Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Lancelets”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

12 recordsLinked to original sources
PubMed1992

Ca2+ current in myotome cells of the lancelet (Branchiostoma lanceolatum).

1. By using the whole-cell patch clamp method Ca2+ and Ba2+ currents were measured in the extremely thin twitch muscle cells of the protochordate Branchiostoma lanceolatum whose Ca2+ channels are likely to resemble the evolutionary ancestors of those found in vertebrate skeletal muscle. 2. When using 10 mM-Ca2+ in the artificial external solution and 1 mM-EGTA in the internal solution two kinetically different Ca2+ inward current components could be observed, showing very similar voltage dependence of activation and inactivation. 3. In solutions containing 10 mM-Ba2+ as an external charge carrier the biphasic inward current turned into a single rapidly activated and slowly inactivating current. 4. Inspecting peak currents, the voltage dependence of fractional activation and inactivation was nearly the same in Ca2+ and in Ba2+. 5. A transformation into a single component of the Ca2+ current could also be observed after perfusing the intracellular lumen with 10 mM of either EGTA or BAPTA. In the case of EGTA this transformation required considerably more time. Probably a higher internal concentration of EGTA is necessary since it binds Ca2+ more slowly than BAPTA. 6. Soon after establishing the whole-cell configuration a gradual increase of the second, slow inward current phase was observed relative to the fast component, indicating an enhancement of the slow component by intermediate intracellular buffer concentrations. 7. We conclude that the Branchiostoma myotome cells have only one Ca2+ channel system. The biphasic appearance of the inward current is caused by an unusually rapid inactivation due to Ca2+ ions, which enter the myoplasm during the current and temporarily bind to an inactivation site at the channel. The second phase probably reflects reactivation from the inactivated state upon dissociation of Ca2+ from the binding site.

Animals↗
PubMed1991

Some considerations on the fine structure of rhabdomeric photoreceptors in the amphioxus, Branchiostoma lanceolatum (Cephalochordata).

This study confirms the close relationship of two of the photoreceptive cells of the amphioxus central nervous system, the Hesse and Joseph cells. Both cells have rhbdoms located at the cell surface and possess 9 + 0 cilia that are not related to the rhabdom structure. The rhabdom of Joseph cells is enclosed by thin glial lamellae containing gliofilaments, whereas that of Hesse cells is associated with a pigmentary cell, the two cell types forming an eyecup. The pigment cell is mostly filled of pigment granules and has a 9 + 2 cilium. A third photoreceptive cell of the lancelet, the lamellate cell, is of ciliary type. The significance of the presence of rhabdomeric and ciliary photoreceptors in the lancelet brain is discussed.

Animals↗
PubMed1992

Excitation-contraction coupling in a pre-vertebrate twitch muscle: the myotomes of Branchiostoma lanceolatum.

The segmented trunk muscle (myotome muscle) of the lancelet (Branchiostoma lanceolatum), a pre-vertebrate chordate, was studied in order to gain information regarding the evolution of excitation-contraction (EC) coupling. Myotome membrane vesicles could be separated on isopycnic sucrose gradients into two main fractions, probably comprising solitary microsomes and diads of plasma membrane and sarcoplasmic reticulum, respectively. Both fractions bound the dihydropyridine PN 200/110 and the phenylalkylamine (-)D888 (devapamil) while specific ryanodine binding was observed in the diad preparation only. Pharmacological effects on Ca2+ currents measured under voltage-clamp conditions in single myotome fibers included a weak block by the dihydropyridine nifedipine and a shift of the voltage dependences of inactivation and restoration to more negative potentials by (-)D888. After blocking the Ca2+ current by cadmium in voltage-clamped single fibers, the contractile response persisted and a rapid intramembrane charge movement could be demonstrated. Both responses exhibited a voltage sensitivity very similar to the one of the voltage-activated Ca2+ channels. Our biochemical and electrophysiological results indicate that the EC coupling mechanism of the protochordate myotome cell is similar to that of the vertebrate skeletal muscle fiber: Intracellular Ca2+ release, presumably taking place via the ryanodine receptor complex, is under control of the cell membrane potential. The sarcolemmal Ca2+ channels might serve as voltage sensors for this process.

