Previous observations have indicated homology in the cellular components between collembolan eyes and the compound eyes of insects. However, behavioral or physiological studies indicating similarities in function are lacking. Collembolan eyes were examined from three species in the Family Isotomidae using scanning electron microscopy. Collembolan eyes are arranged dorsally and laterally on each side of the head in two species, Proisotoma minuta with eight eyes on each side of the head and Folsomia similis with one eye on each side of the head. In both of these species the eyes were located just posterior to the postantennal organ. In Folsomia candida, no external eye structures were detected. These three species were assayed for a series of behavioral preferences using ultraviolet (UV), white light and dark, and temperature conditions. The tests demonstrated that over 76% of all three species, including the eyeless F. Candida, chose white over UV light, over 69% preferred dark over UV, and over 77% favored dark over white light. The results demonstrated that all three species detect both UV and white light and avoid it, preferring cool, dark habitats. From the results of this study, it is hypothesized that F. candida may, in fact, be only “lensless” and may be able to detect light by having internal, non-ocular photoreceptors. Further histological studies are needed to investigate this possibility.

SummaryIn 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 done this 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, where we microdissected the two components of the adhesive interaction and tested their readhesion 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 0.2M sodium periodate at 4 °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 is an important first step 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.

SummaryThe U. S. National Institutes of Health has designated the sea urchin embryo as a model organism because about twenty-five 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 is a specific cell adhesion molecule that may function as such in many organisms, including humans.

Genetic and phenotypic analysis of strawberry notch suggests that its gene product is required during embryogenesis and oogenesis, and for the development of the eye, wing and leg. Several lines of evidence suggest that strawberry notch participates together with Notch in many common pathways. A number of strawberry notch mutant phenotypes are similar to those of Notch mutants and can be rescued by an extra copy of wild-type Notch. In addition, mutations in strawberry notch interact strongly with Notch mutants in a tissue-specific manner. Mutations in the strawberry notch and Notch loci also show very similar interactions with genes like Hairless, Delta, groucho, Serrate, and deltex that have all been proposed to participate in Notch related pathways. The genetic evidence presented here suggests that strawberry notch participates with members of the Notch pathway in facilitating developmentally relevant cell-cell communications.

We developed a novel method to probe mechanisms of cellular interactions by microdissecting the archenteron and blastocoel roof out of 48–54 hr Lytechinus pictus sea urchin ermbryos. These are the two components of a classic cellular interaction in the NIH designated model sea urchin embryo. Here we test the ability of isolated fixed archenterons to bind to agarose beads derivatized with concanavalin A (Con A) in artificial sea water (ASW) at pH 4,6,8 (control), 9 or 10 or in the presence of 4M NaCl or 2M or 4M alpha methyl glucose. The binding of a total of 204 isolated archenterons was only inhibited in 4M alpha methyl glucose (p less than 0.05 compared with controls). All other conditions gave p values of greater than 0.05. As Con A beads bound to the isolated archenterons and alpha methyl glucose inhibited the interaction, the results suggest that Con A binding ligands are present on the isolated archenterons. While 4M sugar is high, the archenterons were fixed, reducing osmolarity concerns. High monosaccharide concentrations are often required to inhibit lectin‐involved binding interactions. Part I of this series provides evidence for glycan involvement in the actual cellular interaction. This microdissection method allows probing of isolated components of cellular interactions outside of the embryo proper, to avoid complex problems that may occur in whole embryos (supported by NIH NIGMS SCORE S0648680, MARC, RISE, the Joseph Drown Foundation, the Sidney Stern Memorial Trust, and CSU Northridge Biology Full Immersion Research Experience (FIRE) course funding).