Biomedical subjects

D R McClay

Publications and source records attributed to D R McClay.

At least 19 recordsLinked to original sources

PubMed1992

Deployment of extracellular matrix proteins in sea urchin embryogenesis.

The apical extracellular matrix of the sea urchin embryo, known as the hyaline layer (HL), is a multi-laminate organelle composed of at least 10 polypeptides. Although integrated into one ECM, HL proteins exhibit individual temporal and spatial dynamics throughout development. These molecules are stockpiled in the oocyte during vitellogenesis in at least four distinct vesicle populations. They are released onto the cell surface at fertilization in a specific order, and interact differentially with embryonic cells as development proceeds. Many experiments have suggested that the HL is vital for embryogenesis, but relatively little is known about the functions and interactions of its constituent molecules. The purpose of the present review has been to gather information on the basic characteristics of the known HL proteins together with data on their expression in the embryo, and where possible, their biological activities. Compiled, these observations may provide some insight into the workings of a uniquely embryonic organelle.

Animals↗

PubMed1992

On the ultrastructure of hyalin, a cell adhesion protein of the sea urchin embryo extracellular matrix.

Hyalin is a large (ca. 350 x 10(3) kD by gel electrophoresis) molecule that contributes to the hyalin layer surrounding the sea urchin embryo. In previous work a mAb (McA Tg-HYL), specific for hyalin, was found to inhibit cell-hyalin adhesion and block morphogenesis of whole embryos (Adelson, D. L., and T. D. Humphreys. 1988. Development. 104:391-402). In this report, hyalin ultrastructure was examined via rotary shadowing. Hyalin appeared to be a filamentous molecule approximately 75-nm long with a globular "head" about 12 nm in diameter that tended to form aggregates by associating head to head. Hyalin molecules tended to associate with a distinct high molecular weight globular particle ("core"). In fractions containing the core particle often more than one hyalin molecule were seen to be associated with the core. The core particle maintained a tenacious association with hyalin throughout purification procedures. The site(s) of McA Tg-HYL binding to the hyalin molecule were visualized by decorating purified hyalin with the antibody and then rotary shadowing the complex. In these experiments, McA Tg-HYL attached to the hyalin filament near the head region in a pattern suggesting that more than one antibody binding site exists on the hyalin filament. From the ultrastructural data and from the cell adhesion data presented earlier we conclude that hyalin is a filamentous molecule that binds to other hyalin molecules and contains multiple cell binding sites. Attempts were made to demonstrate the existence of lower molecular weight hyalin precursors. Whilst no such precursors could be identified by immunoprecipitation of in vivo labeled embryo lysates, immunoprecipitation of in vitro translation products suggested such precursors (ca 40 x 10(3) kD) might exist.

Animals↗

PubMed1992

Commitment along the dorsoventral axis of the sea urchin embryo is altered in response to NiCl2.

Few treatments are known that perturb the dorsoventral axis of the sea urchin embryo. We report here that the dorsoventral polarity of the sea urchin embryo can be disrupted by treatment of embryos with NiCl2. Lytechinus variegatus embryos treated with 0.5 mM NiCl2 from fertilization until the early gastrula stage appear morphologically normal until the midgastrula stage, when they fail to acquire the overt dorsoventral polarity characteristic of untreated siblings. The ectoderm of normal embryos possesses two ventrolateral thickenings just above the vegetal plate region. In nickel-treated embryos, these become expanded as a circumferential belt around the vegetal plate. The ectoderm just ventral to the animal pole normally invaginates to form a stomodeum, which then fuses with the tip of the archenteron to produce the mouth. In nickel-treated embryos, the stomodeal invagination is expanded to become a circumferential constriction, and it eventually pinches off as the tip of the archenteron fuses with it to produce a mouth. Primary mesenchyme cells form a ring in the lateral ectoderm, but as many as a dozen spicule rudiments can form in a radial pattern. Dorsoventral differentiation of ectodermal tissues is profoundly perturbed: nickel-treated embryos underexpress transcripts of the dorsal (aboral) gene LvS1, they overexpress the ventral (oral) ectodermal gene product, EctoV, and the ciliated band is shifted to the vegetal margin of the embryo. Although some dorsoventral abnormalities are observed, animal-vegetal differentiation of the archenteron and associated structures seems largely normal, based on the localization of region-specific gene products. Gross differentiation of primary mesenchyme cells seems unaffected, since nickel-treated embryos possess the normal number of these cells. Furthermore, when all primary mesenchyme cells are removed from nickel-treated embryos, some secondary mesenchyme cells undergo the process of "conversion" (Ettensohn, C. A. and McClay, D. R. (1988) Dev. Biol. 125, 396-409), migrating to sites where the larval skeleton would ordinarily form and subsequently producing spicule rudiments. However, the skeletal pattern formed by the converted cells is completely radialized. Our data suggest that a major effect of NiCl2 is to alter commitment of ectodermal cells along the dorsoventral axis. Among the consequences appears to be a disruption of pattern formation by mesenchyme cells.

