Another biomineralising protostome with an msp130 gene and conservation of msp130 gene structure across Bilateria

Msp130 genes are known for their association with biomineralisation, principally in echinoderm skeletogenesis. Recently, msp130 genes were shown to exist more widely across the animal kingdom, including in molluscs, and a hypothesis was formed that the genes had arisen independently in the deuterostome and mollusc lineages via horizontal gene transfer, thus facilitating the evolution of biomineralisation in these distinct lineages (Ettensohn, 2014). Here we show that another biomineralising protostome, the polychaete Spirobranchus (formerly Pomatoceros) lamarcki also possesses an msp130 gene, and expresses it during a biomineralisation process. However, based on analysis of gene structure, we hypothesize that the protostome and deuterostome msp130 genes did not originate from independent horizontal gene transfers, but instead are descended from a gene already present in the bilaterian ancestor, with the gene being secondarily lost from several lineages.PostprintPeer reviewe

Improved understanding of the role of gene and genome duplications in chordate evolution with new genome and transcriptome sequences

Funding: MEA-R is supported by funding from the University of St Andrews School of Biology and St Leonard’s College. Work in the lab of DEKF is funded by the BBSRC (BB/S016856/1) with additional support from the European project Assemble Plus (H2020-INFRAIA-1-2016–2017; grant no. 730984).Comparative approaches to understanding chordate genomes have uncovered a significant role for gene duplications, including whole genome duplications, giving rise to and expanding gene families. In developmental biology, gene families created and expanded by both tandem and whole genome duplications (WGDs) are paramount. These genes, often involved in transcription and signalling, are candidates for underpinning major evolutionary transitions because they are particularly prone to retention and subfunctionalisation, neofunctionalisation, or specialisation following duplication. Under the subfunctionalisation model, duplication lays the foundation for the diversification of paralogues, especially in the context of gene regulation. Tandemly duplicated paralogues reside in the same regulatory environment, which may constrain them and result in a gene cluster with closely linked but subtly different expression patterns and functions. Ohnologues (WGD paralogues) often diversify by partitioning their expression domains between retained paralogues, amidst the many changes in the genome during rediploidisation, including chromosomal rearrangements and extensive gene losses. The patterns of these retentions and losses is still not fully understood, nor is the full extent of the impact of gene duplication on chordate evolution. The growing number of sequencing projects, genomic resources, transcriptomics, and improvements to genome assemblies for diverse chordates from non-model and under-sampled lineages like the coelacanth, as well as key lineages, such as amphioxus and lamprey, has allowed more informative comparisons within developmental gene families as well as revealing the extent of conserved synteny across whole genomes. This influx of data provides the tools necessary for phylogenetically-informed comparative genomics, which will bring us closer to understanding the evolution of chordate body plan diversity and the changes underpinning the origin and diversification of vertebrates.Publisher PDFPeer reviewe

TCF/Lef regulates the Gsx ParaHox gene in central nervous system development in chordates

This research was supported by a BBSRC-DTG studentship to M.G.G, and Clarendon, ORS and EPA Cephalosporin scholarships to P.W.O.Background The ParaHox genes play an integral role in the anterior-posterior (A-P) patterning of the nervous system and gut of most animals. The ParaHox cluster is an ideal system in which to study the evolution and regulation of developmental genes and gene clusters, as it displays similar regulatory phenomena to its sister cluster, the Hox cluster, but offers a much simpler system with only three genes. Results Using Ciona intestinalis transgenics, we isolated a regulatory element upstream of Branchiostoma floridae Gsx that drives expression within the central nervous system of Ciona embryos. The minimal amphioxus enhancer region required to drive CNS expression has been identified, along with surrounding sequence that increases the efficiency of reporter expression throughout the Ciona CNS. TCF/Lef binding sites were identified and mutagenized and found to be required to drive the CNS expression. Also, individual contributions of TCF/Lef sites varied across the regulatory region, revealing a partial division of function across the Bf-Gsx-Up regulatory element. Finally, when all TCF/Lef binding sites are mutated CNS expression is not only abolished, but a latent repressive function is also unmasked. Conclusions We have identified a B. floridae Gsx upstream regulatory element that drives CNS expression within transgenic Ciona intestinalis, and have shown that this CNS expression is dependent upon TCF/Lef binding sites. We examine the evolutionary and developmental implications of these results, and discuss the possibility of TCF/Lef not only as a regulator of chordate Gsx, but as a deeply conserved regulatory factor controlling all three ParaHox genes across the Metazoa.Publisher PDFPeer reviewe

