Local and global changes in cell density induce reorganisation of 3D packing in a proliferating epithelium

Tissue morphogenesis is intimately linked to the changes in shape and organisation of individual cells. In curved epithelia, cells can intercalate along their own apicobasal axes, adopting a shape named 'scutoid' that allows energy minimization in the tissue. Although several geometric and biophysical factors have been associated with this 3D reorganisation, the dynamic changes underlying scutoid formation in 3D epithelial packing remain poorly understood. Here, we use live imaging of the sea star embryo coupled with deep learning-based segmentation to dissect the relative contributions of cell density, tissue compaction and cell proliferation on epithelial architecture. We find that tissue compaction, which naturally occurs in the embryo, is necessary for the appearance of scutoids. Physical compression experiments identify cell density as the factor promoting scutoid formation at a global level. Finally, the comparison of the developing embryo with computational models indicates that the increase in the proportion of scutoids is directly associated with cell divisions. Our results suggest that apico-basal intercalations appearing immediately after mitosis may help accommodate the new cells within the tissue. We propose that proliferation in a compact epithelium induces 3D cell rearrangements during development.

Sex-specific expression of pheromones and other signals in gravid starfish

BACKGROUND

Many echinoderms form seasonal aggregations prior to spawning. In some fecund species, a spawning event can lead to population outbreaks with detrimental ecosystem impacts. For instance, outbreaks of crown-of-thorns starfish (COTS), a corallivore, can destroy coral reefs. Here, we examine the gene expression in gravid male and female COTS prior to spawning in the wild, to identify genome-encoded factors that may regulate aggregation and spawning. This study is informed by a previously identified exoproteome that attracts conspecifics. To capture the natural gene expression profiles, we isolated RNAs from gravid female and male COTS immediately after they were removed from the Great Barrier Reef.  RESULTS: Sexually dimorphic gene expression is present in all seven somatic tissues and organs that we surveyed and in the gonads. Approximately 40% of the exoproteome transcripts are differentially expressed between sexes. Males uniquely upregulate an additional 68 secreted factors in their testes. A suite of neuropeptides in sensory organs, coelomocytes and gonads is differentially expressed between sexes, including the relaxin-like gonad-stimulating peptide and gonadotropin-releasing hormones. Female sensory tentacles-chemosensory organs at the distal tips of the starfish arms-uniquely upregulate diverse receptors and signalling molecules, including chemosensory G-protein-coupled receptors and several neuropeptides, including kisspeptin, SALMFamide and orexin.

CONCLUSIONS

Analysis of 103 tissue/organ transcriptomes from 13 wild COTS has revealed genes that are consistently differentially expressed between gravid females and males and that all tissues surveyed are sexually dimorphic at the molecular level. This finding is consistent with female and male COTS using sex-specific pheromones to regulate reproductive aggregations and synchronised spawning events. These pheromones appear to be received primarily by the sensory tentacles, which express a range of receptors and signalling molecules in a sex-specific manner. Furthermore, coelomocytes and gonads differentially express signalling and regulatory factors that control gametogenesis and spawning in other echinoderms.

Single-cell RNA-sequencing analysis of early sea star development

Echinoderms represent a broad phylum with many tractable features to test evolutionary changes and constraints. Here, we present a single-cell RNA-sequencing analysis of early development in the sea star Patiria miniata, to complement the recent analysis of two sea urchin species. We identified 20 cell states across six developmental stages from 8 hpf to mid-gastrula stage, using the analysis of 25,703 cells. The clusters were assigned cell states based on known marker gene expression and by in situ RNA hybridization. We found that early (morula, 8-14 hpf) and late (blastula-to-mid-gastrula) cell states are transcriptionally distinct. Cells surrounding the blastopore undergo rapid cell state changes that include endomesoderm diversification. Of particular import to understanding germ cell specification is that we never see Nodal pathway members within Nanos/Vasa-positive cells in the region known to give rise to the primordial germ cells (PGCs). The results from this work contrast the results of PGC specification in the sea urchin, and the dataset presented here enables deeper comparative studies in tractable developmental models for testing a variety of developmental mechanisms.

