Apical Knob Research Articles

Heterogeneity in diagnostic characters across ecoregions: A case study with Botrynema (Hydrozoa: Trachylina: Halicreatidae)

IntroductionBotrynema, a genus of medusozoans in the trachyline family Halicreatidae, currently contains two species: B. brucei and B. ellinorae, distinguished by the presence or absence, respectively, of an apical knob as a diagnostic character. However, no study has corroborated if these taxonomic diagnoses have a biological and evolutionary basis. Therefore, in this study we attempted to address the question “do the two nominal species in the genus Botrynema represent independent phylogenetic lineages, or two phenotypic variants of a single species?MethodsIn this study we took advantage of legacy collections from different research expeditions across the globe from 2000 to 2021 to study the phylogenetics and taxonomy of the genus Botrynema.ResultsB. brucei and B. ellinorae present partially overlapping vertical distributions in the Arctic and as a whole in the Arctic the genus seems to be limited to the Atlantic water masses. The phylogenetic reconstruction based on the concatenated alignment corroborates the validity of the family Halicreatidae and of genus Botrynema as monophyletic groups. However no clear differentiation was found between the two presently accepted species, B. ellinorae and B. brucei.DiscussionBased on the evidence we gathered, we conclude that while the genus Botrynema does contain at least two species lineages, these lineages are not concordant with current species definitions. The species B. ellinorae is reassigned as a subspecies of B. brucei and diagnostic characters are provided.

5HTR3A-driven GFP labels immature olfactory sensory neurons.

The ionotropic serotonin receptor, 5-HT3 , is expressed by many developing neurons within the central nervous system. Since the olfactory epithelium continues to generate new olfactory sensory neurons (OSNs) throughout life, we investigated the possibility that 5-HT3 is expressed in the adult epithelium. Using a transgenic mouse in which the promoter for the 5-HT3a subunit drives expression of green fluorescent protein (GFP), we assessed the expression of this marker in the olfactory epithelium of adult mice. Both the native 5-HT3a mRNA and GFP are expressed within globose basal cells of the olfactory and vomeronasal epithelium in adult mice. Whereas the 5-HT3a mRNA disappears relatively quickly after final cell division, the GFP label persists for about 5 days, thereby labeling immature OSNs in both the main olfactory system and vomeronasal organ. The GFP-labeled cells include both proliferative globose basal cells as well as immature OSNs exhibiting the hallmarks of ongoing differentiation including GAP43, PGP9.5, but the absence of olfactory marker protein. Some of the GFP-labeled OSNs show characteristics of more mature yet still developing OSNs including the presence of cilia extending from the apical knob and expression of NaV1.5, a component of the transduction cascade. These findings suggest that 5-HT3a is indicative of a proliferative or developmental state, regardless of age, and that the 5-HT3A GFP mice may prove useful for future studies of neurogenesis in the olfactory epithelium. J. Comp. Neurol. 525:1743-1755, 2017. © 2016 Wiley Periodicals, Inc.

NaV1.5 sodium channel window currents contribute to spontaneous firing in olfactory sensory neurons.

Olfactory sensory neurons (OSNs) fire spontaneously as well as in response to odor; both forms of firing are physiologically important. We studied voltage-gated Na(+) channels in OSNs to assess their role in spontaneous activity. Whole cell patch-clamp recordings from OSNs demonstrated both tetrodotoxin-sensitive and tetrodotoxin-resistant components of Na(+) current. RT-PCR showed mRNAs for five of the nine different Na(+) channel α-subunits in olfactory tissue; only one was tetrodotoxin resistant, the so-called cardiac subtype NaV1.5. Immunohistochemical analysis indicated that NaV1.5 is present in the apical knob of OSN dendrites but not in the axon. The NaV1.5 channels in OSNs exhibited two important features: 1) a half-inactivation potential near -100 mV, well below the resting potential, and 2) a window current centered near the resting potential. The negative half-inactivation potential renders most NaV1.5 channels in OSNs inactivated at the resting potential, while the window current indicates that the minor fraction of noninactivated NaV1.5 channels have a small probability of opening spontaneously at the resting potential. When the tetrodotoxin-sensitive Na(+) channels were blocked by nanomolar tetrodotoxin at the resting potential, spontaneous firing was suppressed as expected. Furthermore, selectively blocking NaV1.5 channels with Zn(2+) in the absence of tetrodotoxin also suppressed spontaneous firing, indicating that NaV1.5 channels are required for spontaneous activity despite resting inactivation. We propose that window currents produced by noninactivated NaV1.5 channels are one source of the generator potentials that trigger spontaneous firing, while the upstroke and propagation of action potentials in OSNs are borne by the tetrodotoxin-sensitive Na(+) channel subtypes.