Amphioxus muscle transcriptomes reveal vertebrate-like myoblast fusion genes and a highly conserved role of insulin signalling in the metabolism of muscle

Madeleine E. Aase-Remedios and Clara Coll-Lladó were supported by funding from the University of St Andrews, School of Biology and additional support from St Leonards College (MEAR), the CORBEL grant European Research Infrastructure cluster project and European Assemble Plus (H2020-INFRAIA-1-2016-2017; grant no.730984). Transcriptome sequencing was done with an award under the BBSRC TGAC Capacity and Capability Challenge.Background:   The formation and functioning of muscles are fundamental aspects of animal biology, and the evolution of ‘muscle genes’ is central to our understanding of this tissue. Feeding-fasting-refeeding experiments have been widely used to assess muscle cellular and metabolic responses to nutrition. Though these studies have focused on vertebrate models and only a few invertebrate systems, they have found similar processes are involved in muscle degradation and maintenance. Motivation for these studies stems from interest in diseases whose pathologies involve muscle atrophy, a symptom also triggered by fasting, as well as commercial interest in the muscle mass of animals kept for consumption. Experimentally modelling atrophy by manipulating nutritional state causes muscle mass to be depleted during starvation and replenished with refeeding so that the genetic mechanisms controlling muscle growth and degradation can be understood. Results:  Using amphioxus, the earliest branching chordate lineage, we address the gap in previous work stemming from comparisons between distantly related vertebrate and invertebrate models. Our amphioxus feeding-fasting-refeeding muscle transcriptomes reveal a highly conserved myogenic program and that the pro-orthologues of many vertebrate myoblast fusion genes were present in the ancestral chordate, despite these invertebrate chordates having unfused mononucleate myocytes. We found that genes differentially expressed between fed and fasted amphioxus were orthologous to the genes that respond to nutritional state in vertebrates. This response is driven in a large part by the highly conserved IGF/Akt/FOXO pathway, where depleted nutrient levels result in activation of FOXO, a transcription factor with many autophagy-related gene targets. Conclusion:  Reconstruction of these gene networks and pathways in amphioxus muscle provides a key point of comparison between the distantly related groups assessed thus far, significantly refining the reconstruction of the ancestral state for chordate myoblast fusion genes and identifying the extensive role of duplicated genes in the IGF/Akt/FOXO pathway across animals. Our study elucidates the evolutionary trajectory of muscle genes as they relate to the increased complexity of vertebrate muscles and muscle development.Publisher PDFPeer reviewe

More than one-to-four via 2R : evidence of an independent amphioxus expansion and two-gene ancestral vertebrate state for MyoD-related Muscle Regulatory Factors (MRFs)

Funding: Madeleine Aase-Remedios and Dr Clara Coll-Lladówere supported by funding from the University of St Andrews, School of Biology and additional support from the CORBEL grant European Research Infrastructure cluster project.The evolutionary transition from invertebrates to vertebrates involved extensive gene duplication, but understanding precisely how such duplications contributed to this transition requires more detailed knowledge of specific cases of genes and gene families. MyoD (Myogenic differentiation) has long been recognized as a master developmental control gene and member of the MyoD family of bHLH transcription factors (Myogenic regulatory factors, MRFs) that drive myogenesis across the bilaterians. Phylogenetic reconstructions within this gene family are complicated by multiple instances of gene duplication and loss in several lineages. Following two rounds of whole genome duplication (2R WGD) at the origin of the vertebrates the ancestral function of MRFs is thought to have become partitioned amongst the daughter genes, so that MyoD and Myf5 act early in myogenic determination while Myog and Myf6 are expressed later, in differentiating myoblasts. Comparing chordate MRFs, we find an independent expansion of MRFs in the invertebrate chordate amphioxus, with evidence for a parallel instance of subfunctionalisation relative to that of vertebrates. Conserved synteny between chordate MRF loci supports the 2R WGD events as a major force in shaping the evolution of vertebrate MRFs. We also resolve vertebrate MRF complements and organization, finding a new type of vertebrate MRF gene in the process, which allowed us to infer an ancestral two-gene state in the vertebrates corresponding to the early- and late-acting types of MRFs. This necessitates a revision of previous conclusions about the simple one-to-four origin of vertebrate MRFs.Publisher PDFPeer reviewe