Animals↗

PubMed1992

Pattern formation during gastrulation in the sea urchin embryo.

The sea urchin embryo follows a relatively simple cell behavioral sequence in its gastrulation movements. To form the mesoderm, primary mesenchyme cells ingress from the vegetal plate and then migrate along the basal lamina lining the blastocoel. The presumptive secondary mesenchyme and endoderm then invaginate from the vegetal pole of the embryo. The archenteron elongates and extends across the blastocoel until the tip of the archenteron touches and attaches to the opposite side of the blastocoel. Secondary mesenchyme cells, originally at the tip of the archenteron, differentiate to form a variety of structures including coelomic pouches, esophageal muscles, pigment cells and other cell types. After migration of the secondary mesenchyme cells from their original position at the tip of the archenteron, the endoderm fuses with an invagination of the ventral ectoderm (the stomodaem), to form the mouth and complete the process of gastrulation. A larval skeleton is made by primary mesenchyme cells during the time of archenteron and mouth formation. A number of experiments have established that these morphogenetic movements involve a number of cell autonomous behaviors plus a series of cell interactions that provide spatial, temporal and scalar information to cells of the mesoderm and endoderm. The cell autonomous behaviors can be demonstrated by the ability of micromeres or endoderm to perform their morphogenetic functions if either is isolated and grown in culture. The requirement for cell interactions has been demonstrated by manipulative experiments where it has been shown that axial information, temporal information, spatial information and scalar information is obtained by mesoderm and endoderm from other embryonic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Tissue-specific, temporal changes in cell adhesion to echinonectin in the sea urchin embryo.

Echinonectin is a dimeric, glycoprotein found in the hyaline layer of the developing sea urchin embryo. It was found that echinonectin supports adhesion of embryonic cells in vitro. Previous studies have shown that the protein hyalin also supports adhesion. The purpose of this study was to examine the specificity of cell-echinonectin interactions during sea urchin development. Primary mesenchyme cells (PMCs) ingress into the blastocoel during gastrulation. In the process the PMCs lose contact with the hyaline layer. It was found experimentally that differentiating PMCs decreased their adhesion to hyalin at the time of ingression. It was of interest, therefore, to determine whether there was a coordinate loss of adhesion to echinonectin at ingression as well. When cell-echinonectin interactions were quantified using a centrifugal force-based adhesion assay, it was shown that micromeres adhered well to echinonectin. At the time of ingression, PMCs displayed reduced adhesion to echinonectin just as had been found when hyalin was tested as a substrate. There was no change in adhesion of presumptive ectoderm or endoderm to echinonectin over the same time period. Early in gastrulation presumptive ectoderm and endoderm adhered to echinonectin only half as strongly as to equimolar concentrations of hyalin. After gastrulation endoderm cells were observed to retain the same relative affinity to hyalin and echinonectin, while ectoderm cells became equally adhesive for both hyalin and echinonectin. Quantitatively, this represents an overall increase in the affinity of ectodermal cells for echinonectin. Adhesion to combined substrata of echinonectin and hyalin was reduced but not abolished by monoclonal antibodies specific for echinonectin. The antibodies did not cross-react with hyalin. We conclude that both echinonectin and hyalin independently act as adhesive substrata for the developing sea urchin embryo. PMCs lose an affinity for echinonectin and ectodermal cells later increase their affinity for this substrate.

Age Factors↗

PubMed1991

Gastrulation.

At gastrulation, a single layer of cells is converted into an outer ectodermal covering, an inner ectodermal tube, and in triploblastic phyla, a middle mesodermal layer. This morphogenesis is driven by motility and directed by cell interactions, some of which involve adhesion and others that involve information transfer.

