Apical Flaps Research Articles

Mitogenomics suggests a sister relationship of Relicanthus daphneae (Cnidaria: Anthozoa: Hexacorallia: incerti ordinis) with Actiniaria

Relicanthus daphneae (formerly Boloceroides daphneae) was first described in 2006 as a giant sea anemone based on morphology. In 2014, its classification was challenged based on molecular data: using five genes, Relicanthus was resolved sister to zoanthideans, but with mixed support. To better understand the evolutionary relationship of Relicanthus with other early-branching metazoans, we present 15 newly-sequenced sea anemone mitochondrial genomes and a mitogenome-based phylogeny including all major cnidarian groups, sponges, and placozoans. Our phylogenetic reconstruction reveals a moderately supported sister relationship between Relicanthus and the Actiniaria. Morphologically, the cnidae of Relicanthus has apical flaps, the only existing synapomorphy for sea anemones. Based on both molecular and morphological results, we propose a third suborder (Helenmonae) within the Actiniaria to accommodate Relicanthus. Although Relicanthus shares the same gene order and content with other available actiniarian mitogenomes, it is clearly distinct at the nucleotide level from anemones within the existing suborders. The phylogenetic position of Relicanthus could reflect its association with the periphery of isolated hydrothermal vents, which, although patchy and ephemeral, harbor unique chemosynthetic communities that provide a relatively stable food source to higher trophic levels over long evolutionary timescales. The ability to colonize the deep sea and the periphery of new vent systems may be facilitated by Relicanthus’ large and extremely yolky eggs.

Fruit Morphology and Anatomy of the Spondioid Anacardiaceae

The Spondioideae subfamily of the Anacardiaceae is widely distributed today in tropical regions. Recent molecular phylogenetic investigations indicate that the Spondioideae are not monophyletic, but rather comprise at least two separate clades that are difficult to distinguish using vegetative and floral characters. Nevertheless, the syndrome of fruit characters traditionally used in identifying the subfamily is useful in discriminating genera of these clades and for identification of both modern and fossil anacardiaceous fruits. Here we document the morphology and anatomy of endocarps for representatives of all extant genera traditionally treated as Spondioideae, plus two genera that have been placed close to them in molecular investigations, Buchanania and Campnosperma. All genera are characterized by drupe-like fruits with sclerified stones that vary from uni- to multilocular depending on the genus. Germination modes vary throughout the Spondioideae. Some have characteristic plug-like opercula; others have recessed bilabiate germination valves, and still others open by apical flaps or simple slits. Although most currently recognized genera appear to be monophyletic, fruit morphology indicates that current circumscriptions of Cyrtocarpa, Poupartia and Tapirira are in need of revision.

Parapristionchus giblindavisi n. gen., n. sp. (Rhabditida: Diplogastridae) isolated from stag beetles (Coleoptera: Lucanidae) in Japan

A new species of diplogastrid nematode, isolated in a previous survey of nematodes associated with stag beetles in Japan, is described as Parapristionchus giblindavisi n. gen., n. sp. Parapristionchus n. gen. differs from other diplogastrid genera chiefly by its stomatal morphology. Distinguishing the genus are the presence of a claw-like dorsal tooth in both the eurystomatous and stenostomatous forms and the division of the cheilostom into 12 plates lacking apical flaps. According to phylogenetic analysis of nine ribosomal protein gene sequences, Parapristionchus n. gen. shows deep divergence from other known genera. Molecular evidence strongly supports P. giblindavisi n. gen., n. sp. + Pristionchus spp. as monophyletic with respect to all other diplogastrids examined. Congruent with a clade of P. giblindavisi n. gen., n. sp. + Pristionchus spp. is the shared presence of a bifurcate P7 genital papilla. Discovery and description of a close sister group to Pristionchus, a model biological system, enables character polarisation in macroevolutionary studies of Pristionchus nematodes.

Morphology, distribution, and evolution of apical structure of nematocysts in hexacorallia

Cnidae are complex intracellular capsules made by all cnidarians. The most diverse of these capsules are nematocysts, which are made by all members of the phylum; spirocysts and ptychocysts are made only by members of some lineages, and they show less functional and structural diversity. In nematocysts, the apex has been shown to be either a hinged cap (operculum) or three flaps that flex outward during discharge. The operculum is known only from medusozoan nematocysts; flaps are known only from nematocysts of members of the hexacorallian order Actiniaria, although they have been inferred to be characteristic of Anthozoa, the group to which Actiniaria belongs. Using scanning and transmission electron microscopy, we discover a third apical morphology in nematocysts, an apical cap, which we find in all nonactiniarian anthozoans examined. This apical cap is identical structurally to the apical cap of spirocysts, and it resembles the apical structure of ptychocysts, whose apex is documented here for the first time. Additionally, a full survey of nematocysts from all body structures of two actiniarians demonstrates that a particular type of nematocyst, the microbasic p-mastigophore of the mesenterial filaments, does not have apical flaps. The observed variation does not correspond to conventional categorization of capsule morphology and raises questions about the function and structure of capsules across Cnidaria. Despite some ambiguity in optimization of ancestral states across cnidae, we determine that the apical cap is the plesiomorphic structure for anthozoan cnidae and that apical flaps are a synapomorphy of Actiniaria. At present, the operculum is interpreted as a synapomorphy for Medusozoa, but either it or an apical cap is the ancestral state for nematocysts.