Functionally diverse front-end desaturases are widespread in the phylum Annelida

Funding: This study was funded through the project IMPROMEGA Agencia Española de Investigación, Spain, grant no. RTI2018-095119-B-100, MCIN/AEI/ FEDER/UE / MCIN/AEI/10.13039/501100011033/ and FEDER "A way to make Europe". Additionally, this study forms part of the ThinkInAzul programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Generalitat Valenciana (THINKINAZUL/2021/26).Aquatic single-cell organisms have long been believed to be unique primary producers of omega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA). Multiple invertebrates including annelids have been discovered to possess methyl-end desaturases enabling key steps in the de novo synthesis of ω3 LC-PUFA, and thus potentially contributing to their production in the ocean. Along methyl-end desaturases, the repertoire and function of further LC-PUFA biosynthesising enzymes is largely missing in Annelida. In this study we examined the front-end desaturase gene repertoire across the phylum Annelida, from Polychaeta and Clitellata, major classes of annelids comprising most annelid diversity. We further characterised the functions of the encoded enzymes in selected representative species by using a heterologous expression system based in yeast, demonstrating that functions of Annelida front-end desaturases have highly diversified during their expansion in both terrestrial and aquatic ecosystems. We concluded that annelids possess at least two front-end desaturases with Δ5 and Δ6Δ8 desaturase regioselectivities, enabling all the desaturation reactions required to convert the C18 precursors into the physiologically relevant LC-PUFA such as eicosapentaenoic and arachidonic acids, but not docosahexaenoic acid. Such a gene complement is conserved across the different taxonomic groups within Annelida.Publisher PDFPeer reviewe

A revised spiralian homeobox gene classification incorporating new polychaete transcriptomes reveals a diverse TALE class and a divergent Hox gene

The diversity of mechanisms and capacity for regeneration across the Metazoa present an intriguing challenge in evolutionary biology, impacting on the burgeoning field of regenerative medicine. Broad taxonomic sampling is essential to improve our understanding of regeneration, and studies outside of the traditional model organisms have proved extremely informative. Within the historically under-studied Spiralia, the Annelida have an impressive variety of tractable regenerative systems. The biomeralising, blastema-less regeneration of the head appendage (operculum) of the serpulid polychaete keelworm Spirobranchus (formerly Pomatoceros) lamarcki is one such system. To profile potential regulatory mechanisms, we classified the homeobox gene content of opercular regeneration transcriptomes. As a result of retrieving several difficult-to-classify homeobox sequences, we performed an extensive search and phylogenetic analysis of the TALE and PRD-class homeobox gene content of a broad selection of lophotrochozoan genomes. These analyses contribute to our increasing understanding of the diversity, taxonomic extent, rapid evolution, and radical flexibility of these recently discovered homeobox gene radiations. Our expansion and integration of previous nomenclature systems helps to clarify their cryptic orthology. We also describe an unusual divergent S. lamarcki Antp gene, a previously unclassified lophotrochozoan orphan gene family (Lopx), and a number of novel Nk class orphan genes. The expression and potential involvement of many of these lineage- and clade-restricted homeobox genes in S. lamarcki operculum regeneration provides an example of diversity in regenerative mechanisms, as well as significantly improving our understanding of homeobox gene evolution.Publisher PDFPeer reviewe

Genome of the rams horn snail Biomphalaria straminea : an obligate intermediate host of schistosomiasis

