Mechanisms Of Metamorphosis Research Articles

Prefigurations of Thinking about Thinking

The article presents arguments about the difficulties of thinking about thinking, notes the historical nature of both thinking itself and the dialogue about it. The author searches for allies for the thesis that thinking about thinking cannot complete itself because thinking about itself does not follow the cognitive strategy Subject/object. It is not possible, in an act of self-communication (self-recognition), to be both the interpretandum and the interpretans. An interpretandum cannot be simultaneously the interpretans in the thinking of the Self. The author gathers arguments for the thesis that thinking about thinking can be supported by the data on pre-philosophical thinking and on the mechanism of metamorphosis.

The development and metamorphosis of the indirect developing acorn worm Schizocardium californicum (Enteropneusta: Spengelidae)

BackgroundEnteropneusts are benthic marine invertebrates that belong to the deuterostome phylum Hemichordata. The two main clades of enteropneusts are defined by differences in early life history strategies. In the Spengelidae and Ptychoderidae, development is indirect via a planktotrophic tornaria larva. In contrast, development in the Harrimanidae is direct without an intervening larval life history stage. Most molecular studies in the development and evolution of the enteropneust adult body plan have been carried out in the harrimanid Saccoglossus kowalevskii. In order to compare these two developmental strategies, we have selected the spengelid enteropneust Schizocardium californicum as a suitable indirect developing species for molecular developmental studies. Here we describe the methods for adult collecting, spawning and larval rearing in Schizocardium californicum, and describe embryogenesis, larval development, and metamorphosis, using light microscopy, immunocytochemistry and confocal microscopy.ResultsAdult reproductive individuals can be collected intertidally and almost year-round. Spawning can be triggered by heat shock and large numbers of larvae can be reared through metamorphosis under laboratory conditions. Gastrulation begins at 17 h post-fertilization (hpf) and embryos hatch at 26 hpf as ciliated gastrulae. At 3 days post-fertilization (dpf), the tornaria has a circumoral ciliary band, mouth, tripartite digestive tract, protocoel, larval muscles and a simple serotonergic nervous system. The telotroch develops at 5 dpf. In the course of 60 days, the serotonergic nervous system becomes more elaborate, the posterior coeloms develop, and the length of the circumoral ciliary band increases. At the end of the larval stage, larval muscles disappear, gill slits form, and adult muscles develop. Metamorphosis occurs spontaneously when the larva reaches its maximal size (ca. 3 mm), and involves loss and reorganization of larval structures (muscles, nervous system, digestive tract), as well as development of adult structures (adult muscles, tripartite body organization).ConclusionsThis study will enable future research in S. californicum to address long standing questions related to the evolution of axial patterning mechanisms, germ layer induction, neurogenesis and neural patterning, the mechanisms of metamorphosis, the relationships between larval and adult body plans, and the evolution of metazoan larval forms.

Reduced effects of thyroid hormone on gene expression and metamorphosis in a paedomorphic plethodontid salamander.

It has been over a century since Gudernatsch (1912, Wilhelm Roux Arch Entwickl Mech Org 35:457-483) demonstrated that mammalian thyroid gland extracts can stimulate tadpole metamorphosis. Despite the tremendous developmental diversity of amphibians, mechanisms of metamorphosis have mostly been studied in a few model systems. This limits our understanding of the processes that influence the evolution of developmental aberrations. Here we isolated thyroid hormone receptors alpha (TRα) and beta (TRβ) from Oklahoma salamanders (Eurycea tynerensis), which exhibit permanently aquatic (paedomorphic) or biphasic (metamorphic) developmental modes in different populations. We found that TRα and TRβ were upregulated by thyroid hormone (T3 ) in tail tissues of larvae from metamorphic populations, but basal levels of TR expression and T3 responsiveness were reduced in larvae from paedomorphic populations. Likewise, we found that T3 treatment resulted in complete loss of larval epibranchials in larvae from metamorphic populations, but little to no epibranchial remodeling occurred in larvae from paedomorphic populations over the same duration. This is the first study to directly demonstrate reduced gene expression and metamorphic responses to T3 in a paedomorphic plethodontid compared to metamorphic conspecifics, and the first salamander system to show differential expression of thyroid hormone receptors associated with alternative developmental patterns.

