic landscape, similar to other cnidarians and bilaterian invertebrates. Using this transcriptome as a reference, two superfamilies were examined in detail; the homeodomain proteins, and the lectins. Results show a highly diverse repertoire of these large groups, both in Hydractinia and in other early-diverging clades. The lectin complement was found to be not only expansive, but putatively highly conserved in function. However, results have also revealed a surprising amount of species-specific gene loss, particularly within the homeoboxes. Expansion and comparison of these findings in other metazoans has exposed a previously overlooked and potentially evolutionary important phylum-wide loss of galectins in all Cnidaria. These discoveries raise interesting questions about cnidarian life-history, including the possible implications of these loss events in the evolution of and diversification of hydrozoans such as Hydractinia, and for other cnidarians.