Hypothalamic deiodinase type-3 establishes the period of circannual interval timing in mammals

Animals respond to environmental cues to time phenological events, but the intrinsic mechanism of circannual timing remains elusive. We used transcriptomic sequencing and frequent sampling of multiple hypothalamic nuclei in Djungarian hamsters to examine the neural and molecular architecture of circannual interval timing. Our study identified three distinct phases of transcript changes, with deiodinase type-3 (Dio3) expression activated during the early induction phase. Subsequent work demonstrated that targeted mutation of Dio3 using CRISPR–Cas resulted in a shorter period for circannual interval timing. Hamsters that are non-responsive to short photoperiods and fail to show any winter adaptations do not display changes in Dio3 expression and do not show any change in body mass or pelage. Our work demonstrates that changes in Dio3 induction are essential for setting the period of circannual interval timing.