Meeting Abstract
Colloblasts are a novel cell type found only in the tentacles of ctenophores (comb jellies). Upon contact, colloblasts secrete a sticky adhesive facilitating prey capture. These unusual cells were present in the last common ancestor of ctenophores but were lost in the stem of the clade containing Haeckelia and Beroe, the latter of which has lost tentacles altogether. Despite their important role in the ecology of ctenophores, little is known about the origin of colloblasts or the nature of the substance they secrete. We surveyed the transcriptomes of 36 species of ctenophores, including three from the genus Beroe and two from the genus Haeckelia, to identify genes that may have been lost concomitant with the loss of colloblasts and/or tentacles. Using a developmental time course of single-embryo RNA-Seq data from Mnemiopsis leidyi, we show that the expression profiles of candidate colloblast genes are distinct from other genes expressed during embryogenesis, exhibiting higher expression specifically during tentacle development. Functional annotation of these candidates suggests that proteins associated with post-translational modification and ion transport are abundant in colloblasts but no proteins with clear orthology to adhesive proteins from other species (e.g., barnacles) were identified. Additionally, over 30% of the colloblast-specific genes identified from the phylogenomic survey lacked known functional domains, suggesting they encode novel (potentially ctenophore-specific) proteins. Our analyses provide an intriguing first glimpse into the genetic makeup of ctenophore tentacles and their associated novel prey-capturing adhesive cells.
