Effect of biogenic amines on phagocytosis in Tetrahymena thermophila

Serotonin signaling regulates actomyosin contractility during morphogenesis in evolutionarily divergent lineages

Serotonin is a neurotransmitter that signals through 5-HT receptors to control key functions in the nervous system. Serotonin receptors are also ubiquitously expressed in various organs and have been detected in embryos of different organisms. Potential morphogenetic functions of serotonin signaling have been proposed based on pharmacological studies but a mechanistic understanding is still lacking. Here, we uncover a role of serotonin signaling in axis extension of Drosophila embryos by regulating Myosin II (MyoII) activation, cell contractility and cell intercalation. We find that serotonin and serotonin receptors 5HT2A and 5HT2B form a signaling module that quantitatively regulates the amplitude of planar polarized MyoII contractility specified by Toll receptors and the GPCR Cirl. Remarkably, serotonin signaling also regulates actomyosin contractility at cell junctions, cellular flows and epiblast morphogenesis during chicken gastrulation. This phylogenetically conserved mechanical function of serotonin signaling in regulating actomyosin contractility and tissue flow reveals an ancestral role in morphogenesis of multicellular organisms.

Provocation of life functions at a unicellular eukaryote level by extremely low doses of mammalian hormones: Evidences of hormesis

Hormones, characteristic to higher ranked animals, are synthesized, stored, and secreted by unicellular eukaryote animals. The unicells also have receptors for recognizing these materials and transmit the message into the cells for provoking response. The hormones are effective in very low concentrations (down to 10-21 M) and opposite effects of lower and higher concentrations can be observed. However, sometimes linear concentration effects can be found, which means that hormesis exists, nevertheless uncertain, as it is in the phase of formation (evolutionary experimentation). Hormesis, by transformation (fixation) of cytoplasmic receptor-like membrane components to receptors in the presence of the given hormone, likely helps the development of unicellular endocrine character and by this the evolution of endocrine system. The effect by extremely low concentrations of hormones had been forced by the watery way of unicellular life, which could establish the physiological concentrations of hormones in the blood of higher ranked animals. This means that hormetic low doses are the normal, effective concentrations and the high concentrations are artificial, consequently could be dangerous.

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.

Effect of different concentrations of serotonin, histamine and insulin on the hormone (serotonin and ACTH) production of Tetrahymena in nutrient-free physiological milieu

Cell populations of Tetrahymena pyriformisGL were kept in nutrient-free (Losina) milieu and treated with different (10(-6)-10(-21)M) concentrations of serotonin, histamine or insulin for 30 min. Following that the hormone (serotonin and adrenocorticotropin (ACTH) content of the cells were measured by immunocytochemical flow cytometric method. Serotonin reduced histamine when applied in 10(-12) and 10(-15)M concentrations, while elevated ACTH levels when applied in 10(-6), 10(-9) and 10(-21)M concentrations. Histamine reduced serotonin concentration at 10(-9)-10(-21)M concentrations and increased ACTH in 10(-6)M. Insulin elevated both hormones' content in each concentration except at 10(-12)M. The results demonstrate that (1) in nutrient-free conditions the hormonal effects differ from that of nutrient-rich (tryptone+yeast) condition; (2) there is an optimal hormone concentration, which causes the strongest effect and this is different for each hormones; (3) the hormone receptors of Tetrahymena are very sensitive; as they react to zeptomolar concentrations. Such small concentration is even more effective than higher ones. Since hormones must become highly diluted in the natural environment of Tetrahymena, it seems that such low concentrations are the actual physiological concentrations.

Hormetic Dose-Response Relationships in Immunology: Occurrence, Quantitative Features of the Dose Response, Mechanistic Foundations, and Clinical Implications

This article provides an assessment of the occurrence of immune-system-related hormetic-like biphasic dose-response relationships. Such dose-response relationships are extensive, with over 90 different immune response-related endpoints reported, induced by over 70 endogenous agonists, over 100 drugs, and over 40 environmental contaminants. Such hormetic responses were reported in over 30 animal models, over a dozen mammalian and human cell lines. These findings demonstrate that immune-system-related hormetic-like biphasic dose-response relationships are common and highly generalizable according to model, endpoint, and chemical class. The quantitative features of the dose response are generally consistent with previously published examples of hormetic dose responses for other biological endpoints. These findings were generally recognized and explicitly discussed by the original authors, often with consideration given to possible mechanistic foundations as well as numerous clinical implications. Despite the recognition by individual authors of the hormetic nature of these observed responses, the overall widespread nature of immune-related hormetic responses has been only little appreciated, with a general lack of insight into the highly generalizable nature of this phenomenon as well as the complex regulatory networks affecting biological switching mechanisms that result in the hormetic responses.