Formation of the Apical Flaps in Nematocysts of Sea Anemones (Cnidaria: Actiniaria)

Using scanning and transmission electron microscopy, we studied formation of the structure at the apical end of sea anemone nematocysts through which the tubule everts at discharge. In anemones of the genus Metridium, we found that each of the three solid triangular apical flaps comprises two layers that are continuous with those of the capsule wall: the electron-lucent inner layer is bound to the electron-dense outer layer. The two-layer structure is obvious in some discharged capsules in which, perhaps due to fixation, the layers part at the flap's periphery. Before the nematocyst discharges, a channel leads from a pore at the tip of the joined flaps into the lumen of the inverted tubule. The thin laminate layer that coats each flap lines the channel. The base of the nematocyst tubule adheres to the capsule wall near the capsule's apical end, and a branch of the tubule underlies part of the laminate layer that coats the flaps. Thus the tubule is not continuous with the capsule wall but structurally separate from it. This helps reconcile differences in understanding of the number of layers constituting the capsule wall, and makes clear that the tubule should be considered part of the capsule contents.

Closure of Meningomyelocele Defects With Bilateral Modified V-Y Advancement Flaps

Although several different methods were described in the literature, closure of large meningomyelocele defects presents a challenging problem. Wound dehiscence may lead to devastating complications. In this paper, the efficacy of the bilateral modified V-Y advancement flap procedure was investigated in terms of simplicity, donor-site morbidity, and reliability. The authors presented 10 neonates treated with a modified subcutaneous advancement procedure. Unlike the typical V-Y advancement techniques, the apical extensions of the "V" flaps were elevated based on the paraspinous perforators. A standard closure algorithm was not followed, as the well-vascularized apical extensions facilitated intraoperative decision making for the most appropriate adaptation pattern, depending on the size, shape, and localization of the defect. As well as that, transposition of these apical flaps to the defect site was further supported by the advancement of the V-Y flaps to decrease the tension along the closure. Mean follow-up period was 13.6 months (range 3-37 months), and no complications that might be attributable to the operative procedure were observed. Utilization of bilateral modified V-Y flaps for the closure of large meningomyelocele defects is a simple and effective procedure. Main advantages of the method described in this paper may be listed as follows: simplicity, reliability due to coverage of the defect with well-vascularized flaps, minimal bleeding, decreased operative time, and no donor-site morbidity.

Observation of the posterior endothelial surface of the rabbit cornea using atomic force microscopy.

To study the surface of normal corneal endothelium by means of atomic force microscopy (AFM). The central corneal endothelial posterior surface of New Zealand white rabbits was examined. Specimens were observed in Balanced Salt Solution using the contact mode of the AFM either fresh or after fixation in cacodylate-buffered glutaraldehyde solution. Removal of sialic acid residues and hyaluronic acid was achieved by means of enzymatic treatment with neuraminidase and hyaluronidase. Observation of the fresh specimens revealed the presence of an apical endothelial surface coating material (glycocalyx). Removal of sialic acid residues and hyaluronic acid after enzymatic treatment using neuraminidase and hyaluronidase, respectively, permitted the elucidation of the structure of the nondigested coating material. Fixation of the samples resulted in removal of the surface coating material. The imaging of the fixed endothelium surface revealed the mosaic of polygonal cells with the apical flaps of cell junctions emerging over the cell surface. The cell shape and the other characteristics of the posterior surface fixed endothelium were comparable to those described in the literature using scanning electron microscopy. The scanning of very small ranges has provided high-resolution images at the nanometer level in fixed and fresh corneal endothelial surfaces. The atomic force microscope represents a new powerful imaging tool permitting high-resolution observation of corneal endothelium surface in fresh and minimally prepared fixed specimens.

Characterization of corneal endothelium cell cultured on microporous membrane filters.