Acrosome Biosynthesis in Spermatocytes and Spermatids Revealed by HPA Lectin Cytochemistry

The origin of the acrosome is controversial, because of both its lysosomal nature and at the moment of its appearance, which seems to be species-specific. Considering the amazing organization shown by the acrosome of some urodele amphibians, HPA-colloidal gold cytochemistry was used to analyze the biogenesis of the acrosome in the urodele Pleurodeles waltl at electron microscopy level. The results showed that HPA-labeling is useful to label the acrosome and its precursor vesicles and, consequently, HPA-histochemistry could be used as a marker of acrosomal content. Labeling of the Golgi apparatus and precursor vesicles was seen in primary spermatocytes and round (stage I) spermatids, thus contributing solid evidence for the beginning of acrosome biogenesis before meiosis. In both primary spermatocytes and round spermatids, an enigmatic vesicle, probably related to the biosynthesis of the neck piece or the tail, was also labeled. Labeling in elongating spermatids (stage II-IV), showed a homogeneous distribution of colloidal gold particles in the acrosomal cap, but the perforatorium was not positive to the lectin. However, in mature (stage V-VI) spermatids, a regional distribution of labeling in the acrosome was seen, with the apical knob showing a stronger labeling than the lateral barb, and the lateral barb showing a stronger labeling than the principal piece of the acrosomal cap. This regional distribution of the labeling suggests that the acrosome develops several domains with different glycoconjugate compositions.

Putative sensory structures in marine bryozoans

Abstract. SEM studies of 21 species of marine bryozoans demonstrated that the abfrontal side of the tentacles bears a row of mono‐ or multiciliated cells, which are presumably sensory. In stenolaemates, the abfrontal cells, as well as the cells at the tentacle tips and the laterofrontal cells, are monociliated. In the 17 gymnolaemate species studied, each tentacle tip bears at least 3 multiciliated cells, each with a tuft of 5–7 stiff cilia of various lengths. On the abfrontal tentacle surface, mono‐ and multiciliated cells alternate, but all species studied have multiciliated cells at the base and the tip of each tentacle. In live animals, single cilia perform occasional flicks, whereas the tufts of 7–15 cilia on the multiciliated cells are immotile. Length and number of abfrontal cilia vary between species. Two types of multiciliated, putative sensory organs were found on the introvert of some gymnolaemates. One has an apical knob surrounded by a ring of cilia; the other has an apical tuft of cilia. The ultrastructure of the sensory cells of tentacles and introvert was studied in Rhamphostomella ovata. Our observations on both fixed and living material all suggest that these cells are primitive mechanoreceptors. The few species lacking ciliary structures on the introvert have long proximal ciliary tufts on the abfrontal tentacle surface.

A Cytological Study and Reclassification of Trichophrya collini (Saedeleer & Tellier)1

ABSTRACT. Trichophrya collini has a polygonal, dorsoventrally flattened body (up to 75 μm diam.), with capitate tentacles arranged in 1–3 rows within peripheral fascicles. There is a central polymorphic macronucleus, an associated micronucleus, and numerous peripheral contractile vacuoles with ventral discharge pores. The cell has a multilayered cortex and the cytoplasm contains suctorian organelles such as crescentic bodies, elongate dense bodies, and haptocysts. The highly contractile tentacles have an axoneme with an outer ring of 24 microtubules separated into six groups and an inner ring of six curved lamellae, each with five microtubules. The lamellae at the distal and proximal ends of the axoneme are arranged in a helix, and the outer ring microtubules are joined in a distal connective sheath. In the apical knob of the tentacle, the haptocysts are borne on a central capsule, Reproduction is by endogenous budding to produce a single oval‐shaped swarmer, with equatorial ciliature, which metamorphoses within 3 h. These observations suggest that this organism, previously known as Heliophrya collini Saedeleer & Tellier, is synonymous with Platophrya rotunda Gönnert, Craspedophrya rotunda Rieder, and Heliophrya rotunda Matthes. Its endogenous mode of budding assigns it to the genus Trichophrya. but it is distinct from Trichophrya rotunda Hentschel, and should be reclassified to Trichophrya collini (Saedeleer & Tellier).

Scanning and transmission electron microscope study of specialized mantle structures in dorid nudibranchs (Gastropoda: Opisthobranchia: Anthobranchia)

Mantle surfaces of the dorid nudibranchs Rostanga arbutus and Jorunna sp. were examined using scanning and transmission electron microscopy, and two specialized structures are described. These are caryophyllidia and mantle rim organs; the latter being described for the first time. Caryophyllidia occur in large numbers (several thousand) uniformly distributed over the entire upper surface, while the mantle rim organs, numbering only 40 to 60, are restricted to the upper mantle margin. Caryophyllidia are minute (40 to 50 μm diam), erect tubercles supported internally by 4 to 7, vertical, calcareous spicules which emerge in a crown surrounding an apical knob. Caryophyllidia display a high level of spicular organization and incorporate a complex muscle system at their base. The apical knob is formed from specialized epidermis capping a sub-epithelial ganglion. The highly organized structure of the caryophyllidium indicates its potential importance as a new character in dorid taxonomy and phylogeny. Mantle rim organs (80 to 300 μm diam) contain large numbers of vacuolated cells and cells containing pellet-shaped nodules.