How does the unicellular Tetrahymena utilise the hormones that it produces? Paying a visit to the realm of atto-and zeptomolar concentrations

Changes in the hormone content of Tetrahymena pyriformis GL were investigated during histamine, serotonin or insulin treatment at concentrations of 10(-6)M to 10(-21)M for 30 min. The immunologically demonstrable hormone content was studied by using specific antibodies, flow cytometry and confocal microscopy. Histamine at the higher ranges elevated the serotonin content of Tetrahymena, whereas serotonin at the lower ranges (down to 10(-21)M) decreased its histamine levels. Insulin did not affect its serotonin content, whereas serotonin increased its insulin content at each concentration studied (down to 10(-21)M). Insulin between 10(-6)M and 10(-21)M increased the histamine levels of Tetrahymena, although histamine influenced its insulin level only at 10(-6)M. Our results call attention to the presence of hormonal interactions even at "low" levels of phylogeny and to the extreme sensitivity of the hormone receptors of Tetrahymena. These data might explain (1) the requirement of Tetrahymena for (vertebrate) hormone production and hormone receptors and (2) the way that it uses these hormones under natural conditions.

Effects of steroid hormones on five functional parameters of Tetrahymena: evolutionary conclusions

The unicellular Tetrahymena pyriformis was studied for chemotaxis, chemotactic selection, phagocytosis, growth and body shape changes in the presence of water soluble (beta-cyclodextrin-coupled) steroid hormones (testosterone, estradiol, progesterone, hydrocortisone and dexamethasone). Testosterone was chemoattractant over a wide range of concentrations, while progesterone and dexamethasone were active only at one concentration (10(-5) and 10(-6) mg ml(-1) respectively) and were either neutral or repellent at other concentrations. Hydrocortisone and estradiol were unambiguously chemorepellent. Chemotactic selection enhanced the effect of testosterone and estradiol, while in the case of hydrocortisone the action was reversed. The other parameters were mildly influenced by the steroid hormones. The results call attention to the fine molecular recognition capacity of Tetrahymena and to the possible rapid effects of steroid hormones at membrane receptors at a very low evolutionary eukaryotic level.

Oxidative stress in phagocytes--"the enemy within"

Phagocytes represent a powerful defense system against invading microorganisms that threaten the life or functional integrity of the host. The capacity to generate and release substantial amounts of reactive oxygen species is a unique property of activated polymorphonuclear and mononuclear phagocytes. The crucial role of these molecules in killing microorganisms and their consecutive contribution to tissue damage during injury and inflammation is widely known. Although much research has been done to explore the molecular events involved in the interaction of oxygen intermediates with microbes or host tissue, surprisingly little attention has been paid to the effect of reactive metabolites on the phagocyte itself. This fact is especially surprising, since it is apparent that the activated phagocyte is directly exposed to its own toxic metabolites. The potential damage occurring during excessive radical formation might notably alter the vital functions of these primarily immunocompetent cells. Moreover, the critical role of oxygen radicals in apoptosis of leukocytes has been recently revealed. Apoptosis is now supposed to represent a key mechanism in neutrophil deactivation and resolution of inflammation. Therefore, this review will focus on the delicate balance between released oxidants and antioxidative protection within the phagocytes themselves. General and phagocyte-specific antioxidative mechanisms, which have co-evolved with the radical generating machinery of phagocytes, are discussed, since the outcome of local inflammation can directly depend on this antioxidative capacity and might range from adequate elimination of the pathogen with minimal acute tissue damage to progression towards a systemic inflammatory response syndrome.

Immunocytochemical verification of the insulin receptor's specificity in the nuclear envelope of Tetrahymena. Comparison with receptors of the plasma membrane

The unicellular Tetrahymena possess hormone receptors in the nuclear envelope similarly to higher rank animals. These receptors bind insulin and their specificity is detectable by monoclonal antibodies developed to insulin. The hormonal (insulin) pretreatment (imprinting) of the cell did not alter the binding capacity of the nuclear membrane, demonstrated by antibody-technique. The specific binding characteristics of the plasma membrane was demonstrated and this was significantly increased following imprinting. In the nucleus of Tetrahymena presence of insulin was not detected by immunocytochemical method.