Amino Acid Sequence↗

PubMed1990

In vitro biological activities of echinonectin.

Echinonectin (EN) is a 230-kDa extracellular matrix glycoprotein found in the hyaline layer of sea urchin embryos. Dissociated embryonic cells attached strongly to EN-coated microtiter wells in a centrifugal-based in vitro adhesion assay, suggesting that EN is one of the hyaline layer proteins to which cells adhere in vivo (Alliegro et al., 1988). The present study examines the molecular properties of that adhesion using monoclonal antibodies as probes to block cell attachment, and also demonstrates that EN possesses lectin activity. EN binds tenaciously to agarose-based chromatography resins, such as Sepharose. The sugar-binding activity is associated with the polypeptide component of EN, and not with the carbohydrate moiety. Binding is inhibited with galactose and fucoidan, but not with glucose or locust bean gum. Although functional sites both for polysaccharide binding and for cell attachment are present on each subunit of the EN molecule, the sites appear to be functionally distinct because galactose and fucoidan are completely without effect on cell attachment in vitro. Proteolytic digestion of EN yields a highly limited set of immunoreactive peptides. Digestion with trypsin yields a 20-kDa fragment, chymotrypsin, a doublet at 20 kDa, and 20- and 23-kDa fragments with thermolysin. McAb's directed against these peptides block cell adhesion in vitro, suggesting that they possess the cell attachment domain of EN. This is supported by the observations that trypsin-digested EN is an effective substrate in adhesion assays and that adhesion to the tryptic fragments is also blocked by McAb's to the 20-kDa domain.

Animals↗

PubMed1990

Neuronal-glial interactions: complexity of neurite outgrowth correlates with substrate adhesivity of serotonergic neurons.

To study the interactions between neurons of known transmitter phenotype and non-neuronal cells of glial or fibroblastic origin, serotonergic (5-HT) neurons were tested for their strength of adhesion and neurite outgrowth patterns on substrates of astrocytes or fibroblasts using a cell adhesion assay for transmitter-identified neurons, and morphometry of immunocytochemically stained neurons in dissociated cell cultures. Both the strength of adhesion and the rate and complexity of neurite outgrowth by 5-HT neurons were significantly greater on substrates of astrocytes compared to fibroblasts. These results provide evidence that 5-HT neurons can interact selectively with glia via cell surface determinants, and that this process may be important for the development of complex (dendrite-like) neuritic arbors. The methods developed in this study will be useful for future studies of interactions between transmitter-identified neurons and glial cells during ontogeny of the embryonic brain.

Animals↗

PubMed1990

A hyaline layer protein that becomes localized to the oral ectoderm and foregut of sea urchin embryos.

An antigen is described which is a marker for the oral ectoderm and foregut of the sea urchin embryo. In Lytechinus variegatus, the antigen is first detectable by immunofluorescence on the surface of fertilized eggs, and remains globally distributed through the early stages of gastrulation. Thereafter the antigen is localized to the oral ectoderm and foregut, coincident with the morphogenesis of these regions. The antigen is a large, detergent-insoluble, filamentous glycoprotein associated with the tips of the microvilli in the hyaline layer. This glycoprotein is present in two forms, a approximately 350-kDa form that is maternally synthesized and a much larger form which is synthesized at late gastrula stage as a 350-kDa precursor before becoming modified and assembled into the hyaline layer. The timing of synthesis of the zygotic form of the molecule correlates precisely with the localized expression of the antigen. The antigen copurifies with intact hyaline layers and cosediments with hyalin in the presence of calcium, suggesting that it is a structural component of the hyaline layer.

Animals↗

PubMed1990

Target recognition by the archenteron during sea urchin gastrulation.

