Little is known about venom in young developmental stages of animals. The appearance of toxins and stinging cells during early embryonic stages in the sea anemone Nematostella vectensis suggests that venom is already expressed in eggs and larvae of this species. Here, we harness transcriptomic, biochemical and transgenic tools to study venom production dynamics in Nematostella. We find that venom composition and arsenal of toxin-producing cells change dramatically between developmental stages of this species. These findings can be explained by the vastly different interspecific interactions of each life stage, as individuals develop from a miniature non-feeding mobile planula to a larger sessile polyp that predates on other animals and interact differently with predators. Indeed, behavioral assays involving prey, predators and Nematostella are consistent with this hypothesis. Further, the results of this work suggest a much wider and dynamic venom landscape than initially appreciated in animals with a complex life cycle.

Lactation is a key aspect of mammalian evolution for adaptation of various reproductive strategies along different mammalian lineages. Marsupials, such as tammar wallaby, adopted a short gestation and a relatively long lactation cycle, the newborn is immature at birth and significant development occurs postnatally during lactation. Continuous changes of tammar milk composition may contribute to development and immune protection of pouch young. Here, in order to address the putative contribution of newly identified secretory milk miRNA in these processes, high throughput sequencing of miRNAs collected from tammar milk at different time points of lactation was conducted. A comparative analysis was performed to find distribution of miRNA in milk and blood serum of lactating wallaby. Results showed that high levels of miRNA secreted in milk and allowed the identification of differentially expressed milk miRNAs during the lactation cycle as putative markers of mammary gland activity and functional candidate signals to assist growth and timed development of the young. Comparative analysis of miRNA distribution in milk and blood serum suggests that milk miRNAs are primarily expressed from mammary gland rather than transferred from maternal circulating blood, likely through a new putative exosomal secretory pathway. In contrast, highly expressed milk miRNAs could be detected at significantly higher levels in neonate blood serum in comparison to adult blood, suggesting milk miRNAs may be absorbed through the gut of the young. The function of miRNA in mammary gland development and secretory activity has been proposed, but results from the current study also support a differential role of milk miRNA in regulation of development in the pouch young, revealing a new potential molecular communication between mother and young during mammalian lactation.

PIWI-interacting RNAs (piRNAs) and associated proteins comprise a conserved pathway for silencing transposons in metazoan germlines. piRNA pathway components are also expressed in multipotent somatic stem cells in various organisms. piRNA functions have been extensively explored in bilaterian model systems, however, comprehensive studies in non-bilaterian phyla remain limited. Here we investigate the piRNA pathway during the development of Nematostella vectensis, a well-established model system belonging to Cnidaria, the sister group to Bilateria. To date, no population of somatic stem cells has been identified in this organism, despite its long life-span and regenerative capacities that require a constant cell-renewal. We show that Nematostella piRNA pathway components are broadly expressed in early developmental stages, while piRNAs themselves show differential expression, suggesting specific developmental roles of distinct piRNA families. In adults, piRNA associated proteins are enriched in the germline but also expressed in somatic cells, indicating putative stem cell properties. Furthermore, we provide experimental evidence that Nematostella piRNAs cleave transposable elements as well as protein-coding genes. Our results demonstrate that somatic expression of piRNA associated proteins as well as the roles of piRNAs in transposon repression and gene regulation are likely ancestral features that evolved before the split between Cnidaria and Bilateria.

Somatic cells dissociated from an adult sponge can re-organize and develop into a juvenile-like sponge, a remarkable phenomenon of regeneration. However, the extent to which regeneration recapitulates embryonic developmental pathways has remained enigmatic. We have standardized and established a sponge Sycon ciliatum regeneration protocol from dissociated cells. From the morphological analysis, we demonstrated that dissociated sponge cells follow a series of morphological events resembling postembryonic development. We performed high-throughput sequencing on regenerating samples and compared the data with regular postlarval development. Our comparative transcriptomic analysis illuminates that sponge regeneration is equally as dynamic as embryogenesis. We find that sponge regeneration is orchestrated by recruiting pathways like those utilized in embryonic development. We further demonstrated that sponge regeneration is accompanied by cell death at early stages, revealing the importance of apoptosis in remodelling the primmorphs to initiate re-development. Since sponges are likely to be the first branch of extant multicellular animals, we suggest that this system can be explored to study the genetic features underlying the evolution of multicellularity and regeneration.

Small non-coding RNAs (sRNAs) such as microRNAs (miRNAs), small interfering RNAs (siRNAs) and piwi-interacting RNAs (piRNAs) regulate the levels of endogenous, viral and transposable element RNA in plants (excluding piRNAs) and animals. These pathways are explored mainly in bilaterian animals, such as vertebrates, arthropods and nematodes, where siRNAs and piRNAs, but not miRNAs bind their targets with a perfect match and mediate the cleavage of the target RNA. Methylation of the 3′ ends of piRNAs and siRNAs by the methyltransferase HEN1 protects these sRNAs from degradation. There is a noticeable selection in bilaterian animals against miRNA-mRNA perfect matching, as it leads to the degradation of miRNAs. Cnidarians (sea anemones, corals, hydroids and jellyfish), are separated from bilaterians by more than 600 million years. As opposed to bilaterians, cnidarian miRNAs frequently bind their targets with a nearly perfect match. Knowing that an ortholog of HEN1 is widely expressed in the sea anemone Nematostella vectensis, we tested in this work whether it mediates the stabilization of its sRNAs. We show that the knockdown of HEN1 in Nematostella results in a developmental arrest. Small RNA sequencing revealed that the levels of both miRNAs and piRNAs drop dramatically in the morphant animals. Moreover, knockdown experiments of Nematostella Dicer1 and PIWI2, homologs of major bilaterian biogenesis components of miRNAs and piRNAs, respectively, resulted in developmental arrest similar to HEN1 morphants. Our findings suggest that HEN1 mediated methylation of sRNAs reflects the ancestral state, where miRNAs were also methylated. Thus, we provide the first evidence of a methylation mechanism that stabilizes miRNAs in animals, and highlight the importance of post-transcriptional regulation in non-bilaterian animals. Plants and animals use small RNAs to regulate gene expression, virus silencing and genomic integrity. These functions depend on specific binding of small RNAs to longer RNA targets. The methyltransferase HEN1 plays a crucial role in stabilizing small RNAs upon their binding to perfectly-matching targets. Lack of methylation in case of a perfect match will lead to small RNA degradation. In general, methylation of microRNAs, a class of small RNAs, is part of their biogenesis in plants, but not in bilaterian animals such as vertebrates, worms and insects, where perfectly-matching microRNA targets are rare. In contrast, in Cnidaria (sea anemones, corals and jellyfish), the sister group to Bilateria, microRNAs frequently bind their targets with a nearly perfect match. In this study, we show that in the cnidarian Nematostella vectensis methylation of microRNAs and other small RNAs is consistent and frequent throughout development and that knockdown of the cnidarian HEN1 results in a developmental arrest. Small RNA sequencing of the treated animals, reveals that small RNAs are depleted and shortened. Therefore, our findings suggest that HEN1-mediated methylation of small RNAs was present in the last common ancestor of Cnidaria and Bilateria 600 million years ago and was responsible for microRNA stabilization.