Dr. Barbara Tzschentke
Humboldt-University of Berlin
WG Perinatal Adaptation
Institute of Biology
Presented in the Embryo Physics Course, March 26, 2014
‘Imprinting’ describes a fundamental process of life, which occurs during limited periods of fetal (in birds embryonic) development and early phases of life. It has long-lasting effects and may be even passed on the succeeding generations in an epigenetic fashion. In his classical studies on newly hatched goslings, Konrad Lorenz (1935) analysed the development of social binding, applying the term ‘imprinting’ to describe this process. One of his major hypotheses was that ‘imprinting’ occurs during limited and severely restricted critical periods in early life. Later in 1974/1975, Günter Dörner, a pioneering developmental neuroendocrinologist, developed a general origination concept of the epigenetic perinatal programming of the lifetime function of fundamental regulatory systems. Hormones as well as neurotransmitters and cytotokines (as immune cell hormones) play a key role in this concept. They act as critical endogenous effectors, which transmit environmental information to the genome. Ultimately, they too are acting as epigenetic factors. ‘Imprinting’ of regulatory systems is probably realized at the microstructural level in the brain (e.g. in terms of synaptic plasticity), as well as by lasting, environment-induced (epigenetic) modification of the genome.
Because of its independent development from the mother, the bird embryo provides an excellent model for investigations of pre- and perinatal ‘imprinting’ of body functions. It allows high standardized and controlled changes in epigenetic (environmental) factors during different time windows of early development.
In the avian embryo, during final incubation the development of feedback mechanisms of physiological control systems is a ‘critical period’ and therefore sensitive to ‘imprinting’. During this ‘critical period’, the actual level at which physiological parameters are active may pre-determine a life-long ‘set point’ (or ‘set ranges’) for the respective physiological control system.
On the one hand, chronic cold or warm load during the last days of incubation may adapt birds to the expected post-hatching environmental conditions by imprinting of the thermoregulatory system (prenatal epigenetic temperature adaptation). Phenotypic changes occur, which are typical for cold or warm adaptation. On the other hand, perinatal short-term temperature stimulation (“temperature training”) improves robustness of the birds. Because of the integrating role of the thermoregulatory system, it is worth considering that may also induce ‘imprinting’ of other body functions: metabolism, feed intake and body weight, immune system and behaviour, for example.
‘Imprinting’ of body functions under suboptimal environmental conditions could be a basis for the perinatal malprogramming of body functions, producing e.g., metabolic disorders and cardiovascular diseases as well as behavioural disorders during later life. It is known from studies in humans (e.g. development of obesity due to gestational maternal diabetes) as well as in poultry (e.g. development of Acites syndrome due to suboptimum incubation conditions).