Chapter 13 - Transgenerational Hormonal Imprinting in the Unicellular Tetrahymena

Abstract

The unicellular Tetrahymena has a complete hormonal system: It synthesizes hormones, which are characteristic of mammals, has receptors, and signaling pathways. Its first encounter with an exogenously given hormone, or any molecule that acts at receptor level, provokes hormonal imprinting, which, in turn, manifests as changes in physiological parameters at subsequent encounters with the given hormone. As the lifespan of the individual Tetrahymena is short, the manifestation of imprinting can only be studied over many (e.g., thousands) generations. During imprinting, an epigenetic change takes place and this is transmitted transgenerationally. This review introduces the hormonal system and the hormonal imprinting process in Tetrahymena, the role of DNA methylation in the process, the role of signaling pathways, the imprinter molecules studied, and the functions influenced, and the biological importance of this phenomenon is discussed. Hormonal imprinting is very important in the life of Tetrahymena, as it facilitates its escape from dangerous molecules, as well as being valuable in the recognition of useful ones. At the same time, the process plays a crucial role in the evolution of the hormonal system, by helping the selection of molecules suitable for becoming receptors and hormones in higher ranked organisms.