Use of a monoclonal antibody to classify neurons isolated from the head region of Hydra.

A mouse monoclonal antibody (JD1) to Hydra attenuata using the peroxidase-antiperoxidase (PAP) method revealed unipolar, bipolar, and multipolar sensory and ganglion cells in the head region of H. littoralis. Neurons isolated from macerated hypostomes and tentacles were classified according to the number of their cytoplasmic processes and the position of the cilium, when present, relative to the perikaryon. PAP-stained sensory cells had an apical ciliary cone, whereas ganglion cells did not. Neurons with cytoplasmic processes longer than 50 microns stained faintly, whereas those with processes shorter than 50 microns in length stained mainly dense brown. Unipolar neurons had an oval, crescent, round, or elliptic perikaryon with a single short axon. The perikaryal shape of bipolar neurons varied from round to tall triangular, short triangular, crescent, oval, or elliptic with two oppositely directed symmetric or asymmetric processes. Asymmetric processes were present in a bipolar sensory cell with a long apical cilium typical of gastrodermal sensory cells. One type of bipolar ganglion cell had a short perikaryal cilium. Another type had neurites longer than 50 microns. We found seven morphological variations of multipolar neurons, including one with an apical knob, two with a short perikaryal cilium, two with cytoplasmic loops near the perikaryon, one with perpendicular processes projecting from the major neurites, and one with a branched process longer than 50 microns opposite a tangled mass of neurites.

The ultrastructure, function and morphogenesis of the tentacle in Discophrya sp. (suctorida) cileatea

Tentacle structure, feeding and morphogenesis of the suctorian Discophrya sp. have been examined by light, scanning, and transmission electron microscopy. The long, slender mobile tentacles have an apical knob, which is covered only by the plasma membrane and contains haptocysts and clongate dense bodies. The tentacle shaft contains a central microtubular canal (axoneme) running from the base of the knob into the body cytoplasm, where it is surrounded by a unique fibrous collar. The axoneme is composed of two concentric rings of microtubules, the inner organized into curved lamellae. A short distance below the tip, the microtubules of the outer ring are joined by a connective sheath of limited length. Distal to this sheath, the axoneme is composed of helically arranged lamellae, the microtubules of which bear a restricted zone of inwardly pointing projections. Developmental stages of tentacle formation have been identified. New tentacle axonemes are formed in association with subcortical kinetosomes. During feeding the tentacle knob penetrates the prey ciliate body and is displaced laterally by the axoneme microtubules splaying outwards to form a funnel. The projections on the lamellae are thought to mediate the transport of the covering membrane and prey cytoplasm into the suctorian body. A number of possible mechanisms of tentacle movement and prey penetration are discussed.

Shape, size and surface topography of genital organs of Leucochloridium sp. (Digenea), revealed by light and scanning electron microscopy

The opening of the genital atrium in Leucochloridium sp. was always situated on the dorsal side near the terminal end, and below the excretory pore common to Laurer's and the excretory canal. The genital pore was surrounded by an aggregation of domed aciliate papillae. Information on the cirrus pouch (position, shape and size) are given. No distinct Vesiculum seminalis was found. A well-developed metraterm empties into right side of genital artium. The cirrus was unarmed and approximately cylindrical. The cirrus surface was covered with anastomosing ridges giving an irregular net-shaped appearance. Papillae with short apical knob were scarcely scattered around on the cirrus surface with increased frequency near cirrus base. The taxonomical value of the genital characters are discussed in relation to corresponding information on the other species of Leucochloridiidae.

Megalodiscus temperatus: Scanning electron microscopy of the tegumental surfaces

The tegumental surface of Megalodiscus temperatus forms cobblestonelike areas with rows of indentations encircling the worm. This pattern merges in several areas into folds and ridges, some of which represent the musculature of the posterior sucker and genital pore. Papillae surrounding the base of the oral sucker appear as two types: one with a bulb-like base and a short apical knob; the second typified by a hair-like structure (cilium?) of variable length projecting from a pit. From their location on the oral sucker and the resemblance to previously described structures, they are presumed to be sensory receptors. A circle of papillae on the closed posterior sucker was also observed. Rod-shaped bacteria were seen adhering to some of the worms observed but they were not found to be in any special association with the tegument or in any specific areas of the worm's surface.