Metabolism of biogenic monoamines in the ciliated protozoan, Tetrahymena pyriformis

1. The three-dimensional HPLC system was used to detect the presence and determine the levels of biogenic monoamines, including precursor amino acids and metabolites, simultaneously in an extract of the ciliated protozoan, Tetrahymena pyriformis. 2. Representative biogenic monoamines, such as dopamine (DA), 5-hydroxytryptamine (5-HT), epinephrine (E) and kynurenine (KYN) were found to be synthesized in Tetrahymena and released into the growth medium. 3. The following metabolic pathways were suggested to be operative: (L-DOPA)-DA-(Epinine)-E-dihydroxyphenylethyleneglycol (DOPEG)-vanillylmandelic acid (VMA) and tyrosine-4 (TYR-4)-tyramine (TYRA)-hydroxyphenylacetic acid-4 (HPAC-4) in the case of catecholamines, and tryptophan (TRP)-5-HT and TRP-KYN-xanthurenic acid (XA) in the case of indolalkylamines. 4. As judged from the released metabolites, systems for generation of biogenic monoamines in Tetrahymena seem to be active during the logarithmic phase of its growth.

Mammalian hormones in microbial cells

Hormones and hormone-binding proteins resembling those of vertebrates are widespread in fungi, yeast and bacteria. Functional responses of microbial cells to mammalian hormones have also been found. The evolutionary roots of the vertebrate endocrine system may, therefore, be far more ancient than is generally believed.

Insulin antagonizes the phagocytosis stimulating action of histamine in Tetrahymena

Histamine increased specifically the phagocytic activity of the unicellular Tetrahymena, whereas insulin had no influence on it. Insulin antagonized the phagocytosis stimulating action of histamine after simultaneous exposure and after preexposure two days earlier as well, although in the latter case to a lesser degree. Double exposure to a combination of histamine+insulin didn't influence the phagocytic activity at all, demonstrating the histamine antagonizing effect of insulin in this model.

Hormonal effects on insects and other endoparasites in vitro

Metamorphic and reproductive events in vertebrates and invertebrates are under endocrine control and are often correlated with developmental, behavioral, or reproductive changes in the parasites living in or on these hosts. This paper reviews selected examples of a) host hormone mediated influences on endoparasites in vivo, b) host hormone effects in vitro on protozoan, helminth, and insect endoparasites, and c) identifies possible relationships in hormone effects across parasite taxa. The significance of studies on endoparasites in vitro in relation to the impact of host hormones, antihelminthic, and prophylactic drugs on parasite growth and proliferation will also be addressed. A review of the literature indicates only limited studies have been done in vitro in an attempt to elucidate the bases of reported host hormone influences on endoparasites in vivo. Steroid hormones of hosts seem to stimulate growth, molting or encystment or both of helminth, insect, and protozoan parasites. Vertebrate steroids such as estrogen, testosterone, and progesterone had primarily reproduction- or growth-promoting effects or both on protozoan and nematode parasites. Insect ecdysteroids such as ecdysone, 20-hydroxyecdysone, and makisterone were the most widely studied steroids in vitro and induced growth or molting or both of cestode, nematode, and insect parasite larvae. Although juvenile hormone (JH III) stimulated growth in the protozoan and nematode parasites tested, the analogue methoprene and JH precursors, farnesal, farnesol, and farnesol methyl ether had various effects. Biogenic amines also varied in their effects on the nematode parasites tested, while the peptide hormone, insulin, stimulated growth in the protozoans tested. The evidence for in vitro effects of host hormones on their natural endoparasites is patchy at best. Additional studies are needed to identify the biochemical bases for the numerous host hormone mediated effects on parasites.

Phagocytosis in Tetrahymena thermophila: naloxone-reversible inhibition by opiates

1. Nanomolar concentrations of opiates inhibit phagocytosis in the ciliated protozoan Tetrahymena thermophila. 2. Naloxone and naltrexone counteract the effect of the opiate agonists tested. 3. The dose-response curves are U-shaped, with no detectable effect at low or high concentrations. 4. An increase in extracellular calcium and dopamine counteract the inhibition caused by metenkephalin. 5. The recognition mechanism for opiates in Tetrahymena cannot be classified as belonging to any of the mammalian opiate receptor subtypes and is perhaps a primitive receptor.

Biogenic amines stimulate regeneration of cilia in Tetrahymena thermophila

Serotonin and catecholamines affect the regeneration of cilia in Tetrahymena thermophila in a dose-dependent manner: micromolar concentrations are stimulatory, whereas millimolar concentrations have little or no effect. This conclusion is based on motility measurements in regenerating cells and on ciliary counts in scanning electron micrographs. In addition, the recognition mechanism for each hormone appears to be specific and independent. Our results suggest an evolutionary link with hormonal mechanisms in multicellular eukaryotes.