Metamorphosis In Axolotl Research Articles

Differential effects of 3,5-T2 and T3 on the gill regeneration and metamorphosis of the Ambystoma mexicanum (axolotl).

Thyroid hormones (THs) regulate tissue remodeling processes during early- and post-embryonic stages in vertebrates. The Mexican axolotl (Ambystoma mexicanum) is a neotenic species that has lost the ability to undergo metamorphosis; however, it can be artificially induced by exogenous administration of thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3). Another TH derivative with demonstrative biological effects in fish and mammals is 3,5-diiodo-L-thyronine (3,5-T2). Because the effects of this bioactive TH remains unexplored in other vertebrates, we hypothesized that it could be biologically active in amphibians and, therefore, could induce metamorphosis in axolotl. We performed a 3,5-T2 treatment by immersion and observed that the secondary gills were retracted, similar to the onset stage phenotype; however, tissue regeneration was observed after treatment withdrawal. In contrast, T4 and T3 immersion equimolar treatments as well as a four-fold increase in 3,5-T2 concentration triggered complete metamorphosis. To identify the possible molecular mechanisms that could explain the contrasting reversible or irreversible effects of 3,5-T2 and T3 upon gill retraction, we performed a transcriptomic analysis of differential expression genes in the gills of control, 3,5-T2-treated, and T3-treated axolotls. We found that both THs modify gene expression patterns. T3 regulates 10 times more genes than 3,5-T2, suggesting that the latter has a lower affinity for TH receptors (TRs) or that these hormones could act through different TR isoforms. However, both TH treatments regulated different gene sets known to participate in tissue development and cell cycle processes. In conclusion, 3,5-T2 is a bioactive iodothyronine that promoted partial gill retraction but induced full metamorphosis in higher concentrations. Differential effects on gill retraction after 3,5,-T2 or T3 treatment could be explained by the activation of different clusters of genes related with apoptosis, regeneration, and proliferation; in addition, these effects could be initially mediated by TRs that are expressed in gills. This study showed, for the first time, the 3,5,-T2 bioactivity in a neotenic amphibian.

Gradient/Extremely Low-Frequency Magnetic Field Affects Metamorphic Behaviors in Thyroxine-Administrated Axolotls: Regulation of Amphibian Metamorphosis Depending on Field Strength and Exposure Timing

In this paper, we investigated the influences of a gradient magnetic field or extremely low-frequency (ELF) fields on the forced metamorphosis of the Mexican axolotls, which was induced with a thyroid hormone. After the adaptation of the axolotls to our experimental environment, they were individually kept in an L-thyroxine (T4) solution under exposure to a gradient field of 17 T/m or ELF fields of 1.0–5.0 mT at 10 Hz. In order to remove unnecessary stress for the axolotls, we recently developed an original water-renewing system equipped with siphonage, velocity, and temperature controls. The number of days required for the perfect metamorphosis into salamanded axolotls under the ELF exposure of 5.0 mT was 16.9 days on average, contrary to the time period for a control (15.1 days). We assumed that the morphological delays of up to 26% among the ELF-exposed axolotls might be due to the competing situation between alternating field effects and biological adaptive responses to the magnetic forces in the axolotl subjects’ bodies. In addition, we did found that the initiation timings of the gradient-field exposure did affect the survival rates of the following salamanded axolotls. A decrease in the rates was noticeable in the case of an exposure just before the time point of the morphological completion. Our data greatly support the idea that magnetic field exposures might modify axolotl metamorphosis minutely, depending on the exposure timing, the field strength, the frequency, and so on. We strongly propose investigating the magnetic control of axolotl metamorphosis induced with a thyroid hormone.