Optimizing CRISPR/Cas9-based gene manipulation in echinoderms

The impact of new technology can be appreciated by how broadly it is used. Investigators that previously relied only on pharmacological approaches or the use of morpholino antisense oligonucleotide (MASO) technologies are now able to apply CRISPR-Cas9 to study biological problems in their model organism of choice much more effectively. The transitions to new CRISPR-based approaches could be enhanced, first, by standardized protocols and education in their applications. Here we summarize our results for optimizing the CRISPR-Cas9 technology in a sea urchin and a sea star, and provide advice on how to set up CRISPR-Cas9 experiments and interpret the results in echinoderms. Our goal through these protocols and sharing examples of success by other labs is to lower the activation barrier so that more laboratories can apply CRISPR-Cas9 technologies in these important animals.

Post-transcriptional regulation of factors important for the germ line

Echinoderms are a major model system for many general aspects of biology, including mechanisms of gene regulation. Analysis of transcriptional regulation (Gene regulatory networks, direct DNA-binding of proteins to specific cis-elements, and transgenesis) has contributed to our understanding of how an embryo works. This chapter looks at post-transcriptional gene regulation in the context of how the primordial germ cells are formed, and how the factors essential for this process are regulated. Important in echinoderms, as in many embryos, is that key steps of fate determination are made post-transcriptionally. This chapter highlights these steps uncovered in sea urchins and sea stars, and links them to a general theme of how the germ line may regulate its fate differently than many of the embryo's somatic cell lineages.

A conserved node in the regulation of Vasa between an induced and an inherited program of primordial germ cell specification

Primordial germ cells (PGCs) are specified by diverse mechanisms in early development. In some animals, PGCs are specified via inheritance of maternal determinants, while in others, in a process thought to represent the ancestral mode, PGC fate is induced by cell interactions. Although the terminal factors expressed in specified germ cells are widely conserved, the mechanisms by which these factors are regulated can be widely diverse. Here we show that a post-translational mechanism of germ cell specification is conserved between two echinoderm species thought to employ divergent germ line segregation strategies. Sea urchins segregate their germ line early by an inherited mechanism. The DEAD-box RNA - helicase Vasa, a conserved germline factor, becomes enriched in the PGCs by degradation in future somatic cells by the E3-ubiquitin-ligase Gustavus (Gustafson et al., 2011). This post-translational activity occurs early in development, substantially prior to gastrulation. Here we test this process in germ cell specification of sea star embryos, which use inductive signaling mechanisms after gastrulation for PGC fate determination. We find that Vasa-GFP protein becomes restricted to the PGCs in the sea star even though the injected mRNA is present throughout the embryo. Gustavus depletion, however, results in uniform accumulation of the protein. These data demonstrate that Gustavus-mediated Vasa turnover in somatic cells is conserved between species with otherwise divergent PGC specification mechanisms. Since Gustavus was originally identified in Drosophila melanogaster to have similar functions in Vasa regulation (Kugler et al., 2010), we conclude that this node of Vasa regulation in PGC formation is ancestral and evolutionarily transposable from the ancestral, induced PGC specification program to an inherited PGC specification mechanism.

Use of Echinoderm Gametes and Early Embryos for Studying Meiosis and Mitosis

The early embryos of sea urchins and other echinoderms have served as experimental models for the study of cell division since the nineteenth century. Their rapid development, optical clarity, and ease of manipulation continue to offer advantages for studying spindle assembly and cytokinesis. In the absence of transgenic lines, alternative strategies must be employed to visualize microtubules and actin. Here, we describe methods to visualize actin and microtubule using either purified, recombinant proteins, or probes in in vitro-transcribed mRNAs.

