Vebjørn Jacobsen Melum back from the Paul Mandel Symposium in Strasbourg

Vebjørn Jacobsen Melum has just been in Strasbourg to participate at the Paul Mandel symposium at the Institute des Neurosciences Cellulaires et Integratives (INCI), University of Strasbourg. The day was dedicated to the ones that have received funding from the Paul Mandel fund. During the day, he gave a well-received presentation about his ongoing project to investigate the epigenetics of maternal photoperiodic programming. You might wonder: what is maternal photoperiodic programming? In simple terms, maternal photoperiodic programming is the process where a foetus, during gestation, is set on a trajectory of development according to signals received from the mother. Let`s take a closer look at why and how it occurs.

Why is maternal photoperiodic programming beneficial for the offspring?

Offspring of wild rodent species develop differently depending on when they are born. Offspring that`s born in early spring have an accelerated development. Meaning that they grow large and rapidly start to reproduce. This strategy is possible because food abundance is high at this time of year. Offspring that`s born in early fall have a delayed development. They are smaller in size and do not reproduce until the next spring. This strategy is designed to survive on scarce resources and wait until next spring to reproduce. Together both strategies are shown to increase the survival of the offspring and their reproductive success (fitness). For these strategies to work offspring must be born with a sense of the season (time of year) it has been born into. Photoperiod (amount of light each day) is an excellent indicator of time of year and is used by organisms to time seasonal changes in physiology. However, the early born spring offspring and the late born autumn offspring experience similar photoperiods when born but develop differently, therefore the maternal environment is key in programming the trajectory of development.

How is maternal photoperiodic programming achieved?

Programming occurs through the mother’s secretion of a hormone called melatonin. Melatonin is synthesised in the pineal gland and only secreted when it is dark. Since the dark portion of the day varies with season, melatonin signal duration can be used as a robust signal for time of year. The foetus does not have a functional pineal gland, so it uses maternal melatonin. Melatonin therefore creates the link between the external photoperiodic (hours of light per day) environment and the foetus, providing a sense of calendar time. This “calendar” provided by the mother alters the sensitivity of a key cell type in the hypothalamus (tanycyte), resulting in the developmental trajectories upon birth. How maternal melatonin alters the sensitivity of tanycytes to the same photoperiodic signal is the question Vebjørn aims to answer using state of the art epigenetic methods in his PhD project.