Insulin at a unicellular eukaryote level

Abstract

The unicellular ciliate, Tetrahymena, has been the main model for studying the hormonal system of unicellular animals. Tetrahymena produce, store, secrete and take up insulin, the hormone being similar to that of mammals, both immunocytochemically and functionally. The plasma membrane and nuclear envelope of Tetrahymena have insulin receptors, which are structurally similar to the mammalian receptor, as it their binding capacity. The cell has also second messengers and signal pathways for insulin. Insulin influences the synthesis of other hormones. The first short encounter between the cell and insulin provokes the hormonal imprinting that alters the function of the cells and is transmitted to the progeny, and can persist for over 1,000 generations, in hormone binding, hormone content, phagocytosis, cell growth and movement. Insulin has a survival function in Tetrahymena and during stress insulin production and binding are elevated. Other protozoa also react to insulin, and the evolutionary aspects are discussed in this review since it is still not appreciated that the hormones are of great antiquity in the animal kingdom.

Hormonal Imprinting: The First Cellular-level Evidence of Epigenetic Inheritance and its Present State

“…The mammalian hormone, insulin has binding sites (receptors) in the plasma membrane of Tetrahymena [19], which is insulin-like, and this protein can be observed also intracellularly, which is different in insulin imprinted and non-imprinted cells [20]. Insulin and insulin receptor of Tetrahymena is structurally similar to that of mammalian ones [21][22][23]. The effect of imprinting is durable: it can be observed after 1000 generations [24,25], studied either by the hormone synthesis or functional parameters [26][27][28][29].…”

Hormonal actions in the Protozoan stress: A review

“…This is understandable, as the individual life of Tetrahymena is relatively short, two or three hours, the transmission of experience is needed for the survival of the population. The phenomenon is similar to the hormonal imprinting, when the fi rst encounter with a receptor-level acting molecule [10,23] provokes the everlasting (studied up to 1000 generations) alteration of cell functions, however, after stress it is shorter.…”

“…It is very diffi cult to name one of the hormones however, insulin seems to be the most worth to the name. Insulin in Tetrahymena infl uences not only the sugar metabolism [23,24], but many other important functions and it has a life saving property, when only few cells are present [25,26]. In the stress experiments it also had the most consequent behaviour.…”

“…It seems to be the "primus inter pares" in the action against the effect of stress. However, it must be cautious to declare the outstanding role of insulin, as this hormone was studied the most thoroughly [23] when its effects were demonstrated and mammalian-like receptors were found [27][28][29] and there are very scarce data on the role of other hormones from this aspect.…”

Hormones in the immune system and their possible role. A critical review

“…Exactly, it is not known presently, whether the hormone production of immune cells is influenced by feed-back, while it has a decisive role in the regulation of hormone secretion by endocrine glands. Considering the idea, mentioned above, the feed-back in the immune-endocrine system seems not to be likely, as it is also absent in the case of phylogenetically ancient cells [131,132].…”