Search

The dorsal neural tube of chordates and the ventral nerve cord of annelids exhibit a similar molecular mediolateral architecture. Accordingly, the presence of such a complex nervous system (CNS) has been proposed for their last common ancestor. Members of Enteropneusta, a group of non-chordate deuterostomes, possess a less complex CNS including a hollow neural tube, whereby homology to its chordate counterpart remains elusive. Since the majority of data on enteropneusts stem fromSaccoglossus kowalevskii,a derived direct-developer, we investigated expression of key neuronal patterning genes in the indirect-developerBalanoglossus misakiensis.The collar cord ofB. misakiensisshows anteriorSix3/6and posteriorOtx+engrailedexpression, in a region corresponding to the chordate brain. NeuronalNk2.1/Nk2.2expression is absent. Interestingly, we found medianDlxand lateralPax6expression domains, i.e., a condition that is reversed compared to chordates.Comparative analyses reveal that CNS patterning is highly conserved among enteropneusts.BmiDlxandBmiPax6have no corresponding expression domains in the chordate brain, which may be indicative of independent acquisition of a tubular CNS in Enteropneusta and Chordata. Moreover, mediolateral architecture varies considerably among chordates and enteropneusts, questioning the presence of a vertebrate-like patterned nervous system in the last common deuterostome ancestor.

How dispersal strategies impact the distribution of species and subsequent speciation events is a fundamental question in evolutionary biology. Sedentary benthic marine organisms, such as corals or sea anemones usually rely on motile larval stages for dispersal and therefore have a relatively restricted distribution along coasts. Edwardsiella lineata and Edwardsiella carnea are virtually indistinguishable edwardsiid sea anemones native to the east American and the Northern European coast, respectively. E. lineata is a facultative parasite to the ctenophore Mnemiopsis leidyi, while the life cycle of E. carnea is unknown. Recently M. leidyi was found in the Skagerrak carrying Edwardsiella sp. parasites, which raised the intriguing possibility that the invasive comb jellies acted as cargo for the facultative E. lineata parasites to establish a new population in Northern Europe. Here, we assessed the genetic differences between these two cryptic Edwardsiella species and isolated parasites from the invasive comb jelly M. leidyi in Sweden by comparing rRNA, whole transcriptomes, SNPs, ITS2 sequences and the gene complements of key developmental regulators, the Wnt gene family. We show that E. carnea and the parasite transcriptomes are more than 99% identical, hence demonstrating that E. carnea has a previously unknown parasitic life stage. ITS2 sequence analysis of E. carnea and E. lineata suggest that they may not be reproductively isolated. The transcriptomes of E. lineata and E. carnea are ∼97% identical. We also estimate that the species diverged between 18.7 and 21.6 million years ago.

MicroRNAs (miRNAs) are a unique class of short endogenous RNAs, which have become known in the past few decades as major players in gene regulation at the post-transcriptional level. Their regulatory roles make miRNAs crucial for normal development and physiology in several distinct groups of eukaryotes including plants and animals. The common notion is that miRNAs have evolved independently in those distinct lineages, but recent evidence from non-bilaterian metazoans, plants, and various algae raise the possibility that the last common ancestor of these lineages might already have employed an miRNA pathway for post-transcriptional regulation. In this Review we present the commonalities and differences of the miRNA pathways in various eukaryotes and discuss the contrasting scenarios of their possible evolutionary origin and their proposed link to organismal complexity and multicellularity. miRNAs are crucial regulators of normal development in plants and animals, but their origins remain obscure. Exploration of the similarities and differences between different miRNA pathways help to elucidate their origins and role.

Sea anemone venoms have become a rich source of peptide toxins which are invaluable tools for studying the structure and functions of ion channels. In this work, BcsTx3, a toxin found in the venom of a Bunodosoma caissarum (population captured at the Saint Peter and Saint Paul Archipelago, Brazil) was purified and biochemically and pharmacologically characterized. The pharmacological effects were studied on 12 different subtypes of voltage-gated potassium channels (K(V)1.1-K(V)1.6; K(V)2.1; K(V)3.1; K(V)4.2; K(V)4.3; hERG and Shaker IR) and three cloned voltage-gated sodium channel isoforms (Na(V)1.2, Na(V)1.4 and BgNa(V)1.1) expressed in Xenopus laevis oocytes. BcsTx3 shows a high affinity for Drosophila Shaker IR channels over rKv1.2, hKv1.3 and rKv1.6, and is not active on NaV channels. Biochemical characterization reveals that BcsTx3 is a 50 amino acid peptide crosslinked by four disulfide bridges, and sequence comparison allowed BcsTx3 to be classified as a novel type of sea anemone toxin acting on K(V) channels. Moreover, putative toxins homologous to BcsTx3 from two additional actiniarian species suggest an ancient origin of this newly discovered toxin family.