Two-dimensional gel proteome analysis of honeybee, Apis mellifera, worker red-eye pupa hemolymph

Apis mellifera Linnaeus is a holometabolous insect that undergoes complete metamorphosis in its nonfeeding pupal stage before transitioning to the adult stage. Its pupal stages are classifiable by the unique color pigmentation of its compound eyes and thorax; notably, there is a red-eye stage involving an unpigmented body that has a relatively short duration and is easy to recognize. The aim of the current study was to create a proteomic reference map of the worker red-eye pupa hemolymph. Hemolymph was collected from dorsal vessels using glass capillary tubes and was examined using pI 3–10 two-dimensional gel electrophoresis (2DE; 10 and 14 %) and matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF)/TOF protein identification. This experimental approach allowed us to identify 129 different proteins organized into orthologous groups. Overall, the predominant category was post-translational modifications, protein turnover and chaperones (23.3 % of the identified proteins). In addition, we identified proteins in the non-orthologous groups of olfaction (2.3 % of the identified proteins) and storage hexamerins (3.1 % of the identified proteins). Quantitatively, the major protein isoforms that were accurately identified via 10 % 2DE were four forms of storage hexamerin: the 110, 70a, 70b, and 70c forms. The most abundant enzymes identified were short-chain dehydrogenases/reductases with pivotal developmental roles in ecdysteroidogenesis and a sigma class glutathione-S-transferase that most likely serves as a major protectant against the by-products of oxidative stress. Many of the identified proteins are known to be involved in the mechanisms of metamorphosis. All of the identified proteins are useful as markers for future comparative physiological and developmental studies.

“They preach not by speaking out loud but by signifying”: Vitreous Arts as Typology

By citing such scriptural authorizations as the desert tabernacle and its furnishings to justify art, Christian defenders of physical images sought to neutralize the risk of idolatry in material images. Metallic and vitreous arts—mosaic, stained glass, and enamel—crafted from sand, pigments, and metal under intense heat not only approximated the gems and lustrous matter of the sanctioned objects but also comprehended the mechanism of metamorphosis that mimicked the process of finding redolent Christian meaning in the literal Jewish accounts represented on them. In aiming to reveal truth beneath the surface, the crafting and figuring of matter was an analogue of typology. The brazen serpent was a prime example; cited by Christ himself, it both supported the claim that sacred images had replaced Jewish scripture just as Christ had fulfilled the Old Testament “prophecies” with his person and was taken to evoke Christ's two natures in its combination of figure and material, the snake signifying his humanity a...

Artificially-induced Metamorphosis in Echinoderms

IN 1922 (Biol. Bulletin, 43, p. 210) I propounded a theory as to the mechanism of metamorphosis in sea-urchins based upon the study of dedifferentiation in the larva. The Echinoid pluteus responds very readily to various unfavourable conditions by dedifferentiation. Starvation, lack of oxygen, overcrowding, and poisoning with very dilute potassium cyanide or salts of heavy metals, causes the arms to shrink and eventually to be resorbed, and the body to round up and contract; at the same time the gut may dedifferentiate considerably.

Experiments on Amphibian metamorphosis and pigment responses in relation to internal secretions

The problem of metamorphosis in Amphibia attracts attention from many points of view. These organisms have, one may say, acquired interest as being indicators for the action of certain internal secretions; the underlying mechanism of metamorphosis is still imperfectly understood; and the general biological problems involved, especially with respect to the neotenous and perennibranchiate forms, are remarkably fascinating. The experiments here recorded were undertaken with a view to elucidating these issues more fully, and in the course of them data relevant to the pigmental responses of Amphibian larvae also emerged. For various reasons it was deemed desirable to publish an account of the observations so far completed. Acknowledgment is made to Mr. D. F. Leney of New College for assisting in the care of animals, to the Royal Society and the Trustees of the Dixon Fund for grants in aid of the expenses incurred by the authors respectively, and to Prof. E. W. MacBride, F. R. S., for his kindness in reading the MS. 1. Metamorphosis of the Axolotl by Thyroid Administration . ( a )When a note (Huxley, ‘Nature,' 1920) on the metamorphosis of medium-sized but immature Axolotls by means of thyroid feeding was published by one of the authors a year ago, and confirmed a few months later (Hogben,‘ P. Z. S.,' 1920), our attention had not been called to Jensen’s work (1916). Since this appears to be little known and is not readily accessible to English-speaking workers, it is proposed to give a short of some of his most important findings.