Exposure to methylmercury and inorganic mercury in the food does not lead to trophic magnification in the sea star Asterias rubens

Methylmercury accumulated at the top of aquatic food chains constitutes a toxicological risk to humans and other top predators. Biomagnification of methylmercury takes place among vertebrates at the higher trophic levels, but this process is less elucidated in benthic invertebrates at the lower trophic levels. Therefore, we investigated the accumulation from food and elimination of methylmercury and inorganic mercury in the benthic sea star Asterias rubens (L.) - a representative of trophic level ~3 - in laboratory experiments. Sea stars fed over 49 days with contaminated mussels (Mytilus edulis) accumulate methylmercury and inorganic mercury to the highest concentrations in the digestive glands, the pyloric caeca, less in stomach, gonad, tube feet, aboral body wall and not to detectable levels in the coelomic fluid. Concerning whole body contents, steady states were reached for both methylmercury and inorganic mercury during the 7-week feeding period and the sea stars reached approximately ½ and ¼ of the concentrations in the mussel food for the two mercury forms, respectively. Half-lives for the elimination of the two mercury forms varied between 45 and 173 days in a 140-d elimination period following the feeding period; inorganic mercury was eliminated faster than methylmercury. Examination of total mercury concentrations in field-collected sea stars confirmed this lack of trophic magnification in relation to the major food items, soft parts of molluscs. We suggest that mercury is not trophically magnified in sea stars 1) because they eliminate methylmercury faster than larger fish and decapod crustaceans and 2) maybe more importantly, because inorganic mercury with its faster elimination constitutes a larger fraction of the total mercury in the food at the lower trophic levels - as opposed to methylmercury which dominates at the higher trophic levels.

Procuring animals and culturing of eggs and embryos

Echinoderms and especially echinoids have a rich history as model systems for the study of oogenesis, fertilization, and early embryogenesis. The ease of collecting and maintaining adults, as well as in obtaining gametes and culturing large quantities of synchronous embryos, is complemented by the ability to do biochemistry, reverse genetics, embryo manipulations and study gene regulatory networks. The diversity of species and developmental modes as well as unparalleled transparency in early developmental stages also makes echinoderms an excellent system in which to study evolutionary aspects of developmental biology. This chapter provides a practical guide to experimental methods for procuring adults and gametes, achieving synchronous in vitro fertilization, and culturing embryos through early larval stages for several echinoderm species representing four classes (Echinoidea, Asteroidea, Ophiuroidea, and Holothuroidea). We provide specific examples of protocols for obtaining adults and gametes and for culturing embryos of a selected number of species for experimental analysis of their development. The species were chosen to provide breadth across the phylum Echinodermata, as well as to provide practical guidelines for handling some of the more commonly studied species. For each species, we highlight specific advantages, and special note is made of key issues to consider when handling adults, collecting gametes, or setting and maintaining embryo cultures. Finally, information regarding interspecific crosses is provided.

Analysis of sea star larval regeneration reveals conserved processes of whole-body regeneration across the metazoa

Background

Metazoan lineages exhibit a wide range of regenerative capabilities that vary among developmental stage and tissue type. The most robust regenerative abilities are apparent in the phyla Cnidaria, Platyhelminthes, and Echinodermata, whose members are capable of whole-body regeneration (WBR). This phenomenon has been well characterized in planarian and hydra models, but the molecular mechanisms of WBR are less established within echinoderms, or any other deuterostome system. Thus, it is not clear to what degree aspects of this regenerative ability are shared among metazoa.

Results

We characterize regeneration in the larval stage of the Bat Star (Patiria miniata). Following bisection along the anterior-posterior axis, larvae progress through phases of wound healing and re-proportioning of larval tissues. The overall number of proliferating cells is reduced following bisection, and we find evidence for a re-deployment of genes with known roles in embryonic axial patterning. Following axial respecification, we observe a significant localization of proliferating cells to the wound region. Analyses of transcriptome data highlight the molecular signatures of functions that are common to regeneration, including specific signaling pathways and cell cycle controls. Notably, we find evidence for temporal similarities among orthologous genes involved in regeneration from published Platyhelminth and Cnidarian regeneration datasets.

