Glyconectin Cell Adhesion Epitope, β-d-GlcpNAc3S-(1→3)-α-l-Fucp, Is Involved in Blastulation of Lytechinus pictus Sea Urchin Embryos

Glycans, as the most peripheral cell surface components, are the primary candidates to mediate the initial steps of cell recognition and adhesion via glycan–glycan binding. This molecular mechanism was quantitatively demonstrated by biochemical and biophysical measurements at the cellular and molecular level for the glyconectin 1 β-d-GlcpNAc3S-(1→3)-α-l-Fucp glycan structure (GN1). The use of adhesion blocking monoclonal antibody Block 2 that specifically recognize this epitope showed that, besides Porifera, human colon carcinoma also express this structure in the apical glycocalyx. Here we report that Block 2 selectively immune-precipitate a Mr 580 × 103 (g580) acidic non-glycosaminoglycan glycan from the total protein-free glycans of Lytechinus pictus sea urchin hatched blastula embryos. Immuno-fluorescence confocal light microscopy and immunogold electron microscopy localized the GN1 structure in the apical lamina glycocalyx attachments of ectodermal cells microvilli, and in the Golgi complex. Biochemical and immune-chemical analyses showed that the g580 glycan is carrying about 200 copies of the GN1 epitope. This highly polyvalent g580 glycan is one of the major components of the glycocalyx structure, maximally expressed at hatched blastula and gastrula. The involvement of g580 GN1 epitope in hatched blastula cell adhesion was demonstrated by: (1) enhancement of cell aggregation by g580 and sponge g200 glycans, (2) inhibition of cell reaggregation by Block 2, (3) dissociation of microvilli from the apical lamina matrix by the loss of its gel-like structure resulting in a change of the blastula embryonal form and consequent inhibition of gastrulation at saturating concentration of Block 2, and (4) aggregation of beads coated with the immune-purified g580 protein-free glycan. These results, together with the previous atomic force microscopy measurements of GN1 binding strength, indicated that this highly polyvalent and calcium ion dependent glycan–glycan binding can provide the force of 40 nanonewtons per single ectodermal cell association of microvilli with the apical lamina, and conservation of glycocalyx gel-like structure. This force can hold the weight of 160,000 cells in sea water, thus it is sufficient to establish, maintain and preserve blastula form after hatching, and prior to the complete formation of further stabilizing basal lamina.

Chromosomal-level genome assembly of the painted sea urchin Lytechinus pictus, a genetically enabled model system for cell biology and embryonic development

The painted urchin Lytechinus pictus is a sea urchin in the family Toxopneustidae and one of several sea urchin species that are routinely used as an experimental research organism. Recently, L. pictus has emerged as a tractable model system for establishing transgenic sea urchin lines due to its amenability to long term laboratory culture. We present the first published genome of L. pictus. This chromosomal-level assembly was generated using Illumina sequencing in conjunction with Oxford Nanopore Technologies long read sequencing and HiC chromatin conformation capture sequencing. The 998.9 Mb assembly exhibits high contiguity and has a scaffold length N50 of 46.0 Mb with 97% of the sequence assembled into 19 chromosomal-length scaffolds. These 19 scaffolds exhibit a high degree of synteny compared to the 19 chromosomes of a related species Lytechinus variegatus. Ab initio and transcript evidence gene modeling, combined with sequence homology, identified 28,631 gene models that capture 92% of BUSCO orthologs. This annotation strategy was validated by manual curation of gene models for the ABC transporter superfamily, which confirmed the completeness and accuracy of the annotations. Thus, this genome assembly, in conjunction with recent high contiguity assemblies of related species, positions Lytechinus pictus as an exceptional model system for comparative functional genomics and it will be a key resource for the developmental, toxicological, and ecological biology scientific communities.