Animals↗
PubMed1988

Studies on the sites expressing evolutionary changes in the structure of eukaryotic 5S ribosomal RNA.

We have determined the complete sequences of 5S rRNAs from a lamprey (Lampetra reissneri), a lancelet (Branchiostoma belcheri), silkworms (Philosamia cynthia ricini, Bombyx mori, Antheraea pernyi), and a silkworm hybrid (artificially fertilized hybrid species of Philosamia cynthia ricini male x Bombyx mori female), as well as those of cotton seeds (Gossypium hirsutum L.). Having compared more than 170 eukaryotic 5S rRNAs of which seven sequences have been determined by our group as mentioned above, we have found that the "evolutionary sites" that exist at special locations in these structures are closely related to the evolution of eukaryotes. The changes proceed step by step in an orderly way, i.e., the change in nucleotide residues of the "evolutionary sites" depends on the order of the evolution of the species and shows group-specific patterns.

Animals↗
PubMed1992

Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group.

Lampreys and hagfishes (cyclostomes) traditionally were considered to be a natural (monophyletic) group. Recently, the consensus of opinion, based largely on morphological analyses, has shifted to a view that lampreys are more closely related to jawed vertebrates (gnathostomes) than to hagfishes. Phylogenetic comparisons of 18S ribosomal RNA sequences from two hagfishes, two lampreys, a tunicate, a lancelet, and a number of gnathostomes support the monophyly of the cyclostomes. These data force a reassessment of several features of early vertebrate evolution.

Animals↗
PubMed1979

A comparison of epithalamic, hypothalamic and spinal neurosecretory terminals.

Nerve endings of epithalamic, hypothalamic and spinal neurosecretory areas were studied by light and electron microscopy in various vertebrates (from fishes up to mammals) including the lancelet. Areas investigated were the pineal organ, the pulvinar corporis pinealis, the neurohypophysis, the median eminence, the urophysis, the terminal filum and the medullo-spinal neurosecretory zones. We found that in all these areas the neurosecretory endings have common structures, which we call synaptic hemidesmosomes or neurohormonal terminals. These are characterized by accumulation of vesicles, and dense projections in a terminal on the basal lamina of the surface of the nervous tissue. A critical review of the literature suggests that a considerble neuroendocrine activity is associated with synaptic hemidesmosomes as special neurohormonal effector structures of the nerve cells. The cell-to-cell synapses formed by neurosecretory cells are discussed in connection with the dual capacity of these cells to function as both endocrine and "ordinary# neuronal elements. The importance of the external cerebrospinal fluid (CSF) space for the transport of materials released in the so-called neurohemal areas, is stressed.

Amphibians↗
PubMed2026

The highly heterozygous European amphioxus (Branchiostoma lanceolatum) at the edge of panmixia.

Amphioxus (Cephalochordata) are small marine chordates that have broad ecological ranges, yet as adults form local settlements and exhibit limited mobility. Genomic surveys of two amphioxus species have suggested that they rank among the most genetically diverse metazoans. Here, we present the first accurate assessment of genomic diversity in the European amphioxus (Branchiostoma lanceolatum) and investigate the processes underlying this diversity. We leverage whole-genome sequencing data from multiple individuals sampled at two geographically distant Atlantic and Mediterranean locations. Consistent with previous estimates in other amphioxus species, we measure exceptionally high genomic diversity, with an average heterozygosity of 2.73% in B. lanceolatum. Despite the large geographic separation between sampling sites, population differentiation is minimal, indicating extensive gene flow among distant adult settlements. Phylogenetic analyses combined with population genetic simulations confirm that this elevated genomic diversity is primarily driven by a large effective population size. Although adult amphioxus have limited mobility, our results indicate that long-distance larval dispersal mediated by ocean currents is sufficient to generate a near-panmictic population structure across their broad ecological range.

Animals↗