Exogenous hyalin and sea urchin gastrulation, Part II: hyalin, an interspecies cell adhesion molecule

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.

Investigating the establishment of primary cell culture from different abalone (Haliotis midae) tissues

The abalone, Haliotis midae, is the most valuable commodity in South African aquaculture. The increasing demand for marine shellfish has stimulated research on the biology and physiology of target species in order to improve knowledge on growth, nutritional requirements and pathogen identification. The slow growth rate and long generation time of abalone restrict efficient design of in vivo experiments. Therefore, in vitro systems present an attractive alternative for short term experimentation. The use of marine invertebrate cell cultures as a standardised and controlled system to study growth, endocrinology and disease contributes to the understanding of the biology of economically important molluscs. This paper investigates the suitability of two different H. midae tissues, larval and haemocyte, for establishing primary cell cultures. Cell cultures are assessed in terms of culture initiation, cell yield, longevity and susceptibility to contamination. Haliotis midae haemocytes are shown to be a more feasible tissue for primary cell culture as it could be maintained without contamination more readily than larval cell cultures. The usefulness of short term primary haemocyte cultures is demonstrated here with a growth factor trial. Haemocyte cultures can furthermore be used to relate phenotypic changes at the cellular level to changes in gene expression at the molecular level.

Exogenous hyalin and sea urchin gastrulation. Part IV: a direct adhesion assay - progress in identifying hyalin's active sites

In Strongylocentrotus purpuratus the hyalins are a set of three to four rather large glycoproteins (hereafter referred to as 'hyalin'), which are the major constituents of the hyaline layer, the developing sea urchin embryo's extracellular matrix. Recent research from our laboratories has shown that hyalin is a cell adhesion molecule involved in sea urchin embryo-specific cellular interactions. Other laboratories have shown it to consist of 2-3% carbohydrate and a cloned, sequenced fragment demonstrated repeat domains (HYR) and non-repeat regions. Interest in this molecule has increased because HYR has been identified in organisms as diverse as bacteria, flies, worms, mice and humans, as well as sea urchins. Our laboratories have shown that hyalin appears to mediate a specific cellular interaction that has interested investigators for over a century, archenteron elongation/attachment to the blastocoel roof. We have shown this finding by localizing hyalin on the two components of the cellular interaction and by showing that hyalin and anti-hyalin antibody block the cellular interaction using a quantitative microplate assay. The microplate assay, however, has limitations because it does not directly assess hyalin's effects on the adhesion of the two components of the interaction. Here we have used an elegant direct assay that avoids the limitations, in which we microdissected the two components of the adhesive interaction and tested their re-adhesion to each other, thereby avoiding possible factors in the whole embryos that could confound or confuse results. Using both assays, we found that mild periodate treatment (6 h to 24 h in sodium acetate buffer with 0.2 M sodium periodate at 4 degrees C in the dark) of hyalin eliminates its ability to block the cellular interaction, suggesting that the carbohydrate component(s) may be involved in hyalin's specific adhesive function. This first step is important in identifying the molecular mechanisms of a well known cellular interaction in the NIH-designated sea urchin embryo model, a system that has led to the discovery of scores of physiological mechanisms, including those involved in human health and disease.

Exogenous hyalin and sea urchin gastrulation. Part III: biological activity of hyalin isolated from Lytechinus pictus embryos

Hyalin is a large glycoprotein, consisting of the hyalin repeat domain and non-repeated regions, and is the major component of the hyaline layer in the early sea urchin embryo of Strongylocentrotus purpuratus. The hyalin repeat domain has been identified in proteins from organisms as diverse as bacteria, sea urchins, worms, flies, mice and humans. While the specific function of hyalin and the hyalin repeat domain is incompletely understood, many studies suggest that it has a functional role in adhesive interactions. In part I of this series, we showed that hyalin isolated from the sea urchin S. purpuratus blocked archenteron elongation and attachment to the blastocoel roof occurring during gastrulation in S. purpuratus embryos, (Razinia et al., 2007). The cellular interactions that occur in the sea urchin, recognized by the U.S. National Institutes of Health as a model system, may provide insights into adhesive interactions that occur in human health and disease. In part II of this series, we showed that S. purpuratus hyalin heterospecifically blocked archenteron-ectoderm interaction in Lytechinus pictus embryos (Alvarez et al., 2007). In the current study, we have isolated hyalin from the sea urchin L. pictus and demonstrated that L. pictus hyalin homospecifically blocks archenteron-ectoderm interaction, suggesting a general role for this glycoprotein in mediating a specific set of adhesive interactions. We also found one major difference in hyalin activity in the two sea urchin species involving hyalin influence on gastrulation invagination.

Hyalin is a cell adhesion molecule involved in mediating archenteron-blastocoel roof attachment

The US National Institutes of Health has designated the sea urchin embryo as a model organism because around 25 discoveries in this system have led to insights into the physiology of higher organisms, including humans. Hyalin is a large glycoprotein in the hyaline layer of sea urchin embryos that functions to maintain general adhesive relationships in the developing embryo. It consists of the hyalin repeat domain that has been identified in organisms as diverse as bacteria, worms, flies, mice, sea urchins and humans. Here we show, using a polyclonal antibody raised against the 11.6 S species of hyalin, that it localizes at the tip of the archenteron and on the roof of the blastocoel exactly where these two structures bond in an adhesive interaction that has been of interest for over a century. In addition, the antibody blocks the interaction between the archenteron tip and blastocoel roof. These results, in addition to other recent findings from this laboratory that will be discussed, suggest that hyalin is involved in mediating this cellular interaction. This is the first demonstration that suggests that hyalin functions as a cell adhesion molecule in many organisms, including humans.