In these experiments we characterize rabbit and bovine corneal endothelia cell cultured on microporous membrane filters (0.6cm2). Cell cultured bovine or rabbit corneal endothelial cells (subcultures 1-3) were seeded onto Millicell-HA filter inserts. Electrical resistance measured across the cultured monolayers increased steadily through 14 days of culture, reaching 34.2 +/- 0.8 ohm-cm2 (mean +/- SE) for rabbit cells and 33.1 +/- 1.1 ohm-cm2 for bovine cells. Alizarin red staining of the monolayers showed a polygonal morphology comparable to that observed in situ. Transmission electron microscopy showed well developed apical junctional complexes and flaps. Exposure of the monolayers to calcium-free medium resulted in the disruption of intercellular junctions, rounding-up of the cells and a decrease in electrical resistance (to near 0). Transmonolayer fluxes of inulin and dextran correlated well to the resistance measurements. Results of this study demonstrate that corneal endothelium, both bovine and rabbit, grown on filter inserts is comparable in morphology and ultrastructure to corneal endothelium in situ. The cells cultured in this system form functional apical junctional complexes that effect a barrier function comparable to that of the endothelium in situ.

Effects of controlled treatment with trypsin on the functional characteristics of isolated nematocysts of Calliactis parasitica and Aiptasia mutabilis (Cnidaria, Actiniaria)

Glycerol-isolated basitrichs of Calliactis parasitica responsive to thioglycolate had open apical flaps, while unresponsive capsules isolated with Triton X100 or by freezing had closed apical flaps. Limited treatment with trypsin induced the apical flaps to open without causing discharge, suggesting that nematocysts can maintain the resting condition even with open flaps. Trypsin-treated basitrichs acquire a high responsiveness to thioglycolate. Microbasic mastigophores of Aiptasia mutabilis are more responsive to distilled water after controlled trypsin treatment but the apical flaps are unchanged. Ca2+ is inhibitory regardless of trypsin treatment. It is proposed that the capsule tip may control the penetration of the discharging agents rather than providing mechanical resistance to inner pressure.

The corneal endothelial cell interface.

The apical edges of corneal endothelial cells have been separated along lines forming a crisscross pattern, by the help of a special method of preparation. The visualization by SEM of the lateral faces of the cells is thereby made possible. The separation leads to the formation of thin strands spanning the gap between the apical edges of adjoining cells. They are formed by stretching of the normal apical flaps. This stretching demonstrates that the main intercellular adherence is located at the tips of the apical flaps. The basal edges of the endothelial cells can be inspected, and it can be seen that the basal face of the cells has and irregular form. Threadlike processes extend from the basal cell edges. They ascend in the intercellular space and make contact with the lateral face of the neighbouring cell at varying levels. These processes are presumed to mediate intercellular transfer.

Ultrastructure of nematocyst discharge in catch tentacles of the sea anemone Haliplanella luciae (cnidaria: anthozoa)

The mature nematocyst lies just beneath the cnidodyte plasma membrane. A microtubule array surrounds the nematocyst capsule just beneath the capsule tip. We propose that the array helps to hold the capsule at the cnidocyte cell surface until discharge. The undischarged capsule tip is sealed by three apical flaps, joined together along complex radial seams. The seams are filled with subunits that appear to bind the flaps together. Upon discharge, the flaps separate along the radial seams to permit thread eversion. The everted thread is lined on both sides by subunits that are stained by antimonate, indicating that they bind calcium. We suggest that, together, the subunits hold the uneverted thread in its folded and coiled configuration. Thread eversion would follow subunit uncoupling. The capsule and thread interiors of partially discharged nematocysts are stained by antimonate. In contrast, the capsule and thread interiors of fully discharged nematocysts are not stained by antimonate. Thus, nematocyst calcium might be injected into the target tissue where it is presumed to act in conjunction with nematocyst venom to promote cell death.

The differentiation of nematocysts and associated structures in the cnidaria.

The differentiation of nematocysts and associated structures in the tentacles of the sea anemone Metridium senile fimbriatum and in the tentacles of medusae of the hydroid Obelia longissima was studied by electron microscopy. Stages in the morphogenesis of nematocysts are: 1. transformation of an interstitial cell into a cnidoblast in which the primordium of the nematocyst arises from Golgi vacuoles, 2. development of the basal part of the primordium into a capsular region that is continuous with an external tube with which microtubules, Golgi apparatus, and centrioles are associated distally, 3. growth of the capsular region to include most of the external tube, and 4. differentiation of an internal tube with spines from the matrix of the capsule and of the remaining external tube. The external tube is not invaginated to become the internal tube, but is incorporated into the capsular region by distal growth of the capsular wall. At the same time the matrix, both before and during differentiation into a thread, moves into the capsule. The development of nematocysts in Obelia differs from that in Metridium in several respects. In the former the basitrich has an operculum plus associated cnidocil and dense rods whereas in the latter the nematocysts (amastigophore, b-mastigophore and basitrich) have three apical flaps and an associated flagellum, with the exception of the spirocyst.