During sea urchin gastrulation filopodia are sent out by secondary mesenchyme cells (SMCs) at the tip of the archenteron in continual cycles of extension, attachment, and retraction. Eventually the archenteron ceases its elongation and its tip localizes to the animal pole region of the embryo (Gustafson and Kinnander, 1956, Exp. Cell Res. 11, 36-57; Dan and Okazaki, 1956, Biol. Bull. 110, 29-42). We have investigated the mechanisms and specificity of this localization by analyzing filopodial behavior and by experimental manipulation of the interaction of the archenteron with the animal pole region. When the tip of the archenteron nears the animal pole, some filopodia make contact with a well-defined locus within this region. Filopodia that make contact with the locus remain attached 20-50 times longer than attachments observed at any other site along the blastocoel wall. The SMCs bearing the long-lived filopodia eventually change their phenotype by flattening and spreading onto this region. Several lines of experimental evidence indicate that contact with the animal pole locus, or "target" region, is crucial for the change in phenotype of the SMCs: (1) the phenotypic change can be induced precociously by bringing the animal pole region within reach of the tip of the archenteron early in gastrulation. Precocious contact with other regions of the blastocoel wall does not induce a similar change. (2) The phenotypic change can be delayed by placing the animal pole out of reach late in gastrulation, resulting in artificial prolongation of exploratory behavior by filopodia. (3) Ectopic combinations of animal pole ectoderm and archenterons in fused multiple embryos and chimaeras result in attachment of archenterons to the nearest available target, and (4) freely migrating SMCs are observed to migrate randomly within the blastocoel, then stop at the animal pole and undergo the change in phenotype. Filopodia rapidly attach to the animal pole when the shape of early gastrulae is altered such that the animal pole is less than 35 microns from the tip of the archenteron, even though such attachments only occur in normal embryos at the 2/3-3/4 gastrula stage. Since it has previously been shown that the archenteron elongates autonomously to 2/3 of its final length (Hardin, 1988, Development 103, 317-324), it appears that autonomous extension of the archenteron is required to place filopodia close enough to the animal pole to allow them to interact with it.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Embryonic cellular organization: differential restriction of fates as revealed by cell aggregates and lineage markers.

Cleavage-stage Lytechinus variegatus embryos were dissociated and the cells were aggregated in an experimental system designed to address questions of embryonic organizational capability. Using monoclonal antibodies against stage- and structure-specific antigens, it was determined that germ-layer specific molecules were expressed in the expected locations in aggregates and that the germ layers differentiated in the normal temporal sequence, but the dorsoventral axis of the embryo was not reestablished properly. In other experiments individual rhodamine-labeled blastomeres were incorporated into unlabeled aggregates. Micromeres localized and differentiated normally. Mesomeres, however, which in normal embryos form only ectoderm, were found to change their specified fate and participate in gut formation. The sequence of aggregate organization revealed other properties of the embryo. Ectodermal and endodermal epithelia formed via two temporally distinct epithelialization events. Ectoderm separated from a mass of interior cells at about 12 hrs, and endoderm compacted from the interior cells at about 20 hr. A lathrytic agent that prevents gut formation in normal embryos also prevented gut formation in aggregates; however, it did not affect formation of the ectoderm. Hence, formation of the triploblastic structure in aggregates appears to be dependent upon developmentally regulated, distinct cell adhesion events.

Animals↗

PubMed1989

Cell adhesion to fibronectin and tenascin: quantitative measurements of initial binding and subsequent strengthening response.

Cell-substratum adhesion strengths have been quantified using fibroblasts and glioma cells binding to two extracellular matrix proteins, fibronectin and tenascin. A centrifugal force-based adhesion assay was used for the adhesive strength measurements, and the corresponding morphology of the adhesions was visualized by interference reflection microscopy. The initial adhesions as measured at 4 degrees C were on the order of 10(-5)dynes/cell and did not involve the cytoskeleton. Adhesion to fibronectin after 15 min at 37 degrees C were more than an order of magnitude stronger; the strengthening response required cytoskeletal involvement. By contrast to the marked strengthening of adhesion to FN, adhesion to TN was unchanged or weakened after 15 min at 37 degrees C. The absolute strength of adhesion achieved varied according to protein and cell type. When a mixed substratum of fibronectin and tenascin was tested, the presence of tenascin was found to reduce the level of the strengthening of cell adhesion normally observed at 37 degrees C on a substratum of fibronectin alone. Parallel analysis of corresponding interference reflection micrographs showed that differences in the area of cell surface within 10-15 nm of the substratum correlated closely with each of the changes in adhesion observed: after incubation for 15 min on fibronectin at 37 degrees C, glioma cells increased their surface area within close contact to the substrate by integral to 125-fold. Cells on tenascin did not increase their surface area of contact. The increased surface area of contact and the inhibitory activity of cytochalasin b suggest that the adhesive "strengthening" in the 15 min after initial binding brings additional adhesion molecules into the adhesive site and couples the actin cytoskeleton to the adhesion complex.

