Insulin uptake, localization and production in previously insulin treated and untreated Tetrahymena. Data on the mechanism of hormonal imprinting

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

Hormonal imprinting takes place perinatally at the first encounter between the developing hormone receptor and its target hormone. This process is needed for the normal function of the receptor-hormone pair and its effect is life-long. However, in this critical period, when the developmental window is open, related molecules (members of the same hormone family, synthetic hormones and hormone-like molecules, endocrine disruptors) also can be bound by the receptor, causing life-long faulty imprinting. In this case, the receptors’ binding capacity changes and alterations are caused at adult age in the sexual and behavioral sphere, in the brain and bones, inclination to diseases and manifestation of diseases, etc. Hereby, faulty hormonal imprinting is the basis of metabolic and immunological imprinting as well as the developmental origin of health and disease (DOHaD). Although the perinatal period is the most critical for faulty imprinting, there are other critical periods as weaning and adolescence, when the original imprinting can be modified or new imprintings develop. Hormonal imprinting is an epigenetic process, without changing the base sequence of DNA, it is inherited in the cell line of the imprinted cells and also transgenerationally (up to 1000 generations in unicellulars and up to the 3_rd generation in mammals are justified). Considering the enormously growing number and amount of faulty imprinters (endocrine disruptors) and the hereditary character of faulty imprinting, this latter is threatening the whole human endocrine system.

Insulin-like receptors and carbohydrate metabolism in gills of the euryhaline crab Neohelice granulata: Effects of osmotic stress

The present study determined the effect of osmotic stress on the insulin-like receptor binding characteristics and on glucose metabolism in the anterior (AG) and posterior (PG) gills of the crab Neohelice granulata. Bovine insulin increased the capacity of the PG cell membrane to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) and the glucose uptake in the control crab group. The crabs were submitted to three periods of hyperosmotic (HR) and hyposmotic (HO) stress, for 24, 72 and 144 h, to investigate the insulin-like receptor phosphorylation capacity of gills. Acclimation to HO for 24 h or HR for 144 h of stress inhibited the effects of insulin in the PG, decreasing the capacity of insulin to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) and decreasing the glucose uptake. Hyperosmotic stress for the same period of 144 h significantly affected ¹²⁵I-insulin binding in the AG and PG. However, HO stress for 24 h significantly reduced ¹²⁵I-insulin-specific uptake only in the PG. Therefore, osmotic stress induces alterations in the gill insulin-like receptors that decrease insulin binding in the PG. These findings indicate that osmotic stress induced a pattern of insulin resistance in the PG. The free-glucose concentration in the PG decreased during acclimation to 144 h of HR stress and 24 h of HO stress. This decrease in the cell free-glucose concentration was not accompanied by a significant change in hemolymph glucose levels. In AG from the control group, neither the capacity of bovine insulin to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) nor the glucose uptake changed; however, genistein decreased tyrosine-kinase activity, confirming that this receptor belongs to the tyrosine-kinase family. Acclimation to HO (24 h) or HR (144 h) stress decreased tyrosine-kinase activity in the AG. This study provided new information on the mechanisms involved in the osmoregulation process in crustaceans, demonstrating for the first time in an estuarine crab that osmotic challenge inhibited insulin-like signaling and the effect of insulin on glucose uptake in the PG.

Hormonal imprinting in the unicellular Tetrahymena: the proto-model of epigenetics

The unicellular ciliate, Tetrahymena has a complete hormonal system. It has receptors for receiving hormones, produces, stores and secretes hormones, similar to mammalian ones and has signal transduction pathways, for transmitting the information given by the hormones. The first encounter with a hormone provokes the hormonal imprinting under the effect of which the further encounters with the same hormone induces altered (usually enhanced) reaction (hormone binding, hormone synthesis, chemoattraction, movement, growth etc.). The effect of imprinting is durable, it can be observed also after 1000 generations, or after one year in non-dividing cells. Receptors of the nuclear envelope also can be imprinted. The plasma membrane receptors provoked by imprinting are similar to the receptors of mammals. Although steroid hormones are not present in Tetrahymena, the production of them and their receptors can be induced by imprinting. The hormonal imprinting is an epigenetic process and inhibition of DNA-methylation alters the imprinting. Hormonal imprinting in Tetrahymena was likely the first epigenetic phenomenon which was justified at cellular level. It is very useful for the unicells, as it helps to avoid dangerous molecules more easily or to find useful ones and by this contributes to the permanence of the population's life.