Experimentally induced metamorphosis in highly regenerative axolotl (ambystoma mexicanum) under constant diet restructures microbiota

Axolotl (Ambystoma mexicanum) is a critically endangered salamander species and a model organism for regenerative and developmental biology. Despite life-long neoteny in nature and in captive-bred colonies, metamorphosis of these animals can be experimentally induced by administering Thyroid hormones (THs). However, microbiological consequences of this experimental procedure, such as host microbiota response, remain largely unknown. Here, we systematically compared host bacterial microbiota associated with skin, stomach, gut tissues and fecal samples, between neotenic and metamorphic axolotls based on 16S rRNA gene sequences. Our results show that distinct bacterial communities inhabit individual organs of axolotl and undergo substantial restructuring through metamorphosis. Skin microbiota among others, shifted sharply, as highlighted by a major transition from Firmicutes-enriched to Proteobacteria-enriched relative abundance and precipitously decreased diversity. Fecal microbiota of neotenic and metamorphic axolotl shared relatively higher similarity, suggesting that diet continues to shape microbiota despite fundamental transformations in the host digestive organs. We also reproduced the previous finding on reduction in regenerative capacity in limbs of axolotl following metamorphosis, highlighting the need to investigate whether shifts in microbiota is causally linked to regenerative capacity of axolotl. The initial results on axolotl microbiota provide novel insights into microbiological aspects of axolotl metamorphosis and will establish a baseline for future in-depth studies.

Thyroxine-induced metamorphosis in the axolotl (Ambystoma mexicanum).

The axolotl (Ambystoma mexicanum) has remained an important model for regeneration and developmental biology for over a century. Although axolotls in captive-bred colonies usually exist in an aquatic form, they retain the ability to undergo metamorphosis following exposure to thyroid hormone. Here we present a robust method for inducing metamorphosis in adult axolotls that results in high survivability and produces terrestrial animals that can be maintained in long-term captivity.

Experimentally induced metamorphosis in axolotls reduces regenerative rate and fidelity.

While most tetrapods are unable to regenerate severed body parts, amphibians display a remarkable ability to regenerate an array of structures. Frogs can regenerate appendages as larva, but they lose this ability around metamorphosis. In contrast, salamanders regenerate appendages as larva, juveniles, and adults. However, the extent to which fundamental traits (e.g., metamorphosis, body size, aging, etc.) restrict regenerative ability remains contentious. Here we utilize the ability of normally paedomorphic adult axolotls (Ambystoma mexicanum) to undergo induced metamorphosis by thyroxine exposure to test how metamorphosis and body size affects regeneration in age‐matched paedomorphic and metamorphic individuals. We show that body size does not affect regeneration in adult axolotls, but metamorphosis causes a twofold reduction in regeneration rate, and lead to carpal and digit malformations. Furthermore, we find evidence that metamorphic blastemal cells may take longer to traverse the cell cycle and display a lower proliferative rate. This study identifies the axolotl as a powerful system to study how metamorphosis restricts regeneration independently of developmental stage, body size, and age; and more broadly how metamorphosis affects tissue‐specific changes.

Induction of Metamorphosis in Axolotls (Ambystoma mexicanum)

INTRODUCTIONThe Mexican axolotl (Ambystoma mexicanum) follows a very different pattern of development from other closely related tiger salamanders. Whereas many tiger salamanders undergo an obligatory metamorphosis, axolotls rarely if ever transform in the lab. As a consequence, axolotls retain larval features into adulthood and therefore require aquatic husbandry procedures throughout life. However, it is possible to induce metamorphosis in axolotls by simply adding thyroid hormone to the rearing water. If thyroid hormone is provided at an appropriate concentration and at a time during development that related tiger salamanders normally transform, healthy and robust terrestrial axolotls can be generated. The procedure is useful for studying molecular mechanisms of tissue-specific developmental programs that depend upon thyroid hormone. Also, because thyroid hormone brings about the maturation of tissues, the axolotl model can be used to study the molecular correlates of aging. Finally, the axolotl model can be used to study ecotoxicological factors that disrupt thyroid hormone signaling and tissue remodeling. The ability to precisely activate metamorphosis in the axolotl provides an advantage over anuran models that are always developing toward a metamorphic outcome. The protocol described here induces metamorphosis in axolotls using the less active form of thyroid hormone called T4 (tetraiodothyronine).