Conclusions

These analyses show that sea star larval regeneration includes phases of wound response, axis respecification, and wound-proximal proliferation. Commonalities of the overall process of regeneration, as well as gene usage between this deuterostome and other species with divergent evolutionary origins reveal a deep similarity of whole-body regeneration among the metazoa.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0633-9) contains supplementary material, which is available to authorized users.

Genomic resources for the study of echinoderm development and evolution

Echinoderms are important research models for a wide range of biological questions. In particular, echinoderm embryos are exemplary models for dissecting the molecular and cellular processes that drive development and testing how these processes can be modified through evolution to produce the extensive morphological diversity observed in the phylum. Modern attempts to characterize these processes depend on some level of genomic analysis; from querying annotated gene sets to functional genomics experiments to identify candidate cis-regulatory sequences. Given how essential these data have become, it is important that researchers using available datasets or performing their own genome-scale experiments understand the nature and limitations of echinoderm genomic analyses. In this chapter we highlight the current state of echinoderm genomic data and provide methodological considerations for common approaches, including analysis of transcriptome and functional genomics datasets.

Culturing echinoderm larvae through metamorphosis

Echinoderms are favored study organisms not only in cell and developmental biology, but also physiology, larval biology, benthic ecology, population biology and paleontology, among other fields. However, many echinoderm embryology labs are not well-equipped to continue to rear the post-embryonic stages that result. This is unfortunate, as such labs are thus unable to address many intriguing biological phenomena, related to their own cell and developmental biology studies, that emerge during larval and juvenile stages. To facilitate broader studies of post-embryonic echinoderms, we provide here our collective experience rearing these organisms, with suggestions to try and pitfalls to avoid. Furthermore, we present information on rearing larvae from small laboratory to large aquaculture scales. Finally, we review taxon-specific approaches to larval rearing through metamorphosis in each of the four most commonly-studied echinoderm classes-asteroids, echinoids, holothuroids and ophiuroids.

Involvement of sulfated biopolymers in adhesive secretions produced by marine invertebrates

Many marine invertebrates use adhesive secretions to attach to underwater surfaces and functional groups borne by their adhesive proteins and carbohydrates, such as catechols and phosphates, play a key role in adhesion. The occurrence of sulfates as recurrent moieties in marine bioadhesives suggests that they could also be involved. However, in most cases, their presence in the adhesive material remains speculative. We investigated the presence of sulfated biopolymers in five marine invertebrates representative of the four types of adhesion encountered in the sea: mussels and tubeworms for permanent adhesion, limpets for transitory adhesion, sea stars for temporary adhesion and sea cucumbers for instantaneous adhesion. The dry adhesive material of mussels, sea stars and sea cucumbers contained about 1% of sulfate. Using anti-sulfotyrosine antibodies and Alcian Blue staining, sulfated proteins and sulfated proteoglycans and/or polysaccharides were identified in the secretory cells and adhesive secretions of all species except the tubeworm. Sulfated proteoglycans appear to play a role only in the non-permanent adhesion of sea stars and limpets in which they could mediate cohesion within the adhesive material. In mussels and sea cucumbers, sulfated biopolymers would rather have an anti-adhesive function, precluding self-adhesion.

Complete mitochondrial genome analysis of Distolasterias nipon (Echinodermata, Asteroidea, Forcipulatida)

In this study, we determined the complete mitochondrial genome sequences of Distolasterias nipon belonging to the class Asteroidea in the phylum Echinodermata. The complete mitogenome of D. nipon was 16,193 bp in length and consisted of 13 protein-coding genes (PCGs), 22 tRNAs, and 2 rRNAs. The orders of PCGs and rRNAs were identical to those of the eight recorded mitogenomes of asteroids. The phylogenetic tree determined by the maximum likelihood method revealed that D. nipon was clearly grouped with Aphelasterias japonica and Asterias amurensis, which belong to the family Asteriidae.