Animals↗

PubMed1988

Storage and mobilization of extracellular matrix proteins during sea urchin development.

After fertilization, sea urchin embryos surround themselves with an extracellular matrix, or hyaline layer, to which cells adhere during early development. Hyalin, the major protein component of the hyaline layer has been isolated and partially characterized in several laboratories. Although other proteins are present in the hyaline layer, little is known about their origin, distribution, or functions. The present report characterizes a set of hyaline layer proteins that are secreted after fertilization from a class of vesicles that are distinct from cortical granules. The group of proteins in these vesicles were identified by a monoclonal antibody (8d11) which recognizes a carbohydrate epitope common to each of these molecules. 8d11 polypeptides range in molecular weight from 105 to 225 kDa. Oogonia and oocytes in early stages of vitellogenesis do not express the antigen. The proteins are first observed by immunofluorescence during oogenesis as a peripheral band in mid-vitellogenic oocytes. Following germinal vesicle breakdown 8d11 moves to be distributed evenly throughout the cytoplasm. The proteins are transported to the egg surface by a cytochalasin-sensitive mechanism after fertilization, and secreted predominately within the first 30 min of development. 8d11 proteins are depleted in areas of cell contact during early embryogenesis, and become concentrated on the apical surface of ectoderm cells where they are assembled into high-molecular-weight aggregates. Three of the molecules in this group may be proteins previously described as "apical lamina" proteins. These observations provide evidence of a third pathway (cortical granules and basal lamina granules being the other two) for synthesis, storage, and exocytosis of matrix proteins that are release after fertilization.

Animals↗

PubMed1988

Cell lineage conversion in the sea urchin embryo.

The mesoderm of the sea urchin embryo conventionally is divided into two populations of cells; the primary mesenchyme cells (PMCs), which produce the larval skeleton, and the secondary mesenchyme cells (SMCs), which differentiate into a variety of cell types but do not participate in skeletogenesis. In this study we examine the morphogenesis of embryos from which the PMCs have been removed microsurgically. We confirm the observation of Fukushi (1962) that embryos lacking PMCs form a complete skeleton, although in a delayed fashion. We demonstrate by microsurgical and cell marking experiments that the appearance of skeletogenic cells in such PMC-deficient embryos is due exclusively to the conversion of other cells to the PMC phenotype. Time-lapse video recordings of PMC-deficient embryos indicate that the converting cells are a subpopulation of late-ingressing SMCs. The conversion of these cells to the skeletogenic phenotype is accompanied by their de novo expression of cell surface determinants normally unique to PMCs, as shown by binding of wheat germ agglutinin and a PMC-specific monoclonal antibody. Cell transplantation and cell marking experiments have been carried out to determine the number of SMCs that convert when intermediate numbers of PMCs are present in the embryo. These experiments indicate that the number of converting SMCs is inversely proportional to the number of PMCs in the blastocoel. In addition, they show that PMCs and converted SMCs cooperate to produce a skeleton that is correct in both size and configuration. This regulatory system should shed light on the nature of cell-cell interactions that control cell differentiation and on the way in which evolutionary processes modify developmental programs.

Animals↗

PubMed1988

Cell polarity in sea urchin embryos: reorientation of cells occurs quickly in aggregates.

Four apical components were used as markers for the apical end of the cell in studies centering on cell polarity in the early blastula stage of sea urchin embryos and in aggregates of cleavage stage cells. Cells were observed to maintain their polarity for several hours if dissociated and cultured in suspension. Orientation of cells in aggregates initially is random; however, within 3 hr the cells have reoriented so that their apical-basal axis corresponds to the correct inside-outside position in the aggregate. This reorientation occurs before formation of a basal lamina or a new hyalin layer in the aggregate, and appears to take place by a rotation or other movement of individual cells. The polarity within each cell is maintained during reorientation. An apical surface antigen is colocalized with concentrations of filamentous actin. Treatment of isolated cells with cytochalasin B causes the antigen to lose its apical position and eventually become distributed around the outside of the cell. Microtubules are visible radiating from two foci closely associated with the nucleus in untreated cells. Treatment of isolated cells with nocodazole leaves the apical cell surface marker and its associated actin undisturbed, but causes the nucleus to lose its apical position. Cytochalasin B and colchicine both prevent reorientation of cells in aggregates. Thus polarity appears to be a constant for the cells, and their reorientation in aggregates occurs prior to the polarized release of extraembryonic matrix and basal lamina.

