Hamsters take cues from decreasing day length to prepare for the long winter

JUNE 10, 2019

by University of Chicago Medical Center

Analysis of the first fully-sequenced genome of the Siberian hamster shows how these small, seasonal breeders adapt their bodies and energy usage to survive the winter.

The research, published this week in the Proceedings of the National Academy of Sciences, also includes transcriptome analysis of gene expression in the brain during both summer and winter conditions, which reveals the cascade of signals that prepare the hamster for winter, triggered by decreasing day length.

The Siberian hamster (Phodopus sungorus) is a model organism for studying seasonal biological rhythms. They breed during the spring and early summer, but as fall approaches and day length shortens, their bodies change dramatically. The hamsters lose almost half their body weight, mostly through fat, and limit food intake by 30 to 40%. They don't hibernate, but modestly reduce their body temperature during the daytime to conserve energy. Their fur thickens and changes color to stark white, and they become infertile until they begin reversing course to prepare for the next breeding season.

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Siberian Hamsters Show What Helps Make Seasonal Clocks Tick

Sep. 23, 2013 — Many animals, including humans, have internal clocks and calendars to help them regulate behavior, physiological functions and biological processes. Although scientists have extensively studied the timekeeping mechanisms that inform daily functions (circadian rhythms), they know very little about the timekeeping mechanisms that inform seasonal functions.

New research to be published this week in the online early edition of the Proceedings of the National Academy of Sciences shows, for the first time, that this measurement of seasonal time has an epigenetic component. Epigenetics refers to an alteration in gene expression that occurs without a change in the sequence of DNA molecules.

The research used Siberian hamsters, which only breed in the late spring and early summer, when days are the longest. It revealed the molecular mechanism behind how these hamsters avoid breeding in the fall and winter, thereby preventing births during the cold, resource-scarce winter months.

Here's how the mechanism works: Exposure to short periods of daylight decreases DNA methylation in the hamsters' hypothalamus. (With DNA methylation, a methyl group -- one carbon atom and three hydrogen atoms -- attaches to a gene, thereby altering its expression.) In turn, the decreased DNA methylation stimulates the expression of a gene that shuts down the hamster's reproductive competency.

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