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PubMedDate not supplied

Involvement of cyclic nucleotides and IP(3) in the regulation of luminescence in the brittlestar Amphipholis squamata (Echinodermata).

We investigated the effects of cyclic nucleotides (cGMP, cAMP) and the phosphoinositide IP(3) on the luminescence of the ophiuroid Amphipholis squamata. The cGMP analogue, dibutyryl-cGMP, and the guanylate cyclase activator, sodium nitroprusside, had no effect on the luminescence. The cAMP analogue, dibutyryl-cAMP, and the adenylate cyclase activator, forskolin, triggered luminescence. Moreover, the adenylate cyclase inhibitor, MDL-12330A, significantly reduced ACh-induced luminescence. The phospholipase C inhibitor, U-73122, also significantly reduced ACh-induced luminescence. The results suggest that ACh-induced luminescence is mediated by both cAMP and IP(3) pathways but not by cGMP. The effects of calcium-free ASW confirmed this hypothesis. A hypothetical scheme of the transduction mechanisms involved in the intracellular control of luminescence is presented.

Adenylyl Cyclase Inhibitors↗
PubMed2004

Regrowth of the stalk of the sea lily, Metacrinus rotundus (Echinodermata: Crinoidea).

Sea lilies are critical to understanding the evolution of the echinoderm body plan, because they are the only extant group whose adults possess a stalk, a prevalent feature in the radiation of a number of primitive echinoderm lineages. Extensive crown regeneration ability has been reported in Metacrinus rotundus, but the regenerative potential of the stalk has never been determined in any species of sea lilies. In this study, we show that M. rotundus whose stalks have been completely excised are capable of stalk regeneration. The process is similar to the growth of the original stalk, but much slower, and the regenerated stalks are not morphologically identical to the original stalk. Since stalk regeneration, in contrast to well-studied regeneration events, probably requires little additional activation of morphogenetic programs, we refer to the stalk regeneration phenomenon as "stalk regrowth" to distinguish it as a special form of regeneration. Since specimens whose entire stalk below the basal plates had been removed were able to regrow, the basal plates, and probably the aboral nerve center within them, are essential for stalk regrowth. Sea lily stalk regrowth is described in detail, and the evolution of feather stars is discussed in light of the growth pattern of the sea lily stalk.

Animal Structures↗
PubMed2006

Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida).

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.

Animals↗
PubMed1998

Synthesis of testosterone and 5alpha-androstanediols during nutritionally stimulated gonadal growth in Lytechinus variegatus lamarck (Echinodermata:Echinoidea).

Although sex steroids and steroid converting enzymes have been found in echinoids, the relationship between steroids and reproduction has not been demonstrated. On days 0, 4, 8, 16, 32, and 48 of feeding, the gonads of previously starved Lytechinus variegatus were excised and incubated with [3H]androstenedione for 0.5 h to determine if changes in steroidogenic capacity are correlated with gonadal growth. Total rates of androstenedione conversion in the testes and ovaries increased significantly during feeding. In addition, the types and relative quantities of metabolites synthesized varied, suggesting that androstenedione metabolism is influenced by nutritional status. Both testes and ovaries synthesized testosterone, 5alpha-androstane-3alpha,17beta-diol, and 5alpha-androstane-3beta, 17beta-diol (5alpha-adiols), 5alpha-androstanedione, epiandrosterone, and androsterone on all days of feeding. In the testes, the relative quantities of testosterone and 5alpha-adiols increased greatly on day 4 of feeding. In contrast, in the ovaries testosterone synthesis was not detectable on day 4, although the relative quantities of 5alpha-adiols increased threefold. The sex-specific changes in the synthesis of these metabolites reflect a shift in the metabolic pathway indicated by changes in the relative enzyme activity indices for 5alpha-reductase (5alpha-R) (necessary for the synthesis of 5alpha-reduced androgens) and 3alpha/beta-hydroxysteroid dehydrogenase (3alpha/beta-HSDs, necessary for the synthesis of 3alpha- or 3beta-hydroxylated androgens). In both testes and ovaries the relative activities of 5alpha-R and 3alpha/beta-HSD increased on day 4 of feeding. The physiological significance of changes in androstenedione metabolism may be associated with the initiation of biosynthetic processes associated with gametogenesis.

Androstanes↗
PubMed1978

Fine structure of the axial complex of Sphaerechinus granularis (Lam.) (Echinodermata: Echinoidea).

Three regions of the axial complex in Sphaerechinus granularis can be distinguished: 1) The axial organ which protrudes from one side of the axial sinus; the sinus septum which separates the sinus from the body cavity and encloses the stone canal; the pulsating vessel which runs along the inside of the axial organ. 2) The blindly-ending terminal sinus in which the pulsating vessel broadens out to the contractile terminal process. 3) The ampulla of the stone canal which connects the axocoel and water vascular system and which opens out through the madreporite. A single-layered, monociliated coelomic epithelium surrounds all regions of the axial complex. This epithelium contains smooth muscle cells at the contractile areas. Canaliculi, surrounded by basal lamina, are formed through infolding of epithelia; they end blindly in the fluid- and connective tissue-matrix of the inner structures. The lacunae of the dorso-ventral mesentery connect the periesophageal and the perianal haemal ring with the axial organ. The axial organ contains many coelomocytes rich in pigment and granules. These coelomocytes are separated into compartments by elastic fibres. Phagocytosis of whole cells and transformational stages of coelomocytes suggest storage and degradation functions. An excretory function via the water vascular system is also suggested.

