IRES mediated initiation of translation during mammalian hibernation

Abstract

Concordant with energetic constraints, protein synthesis is depressed during hibernation in golden‐mantled ground squirrels, Spermophilus lateralis, to values of 0.13 to 0.5% of active rates. Roles for both passive and active mechanisms in the regulation of translational initiation have been demonstrated. Phosphorylation events appear to regulate cap‐dependent translation during torpor. However, a subset of mRNAs contain internal ribosome entry sites (IRESs) which allow initiation to occur independent of the 5? mRNA cap. IRES regulated translation may be important in stress responses. We asked if there was a preference for IRES mediated initiation in one particular state of the torpor cycle e.g. as animals begin to arouse from torpor. Initiated mRNAs associate with polysomes. We used sucrose gradient fractionation to isolate polysomes from the animals in various stages of a torpor bout, including summer active (SA), entrance to torpor (ENT, at 10°C, 20°C, and 30°C), early torpor (ET), late torpor (LT), arousal from torpor (ARO, natural and alarm arousals at 10°C, 20°C, and 30°C), and interbout arousal (IBA). We performed quantitative real time PCR to investigate whether known IRES transcripts preferentially associate with ribosomes at the various states as compared to known cap‐dependent transcripts. Current efforts are underway to analyze the data.