Sea urchin reproductive performance in a changing ocean: poor males improve while good males worsen in response to ocean acidification

Ocean acidification (OA) is predicted to be a major driver of ocean biodiversity change. At projected rates of change, sensitive marine taxa may not have time to adapt. Their persistence may depend on pre-existing inter-individual variability. We investigated individual male reproductive performance under present-day and OA conditions using two representative broadcast spawners, the sea urchins Lytechinus pictus and Heliocidaris erythrogramma. Under the non-competitive individual ejaculate scenario, we examined sperm functional parameters (e.g. swimming speed, motility) and their relationship with fertilization success under current and near-future OA conditions. Significant inter-individual differences in almost every parameter measured were identified. Importantly, we observed strong inverse relationships between individual fertilization success rate under current conditions and change in fertilization success under OA. Individuals with a high fertilization success under current conditions had reduced fertilization under OA, while individuals with a low fertilization success under current conditions improved. Change in fertilization success ranged from −67% to +114% across individuals. Our results demonstrate that while average population fertilization rates remain similar under OA and present-day conditions, the contribution by different males to the population significantly shifts, with implications for how selection will operate in a future ocean.

Equinoideos de mar profundo (Echinodermata: Echinoidea) del Pacífico mexicano

Deep-sea echinoderms (Echinodermata: Echinoidea) from the Mexican Pacific. The coastal strip of the Mexican Pacific and Gulf of California includes 11 states, and considering Isla Guadalupe and the Revillagigedo archipelago, Mexico has 2 364 200 km2 of marine extension in the Pacific Ocean. Studies of deep benthic macroinvertebrates for this area began with the Albatross, which traveled from the Guadalupe Islands to Guaymas in 1891. To date, 26 species of echinoids have been reported, with a bathymetric range that exceeds 200 m. In the present work, the previous bibliographic records for echinoids that were collected within the limits of the Mexican Pacific were corroborated. The taxonomic identity of the 26 species reported was also corroborated by 11 689 specimens deposited in four scientific collections: two Mexican collections (3 322 specimens in the National Collection of Echinoderms “Dra. M. E. Caso” of the ICML, UNAM and 6 673 specimens deposited in the Invertebrate Reference Collection of the Mazatlán Station - ICML, UNAM) and two international collections (1 420 specimens deposited at the National Museum of Natural History, Smithsonian Institution, Washington, DC, and 140 specimens deposited at the Museum of Comparative Zoology, Harvard University). No collection records were found at depths greater than 200 m for the species Lytechinus pictus (Verrill, 1867), Clypeaster europacificus H.L. Clark, 1914, Dendraster excentricus (Eschscholtz, 1831), Lovenia cordiformis A. Agassiz, 1872 and Brissus obesus Verrill, 1867. No records were found for Kamptosoma asterias (A. Agassiz, 1881), Araeolampas fulva (A. Agassiz, 1879) and Nacospatangus depressus H.L. Clark, 1917, which belonged to specimens collected within the limits of the Mexican Pacific. Within the material examined in the scientific collections specimen records were found only for 18 of the 26 species of sea urchins that were collected at a depths greater than 200 m in the Mexican Pacific. No bibliographic record or specimens were found to validate geographic or bathymetric distribution for eight species. Rev. Biol. Trop. 65(Suppl. 1): S244-S252. Epub 2017 November 01.

Terminal alpha-d-mannosides are critical during sea urchin gastrulation

SummaryThe sea urchin embryo is a United States National Institutes of Health (NIH) designated model system to study mechanisms that may be involved in human health and disease. In order to examine the importance of high-mannose glycans and polysaccharides in gastrulation, Lytechinus pictus embryos were incubated with Jack bean α-mannosidase (EC 3.2.1.24), an enzyme that cleaves terminal mannose residues that have α1–2-, α1–3-, or α1–6-glycosidic linkages. The enzyme treatment caused a variety of morphological deformations in living embryos, even with α-mannosidase activities as low as 0.06 U/ml. Additionally, formaldehyde-fixed, 48-hour-old L. pictus embryos were microdissected and it was demonstrated that the adhesion of the tip of the archenteron to the roof of the blastocoel in vitro is abrogated by treatment with α-mannosidase. These results suggest that terminal mannose residues are involved in the adhesion between the archenteron and blastocoel roof, perhaps through a lectin-like activity that is not sensitive to fixation.