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The marine silicon cycle is intrinsically linked with carbon cycling in the oceans via biological production of silica by a wide range of organisms. The stable silicon isotopic composition (denoted by δ30Si) of siliceous microfossils extracted from sediment cores can be used as an archive of past oceanic silicon cycling. However, the silicon isotopic composition of biogenic silica has only been measured in diatoms, sponges and radiolarians, and isotopic fractionation relative to seawater is entirely unknown for many other silicifiers. Furthermore, the biochemical pathways and mechanisms that determine isotopic fractionation during biosilicification remain poorly understood. Here, we present the first measurements of the silicon isotopic fractionation during biosilicification by loricate choanoflagellates, a group of protists closely related to animals. We cultured two species of choanoflagellates, Diaphanoeca grandis and Stephanoeca diplocostata, which showed consistently greater isotopic fractionation (approximately −5 ‰ to −7 ‰) than cultured diatoms (−0.5 ‰ to −2.1 ‰). Instead, choanoflagellate silicon isotopic fractionation appears to be more similar to sponges grown under similar dissolved silica concentrations. Our results highlight that there is a taxonomic component to silicon isotope fractionation during biosilicification, possibly via a shared or related biochemical transport pathway. These findings have implications for the use of biogenic silica δ30Si produced by different silicifiers as proxies for past oceanic change.

This work was supported by Cancer Research UK [GS], a Wellcome Trust Senior Investigator Award (107116/Z/15/Z) [GS], and University College London [GS]. This work was further supported by the German Research Foundation (DFG; grant BL787/7-1) and an EU ASSEMBLE grant (No. 227799; http://www.assemblemarine.org) to CB. We acknowledge support from the German Research Foundation (DFG) and Universität Leipzig within the program of Open Access Publishing. [Background]: We present the first molecular characterization of glycerotoxin (GLTx), a potent neurotoxin found in the venom of the bloodworm Glycera tridactyla (Glyceridae, Annelida). Within the animal kingdom, GLTx shows a unique mode of action as it can specifically up-regulate the activity of Cav2.2 channels (N-type) in a reversible manner. The lack of sequence information has so far hampered a detailed understanding of its mode of action. [Conclusions]: Our results overturn a century old textbook view on the glycerid venom system, suggesting that it is anatomically and functionally much more complex than previously thought. The herein presented GLTx sequence information constitutes an important step towards the establishment of GLTx as a versatile tool to understand the mechanism of synaptic function, as well as the mode of action of this novel neurotoxin. [Results]: Our analyses reveal three ~3.8 kb GLTx full-length transcripts, show that GLTx represents a multigene family, and suggest it functions as a dimer. An integrative approach using transcriptomics, quantitative real-time PCR, in situ hybridization, and immunocytochemistry shows that GLTx is highly expressed exclusively in four pharyngeal lobes, a previously unrecognized part of the venom apparatus. © The Author(s). Peer Reviewed

The brittle star Amphiura filiformis, which regenerates its arms post autotomy, is emerging as a useful model for studying the molecular underpinnings of regeneration, aided by the recent availability of some molecular resources. During regeneration a blastema initially is formed distally to the amputation site, and then a rapid rebuild is obtained by adding metameric units, which will eventually differentiate and become fully functional. In this work we first characterize the developmental process of the regenerating arms using two differentiation markers for muscle and skeletal structures – Afi-trop-1 and Afi-αcoll. Both genes are not expressed in the blastema and newly added undifferentiated metameric units. Their expression at different regenerating stages shows an early segregation of muscle and skeletal cells during the regenerating process, long before the metameric units become functional. We then studied the expression of a set of genes orthologous of the sea urchin transcription factors involved in the development of skeletal and non-skeletal mesoderm: Afi-ets1/2, Afi-alx1, Afi-tbr, Afi-foxB and Afi-gataC. We found that Afi-ets1/2, Afi-alx1, Afi-foxB and Afi-gataC are all expressed at the blastemal stage. As regeneration progresses those genes are expressed in a similar small undifferentiated domain beneath the distal growth cap, while in more advanced metameric units they become restricted to different skeletal domains. Afi-foxB becomes expressed in non-skeletal structures. This suggests that they might play a combinatorial role only in the early cell specification process and that subsequently they function independently in the differentiation of different structures. Afi-tbr is not present in the adult arm tissue at any stage of regeneration. In situ hybridization results have been confirmed with a new strategy for quantitative PCR (QPCR), using a subdivision of the three stages of regeneration into proximal (differentiated) and distal (undifferentiated) arm segments. Highlights • Analysis of brittle star regenerating arms using differentiation markers. • Identification of the early segregation of skeletal and muscle progenitor cells. • Expression of skeletal and non-skeletal genes at different stages of regeneration. • Combinatorial role of TF genes in early specification of skeletal cells. • Same TF genes identify different skeletal structures later in regeneration.

The reaction sequences of central metabolism, glycolysis and the pentose phosphate pathway provide essential precursors for nucleic acids, amino acids and lipids. However, their evolutionary origins are not yet understood. Here, we provide evidence that their structure could have been fundamentally shaped by the general chemical environments in earth's earliest oceans. We reconstructed potential scenarios for oceans of the prebiotic Archean based on the composition of early sediments. We report that the resultant reaction milieu catalyses the interconversion of metabolites that in modern organisms constitute glycolysis and the pentose phosphate pathway. The 29 observed reactions include the formation and/or interconversion of glucose, pyruvate, the nucleic acid precursor ribose‐5‐phosphate and the amino acid precursor erythrose‐4‐phosphate, antedating reactions sequences similar to that used by the metabolic pathways. Moreover, the Archean ocean mimetic increased the stability of the phosphorylated intermediates and accelerated the rate of intermediate reactions and pyruvate production. The catalytic capacity of the reconstructed ocean milieu was attributable to its metal content. The reactions were particularly sensitive to ferrous iron Fe(II), which is understood to have had high concentrations in the Archean oceans. These observations reveal that reaction sequences that constitute central carbon metabolism could have been constrained by the iron‐rich oceanic environment of the early Archean. The origin of metabolism could thus date back to the prebiotic world.