Meeting Abstract
The process of regeneration depends on proper cell growth throughout numerous cycles of cell division that, in turn, depend on the timely and flawless assembly of ribosomes. Hydractinia, a colonial marine hydroid from the phylum Cnidaria, is a proven model for the study of regeneration, as their stem cells are both pluripotent and have homologs to human genes associated with self-renewal and differentiation. We have determined the consensus sequence of rDNA repeats in Hydractinia, with four times as many rDNA repeats in its genome than seen in humans. While the coding sequences for each ribosomal component are similarly organized and roughly the same size, its intergenic spacer is 100 times shorter than in human. This suggests that Hydractinia rDNA array(s) may be under the control of a single promoter, enabling it to meet the high demand for ribosomes during regeneration. Protein domain structural analyses indicates that Hydractinia does not possess the canonical UBF protein, a transcription factor that binds to rDNA and required for the recruitment of the Pol I transcription machinery during ribosome biogenesis. The absence of UBF suggests that Hydractinia may employ a different mechanism for regulating transcription of rDNA genes than that used by higher eukaryotes, perhaps providing important insight as to the regenerative capacity of this organism. A comparison of de novo assembled transcriptomes across a wide taxonomic range indicates the canonical UBF protein is not present in non-bilaterians, suggesting the involvement of a novel protein or UBF precursor. This systematic characterization of rDNA repeats and transcription factors using comparative genomic approaches has already provided important clues as to the mechanisms underlying regeneration, providing a strong foundation for developing new clinical approaches to improve human health.
