Quick results for thyroid hormone

The body often responds to increased energy demands during growth or development by secreting thyroid hormone. Activated thyroid hormone receptors (TRs) increase long-term mitochondrial output through transcriptional changes. But on page 915, Saelim et al. show that some TRs supersede transcription to cause rapid, transient changes in mitochondrial function.

The fast-acting TRs were those that were targeted to mitochondria rather than to the nucleus. Using frog oocytes, which lack their own TRs, the authors show that mitochondrial TRs energize respiration in response to thyroid hormone. These TRs did not require either their DNA-binding domains or transcriptional activities.

How respiration was initially jump-started is not clear, but the mitochondria consumed more oxygen and had increased membrane potentials when mitochondrial TRs were activated. Presumably as a result of...