Identification of a novel antimicrobial peptide from the sea star Patiria pectinifera

Antimicrobial peptides (AMPs) are components of innate immunity found in many forms of life. However, there have been no reports of AMPs in sea star (Phylum Echinodermata). Here we report the isolation and characterization of a novel antimicrobial peptide from the coelomic epithelium extract of the sea star Patiria pectinifera. The isolated peptide comprises 38 amino acid residues, is cationic (pI 9.2), has four cysteine residues that form two disulfide bonds (C1-C3 and C2-C4), is amidated at the C-terminus, and is designated P. pectinifera cysteine-rich antimicrobial peptide (PpCrAMP). Synthetic PpCrAMP identical to the native peptide exhibited the most potent antimicrobial activity compared to analogs with different disulfide bond configurations. Expression analysis of PpCrAMP precursor transcripts revealed constitutive expression in the coelomic epithelium and tube feet of P. pectinifera. Analysis of genomic DNA and cDNA encoding the PpCrAMP precursor protein revealed that an intron splits the coding region of the mature peptide into a positively charged N-terminal domain and a C-terminal domain harboring four cysteine residues and a glycine for C-terminal amidation. No significant homology with other known AMPs was observed, while orthologs of PpCrAMP were found in other echinoderm species. These findings indicate that PpCrAMP is the prototype of a family a novel cysteine-rich AMPs that participate in mechanisms of innate immunity in echinoderms. Furthermore, the discovery of PpCrAMP may lead to the identification of related AMPs in vertebrates and protostome invertebrates.

Nodal induces sequential restriction of germ cell factors during primordial germ cell specification

Specification of the germ cell lineage is required for sexual reproduction in animals. The mechanism of germ cell specification varies among animals but roughly clusters into either inherited or inductive mechanisms. The inductive mechanism, the use of cell-cell interactions for germ cell specification, appears to be the ancestral mechanism in animal phylogeny, yet the pathways responsible for this process are only recently surfacing. Here, we show that germ cell factors in the sea star initially are present broadly, then become restricted dorsally and then in the left side of the embryo where the germ cells form a posterior enterocoel. We find that Nodal signaling is required for the restriction of two germ cell factors, Nanos and Vasa, during the early development of this animal. We learned that Nodal inhibits germ cell factor accumulation in three ways including: inhibition of specific transcription, degradation of specific mRNAs and inhibition of tissue morphogenesis. These results document a signaling mechanism required for the sequential restriction of germ cell factors, which causes a specific set of embryonic cells to become the primordial germ cells.

EchinoBase: Tools for Echinoderm Genome Analyses

The echinoderms are a phylum of invertebrate deuterostome animals that constitute important research models for a number of biological disciplines. EchinoBase ( www.echinobase.org ) is an echinoderm-specific genome database and web information system that provides a platform for the interrogation and exploration of echinoderm genomic data. This chapter outlines the datasets available on EchinoBase; from assembled genomes and genome annotations, to spatial and quantitative expression data, as well as functional genomics datasets. We also highlight the bioinformatic tools available on the website to facilitate rapid inquiries using these data (genome browsers, precompiled BLAST databases, etc.), and suggest optimized strategies for performing these inquiries. We conclude with a perspective on how one could integrate various genomic resources to predict putative noncoding regulatory regions. The available datasets and analyses they permit provide the basic components required for developing an understanding of how echinoderm genomes are regulated, especially during early development, and provides a platform for comparative genomic inquiries among species in this phylum.