This work was supported by the Hong Kong Research Grant Council Collaborative Research Fund (C4015-20EF), General Research Fund (14100919), NSFC/RGC Joint Research Scheme (N_CUHK401/21), and The Chinese University of Hong Kong Direct Grant (4053433, 4053489). Y.Y., W.L.S., C.F.W., S.T.S.L., and Y.L. were supported by the Ph.D. studentships of The Chinese University of Hong Kong. A.H. is supported by a Biotechnology and Biological Sciences Research Council (BBSRC) David Phillips Fellowship (BB/N020146/1). T.B. is supported by a studentship from the Biotechnology and Biological Sciences Research Council-funded South West Biosciences Doctoral Training Partnership (BB/M009122/1). M.E.A.R. is supported by a Ph.D. studentship from the School of Biology and St Andrews University.Background: Schistosomiasis, or bilharzia, is a parasitic disease caused by trematode flatworms of the genus Schistosoma. Infection by Schistosoma mansoni in humans results when cercariae emerge into water from freshwater snails in the genus Biomphalaria and seek out and penetrate human skin. The snail Biomphalaria straminea is native to South America and is now also present in Central America and China, and represents a potential vector host for spreading schistosomiasis. To date, genomic information for the genus is restricted to the neotropical species Biomphalaria glabrata. This limits understanding of the biology and management of other schistosomiasis vectors, such as B. straminea. Findings: Using a combination of Illumina short‐read, 10X Genomics linked‐read, and Hi‐C sequencing data, our 1.005 Gb B. straminea genome assembly is of high contiguity, with a scaffold N50 of 25.3 Mb. Transcriptomes from adults were also obtained. Developmental homeobox genes, hormonal genes, and stress-response genes were identified, and repeat content was annotated (40.68% of genomic content). Comparisons with other mollusc genomes (including Gastropoda, Bivalvia, and Cephalopoda) revealed syntenic conservation, patterns of homeobox gene linkage indicative of evolutionary changes to gene clusters, expansion of heat shock protein genes, and the presence of sesquiterpenoid and cholesterol metabolic pathway genes in Gastropoda. In addition, hormone treatment together with RT-qPCR assay reveal a sesquiterpenoid hormone responsive system in B. straminea, illustrating that this renowned insect hormonal system is also present in the lophotrochozoan lineage. Conclusion: This study provides the first genome assembly for the snail B. straminea and offers an unprecedented opportunity to address a variety of phenomena related to snail vectors of schistosomiasis, as well as evolutionary and genomics questions related to molluscs more widely.Publisher PDFPeer reviewe

Mechanisms of gene duplication and translocation and progress towards understanding their relative contributions to animal genome evolution

Duplication of genetic material is clearly a major route to genetic change, with consequences for both evolution and disease. A variety of forms and mechanisms of duplication are recognised, operating across the scales of a few base pairs upto entire genomes. With the ever-increasing amounts of gene and genome sequence data that are becoming available, our understanding of the extent of duplication is greatly improving, both in terms of the scales of duplication events as well as their rates of occurrence. An accurate understanding of these processes is vital if we are to properly understand important events in evolution as well as mechanisms operating at the level of genome organisation. Here we will focus on duplication in animal genomes and how the duplicated sequences are distributed, with the aim of maintaining a focus on principles of evolution and organisation that are most directly applicable to the shaping of our own genome.Publisher PDFPeer reviewe

Biomineralisation during operculum regeneration in the polychaete Spirobranchus lamarcki

RS was supported by a Carnegie Scholarship.Formation of calcified biominerals is widespread in marine animals and is often associated with important elements of their biology, such as support and protection. Serpulid polychaetes are relatively understudied examples of biomineralisation despite their prominence in many marine ecosystems. An investigation of calcification in the regenerating opercular plate of the serpulid polychaete Spirobranchus (formerly Pomatoceros) lamarcki was performed using optical microscopy, calcein labelling and powder diffraction analysis. Worms were collected between January 2012 and June 2013 from East Sands beach, St Andrews, Scotland (56.33° N, 2.78° W). The earliest visible signs of calcification were birefringent grains. Later-stage regenerates displayed a complex mixture of calcified structures including grains, round, smooth tiles, and larger tiles with a rugged appearance. The plate matures by the growth and eventual merging of tiles into a contiguous crust. Calcein pulse-chase experiments showed the progression of calcification from the centre towards the edge of the plate, and powder diffraction analysis of three regenerative stages revealed a major shift in mineralogy from a predominantly calcitic to a predominantly aragonitic composition. The mechanisms underlying the shift are currently unknown. These are the first mineralogical data comparing different developmental stages in a serpulid operculum, and contribute to the understanding of biomineralisation in this group.PostprintPeer reviewe