Animals↗
PubMed1975

Ultrastructure of the dorsal hemal vessel in the sea-cucumber Parastichopus tremulus (Echinodermata: Holothuroidea).

The dorsal hemal vessel in Parastichopus consists of three distinct layers: An outer flagellated epithelium, an intermediate circular muscle layer and an inner connective tissue layer which nearly fills the lumen. Between the outer and intermediate layer runs strands of nerve fibers. Each coelomic epithelial cell has one flagellum and some microvilli. It contains a number of different vacuoles and a few bundles of tonofilaments. One special type of vacuole which contains well organized myofilaments is described. Each muscle cell contains one myofibril of a non-striated type consisting of thick and thin filaments and no dense bodies. The sarcoplasmic reticulum is poorly developed, but peripheral coupling are frequently found. The muscle cells in the dorsal hemal vessel of Parastichopus are compared with other muscles in echinoderms and muscle types described in other phyla.

Animals↗
PubMed1979

The juxtaligamental cells of Ophiocomina nigra (Abildgaard) (Echinodermata: Ophiuroidea) and their possible role in mechano-effector function of collagenous tissue.

The intervertebral ligament of the brittlestar Ophiocomina nigra contains numerous cellular processes which belong to perikarya located on the outer surfaces of the ligament. These are described as the juxtaligamental cells and have been studied by light and electron microscopy. The cells are mainly concentrated in four pairs of ganglion-like nodes associated with the intervertebral ligament and in similar nodes adjacent to every other major connective tissue component of the arm. Although their histochemistry and ultrastructure indicate a neurosecretory function, they are anomalous in containing unusually large electron-dense granules probably associated with calcium. The ganglion-like nodes are innervated by hyponeural nerves, though synaptic contacts with the juxtaligamental cells have yet to be demonstrated. The function of the cells is discussed and it is suggested that they may be involved in the rapid loss of tensil strength which the intervertebral ligament sustains during arm autotomy. They may achieve this by controlling the availability of Ca2+ ions to the extracellular compartment of the ligament.

Animals↗
PubMed1981

Fine structure of the cirri and a possible mechanism for their motility in stalkless crinoids (Echinodermata).

Crinoid cirri are jointed appendages that can slowly bend and straighten. The structures causing each cirrus to move have not been identified unequivocally by light microscopy; therefore, we examined them by electron microscopy. No muscle cells were found, but a probable contractile apparatus was demonstrated in the cytoplasm of epithelial cells lining the oral and aboral coeloms running the length of the cirrus. The presumed contractile apparatus is a bundle of 5 nm filaments oriented parallel to each other and to the long axis of the appendage. We have proposed that contractile shortening of the coelomic epithelia bends the cirrus in an aboral direction, since the fulcral articulations of the skeletal ossicles are oral to the contractile tissue; this active bending is presumably opposed by an elasticity of the oral ligaments, which seem to straighten the cirrus. It is possible that ligaments of the cirrus may undergo neurosecretion-mediated changes in consistency that could lock the appendage into a rigid state; however, active contraction by the ligaments appears unlikely.

Animals↗
PubMed1983

Chromatographic separation of coelomic fluid from Holothuria polii (echinodermata) and partial characterization of the fractions reacting with erythrocytes.

Coelomic fluid preparations from Holothuria polii were passed through a Bio-gel A5m column. The 3 separated protein peaks possess hemagglutinating or hemolytic activity against rabbit erythrocytes. Electrophoretic and immunochemical methods showed that 2 identical protein subunits characterized hemagglutinins of different size. Hemolysin differs from hemagglutinin in molecular weight and organization of subunits.

Animals↗
PubMed1987

Membrane damage by coelomic fluid from Holothuria polii (Echinodermata).

Rabbit erythrocyte membranes lyzed by Holothuria polii coelomic fluid, observed under the electron microscope, present lesions consisting of irregular holes which are heterogeneous in size (ranging from 50 A to 250 A) and ultrastructurally different from the ring-like structure produced by human complement. The protein pattern associated with the lyzed membrane was also examined.

Animals↗
PubMed2000

Cytological changes during bioluminescence production in dissociated photocytes from the ophiuroid Amphipholis squamata (Echinodermata).

Bioluminescence in the ophiuroid Amphipholis squamata is produced by photocytes located within the spinal ganglia of arm spines. Ganglionic cells were dissociated (pronase digestion) and photocytes separated from other cell types by using a continuous density Percoll gradient. Aliquots from a stock suspension of photocytes in artificial sea water were stimulated to produce light by using KCl or acetylcholine and fixed for ultrastructural observation at different times of the luminous process. Preluminescent, luminescent, and postluminescent photocytes contained various intracytoplasmic structures, such as Golgi, flat and distended rough endoplasmic reticulum cisternae, bundles of fibrils, and up to six types of membrane-bounded vesicles. These structures either co-occurred or succeeded one another during the process of light production, indicating that they were most probably participating in the luminescence reaction. Two types of vesicles, sharing some ultrastructural features, probably represented the microsources of the photocytes. One type occurred almost exclusively in luminescent photocytes, and the other almost exclusively in postluminescent photocytes, suggesting that one may be transformed into the other. The latter type of vesicle contained densely packed fibro-tubular units, giving a characteristic paracrystalline appearance to postluminescent photocytes.

Animals↗