A gene regulatory network for apical organ neurogenesis and its spatial control in sea star embryos

How neural stem cells generate the correct number and type of differentiated neurons in appropriate places remains an important question. Although nervous systems are diverse across phyla, in many taxa the larva forms an anterior concentration of serotonergic neurons, or apical organ. The sea star embryo initially has a pan-neurogenic ectoderm, but the genetic mechanism that directs a subset of these cells to generate serotonergic neurons in a particular location is unresolved. We show that neurogenesis in sea star larvae begins with soxc-expressing multipotent progenitors. These give rise to restricted progenitors that express lhx2/9 soxc- and lhx2/9-expressing cells can undergo both asymmetric divisions, allowing for progression towards a particular neural fate, and symmetric proliferative divisions. We show that nested concentric domains of gene expression along the anterior-posterior (AP) axis, which are observed in a great diversity of metazoans, control neurogenesis in the sea star larva by promoting particular division modes and progression towards becoming a neuron. This work explains how spatial patterning in the ectoderm controls progression of neurogenesis in addition to providing spatial cues for neuron location. Modification to the sizes of these AP territories provides a simple mechanism to explain the diversity of neuron number among apical organs.

Low coverage sequencing of three echinoderm genomes: the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis

BACKGROUND

There are five major extant groups of Echinodermata: Crinoidea (feather stars and sea lillies), Ophiuroidea (brittle stars and basket stars), Asteroidea (sea stars), Echinoidea (sea urchins, sea biscuits, and sand dollars), and Holothuroidea (sea cucumbers). These animals are known for their pentaradial symmetry as adults, unique water vascular system, mutable collagenous tissues, and endoskeletons of high magnesium calcite. To our knowledge, the only echinoderm species with a genome sequence available to date is Strongylocentrotus pupuratus (Echinoidea). The availability of additional echinoderm genome sequences is crucial for understanding the biology of these animals.

FINDINGS

Here we present assembled draft genomes of the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis from Illumina sequence data with coverages of 12.5x, 22.5x, and 21.4x, respectively.

CONCLUSIONS

These data provide a resource for mining gene superfamilies, identifying non-coding RNAs, confirming gene losses, and designing experimental constructs. They will be important comparative resources for future genomic studies in echinoderms.

What doesn't kill them makes them stronger: an association between elongation factor 1-α overdominance in the sea star Pisaster ochraceus and "sea star wasting disease"

In recent years, a massive mortality event has killed millions of sea stars, of many different species, along the Pacific coast of North America. This disease event, known as 'sea star wasting disease' (SSWD), is linked to viral infection. In one affected sea star (Pisaster ochraceus), previous work had identified that the elongation factor 1-α locus (EF1A) harbored an intronic insertion allele that is lethal when homozygous yet appears to be maintained at moderate frequency in populations through increased fitness for heterozygotes. The environmental conditions supporting this increased fitness are unknown, but overdominance is often associated with disease. Here, we evaluate populations of P. ochraceus to identify the relationship between SSWD and EF1A genotype. Our data suggest that there may be significantly decreased occurrence of SSWD in individuals that are heterozygous at this locus. These results suggest further studies are warranted to understand the functional relationship between diversity at EF1A and survival in P. ochraceus.

Molecular phylogeny of four homeobox genes from the purple sea star Pisaster ochraceus

Homeobox genes cloned from the purple sea star Pisaster ochraceus (Phylum Echinodermata/Class Asteroidea) were used along with related sequences available from members of other representative animal phyla to generate molecular phylogenies for Distal-less/Dlx, Hox5, Hox7, and Hox9/10 homeobox genes. Phylogenetic relationships were inferred based on the predicted 60 amino acid homeodomain, using amino acid (AA) and nucleotide (NT) models as well as the recently developed codon substitution models of sequence evolution. The resulting phylogenetic trees were mostly congruent with the consensus species-tree, grouping these newly identified genes with those isolated from other Asteroidea. This analysis also allowed a preliminary comparison of the performance of codon models with that of NT and AA evolutionary models in the inference of homeobox phylogeny. We found that, overall, the NT models displayed low reliability in recovering major clades at the Superphylum/Phylum level, and that codon models were slightly more dependable than AA models. Remarkably, in the majority of cases, codon substitution models seemed to outperform both AA and NT models at both the Class level and homeobox paralogy-group level of classification.

