New genes are thought to arise rapidly via duplication and divergence but the proportion of novel genes that become functionally integrated into signaling networks may be very small. During the ~500 million years since cnidarians and bilaterians shared a common ancestor, over 30,000 genes are estimated to have duplicated (Lynch and Conery, 2000); yet, the genome of N. vectensis encodes only ~3,000 novel genes (Putnam et al., 2007), suggesting that gene duplication and gene loss are tightly coupled. Why, then, are some gene families disproportionately retained following duplication?
Trypsins are an important group of serine endopeptidases with broad proteolytic functions across animals. A recent investigation of the evolution of this gene family revealed a surprising level of trypsin functional diversity, even among the supposedly "simple" cnidarians (Babonis et al., 2019). This result suggests that rapid functional diversification promoted the retention of duplicates in this gene family, but why is this important? It suggests two things: first, that secretory (exocrine) cell identity underwent massive expansion in cnidarians despite the fact that these animals have only two tissue layers (endo- and ectoderm). Second, these results suggest the origin of the the secretory vesicle was essential for facilitating novel cell diversification in early animal lineages.
Photosensitive proteins play diverse roles in the biology of cnidarians (check out these cool examples: Quiroga Artigas et al., 2018; Plachetzki et al., 2012). Opsins present a curious case of duplication and retention in Nematostella vectensis as the genome of this eyeless cnidarian encodes ~30 unique opsin genes. (For comparison, the human genome encodes only 9.) Our examination of the tissue-specific expression patterns of these extraocular opsins, suggests cryptic functional diversity in this seemingly simple sea anemone. Using genome editing and pharmacological inhibition assays we are investigating the links between opsin function and photosensitive behaviors to understand the evolution of cell- and tissue complexity.
Babonis, LS, JF Ryan, C Enjolras, and MQ Martindale. (2019) Genomic analysis of the tryptome reveals molecular mechanisms of gland cell evolution. EvoDevo 10:23 Link
Lynch M, Conery JS. (2000) The evolutionary fate and consequences of duplicate genes. Science 290(5494):1151-5 Link
Plachetzki DC, Fong CR, Oakley TH. (2012) Cnidocyte discharge is regulated by light and opsin-mediated phototransduction. BMC Biol.10:17 Link
Putnam NH, Srivastava M, Hellsten U, Dirks B, Chapman J, Salamov A, et al. (2007) Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization. Science 317(5834):86–94 Link
Quiroga Artigas G, Lapébie P, Leclère L, et al. (2018) A gonad-expressed opsin mediates light-induced spawning in the jellyfish Clytia. Elife. 7:e29555 Link