Expansion of the visual projection to the tectum of axolotls during metamorphosis.

During artificially induced metamorphosis in axolotls, the indirect visual projection from the ipsilateral eye develops followed by the expansion of the contralateral direct projection to occupy most of the tectal surface. During expansion the ipsilateral input is temporarily lost indicating the functional interdependence of the two projections. Final stabilization of the projections and congruence of the ipsilateral and contralateral inputs is achieved a month after arrival on land.

Effect of TSH and long-acting thyroid stimulator on thyroid 131I-metabolism and metamorphosis of the Mexican axolotl ( Ambystoma mexicanum)

Metamorphosis in the Mexican axolotl was induced by daily injection of purified ovine TSH, but not by injection of large doses of iodide. Thyroxine was effective in inducing metamorphosis when injected in a dose as low as 0.5 μg per 100 g per day, suggesting that axolotl tissue is normally sensitive to thyroid hormone. It is unlikely, therefore, that neoteny in this species is attributable to tissue resistance to the action of thyroid hormone. Thyroid 131I uptakes in axolotls were of the order of 1–2% after 48 hr, and 131T-T 4 comprised only 2–4% of the total. 131I-T 4 was not detected in the circulation. After chronic administration of TSH, thyroid 131I uptakes rose greatly, 131I-T 4 comprised 15–18% of glandular 131I, and 131I-T 4 was readily detectable in the circulation. In all these respects 131I metabolism in the axolotl resembled that seen previously in hypophysectomized rats. These results support the view that failure of metamorphosis in Ambystoma mexicanum is related to a very low rate of TSH secretion by the pituitary. Chronic injection of long-acting thyroid stimulator induced none of the changes associated with metamorphosis in Mexican axolotls and bad no effect on thyroid 131I metabolism. Plasma protein patterns in larval and metamorphosed axolotls and in tiger salamanders were determined by electrophoresis on cellulose acetate. In all cases the fastest-migrating component displayed a mobility considerably less than that of frog plasma albumin. An increase in total plasma protein was observed after metamorphosis in axolotls, but not in tiger salamanders. A shift toward an increase in the proportion of the fast-moving component was more apparent in the tiger salamander.

THE RESPONSE TO THYROXINE AFTER SUBTOTAL HEPATECTOMY1

WHEN THYROXINE is injected into an animal and the bile assayed, definite amounts of iojiine may be detected, amounting in some experiments to an excretion within three hours after injection of as much as 47 per cent of the total quantity administered (Kendall 1919, Krayer 1928). Bioassay (by the method of axolotl metamorphosis) indicates that, while some of the iodine is present in an hormonally active form, there has been considerable destruction of the administered hormone (Krayer 1928). Chemical fractionation methods, on the other hand, indicate that as much as one-half to twothirds of the thyroxine may be excreted unchanged (Barnes 1933, Zawadowsky & Perelmutter 1927). It appears from these experiments that the liver is able either to excrete thyroxine in the bile, or to destroy the hormone and excrete the iodine in a physiologically inactive form.