Two-pore channels function in calcium regulation in sea star oocytes and embryos

Egg activation at fertilization is an excellent process for studying calcium regulation. Nicotinic acid adenine dinucleotide-phosphate (NAADP), a potent calcium messenger, is able to trigger calcium release, likely through two-pore channels (TPCs). Concomitantly, a family of ectocellular enzymes, the ADP-ribosyl cyclases (ARCs), has emerged as being able to change their enzymatic mode from one of nucleotide cyclization in formation of cADPR to a base-exchange reaction in the generation of NAADP. Using sea star oocytes we gain insights into the functions of endogenously expressed TPCs and ARCs in the context of the global calcium signals at fertilization. Three TPCs and one ARC were found in the sea star (Patiria miniata) that were localized in the cortex of the oocytes and eggs. PmTPCs were localized in specialized secretory organelles called cortical granules, and PmARCs accumulated in a different, unknown, set of vesicles, closely apposed to the cortical granules in the egg cortex. Using morpholino knockdown of PmTPCs and PmARC in the oocytes, we found that both calcium regulators are essential for early embryo development, and that knockdown of PmTPCs leads to aberrant construction of the fertilization envelope at fertilization and changes in cortical granule pH. The calcium signals at fertilization are not significantly altered when individual PmTPCs are silenced, but the timing and shape of the cortical flash and calcium wave are slightly changed when the expression of all three PmTPCs is perturbed concomitantly, suggesting a cooperative activity among TPC isoforms in eliciting calcium signals that may influence localized physiological activities.

Conservation of sequence and function in fertilization of the cortical granule serine protease in echinoderms

Conservation of the cortical granule serine protease during fertilization in echinoderms was tested both functionally in sea stars, and computationally throughout the echinoderm phylum. We find that the inhibitor of serine protease (soybean trypsin inhibitor) effectively blocks proper transition of the sea star fertilization envelope into a protective sperm repellent, whereas inhibitors of the other main types of proteases had no effect. Scanning the transcriptomes of 15 different echinoderm ovaries revealed sequences of high conservation to the originally identified sea urchin cortical serine protease, CGSP1. These conserved sequences contained the catalytic triad necessary for enzymatic activity, and the tandemly repeated LDLr-like repeats. We conclude that the protease involved in the slow block to polyspermy is an essential and conserved element of fertilization in echinoderms, and may provide an important reagent for identification and testing of the cell surface proteins in eggs necessary for sperm binding.

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.

Expression of wnt and frizzled genes during early sea star development

The Wnt signaling pathway is highly conserved across metazoa and has pleiotropic functions in the development of many animals. Binding of a secreted Wnt ligand to its Frizzled (Fz) receptor activates Dishevelled, which then drives one of three major signaling cascades, canonical (β-catenin), calcium, or planar cell polarity signaling. These pathways have distinct developmental effects and function in different processes in different organisms. Here we report the expression of six wnt and three fz genes during embryogenesis of the sea star, Patiria miniata, as a first step in uncovering the roles of Wnt signaling in the development of this organism. wnt3, wnt4, wnt8, and wnt16 are expressed in nested domains in the endoderm and lateral ectoderm from blastula through late gastrula stages; wnt2 and wnt5 are expressed in the mesoderm and anterior endoderm. Expression of different fz paralogs is detected in the mesoderm; posterior endoderm and ectoderm; and anterior ectoderm. Taken together, this suggests that Wnt signaling can occur throughout most of the embryo and may therefore play multiple roles during sea star development.