Unsaturated fatty acids as high-affinity ligands of the C-terminal Per-ARNT-Sim domain from the Hypoxia-inducible factor 3α

Hypoxia-inducible transcription factors (HIF) form heterodimeric complexes that mediate cell responses to hypoxia. The oxygen-dependent stability and activity of the HIF-α subunits is traditionally associated to post-translational modifications such as hydroxylation, acetylation, ubiquitination, and phosphorylation. Here we report novel evidence showing that unsaturated fatty acids are naturally occurring, non-covalent structural ligands of HIF-3$\alpha$, thus providing the initial framework for exploring its exceptional role as a lipid sensor under hypoxia

Cryptochrome mediates light-dependent magnetosensitivity in Drosophila

Although many animals use the Earth\u27s magnetic field for orientation and navigation, the precise biophysical mechanisms underlying magnetic sensing have been elusive. One theoretical model proposes that geomagnetic fields are perceived by chemical reactions involving specialized photoreceptors. However, the specific photoreceptor involved in such magnetoreception has not been demonstrated conclusively in any animal. Here we show that the ultraviolet-A/blue-light photoreceptor cryptochrome (Cry) is necessary for light-dependent magnetosensitive responses in Drosophila melanogaster. In a binary-choice behavioural assay for magnetosensitivity, wild-type flies show significant naive and trained responses to a magnetic field under full-spectrum light ( approximately 300-700 nm) but do not respond to the field when wavelengths in the Cry-sensitive, ultraviolet-A/blue-light part of the spectrum (nm) are blocked. Notably, Cry-deficient cry(0) and cry(b) flies do not show either naive or trained responses to a magnetic field under full-spectrum light. Moreover, Cry-dependent magnetosensitivity does not require a functioning circadian clock. Our work provides, to our knowledge, the first genetic evidence for a Cry-based magnetosensitive system in any animal

Inhomogeneous ensembles of radical pairs in chemical compasses

The biophysical basis for the ability of animals to detect the geomagnetic field and to use it for finding directions remains a mystery of sensory biology. One much debated hypothesis suggests that an ensemble of specialized light-induced radical pair reactions can provide the primary signal for a magnetic compass sensor. The question arises what features of such a radical pair ensemble could be optimized by evolution so as to improve the detection of the direction of weak magnetic fields. Here, we focus on the overlooked aspect of the noise arising from inhomogeneity of copies of biomolecules in a realistic biological environment. Such inhomogeneity leads to variations of the radical pair parameters, thereby deteriorating the signal arising from an ensemble and providing a source of noise. We investigate the effect of variations in hyperfine interactions between different copies of simple radical pairs on the directional response of a compass system. We find that the choice of radical pair parameters greatly influences how strongly the directional response of an ensemble is affected by inhomogeneity

Magnetoreception systems in birds: A review of current research

At least two independent systems of magnetoreception are currently believed to exist in birds, based on different biophysical principles, located in different parts of their bodies, and with different neuroanatomical mechanisms. One magnetoreceptory system is located in the retina, and may be based on photochemical reactions on the basis of cryptochrome. Information from these receptors is processed in a specialized part of visual Wulst, the so-called Cluster N. There are good reasons to believe that this visual magnetoreceptor processes compass magnetic information necessary for migratory orientation. The second magnetoreceptory system is probably iron-based (biogenic magnetite), located somewhere in the upper beak (its exact location and ultrastructure of receptors remain unknown) and innervated by the ophthalmic branch of trigeminal nerve. It cannot be ruled out that this system participates in spatial representation and helps forming either a kind of map or more primitive signpost sense (identification of specific geographic regions), based on regular spatial variation of the geomagnetic field. The magnetic map probably enables navigation of migrating birds across hundreds and thousands of kilometres. Apart from these two systems, whose existence has been convincingly shown (even if some details are not fully clear yet), there is evidence for the existence of magnetoreceptors based on the vestibular system. It cannot be ruled out that iron-based magnetoreception takes place in lagena (a part of inner ear in fishes, amphibians, reptiles and birds), and the information perceived is processes in vestibular nuclei. The very existence of this magnetoreception system needs verification, and its function remains completely open