On the Activity of the Anterior Lobe Pituitary

ABSTRACT The standardisation of the method of preparation of extracts and the adoption of a uniform procedure for the estimation of their ability to induce metamorphosis in axolotls or accelerate the transformation of tadpoles to adults permit a biological assay of the metamorphic activity of extracts of the anterior lobe. The metamorphic activity of the anterior lobe is specific, since similar tissue extracts fail to excite a like response and qualitative and quantitative characteristics distinguish it from the activity of the thyroid in metamorphosis. Active preparations are not produced when neutral media or inorganic acids are used for extraction from fresh gland by decoction. The potency of extracts depends upon the strength of the acetic acid used for extraction, the concentration of the extract and the hydrogen-ion concentration. The threshold value of the dose inducing metamorphosis in axolotls by injection and the amount inducing the maximum rate of change increase with the size of the animal. Injections must be continued at regular and suitably short intervals till the completion of the change to maintain the maximum response to any particular dose. The activity of extracts is destroyed by pepsin and trypsin and diminished by dilute hydrochloric acid. Neutralised extracts are inactive. Ringer’s and distilled water extracts of thyroid are more active than similar extracts in dilute acetic acid. There is no relation between the activity of these extracts and the hydrogen-ion concentration. There is evidence of an inhibiting influence of the posterior lobe upon metamorphosis. The distribution of the factor responsible for the metamorphic activity of the anterior lobe is not uniform throughout the lobe, less being present at the border than within. No definite localisation is apparent. The anterior lobe influences metamorphosis and growth in size, but the same influence does not appear to operate in the production of each of these effects. The extent to which the growth stimulus is dependent upon and determined by other factors has yet to be determined. The thyroid and pituitary are interdependent, but both seemingly are able to Induce metamorphosis in the axolotl independently, and in the absence of the other. In the tadpole independent action in stimulating metamorphosis appears to be possible only in the later stages, co-operation being necessary in development and the earlier stages. The thyroid and pituitary of the adult axolotl appear to be at a low level of functional activity, and metamorphosis is dependent upon the stimulus of glands from external sources when suitably administered, since the rate of change induced is approximately the same in these animals, whether normal, thyroidless, pituitary-less or with both thyroid and pituitary removed. The relationship between the endocrine balance and metamorphosis in the amphibia and its evolutionary significance is discussed. The anterior lobe appears to have a regulative and directive effect within the organism which, as a factor in the internal environment, may have some evolutionary significance.

APPLICATION OF THE AXOLOTL METAMORPHOSIS REACTION TO THE QUANTITATIVE ASSAY OF THYROID GLAND HORMONES

The Biological Laboratory and the Museum of the Sverdlov University have been conducting, since 1921, experiments on the process and conditions of metamorphosis of axolotls under the influence of the thyroid gland. In a number of papers since 1923–24 (1, 2, 3, 4), the method is described of implantation of tissues and organs of animals into the bodies of the axolotls for the purpose of detecting the thyroid gland hormone in those tissues and organs. In this connection has been discovered not only the possibility of finding thyroxin in the tissues of hyperthyroidized fowls and mammals, but also of making deductions with regard to the quantitative distribution of the thyroxin, depending upon the velocity and degree of axolotl reaction. We base this idea on the natural assumption that the greater the velocity of the metamorphosis, the greater the amount of thyroxin in the tissue implanted into the given axolotl.

Iodine and Amphibian Metamorphosis

Summary. Free iodine is incapable of producing metamorphosis in Axolotls when administered alone, but, if thyroid extract is given as well, it is utilized producing greatly accelerated transformation. The rate of metamorphosis induced by thyroid and iodine is much greater and the period before completion shorter than that produced by thyroid alone, when the same dose is given. The inetamorphic principle of the Anterior Pituitary does not utilize or combine with iodine to produce greater acceleration of metamorphosis. The posterior lobe pituitary exerts an inhibitory influence on inetamorphic changes induced by thyroid and iodine.

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.

Metamorphosis of Axolotl caused by Thyroid-feeding

THE fact that a diet of mammalian thyroid will induce frog-tadpoles to metamorphose precociously into the adult form is now well established. It is of some interest to find that this diet produces a similar effect in a form which usually does not metamorphose—the Axolotl. This is the larva of a salamander known as Amblystoma, but is remarkable in being neotenic, i.e. it normally fails to metamorphose, and attains full size and sexual maturity while keeping its larval characters. Chief among these are the external gills and the fin along the back and both borders of the tail, but the adult also differs from the larva in colour, in shape of head, in the development of eyes and eyelids, in the rounded form of the tail, and, of course, in the use of its limbs for progression on land.

A Remarkable Axolotl from North Dakota

Previous articleNext article FreeA Remarkable Axolotl from North DakotaHenry Leslie OsbornHenry Leslie Osborn Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 34, Number 403Jul., 1900 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/277703 Views: 119Total views on this site PDF download Crossref reports no articles citing this article.