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

Abstract

The unicellular ciliate,Tetrahymenahas 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 10−21M concentration, which makes likely that the function could work by the effect of hormones produced by theTetrahymenaitself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by theTetrahymena, 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 ofTetrahymena. The possible and justified role of hormonal system in theTetrahymenaas a single cell and inside theTetrahymenapopulation, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.