Actin Cytoskeleton↗

PubMed1988

Echinonectin: a new embryonic substrate adhesion protein.

An extracellular matrix molecule has been purified from sea urchin (Lytechinus variegatus) embryos. Based on its functional properties and on its origin, this glycoprotein has been given the name "echinonectin." Echinonectin is a 230-kD dimer with a unique bow tie shape when viewed by electron microscopy. The molecule is 12 nm long, 8 nm wide at the ends, and narrows to approximately 4 nm at the middle. It is composed of two 116-kD U-shaped subunits that are attached to each other by disulfide bonds at their respective apices. Polyclonal antibodies were used to localize echinonectin in paraffin-embedded, sectioned specimens by indirect immunofluorescence. The protein is stored in vesicles or granules in unfertilized eggs, is released after fertilization, and later becomes localized on the apical surface of ectoderm cells in the embryo. When used as a substrate in a quantitative in vitro assay, echinonectin is highly effective as an adhesive substrate for dissociated embryonic cells. Because of the quantity, pattern of appearance, distribution, and adhesive characteristics of this protein, we suggest that echinonectin serves as a substrate adhesion molecule during sea urchin development.

Animals↗

PubMed1988

The origin of spicule-forming cells in a 'primitive' sea urchin (Eucidaris tribuloides) which appears to lack primary mesenchyme cells.

The calcareous larval skeleton of euechinoid sea urchins is synthesized by primary mesenchyme cells which ingress prior to gastrulation. In embryos of the cidaroid sea urchin Eucidaris tribuloides, no mesenchyme cells ingress before gastrulation, yet larvae later contain skeletons. This apparent paradox is resolved by immunochemical, cell lineage and morphological evidence showing that spicule-forming cells of Eucidaris are homologous to primary mesenchyme cells of euechinoids. In particular, these two cell types share expression of two cell lineage-specific gene products, are derived from the same cellular precursors, the micromeres, and undergo a similar migratory phase prior to skeletogenesis. Despite these similarities, there are far fewer spicule-forming cells in Eucidaris than in typical euechinoids and they assume a different pattern during spiculogenesis. The homology between Eucidaris spicule-forming cells and euechinoid primary mesenchyme cells indicates that a heterochrony in the time of spicule-forming cell ingression has occurred since the divergence of their respective lineages.

Animals↗

PubMed1987

Stage-specific expression of beta-1, 3-glucanase in sea urchin embryos and hybrids.

In some species of sea urchin, such as Lytechinus variegatus beta-1, 3-glucanase activity is present at two distinct developmental stages (in the unfertilized egg and again following gastrulation). There is a different form of the enzyme beta-1, 3-glucanase specific to each stage, and these forms can be distinguished immunologically and biochemically. The distinguishing characteristics of the egg and embryonic enzymes were used to analyze the forms of beta-1, 3-glucanase present in other species that express activity at only one of the two stages. The enzyme present in Tripneustes esculentes, which has activity only early in development, is an 80,000 dalton enzyme antigenically similar to the egg enzyme in Lytechinus. The enzyme present following gastrulation in Echinometra lucunter, however, is distinct from the egg enzyme and is similar to the embryonic enzyme in Lytechinus, despite the absence of activity in the eggs of Echinometra. These results indicate the two forms of beta-1, 3-glucanase (egg and embryonic) are expressed independently and in a stage-specific manner, suggesting they are not functionally equivalent. beta-1, 3-glucanase activity was also analyzed in interspecific hybrids. Tripneustes esculentes (which normally lacks the embryonic form) suppressed the expression of the embryonic enzyme in crosses with Lytechinus variegatus (which normally does express it). This suppression occurred whether the Tripneustes genetic material was maternal or paternal in origin. However, the embryonic enzyme normally expressed by Echinometra was expressed in crosses of this species with Tripneustes, i.e, Tripneustes did not suppress enzyme expression in these hybrids.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